HK1243612B - Scanning mechanisms for imaging probe - Google Patents

Description

Scanning mechanism for imaging probe

This application is a divisional application based on the patent application of the applicant Sunnybrook Health Sciences Center, with the application date of January 21, 2008, national application number 200880009253.8 (international application number PCT/CA2008/000092), and invention name “Scanning mechanism for imaging probe”, and its divisional application filed on January 15, 2013, with application number 201310015205.2, and invention name “Scanning mechanism for imaging probe”.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to and claims priority from U.S. Provisional Patent Application No. 60/881,169, filed in English on January 19, 2007, entitled "IMAGING PROBE," which is hereby incorporated by reference in its entirety.

Technical Field

The present invention generally relates to the field of imaging probes for imaging mammalian tissue and structures using high-resolution imaging, including high-frequency ultrasound and optical coherence tomography. More specifically, the present invention relates to an imaging assembly incorporating a scanning mechanism for providing forward and side-viewing capabilities of the imaging probe.

Background Art

High-resolution imaging of the human body is used for a variety of purposes, including any of the following: i) assessing tissue structure and anatomy; ii) planning and/or guiding interventions on localized regions of the human body; and iii) assessing the results of interventions that alter the structure, composition, or other properties of a localized region. High-resolution imaging in this particular context refers to high-frequency ultrasound and optical imaging methods. For the purposes of the present invention, high-frequency ultrasound generally refers to imaging at frequencies greater than 3 MHz, and more typically refers to frequencies in the range of 9 to 100 MHz. High-frequency ultrasound is very useful for intravascular and intracardiac procedures. For these applications, ultrasound transducers are incorporated into catheters or other devices that can be inserted into the human body. As examples, two particularly important embodiments of high-frequency ultrasound are intravascular ultrasound (IVUS) for imaging blood vessels and intracardiac echocardiography (ICE) for imaging cardiac chambers. Both ICE and IVUS are minimally invasive and involve placing one or more ultrasound transducers within blood vessels or cardiac chambers to obtain high-quality images of these structures.

Optical imaging methods based on fiber optic technology used in the medical field include optical coherence tomography, angiography, near-infrared spectroscopy, Raman spectroscopy, and fluorescence spectroscopy. These methods generally require the use of one or more optical fibers for transmitting light energy along the axis between the imaging position and the imaging detector. Optical coherence tomography is an optical analog of ultrasound and provides imaging resolution on the order of 1-30 microns, but in most cases does not penetrate as deeply into the tissue as ultrasound. Optical fibers can also be used to transmit energy to therapeutic operations (such as laser ablation of tissue and photodynamic therapy). Other imaging modalities related to the present invention include angiography, endoscopy, and other similar imaging mechanisms, which are based on the back reflection of light in the visible or infrared range of the spectrum through a probe and to acquire images, thereby imaging a position in the patient's body. In addition, other high-resolution imaging modalities can use acoustic energy to generate optical energy (sonoluminescence imaging) or use optical energy to generate acoustic energy (photoacoustic imaging).

High-resolution imaging devices have been implemented in various forms for assessing a variety of different areas of mammalian anatomy, including the gastrointestinal system, cardiovascular system (including coronary, peripheral, and neurovascular systems), skin, eye (including retina), genitourinary system, breast tissue, liver tissue, and others. As an example, imaging of the cardiovascular system using high-frequency ultrasound or optical coherence tomography has been developed for assessing the structure and composition of arterial plaque. High-resolution imaging has been used to measure vessel or plaque shape, blood flow through diseased arteries, and the effectiveness of interventions on arterial plaques (e.g., by atherectomy, angioplasty, and/or stenting). Attempts have also been made to use high-resolution imaging to identify vascular damage that has not yet caused clinical symptoms but is at increased risk of rupture or erosion and causing a severe myocardial infarction. These so-called "vulnerable plaques" are areas of particular interest because the prospect of treating such plaques to proactively address adverse clinical events is conceptually attractive. However, no specific imaging modality has yet proven effective in this regard.

Chronic total occlusion (CTO) is a specific subset of vascular lesions in which the entire lumen of the vessel is blocked (according to angiography of the lesion) within approximately one month. Most intravascular imaging modalities are "side-view" and require a tunnel for passing the intravascular imaging device through the lesion. To image CTOs, high-resolution imaging methods would be more useful if they could be adapted for a "front-view" rather than a "side-view" configuration.

Another area of growing interest is the use of imaging guidance in tissue heart therapy and electrophysiology therapy. It is often necessary to position a catheter at a specific location within the heart chamber to perform a therapeutic procedure, such as the implantation of a device (e.g., a closure device for the foramen ovale, a valve repair or replacement device, a left atrial appendage occlusion device) or the placement of a therapeutic catheter (e.g., a local ablation or cryotherapy catheter). There is also a need to guide intermediate steps in the treatment, such as crossing the atrial septum of the heart. The use of high-resolution imaging can facilitate these steps. Intracardiac echo (ICE) using a phased array is one such technology currently used for this purpose.

Summary of the Prior Art

Yock (US Pat. No. 4,794,931) describes a catheter-based system for intravascular ultrasound that provides high-resolution imaging of intravascular structures. The system includes a housing containing an ultrasound transducer near the distal end of a long torque cable. When a motor rotates the torque cable and ultrasound transducer assembly, a 2D cross-sectional image of an anatomical structure (e.g., a blood vessel) can be generated. Linear translation of the catheter or torque cable, combined with the rotational motion of the ultrasound transducer, allows acquisition of a series of 2D images along the length of the catheter.

The use of intravascular ultrasound (IVUS) has become widespread, with many improvements and adaptations to the technology. Flexible torque cables (Crowley, US Pat. No. 4,951,677) improve the fidelity of transmission of rotational torque along the length of an IVUS catheter, minimizing an artifact known as non-uniform rotational distortion.

Liang et al. (U.S. Patents 5,606,975 and 5,651,366) describe a device for performing forward-view intravascular ultrasound in which ultrasound is directed toward a mirror having a fixed tilt, causing the ultrasound beam to sweep across a surface in front of the probe. The swept surface approximates the shape of a curved plane, and the resulting shape is derived from the relative rotational motion between the ultrasound transducer and the mirror. Liang et al. also describe devices that use a micromotor, a gear clutch mechanism, a steering cable, or a bimorph element such as a shape memory alloy, a piezoelectric array, or a conductive polymer to change the deflection angle of the mirror.

Suorsa et al. (US Patent 6,315,732) describe a catheter for intravascular delivery having an ultrasound sensor that is pivotable by a cable system about an axis other than the longitudinal axis of the catheter.

Maroney et al. (US Patent 5,373,849) and Gardineer (US Patent 5,373,845) also describe a catheter for pivoting an ultrasound transducer via a pivot/cable mechanism.

Hossack et al. (WO/2006/121851) describe a forward-looking ultrasonic sensor that uses a capacitive micromachined ultrasonic transducer (CMUT) and a reflective surface.

Couvillon et al. (US Patent 7,077,808) describe an intravascular ultrasound catheter having a reflective component that is actuated by an electroactive polymer to achieve a variable imaging angle relative to the longitudinal axis of the catheter.

Ultrasonic sensors themselves have also improved considerably, including the use of single crystal ultrasonic sensors as well as composite ultrasonic sensors.

The center frequency of IVUS is in the range of 3 to 100 MHz, more typically in the range of 20 to 50 MHz. Higher frequencies provide higher resolution, but result in lower signal penetration and thus a smaller observation area. Depending on a number of parameters, such as the center frequency and shape of the sensor, the sensitivity of the sensor, the attenuation of the medium through which the image is taken, and the specific implementation specifications that affect the signal-to-noise ratio of the system, the penetration depth ranges from less than 1 mm to several centimeters.

There are variations of high frequency ultrasound in which the signal acquisition and/or analysis of the backscattered signal is modified to facilitate obtaining or inferring further information about the imaged tissue. These include: elastography, in which the strain within the tissue is assessed as it is compressed at different blood pressures (de Korte et al., Circulation, April 9, 2002, 105(14):1627-30); Doppler imaging, which assesses motion (e.g., blood flow in anatomy); virtual histology, which attempts to infer tissue composition by combining the radiofrequency properties of the backscattered signal with pattern recognition algorithms (Nair, U.S. Patent 6,200,268); second harmonic imaging (Goertz et al., Invest Radiol, August 2006; 41(8):631-8), and others. Each of these imaging modalities can be improved by the apparatus described herein.

It is well known that many tissue structures exhibit a degree of angle dependence when imaged using ultrasound from different angles. Courtney et al. (Ultrasound in Medicine and Biology, 2002 Jan, 28:81-91) showed that the inner layers (media and intima) of a typical coronary artery have different angle-dependent backscattering properties compared to the outer layer (adventitia). Picano et al. (Circulation, 1985;72(3):572-6) showed angle-dependent ultrasound properties of normal, fatty, fibrofatty, fibrous, and calcified tissues. The ability to image tissue (e.g., arterial plaque) at different angles is a useful tool for improving the characterization of tissue in vivo using intravascular imaging devices.

Tearney et al. (U.S. Patent 6,134,003) describe several embodiments that enable optical coherence tomography to provide higher resolution imaging than readily available through high frequency ultrasound. Boppart et al. (U.S. Patent 6,485,413) describe several embodiments of optical coherence tomography, including a forward viewing implementation tool. Fiber or gradient refractive index (GRIN) lenses can be positioned by mechanisms such as motors, piezoelectrics, movable wires, expansion devices, and other mechanisms. Mao et al. (Appl Opt. 2007 Aug 10;46(23):5887-94) describe a method for making an ultra-small OCT probe from a single-mode fiber connected to a small length of GRIN fiber that acts as a lens. Introducing an optical spacer between the fiber and the lens can change the working distance of the fiber-lens system. Additionally, adding a small length of uncovered fiber at the distal end and beveling the uncovered fiber at an angle can add a deflection element to the end of the fiber-lens system.

Optical coherence tomography generally has a higher resolution than ultrasound and has the potential to better identify certain structures or components in blood vessels and other tissues. Optical coherence tomography also has better penetration into certain tissue components (e.g., calcified components) than ultrasound. For example, the thickness of the fibrous cap or the presence of inflammation or necrotic areas near the surface of the artery can be better resolved with optical coherence tomography. However, optical coherence tomography is limited by its smaller penetration depth (on the order of 500 to 3000 microns) in most biological media. Most of these media are not optically transparent.

Variations of optical coherence tomography (OCT) include polarity-sensitive OCT (PS-OCT), in which the birefringence properties of tissue components can be exploited to obtain additional information about structure and composition; spectroscopic OCT, which similarly provides improved information about the composition of imaged structures; Doppler OCT, which provides information about flow and motion; elastic imaging via OCT; and optical frequency domain imaging (OFDI), which allows for significantly faster acquisition of imaging data and, thus, can produce images over a larger volume of interest in a shorter time. Again, each of these imaging modalities can be improved by the present invention.

Compared to OCT, ultrasound has better penetration capabilities through biological media (e.g., blood and soft tissue) and its penetration depth is typically several millimeters greater than that of optical coherence tomography. The ability to perform imaging using one or both of these imaging methods using a combined imaging device offers advantages in selecting the desired resolution and penetration depth.

In addition to OCT, there are many other fiber-based imaging modalities. Amundson et al. describe a system that uses infrared light to image through blood (U.S. Patent No. 6,178,346). The range of the electromagnetic spectrum used for this imaging system is selected to optimize penetration into blood, allowing optical imaging through blood similar to that provided by angiography in the visible spectrum, but without the need to flush the blood out of the imaging area.

Angioscopy, endoscopy, bronchoscopy, and various other imaging devices have been described that are based on the principle of illuminating an area near the distal end of a rigid or flexible shaft within the human body, allowing visualization of internal ducts and structures within the mammalian body (e.g., blood vessels, the gastrointestinal cavity, and the pulmonary system). An image is then generated by positioning a photodetector array (e.g., a CCD array) near the end of the shaft or by having a bundle of optical fibers transmit light received from the distal end of the shaft to the distal end, where the photodetector array or other system allows an operator to generate or view an image display of the illuminated area. Among other disadvantages, the optical fiber bundle occupies a large volume and reduces the flexibility of the shaft.

Other fiber-optic-based minimally invasive assessment modalities for anatomical structures include Raman spectroscopy as described by Motz et al. (J Biomed Opt. 2006 Mar-Apr; 11(2)), near-infrared spectroscopy as described by Caplan et al. (J Am Coll Cardiol. 2006 Apr 18; 47(8suppl): C92-6), and fluorescence imaging, such as fluorescent imaging of labeled proteolytic enzymes in tumors (Radiology. 2004 Jun; 231(3): 659-66).

Advantageously, a high-resolution imaging probe is provided for acoustic or optical imaging as a "forward-looking" probe rather than a "side-looking" probe. It would also be useful to provide a similar probe capable of looking rearward, or from multiple angles in a basic side-looking configuration. It would also be useful to provide a similar probe capable of generating 3D imaging data sets.

It would also be advantageous to provide a 3D high resolution imaging probe that combines ultrasound imaging with one or more optical imaging devices.

It would also be advantageous to provide a minimally invasive imaging probe that can be used for photoacoustic or sonoluminescent imaging.

The present invention provides several embodiments for a novel scanning mechanism that can be widely used in medical imaging.

To the best of the inventor's knowledge, there has been no description of a system or apparatus utilizing the scanning mechanism described in the present invention.

Summary of the Invention

The present invention provides an imaging probe for imaging mammalian tissue and structures using high-resolution imaging, including high-frequency ultrasound imaging and/or optical coherence tomography. More specifically, the present invention relates to an imaging assembly incorporating a scanning mechanism for providing forward and side-viewing capabilities of the imaging probe.

Thus, in one embodiment, the present invention provides an imaging probe for insertion into a human body cavity or cavity to image the interior of the human body cavity or cavity or the external surface of the human body, or to image structures near the imaged surface, the imaging probe comprising:

a) an elongated hollow shaft having a longitudinal axis, the elongated hollow shaft having a distal portion, a proximal portion, and an elongated middle portion, an imaging assembly disposed in the elongated hollow shaft away from the proximal portion, the imaging assembly configured to emit an energy beam and receive a reflected energy signal reflected from an inner surface or an outer surface of the human body cavity, the imaging assembly being connected to a first end of an imaging catheter, the imaging catheter extending through the elongated hollow shaft and connected to an image processing system at a second end thereof through the proximal portion, the imaging catheter being configured to transmit energy to the imaging assembly;

b) a rotational drive mechanism for imparting rotational motion about the longitudinal axis at an angular velocity to the imaging catheter and the imaging assembly, the rotational drive mechanism including adjustment means for varying the angular velocity;

c) the imaging assembly includes a scanning mechanism, the scanning mechanism including a movable member configured to transmit the energy beam along a path outward of the elongated hollow shaft at a variable angle relative to the longitudinal axis to provide forward or side viewing capability of the imaging assembly, wherein the movable member is mounted such that the variable angle is a function of the angular velocity, the scanning mechanism configured to receive the reflected energy signal and transmit the reflected energy signal to the image processing system through the imaging catheter;

d) a controller connected to the rotation drive mechanism and the image processing system;

e) the image processing system is configured to process the received energy signals and generate images of the internal surfaces of the human body cavities and cavities or adjacent structures or images of the external surfaces of the human body or adjacent structures; and

f) a display device connected to the image processing system, for displaying images.

In another embodiment, the present invention provides an imaging probe for insertion into a human body cavity or hollow space to image the interior of the human body cavity or hollow space or to image the external surface of the human body, the imaging probe comprising:

a) an elongated hollow shaft having a longitudinal axis, the elongated hollow shaft having a distal portion, a proximal portion, and an elongated middle portion, an imaging assembly disposed in the elongated hollow shaft away from the proximal portion, the imaging assembly being configured to emit an energy beam and receive a reflected energy signal reflected from the inner surface of the human body cavity or cavity or the outer surface of the human body, the imaging assembly being connected to a first end of an imaging catheter, the imaging catheter extending through the elongated hollow shaft and connected to an image processing system at a second end thereof through the proximal portion, the imaging catheter being configured to transmit energy to the imaging assembly;

b) a rotational drive mechanism for imparting rotational motion about the longitudinal axis at a preselected angular velocity to the imaging catheter and the imaging assembly, the rotational drive mechanism including adjustment means for varying the preselected angular velocity;

c) the imaging assembly includes a scanning mechanism, the scanning mechanism including a movable member configured to transmit the energy beam along a path outward of the elongated hollow shaft at a variable angle relative to the longitudinal axis to provide forward or side viewing capability of the imaging assembly, the movable member including a magnet mounted on a periphery of the movable member, the scanning mechanism including an electromagnet spaced sufficiently closely to the pivotally mounted reflective member for the magnet to interact with the electromagnet, the electromagnet being connected to a power source, wherein the movable member is mounted at a variable angle as a function of power applied to the electromagnet, the scanning mechanism configured to receive the reflected energy signal and transmit the reflected energy signal through the imaging catheter to the image processing system;

d) a controller connected to the rotational drive mechanism, the electromagnetic power source, and the image processing system, the controller being configured to process the received energy signals and generate images of the inner wall structures of the human body cavities and cavities or images of the external surface of the human body; and

e) a display device connected to the image processing system, for displaying images.

A further understanding of the functionality and advantages of the present invention may be realized by referring to the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

FIG1 is a schematic diagram of an imaging system for ultrasound imaging and/or optical imaging;

FIG2 is a perspective view of a flexible imaging probe with a connector, a catheter, and an imaging assembly;

FIG2 a is a cross-sectional view of the middle portion of the imaging probe in FIG2 taken along the dotted line;

FIG2 b is an enlarged perspective view of the distal end region of the imaging probe of FIG2 ;

FIG2 c shows a schematic diagram of how the rotating and non-rotating parts of the imaging probe can be connected to the rest of the imaging system via an adapter;

FIG2 d is a perspective view of an example of a rotating component and a non-rotating component of a probe connected to an adapter;

3a to 3e are representative of general imaging catheter configurations described in the prior art;

FIG3 a illustrates one embodiment of an over-the-wire configuration for an overcoat in combination with an imaging probe having a guidewire lumen;

FIG3 b shows a cross-sectional view through the imaging probe along the vertical line 3 b - 3 b in FIG3 a , illustrating the guidewire lumen configuration;

FIG3 c shows a rapid access configuration for a jacket incorporating an imaging probe while having a guidewire lumen;

FIG3 d shows a cross-sectional view taken along the vertical line 3 d - 3 d in FIG3 c through the portion of the imaging probe that does not include the guide wire lumen;

FIG3 e shows a cross-sectional view taken along vertical line 3 e - 3 e in FIG3 c through the portion of the imaging probe containing the guide wire lumen;

FIG4a is a partially cutaway perspective view of an assembled housing of the distal portion of the imaging probe including a tiltable component;

FIG4 b shows the relative axes for an imaging assembly incorporating the tiltable component of FIG4 a ;

4 c to 4 l show various examples of longitudinal and axial cross-sections of a tiltable member that may have a preferred orientation if rotated about the longitudinal axis of the imaging probe in the absence of external forces, wherein the tilt axis is substantially perpendicular to the longitudinal axis;

5a to 5g illustrate the distal end of an imaging probe capable of acoustic and optical imaging, wherein a tiltable reflective surface is capable of varying the imaging angle as a function of the rotational speed of the imaging assembly;

5h and 5i illustrate collapsed and exploded perspective views of an imaging assembly that can be used to implement the embodiment described in FIGs. 5e to 5g;

6a to 6e illustrate the distal end of an imaging probe capable of acoustic imaging, wherein the acoustic sensor is mounted directly on a tiltable component;

6f to 6j illustrate a distal end of an imaging probe capable of optical imaging, wherein at least a portion of an optical transmitter and/or receiver is mounted directly on a tiltable member;

Figures 7a to 7c illustrate an example of a distal end of an imaging probe capable of acoustic imaging, wherein a deformable member carries an emitter and/or receiver of imaging and/or therapeutic energy. The imaging angle varies as a function of the rotational speed of the imaging assembly.

Figures 8a and 8b show examples of imaging probes in which the deformable member is reinforced by a resilient support structure and the imaging assembly and housing have optional irrigation ports;

Figures 8c and 8d show examples of imaging probes in which the deformable member is surrounded by an inflatable balloon that provides a protected area within which the probe can move when the balloon is inflated;

Figures 9a and 9b illustrate the use of a GRIN lens or refractive medium to amplify the resulting imaging angle;

Figures 10a and 10b illustrate examples of imaging probes in which the deformable member carries energy deflection components rather than emitters and/or receivers;

Figures 11a to 11d are examples of tiltable members in which the tilting action is accommodated and preferably enhanced by incorporating one or more structural features on the tiltable member to act as wings within the fluid medium of the imaging assembly;

FIG12 is an example of a deformable member in which deformation is accommodated and preferably increased by incorporating one or more structural features on the tiltable member to act as wings within the fluid medium of the imaging assembly;

Figures 13a and 13b are examples of some forward viewing scan patterns that can be achieved with the present invention;

Figures 13c and 13d are examples of lateral viewing spaces that can be imaged by the present invention;

FIG14a is an example of an imaging probe including a tiltable component serving as a deflector and an optical rotary encoder for determining the angular position of the imaging assembly relative to the outer jacket;

FIG14 b provides a cross-sectional view of a probe including a rotary encoder;

FIG15 is an example of an imaging probe in which tilting of a tiltable component is achieved in part by mechanically connecting to another tiltable component;

16a to 16c are examples of imaging probes in which the ultrasound transducer or optical imaging transmitter is configured primarily for side-view imaging, where the scanning mechanism allows for changes in imaging angle;

Figures 17a to 17g illustrate an embodiment suitable for combining optical imaging with an ultrasonic sensor for use with the present invention;

FIG18a is a perspective view of a deflection member comprising a flat optical reflective layer and a shaped acoustic reflective layer;

Figures 18b to 18d show cross sections of the deflection member;

19a and 19b illustrate an example of using a flexible imaging probe or imaging catheter with a steerable guidewire to deflect the distal region of a forward viewing catheter;

Figures 19c and 19d illustrate examples of imaging probes in which a steerable guide catheter is used to deflect the distal region of the imaging probe;

19e to 19h illustrate an example of an imaging probe used with a steerable guidewire having an inflatable balloon incorporated over its distal region to create a passageway large enough for advancement of the imaging probe through an occlusion; and

Figures 20a and 20b illustrate how a weighted resilient member can be connected to the tiltable member to help induce deflection of the tiltable member.

DETAILED DESCRIPTION

In general, the systems described herein refer to imaging probes that use optical or ultrasonic (or both) imaging. As needed, embodiments of the present invention are disclosed herein. However, the disclosed embodiments are merely exemplary, and it should be understood that the present invention can be implemented in a variety of and alternative forms. The drawings are not drawn to scale, and some features are enlarged or reduced to show the details of specific elements, while related elements may be omitted to prevent obstruction of novel parts. Therefore, the specific structural and functional details disclosed herein are not to be construed as limiting, but merely as a basis for the claims and as a representative basis for teaching those skilled in the art to implement the present invention in various ways. For illustrative and non-limiting purposes, the illustrated embodiments relate to imaging probes.

As used herein, when used in conjunction with ranges for dimensions, temperatures, or other physical properties or characteristics, the terms "about" and "approximately" are intended to encompass minor variations between the upper and lower limits of the dimensional range, thereby not excluding embodiments where, on average, most dimensions meet the range but statistically some dimensions may fall outside the range. For example, in embodiments of the present invention, dimensions of components of an imaging probe are given, but it should be understood that these are not intended to be limiting.

As used herein, the phrase "co-registration of images" refers to the process of identifying a subset of imaging data acquired by one imaging modality with a subset of imaging data acquired using another imaging modality, where the imaging data from both modalities were acquired by detecting a form of imaging energy (e.g., photons or ultrasound) from the same object (or, in the present case, tissue). Each co-registered point in the first subset can then be mapped to a corresponding point in the second subset, such that the two points from the two different imaging modalities are considered to be acquired from similar focal regions of the imaged object (or tissue).

Successful and accurate co-registration of images or portions of images between images acquired using two or more imaging modalities is useful because it can provide multiple opportunities to assess features of interest of the imaged object by more than one imaging modality.

1 shows an overview of an exemplary imaging system constructed in accordance with the present invention, generally designated 10. The system includes an imaging probe 12 connected to an image processing and display system 16 via an adapter 14. The image processing and display system 16 includes the necessary hardware to support one or more of the following imaging modalities: 1) ultrasound, 2) optical coherence tomography, 3) angioscopy, 4) infrared imaging, 5) near infrared imaging, 6) Raman spectroscopy, and 7) fluorescence imaging.

Implementations of optical coherence tomography, ultrasound, angioscopy, and infrared imaging circuits have been described in the prior art.

The systems described herein typically further include a controller and processing unit 18 to facilitate the coordinated behavior of the multiple functional units of the system, and may further include a display and/or user interface, and may further include electrode sensors to acquire an electrocardiogram signal from the body of the patient being imaged. The electrocardiogram signal can be used to set the time for imaging data acquisition in situations where cardiac motion may affect image quality. The electrocardiogram can also be used as a trigger for when to start an acquisition sequence, such as when to start changing the rotational speed of the motor to enable a desired scanning pattern to take effect. For example, an ECG-triggered start of an imaging sequence can enable images to be acquired during a specific phase of the cardiac cycle (e.g., systole or diastole).

If included in a particular embodiment of the present invention, the optical circuitry and electronics 21 forming the image processing and display system may include any or all of the following components: interferometer components, one or more optical reference arms, optical multiplexers, optical demultiplexers, light sources, light detectors, spectrometers, piezoelectric filters, timing circuits, analog-to-digital converters, and other components known for implementing any of the optical imaging techniques described in the Background and Prior Art sections. The ultrasound circuitry 20 may include any or all of the following components: pulse generators, electronic filters, analog-to-digital converters, parallel processing arrays, envelope detection, amplifiers including time gain compensation amplifiers, and other components known for implementing any of the acoustic imaging techniques described in the Background and Prior Art sections.

If included in certain embodiments of the present invention, the controller and processing unit 18 serves a variety of purposes, and the components will be significantly adapted to the needs of a particular imaging system. The controller and processing unit 18 may include one or a combination of motor drive controllers, data storage components (e.g., memory, hard disk, removable storage, readers and recorders for portable storage media such as CDs and DVDs), position detection circuitry, timing circuitry, cardiac gating functionality, a volumetric image processor, a scan converter, and other devices. Optionally, a display and user interface 22 may also be provided for displaying the imaging data in real time or at a time subsequent to the acquisition of the imaging data.

The imaging probe 12 includes an imaging assembly 30 near its distal end 32, an optional imaging catheter 34 along most of its length, and a connector 36 at its proximal end 38. For purposes of the present invention, the imaging assembly 30 generally refers to the portion of the imaging probe 12 from which signals (acoustic or optical, or both) are collected for imaging of an area proximate to the imaging assembly 30. The imaging assembly 30 includes one or more imaging energy transmitters and one or more imaging energy receivers. For purposes of the present invention, "imaging energy" refers to light energy or acoustic energy, or both. Specifically, light refers to electromagnetic waves covering wavelengths in the ultraviolet, visible, and infrared spectrums. For example, for acoustic imaging, the imaging assembly 30 includes an ultrasonic sensor that is both a transmitter and a receiver of acoustic energy.

For optical imaging, the optical assembly 30 generally includes the distal end of an optical fiber and a combination of optical components, such as a lens (e.g., a ball lens or a GRIN lens), which collectively serve as an optical receiver and can serve as an optical transmitter. A mirror and/or prism is typically incorporated as part of the optical transmitter and/or receiver. The imaging assembly 30, connector 36, and/or imaging catheter 34 can be fluid-filled (e.g., saline) and flushable.

The imaging probe 12 may include ports at one or more points along its length to facilitate flushing. For optical imaging, a gas-filled imaging probe 12 may be considered. Preferably, the gas consists essentially of carbon dioxide or other readily soluble gases. Alternatively, the imaging assembly may be partitioned so that there is at least one gas-filled partition or cavity for optical imaging and at least one liquid-filled partition or cavity for acoustic imaging.

Imaging catheter 34 includes at least one optical waveguide or at least one wire (preferably two or more) that connects the transmitter and/or receiver to the adapter via a connector. Imaging catheter 34 can also serve as a mechanical force transmission mechanism for rotating or translating the imaging assembly. For example, imaging catheter 34 can include an optical fiber wrapped around two layers of insulated wire. Imaging catheter 34 can be further enhanced by other structural features, such as a helical winding or other design for forming an imaging torque cable for rotating the scanning mechanism, as described in the related art.

The adapter 14 facilitates the transmission of signals from any optical fiber and/or wire to an appropriate image processing unit. The adapter preferably includes a motor drive unit for imparting rotational motion to the rotating components of the imaging probe. The adapter 14 may also incorporate a pullback mechanism 49 ( FIG. 2 d ) or a reciprocating push-pull mechanism to facilitate longitudinal translation of the imaging assembly. This longitudinal translation of the imaging assembly 30 may occur in conjunction with longitudinal translation of the outer shaft surrounding the imaging catheter 34, or within a relatively stationary outer shaft.

Additional sensors may be incorporated as part of the adapter 14, such as position sensing circuitry for sensing the rotational angle of rotating components within the imaging probe 12. The imaging probe 12 may also include a storage component, such as an EEPROM or other programmable storage device, that contains information about the imaging probe to the rest of the imaging system. For example, it may include instructions for identifying the specifications of the imaging probe 12 and may also include calibration information about the probe 12. Furthermore, the adapter 14 may include an amplifier to enhance the transmission of electrical signals or power between the imaging probe and the rest of the system.

It is important to recognize the need to optimize the geometry of minimally invasive probes so that they can be as small as reasonably possible to achieve their intended purpose. Current IVUS and ICE probes are approximately 0.9 to 4 mm in diameter, and the smaller size of the probe allows it to be delivered farther into the vascular tree of the coronary anatomy as the vessel size tapers. Therefore, the smaller size generally allows access to most of the coronary anatomy. It is therefore desirable to enable probe embodiments to perform imaging in a configuration that minimizes certain dimensions of the probe (e.g., probe diameter), such as imaging using the scanning mechanisms described herein.

FIG2 is a perspective view of a flexible catheter containing an optical fiber 40 and a coaxial wire 50. The proximal connector contains the optical fiber 40, which can be received by an adapter to optically connect the imaging fiber 40 to the "back end" of the optical imaging system. An electrical connector 56 is also provided, which allows one or more electrical conduits to be connected to the ultrasound circuit and/or the controller and processing unit. In embodiments where the imaging catheter rotates about its longitudinal axis, it may be necessary to connect the rotating component of the imaging fiber to a relatively stationary optical fiber, which is connected to the back end 16 of the optical imaging system. Connection to the rotating fiber optic probe can be achieved through a fiber optic rotary joint, which is incorporated as part of the proximal connector of the imaging probe 36 or as part of the adapter 14. Similarly, in embodiments where the imaging catheter rotates about its longitudinal axis, it may be necessary to connect the wires that rotate with the imaging catheter to relatively stationary conductors of the ultrasound circuit and/or the controller and processing unit, preferably through slip rings. These slip rings can be incorporated as part of the proximal connector of the imaging probe 36 or as part of the adapter 14.

FIG2 a shows a cross-sectional view of the middle portion of the imaging probe of FIG2 taken along the dashed line, showing the optical fiber 40, the guidewire port 44 and the guidewire 42, the imaging catheter 34, the imaging catheter lumen 46, the hollow outer sleeve 48, the flexible elongated shaft (made of a physiologically compatible material and having a diameter suitable for allowing the hollow elongated shaft to be inserted into a body lumen and cavity), and the coaxial wire 50. The enlarged detail view of the end of the imaging probe 10 shown in FIG2 b shows the distal end of the guidewire 42 extending beyond the end of the outer sleeve 48 and the irrigation port 54 at the end of the outer sleeve 48. In FIG2 , the proximal end of the imaging probe 10 includes the connector assembly 36 and another guidewire port 55 into which the guidewire 42 is inserted, and the connector assembly 36 includes an irrigation port 58 and electrical contacts 56 along the connector body.

FIG2 c shows a schematic diagram of how the rotating and non-rotating components of the imaging probe can be connected to the rest of the imaging system via an adapter. FIG2 d schematically shows how the rotating component of the imaging probe can be connected to the rotating component of the adapter. The rotating components can be connected electrically, optically, and/or mechanically via connectors and other configurations known in the art. Similarly, the non-rotating component of the imaging probe can be connected to the non-rotating component of the adapter 14. The adapter 14 may include slip rings, optical rotary joints, and other tools that can electrically or optically connect the rotating component to the non-rotating component and enable the necessary electrical and optical signal communication with the rest of the system.

A dual fiber optic rotary joint can also be used, but is much more complex. Electrical connections between any conductors affixed to a rotating component in the imaging probe 12 can be made to a non-rotating conductive element via a metal slip ring and spring, a metal slip ring and brush, or other generally known methods of making conductive contact between a stationary conductor and a rotating conductor.

Although the electrical, optical, and mechanical connections are shown separately in FIG. 2 d , the number of connectors that must be individually connected between the probe and the adapter can be reduced by combining multiple connectors into a combined connector to obtain fewer connectors, as desired for a particular embodiment.

Although the above embodiments are illustrated by both acoustic and optical imaging, it is possible to implement a catheter without acoustic means or without optical means.

Figure 3a shows one embodiment of an over-the-wire configuration for outer sleeve 48, and Figure 3b shows a cross-section of outer sleeve 48 taken along vertical line 3b-3b in Figure 3a through the portion containing imaging assembly 30. In Figure 3a, as viewed in the cross-section of Figure 3b taken along vertical line 3b-3b in Figure 3a, guidewire catheter 44 is located in a thicker portion of outer sleeve 48.

FIG3c shows another embodiment of a cover 60 that is a "quick-change" configuration for a cover that can be combined with an imaging probe if a guidewire is required. The cover 60 in FIG3c includes the access port 55 shown in FIG2. FIG3d shows a cross-section of the "quick-change" configuration 60 along line 3d-3d in FIG3c through a portion near the access port 55 for the guidewire. FIG3e shows a cross-section along line 3e-3e in FIG3c.

The present invention discloses embodiments of scanning mechanisms for providing forward and lateral viewing ultrasound (IVUS) and optical coherence tomography (OCT) imaging. For ultrasound and optical coherence tomography, the ability to adjust the propagation angle of emitted and/or received imaging energy, when combined with rotational motion of the imaging assembly, allows for scanning of 3D space. For angioscopy and infrared imaging, the ability to adjust the propagation angle of emitted and/or received imaging energy, when combined with rotational motion of the imaging assembly, allows for the use of a single optical fiber rather than requiring a bundle of optical fibers or an array of photosensitive elements to produce an image. This improvement allows for greater flexibility and/or allows for further miniaturization of the imaging device.

Another advantage of the present invention is that optical and acoustic imaging can be performed in a configuration where the optical and acoustic imaging energies travel through the same overall space, thereby facilitating co-registration of the optical and acoustic images and minimizing the volume required to accommodate more than one imaging modality within the imaging assembly. Nevertheless, the scanning mechanism can be used in conjunction with a single imaging modality (e.g., ultrasound or a single optical imaging technique). Similarly, two or more optical imaging techniques (with or without ultrasound) can simultaneously use the scanning mechanism on a single probe.

4a shows a partially cut-away perspective view of the distal region of the imaging probe 12, showing a portion 605 of the outer casing 601 removed. The imaging probe 12 is internally provided with a tiltable member 602, which forms part of the imaging assembly and is mounted on a pin 603 that extends through a tilt axis 604 of the tiltable member 602.

In various embodiments of the present invention capable of scanning a space for imaging purposes, the principle of centripetal acceleration is advantageously utilized. Prior art mechanisms have proposed mechanisms for directly tilting sensors or reflectors, such as motors or cable and pulley systems. Various embodiments of the present invention disclosed herein provide the ability to tilt or deform components by varying the rotational speed of the imaging assembly.

Referring to FIG. 4 b , tilting or deforming the component is used to change the tilt angle α. The imaging angle is defined as the angle between the longitudinal axis 606 of the imaging probe 12 and the direction of emission and/or reception of imaging energy. In the present invention, the imaging angle is a function of the tilt angle α of the tiltable component 602, or a function of the degree of deformation of the deformable component, which is also generally represented by the tilt angle α.

4 b shows a schematic illustration of the tilt angle α relative to the axis of rotation of the tiltable component 602, where the tiltable component 602 is shown as a disc that pivots about a tilt axis 604. The ability to vary the angular velocity of the tiltable or deformable component 602 of the imaging system, and subsequently the imaging angle, will be demonstrated in the following description of the invention and through experimental results.

First, the case of changing the imaging angle by using a tiltable component 602 will be described. The imaging assembly includes a tiltable component 602 that can rotate about an axis 604 (tilt axis), which is substantially perpendicular to the longitudinal axis 606 of the imaging probe. For example, the tiltable component 602 can be mounted on or otherwise associated with a hinge, mounted on or otherwise associated with one or more pins (such as the aforementioned pin 603), mounted on or otherwise associated with a spring or a deformable substrate, so as to be able to rotate about the tilt axis 604.

The tiltable member 602 has the following characteristics: when the imaging assembly is rotated about an axis other than the tilt axis, the tiltable member 602 has a discrete plurality of preferred orientations (typically one or two). Preferably, the imaging assembly's axis of rotation is substantially coincident with (i.e., substantially parallel to or close to) the longitudinal axis 606 of the imaging probe. Preferably, the tilt axis is orthogonal to the longitudinal axis. In the absence of gravity or any other forces other than the centripetal force involved in the rotation of the imaging assembly (e.g., the restoring force described below), the tiltable member 602 will orient itself to a preferred orientation about the tilt axis.

4c to 41 show several non-limiting examples of longitudinal and axial cross-sections of a tiltable component having a preferred orientation if rotated about the longitudinal axis 606 of the imaging probe 12 in the absence of external forces, wherein the tilt axis 604 is substantially perpendicular to the longitudinal axis 606.

Specifically, Figure 4c is a longitudinal cross-sectional view of an example of an embodiment of an imaging probe in which the tiltable component is a disc 610 mounted on pins 611. Figure 4d is a corresponding cross-sectional view taken along line 4d-4d.

Figure 4e is a longitudinal cross-sectional view of an embodiment of an imaging probe in which the tiltable member is part of a ball 612 mounted on a bracket 613. Figure 4f is a corresponding cross-sectional view taken along line 4f-4f of Figure 4e.

FIG4 g is a longitudinal cross-sectional view of an embodiment of an imaging probe in which the tiltable member 614 has a more arbitrary shape and is mounted on the pin 611 with a spacer 615 (only visible in FIG4 h ) that helps stabilize the position of the tiltable member 614 on the pin 611. FIG4 h is a corresponding cross-sectional view taken along line 4 h - 4 h of FIG4 g .

FIG4i is a longitudinal cross-sectional view of an embodiment of an imaging probe in which a tiltable member 620 is mounted via a pin 622, allowing the tiltable member 620 to pivot about a pivot axis 626. FIG4j is a corresponding cross-sectional view taken along line 4j-4j of FIG4i , showing the pin 622 extending into a divot 624 located on the side of the tiltable member 620 and receiving the pin 622. The small surface area of the pivot mechanism in this embodiment helps minimize friction about the pivot axis 626. Preferably, the pin 622 contacts the tiltable member 620 only near the pin tip, thereby minimizing the surface contact area.

FIG4k is a longitudinal cross-sectional view of an embodiment of an imaging probe in which a tiltable member 630 is mounted using a pivot axis 632 that does not intersect the imaging probe's rotational axis 606. FIG4l is a corresponding cross-sectional view taken along line 41-41 of FIG4k. Functionally, in embodiments including a tiltable member, the pivot axis is identical to the tilt axis.

The functional purpose of the tiltable component 70 is to be able to change the angle relative to the longitudinal axis of the imaging probe 31 ( FIG. 5 a ) at which imaging energy (e.g., light beam or acoustic energy) is transmitted to and/or received from the surrounding environment. This can be achieved by mounting a transmitter and/or receiver (e.g., an ultrasound sensor or optical components) on the tiltable component 70. By varying the rotational speed of the imaging assembly, the tilt angle will change, and thereby the angle at which light or acoustic energy is transmitted and/or received will change.

Alternatively, a tiltable member can be used to deflect imaging energy emitted and/or received by a member 88 that is not directly connected to the tiltable member 70, as shown in FIG5 a. For example, as described above, an ultrasound transducer 88 or an optical transmitter 92 can direct imaging energy toward the tiltable member 70. The imaging energy is then deflected by an energy deflection member mounted on the tiltable member 70. For ultrasound imaging, the energy deflection member (tiltable member 70) can include an acoustically reflective surface, such as a solid metal surface (e.g., stainless steel) or a crystalline surface, such as quartz crystal or glass or a hard polymer.

For optical imaging, the energy deflection member (tiltable member 70) may include an optically reflective surface, such as a mirror made of polished metal, a metallized polymer (e.g., metallized biaxially oriented polyethylene terephthalate (Mylar)), sputtered or electrochemically deposited metal, metal foil, or other reflective member (e.g., a thin film reflector). Common metals used to make mirrors include aluminum, silver, steel, gold, or chromium.

FIG5 a shows an embodiment of the distal end 29 of an imaging probe 31 having an imaging assembly 30 including a tiltable member 70, wherein the tiltable member is a disc mounted on a pin 72 that enables the disc 70 to pivot about the pin, similar to FIG4 b discussed above. The pin 72 defines the tilt axis of the tiltable disc 70. When the imaging assembly 30 is stationary, the disc 70 will remain in an arbitrary starting position. In the example shown, the starting position is defined by a stop 80 corresponding to the maximum imaging angle, wherein the restoring force provided by the torsion spring 76 pushes the disc 70 toward the aforementioned stop 80. FIG5 b shows a cross-section along line 5 b-5 b of FIG5 a.

If the tiltable component 70 tilts away from its preferred orientation under the action of an external force (such as gravity, magnetism, electrostatics, friction with other moving components or fluids, compression, cantilever forces, normal forces, or any other source of non-completely opposite moments on the tiltable component 70 about the tilt axis), the tilt angle will increase.

One or more stops 80 and 82 can limit the tilt angle range of the tiltable component 70. For example, the stop 80 can be a post or lip extending from the sleeve 84 of the imaging assembly 30, which acts as a stop to prevent the tiltable component 70 from further changing its tilt angle when the tiltable component 70 contacts the stop 80. Thus, the stop can be used to limit the tilt angle to a maximum value determined by the position of the stop. Once the maximum tilt angle is reached, the normal force applied to the tiltable component 70 by the stop 80 resists the return mechanism. In various embodiments, the maximum tilt angle is the tilt angle achieved when the imaging assembly 30 is at rest and at a low rotational speed.

An additional or alternative stop 82 may be included to create a minimum tilt angle that is achieved when the tilt member 70 is at a rotational speed at the upper end of its operating range. In fact, in many cases there is no significant benefit to allowing the tilt angle to reach zero, as will become clear from the subsequent description of specific embodiments.

Preferably, the imaging assembly 30 includes one or more mechanisms that tend to increase the tilt angle of the tiltable member 70. For purposes of the present invention, such mechanisms are referred to as return mechanisms. A torsion spring 76 (as shown in Figures 5a and 5c) or a compression spring can be used as the return mechanism, wherein one end of the torsion spring 76 is mechanically in contact with or connected to the tiltable member 70. The other end is mechanically connected to another portion of the imaging probe 31, such as the main body of the imaging assembly.

As the imaging assembly 30 rotates, the tray 70 will tend to align itself so that the normal to the plane defined by the surface of the tray 70 is substantially parallel to the longitudinal axis. As shown in FIG5 c , another stop 82 (corresponding to the minimum imaging angle) is shown to prevent the tray 70 from reaching its preferred orientation at high rotational speeds of the imaging assembly. With a suitably configured imaging assembly, the stop 82 corresponding to the minimum imaging angle can correspond to zero angle, thereby providing imaging in a direction parallel to the longitudinal axis of the imaging probe. FIG5 d shows a cross-section along line 5 d - 5 d of FIG5 c .

Alternatively, a magnetic, electrostatic, hydraulic or other mechanism capable of applying a torque to the tiltable component about the tilt axis may be applied. Other examples of mechanisms that can be used to provide a restoring force include tension from an elastomer (e.g., rubber, polyurethane, silicone, fluoroelastomer, thermoplastic elastomer, and many other materials) or by using a cantilever spring or foil. In very few embodiments of the imaging device, in which intermolecular forces (e.g., electrostatic forces) and van der Waals forces between the components of the imaging assembly may become significant even in the absence of an applied external voltage, the inherent intermolecular forces between the tiltable component and structures proximate to the tiltable component (e.g., stops 80 and 82 described below) are sufficient to provide a net restoring force. For example, stops comprising a surface made of PVC or LDPE can provide sufficient attractive force between the tiltable component and the stop. This is similar to the way plastic film is used to cover household containers for food storage (i.e., Glad Wrap).

FIG5e shows an embodiment of a scanning mechanism for an imaging probe 600, in which the torsion spring 76 of FIG5a is replaced by a simple cantilever wire 640 that contacts the surface of the tiltable member 70 and is connected to a post 787 to generate a restoring force. The cantilever 640 can be made of nitinol, platinum, gold, or a variety of other suitable materials including polymers.

FIG5 f shows an embodiment of a scanning mechanism for an imaging probe 670, wherein the tiltable component 70 includes a magnet 680 and the non-tilting component of the imaging assembly includes a magnet 681 that is used to generate a restoring force. The magnets can be oriented so that they attract or repel each other depending on their relative positions within the imaging assembly. One of the magnets 681 can be an electromagnet so that its strength can be adjusted or changed as needed to change the imaging angle. The electromagnet can be energized by a conductor (not shown) extending from the magnet to the proximal end of the probe. If the tiltable component 70 has a certain degree of ferromagnetism, then the tiltable component 70 may not have a magnetic component, and a single magnet may be sufficient to generate the restoring force, as shown in FIG5 g.

It should be noted that electromagnets can be used to deflect the tiltable member 70 and produce a scan pattern for imaging by varying the current through the electromagnets without any rotational movement of the imaging assembly or imaging catheter.

Figure 5h provides a perspective view of an embodiment of the imaging assembly 30, while Figure 5i provides an exploded view of the same embodiment. The tiltable component 70 serves as a deflector for the imaging energy generated by the ultrasonic transducer 88. Pins 752 are recessed into holes in the side of the tiltable component 70 and secured thereto by press-fit or adhesive bonding. In this embodiment, the pins point outward and are received by tenons (not shown) in respective pin retainers 751. During assembly, the pin retainers 751 are secured within sleeves 753 of the imaging assembly 30. The pins 751 and pin retainers 752 form a pivot axis about which the tiltable component can pivot with low friction. A stop 82 connected to the sleeve 753 limits the maximum tilt angle of the tiltable component 70. A cantilever spring extends from the rear of the sleeve and contacts the bottom surface of the tiltable component, ensuring that the tiltable component remains at its maximum imaging angle when there is minimal or no rotation of the imaging assembly about its longitudinal axis.

5a to 5g, the imaging assembly 30 may include an optical transmitter/receiver and associated directional and focusing optical and/or ultrasonic sensors. The ultrasonic sensor 88 is mounted at the end of a small coaxial cable 89. An optional optical isolator (not shown) and lens 92 are mounted at the end of a fiber optic cable 96 near the mirror 94 in the imaging assembly 30 of FIG5a, where the optical and ultrasonic transmitters are configured to transmit imaging energy to and receive imaging energy from the tiltable member 70. The optional optical isolator may simply be a transparent medium, such as glass or polymer (e.g., unclad fiber), which may be placed between the distal end of the fiber and the lens to increase the working distance or tolerance of the optical imaging system, as described by Mao.

Preferably, the transmitter and/or receiver are mounted on a component of the imaging assembly that rotates with the imaging assembly. However, it is also possible to mount the transmitter and/or receiver on a component of the imaging probe that does not rotate with the imaging assembly when the energy deflection mechanism within the imaging assembly rotates. This can be achieved by mounting the transmitter and/or receiver on a housing or by dividing the imaging assembly into two or more subassemblies, one of which rotates and includes the tiltable component 70.

As shown in Figures 5a to 5i, it is advantageous to use an energy deflection component to change the imaging angle rather than mounting the transmitter and/or receiver directly on a tiltable component (as shown in Figures 6a to 6e). When the sensor is mounted directly on the tiltable component, the tilting motion may be hindered by the mechanical properties of the transmitter and/or receiver and the mechanical properties of the electrical and/or optical conduits that connect the transmitter and/or receiver to the rest of the imaging system. The transmitter and/or receiver may be too bulky to be conveniently placed on a tiltable or bendable component.

Furthermore, the use of a reflective surface effectively doubles the change in imaging angle. For example, a change in the tilt angle of the reflective surface results in a change in imaging angle that is typically twice the change in tilt angle. This doubling of the imaging angle can increase the size of the field of view obtainable by the scanning mechanism in various embodiments.

In the case of acoustic imaging, it is possible that a strong acoustic pulse applied to an acoustically reflective surface will distribute some mechanical energy into the tiltable component. This can occur when the acoustically reflective surface does not act as a theoretically perfect reflector and can cause the tiltable component, or certain subcomponents of the tiltable component, to vibrate. Such vibrations can contribute to artifacts in any resulting image, particularly when the energy of such vibrations is directed back toward the acoustic receiver. Therefore, a damping mechanism must be incorporated into the tiltable component. Materials suitable for backing acoustic ultrasonic sensors can be used for this purpose, such as epoxy resin mixed with tungsten powder. The damping mechanism can be an additional layer within the tiltable component, or it can be incorporated into the design of the hinge or pin to which the tiltable component is mounted, for example by adding a layer of damping material to the pin or to any hole in the tiltable mechanism that receives the pin.

Figures 6a through 6e illustrate the distal end of an imaging probe, including an imaging probe capable of acoustic imaging, wherein the scanning mechanism includes an acoustic sensor mounted directly on a tiltable member. More specifically, Figure 6a illustrates an embodiment of an imaging assembly 300 including a tiltable member 302 pivotally mounted on a pin 312, and an acoustic sensor 304 mounted on the tiltable member 302. A stop 306 defines the maximum achievable imaging angle. A pair of conductive elements 308 extend from the imaging catheter 34 to the acoustic sensor 304. The conductive elements 308 preferably have a highly flexible construction (e.g., a thin coaxial line) or a thin film construction that allows for one or more conductive pathways within the film. Due to the mechanical properties of the conductive elements 308, the conductive elements 308 can provide a restoring mechanism, thereby tending to urge the tiltable member 302 to a setting having a maximum tilt angle.

For example, as shown in FIG6a, the stiffness of the conductive element 308 provides sufficient force to urge the tiltable component 302 against the stop 306, thereby achieving the maximum imaging angle for a particular embodiment. This angle can be achieved when the imaging assembly 300 is not rotating or is rotating at a low angular velocity about the longitudinal axis of the imaging probe. The imaging assembly 300 shown in FIG6b shows how the tiltable component 302 aligns itself to a preferred configuration and thereby changes the imaging angle as the angular velocity increases.

It should be noted that while the imaging angle and tilt angle shown in Figures 6a and 6b are substantially equal, the acoustic sensor 304 can be mounted on the tiltable component 302 to offset the imaging angle and tilt angle. For example, the geometry of the tiltable component 302 can include an angled surface for mounting the sensor 304, or a thin shim can be inserted between the sensor 304 and the tiltable component 302 to offset the imaging angle and tilt angle. It should also be noted that the embodiments shown in Figures 6a and 6b can also include other restoring mechanisms. The acoustic sensor 304 can also be recessed within the tiltable component 302, as shown in Figure 6c.

For some embodiments, the connection of the conductor to the acoustic sensor on the tiltable member may result in the conductor being too rigid to allow the tiltable member to tilt with sufficient fidelity for the desired application. In such cases, a conductive connector, such as that described by Maroney et al. in U.S. Patent 5,373,849, may be used. Alternatively, one or more portions of the pivot mechanism (e.g., one or more pins of the pivot mechanism for the tiltable mechanism) may serve a secondary purpose of making electrical contact with the electrically insulated conductor on the tiltable member.

Figures 6d and 6e illustrate the use of a pin 310 electrically connected to a coaxial cable to provide electrical contact with a conductive path within the tiltable component 302, thereby providing a connection to the sensor 304 on the tiltable component 302. The conductive path is insulated within the core of the pin 310, except at the tip where the pin 310 contacts the tiltable component 302. Similarly, the recess of the tiltable component for receiving the pin 310 can be electrically insulated, except at the point of contact with the tip of the pin 310. In this case, the fluid near the tiltable component 302 can optionally include a fluid with a lower conductivity than salt water, such as distilled water or mineral oil. Alternatively, an O-ring can be used to improve electrical insulation at the electrical contact point.

Alternatively, the conductive element 308 may be replaced by an optical fiber, and the acoustic sensor 304 may be replaced by one or more optical receivers and/or transmitters.

Figures 6f to 6j illustrate the distal end of an imaging probe capable of optical imaging, wherein at least a portion of the optical transmitter and/or receiver is mounted directly on the tiltable component. In Figures 6f and 6g, the energy deflection component is made of a transmissive refractive element 392 (e.g., glass, pure polymer, and many other materials) and deflects the imaging energy in a manner similar to a prism or lens. Light from an optical fiber 391 mounted within the imaging assembly 30 is directed toward the refractive element 392 mounted on the tiltable component 70. The distal end of the optical fiber can be terminated by an optical isolator or GRIN lens, as shown in other figures of the present invention. In the embodiments of Figures 6f and 6g, only a portion of the optical transmitter and/or receiver is mounted directly on the tiltable component. The transmissive refractive element 392 is not directly connected to the distal end of the optical fiber 391, thereby allowing the tiltable component 70 to be tilted more easily without being hindered by any mechanical influence from the optical fiber 391.

In Figures 6h to 6j, the entire distal end of the optical transmitter and/or receiver (including the distal end of the optical fiber 391) is mechanically connected to the tiltable member 70. The optical fiber 391 also serves as a mechanical component for providing a restoring force that tilts the tiltable member 70 at the maximum tilt angle, as shown in Figure 6h. At higher rotational speeds, the tiltable member 70 will tend to align as shown in Figure 6i. Figure 6 provides a front view of the imaging assembly 30.

Alternatively, the conductive element 308 and the optical fiber 391 in Figures 6a to 6j may be replaced by a combination of the conductive element 308 and one or more optical fibers 391, while the acoustic sensor 302 is replaced by a combination of the conductive element 308 and one or more optical fibers 391. It should be noted that in some embodiments, increasing the number of conductive elements 308 and/or optical fibers may affect the range of imaging angles that can be achieved by the tiltable component, as a result of the increased stiffness of the conductive elements 308 and/or optical fibers.

For some embodiments, a rotary optical joint can be incorporated into a pivoting mechanism, such as by introducing an optical fiber via a pin and a pin-receiving element. While such a rotary joint for single-mode fiber transmission would require considerable precision (for alignment of optical fibers of the order of 4-12 microns in diameter), a rotary joint suitable for connecting optical light paths having dimensions similar to those found in multimode fibers (of the order of 50 to 250 microns in diameter) can be readily implemented. Planar lightwave circuits (e.g., available from Grintech, Germany), free-space channels, prisms, and lenses can be used to direct light through components combined with tiltable components to direct light in a manner suitable for optical imaging, such as for OCT, angioscopy, infrared imaging, near-infrared spectroscopy, and fluorescence imaging.

Other alternative embodiments exist in which the imaging angle can be varied by varying the rotational speed of the imaging assembly. Rather than causing the tiltable member to tilt about a pivot axis, the bendable member can be used to carry a transmitter and/or receiver or an energy deflection mechanism. The bendable member comprises a structural assembly that is constrained at one or more points along its length with respect to its radial distance from the imaging assembly's axis of rotation, but is unconstrained along the majority of its length.

For purposes of this specification, a "radially constrained" portion of a bendable component is that portion of the bendable component that is at a relatively fixed distance from the axis of rotation of the imaging assembly. Similarly, a "radially unconstrained" portion of a bendable component is that portion of the bendable component that is capable of varying its radial distance from the axis of rotation of the imaging assembly in response to centripetal, gravitational, electrostatic, magnetic, and other forces. The structural assembly may comprise an elongated portion of bendable plastic, a wire, sheet, or even a rod made of optical fiber. It may comprise a collection of subcomponents that vary mechanical properties such as strength, elasticity, mechanical hysteresis to deformation, and other aspects.

The operating principle of using a bendable component to change the imaging angle is that as the imaging assembly rotates, the bendable component will bend due to centripetal acceleration. For a given rotation, different parts of the bendable component may bend in different directions or to different degrees depending on many factors, including the mechanical properties of the bendable component and its subcomponents, and the geometry of the bendable component. For the purpose of explanation, the bendable component can be molded as a collection of infinitesimally small volumes (referred to as cells). The cells in the radially constrained portion of the bendable component will maintain their approximate distance from the axis of rotation, while the cells in the radially unconstrained portion will tend to travel in a direction tangential to their generally circular path due to inertia.

Internal forces (tension, compression, etc.) within the bendable member will generally prevent the body unit from following a completely tangential path. The shape that the bendable member assumes depends primarily on the material properties and shape of the bendable member, but it will change its shape as the rotational speed changes. Examples of different shapes and expected changes in shape are described below. Optional components can be added along the length of the bendable member that, due to their mass, will adjust the bending properties of the bendable member when rotated. Weighted components can be used solely to adjust the bending properties of the bendable member, or they can also have a functional purpose, such as serving as deflection components to deflect imaging energy.

An example of an imaging assembly is provided below in which the imaging axis changes due to a bendable component. Assume a bendable rod that is fixed to the imaging assembly at its proximal end but has no other connection or anchoring to the imaging assembly. When stationary, the longitudinal axis of the bendable rod is roughly parallel to the axis of rotation and can be slightly offset from the axis of rotation. As the imaging assembly rotates, each body unit in the unconstrained portion of the bendable rod gradually increases the distance from the axis of rotation. In the radially unconstrained portion of the rod, the rod will appear bent in curvature. If the bendable rod is an optical fiber (light is emitted and/or received through the optical fiber), then this is useful for imaging purposes. As the rod bends, the imaging angle will change.

The distal end of the optical fiber may have a lens, which may be a weighted component that increases the degree of curvature of the bendable rod at a given rotational speed. Optionally, additional weight (e.g., a stainless steel cylinder or ring) may be added to further increase the degree of curvature. Similarly, if the bendable rod is a flexible conduit that houses a wire that is used to send electrical signals to or from an ultrasonic sensor, then the rod is useful for imaging purposes, and the wire is used to send electrical signals to or from an ultrasonic sensor. The ultrasonic sensor may be a weighted component that increases the degree of curvature of the bendable rod at a given rotational speed. The bendable component may be reinforced by changing its mechanical properties using other materials. For example, a thin nitinol rod may be used to reinforce the optical fiber or electrical conduit, thereby reducing the degree of curvature induced at a given rotational speed and improving the predictability of the bendable component's return to a straight configuration when stationary. In this example, the transmitter and/or receiver of imaging energy are mounted directly on the bendable component.

Bendable components can include a variety of different geometries, including round, square, or rectangular rods, as well as thin films or sheets. Bendable components may alternatively or additionally include spiral or helical geometries, such as those found in compression springs. Ideally, the materials used possess a degree of elasticity, allowing them to return to their initial positions in a predictable and repeatable manner. Examples include polymers such as polyimides and polyurethanes, as well as silicone rubber, rubber, and a variety of other materials. Metals with good elasticity include nitinol, brass, gold, silver, platinum, steel, and a variety of other metals. The degree of elasticity required as an inherent property of the material will vary significantly depending on the shape of the material in the bendable component. For example, a given material may not be sufficiently flexible or elastic in the form of a square rod, but may be sufficiently flexible and elastic if incorporated into a spring-shaped component.

Figures 7a through 7c illustrate an embodiment of an imaging assembly 320 near the distal end of an imaging catheter 322. A deformable component 324 includes an optical fiber 326 extending from within the imaging catheter 322 and having a substantially constrained proximal portion 326 and a substantially unconstrained portion 328 near the distal end of the optical fiber 326. In Figures 7a through 7c, the constrained portion 326 is located within the volume of the imaging catheter 322, while the unconstrained portion 328 is located at the distal end of the imaging catheter 322. When the imaging probe is not rotating, as shown in Figure 7a, the optical fiber 324 tends to minimize internal stresses, which in this example results in the optical fiber 324 assuming a substantially straight configuration. However, as the imaging catheter 322 and the optical fiber 324 therein rotate about the longitudinal axis 330, as shown in Figure 7b, the centripetal acceleration experienced by the optical fiber 324 causes the unconstrained portion 326 of the deformable component to deform from its resting position and change the imaging angle. Further increases in the rotational speed can result in further changes in the imaging angle α, as shown in Figure 7c. The use of one or more optional weighted members 322 may increase the amount of deformation achieved at a given rotational speed.Acoustic sensors may replace or accompany optical imaging transmitters/receivers.

FIG8 a shows an embodiment of an imaging assembly 340 near the distal end of an imaging catheter 342, wherein a deformable member 344 is associated with a resilient support 346. The mechanical properties of the deformable member (e.g., an optical fiber 348 when the imaging sensor is an optically based system) make it difficult to adequately return the optical fiber 348 to a resting configuration, such as a straight configuration. Thus, the use of a resilient support 346 (e.g., a length of nitinol wire) can be associated with the distal region of the deformable member to improve the performance of embodiments incorporating the deformable member 346. FIG8 b shows an axial cross-section of an embodiment 340 incorporating a resilient support 346. The deformable member 344 can be used to facilitate optical imaging and/or acoustic imaging.

8a shows an optional irrigation port 356 in the sheath 352 of the imaging probe 340. The port 356 facilitates use in conjunction with one or more irrigation ports near the proximal end of the imaging probe (as shown in FIG2 ) to irrigate the imaging probe 340 with a desired fluid medium, such as water or saline. An irrigation port is optionally included in all embodiments of the present invention.

Figures 8c and 8d show an embodiment in which the distal end of the imaging probe 30 includes an expandable component 395. The expandable component 395 serves to provide a larger safety zone 396 in which the deformable component can deflect at higher rotational speeds without contacting anatomical structures. The expandable component 395 can be expanded via a separate expansion lumen (not shown) or via the imaging catheter lumen. As shown in Figure 8d, an additional outer sleeve 396 may be included for sliding over the expandable component 395 during transport or removal of the imaging probe.

FIG9 a shows an embodiment of an imaging probe 370 that utilizes a GRIN lens 372 (gradient index lens) to increase the imaging angle achievable through optical imaging. GRIN lens 372 is positioned near the distal end of the probe and behind an imaging catheter 374 containing an optical fiber 376. GRIN lens 372 is positioned adjacent to the distal end of optical fiber 376. A GRIN lens can be selected that exhibits the following properties: displacement of the distal end of optical fiber 376, which emits light toward one end of lens 372, causes a change in the angle of light emitted from the other end of the lens. Light from the imaged tissue received by lens 372 is focused back toward optical fiber 376 along the same path as the emitted light, but in a reciprocal manner. While an initial imaging angle 398 is shown in FIG9 a, the presence of GRIN lens 372 results in a larger effective imaging angle 397, also shown in this figure. This is useful because many deformable components may have limitations in the range of achievable imaging angles due to various deformable component properties, such as flexibility and geometry. For example, optical fiber 376 has a minimum radius of curvature that can be achieved before the fiber breaks or fails. At the same time, for many imaging probes for intravascular use, the desire to miniaturize the imaging components leads to geometric constraints on the deformable components. The use of GRIN lenses 372 can help to expand the range of effective imaging angles available in these environments.

Other transmissive optical elements may be added to amplify the effective imaging angle. For example, hemisphere 382 may be made of a medium having a refractive index less than that within imaging assembly 380 shown in FIG9 b. Such element 382 may include a gas-filled cavity, such as one filled with carbon dioxide, or it may be a cavity filled with air. If the refractive index of the low-refractive-index medium is not strongly dependent on wavelength, scattering effects will be minimized. Similarly, if the light used for imaging spans a narrow wavelength spectrum, scattering effects will be minimized.

The bendable member can be used with the imaging energy deflection member to change the imaging angle. At least one transmitter and/or receiver is oriented to direct imaging energy toward and/or receive imaging energy from the energy deflection member.

Figures 10a and 10b provide an example of an imaging assembly including an energy deflection member mounted to a flexible member within a rotating imaging assembly.

FIG10a illustrates an embodiment of a probe at 120, in which an energy deflection element 122 is mounted to a deformable element 124, enabling imaging at different angles depending on the rotational speed. In the top view 10a, the deformable element 124 holds the deflection element 122 at an angle that results in a larger imaging angle. As previously described for the deformable element, the deformable element 124 can be a thin sheet, a spring, a metal or polymer element such as a nitinol rod, or various other forms. To enhance the deformation produced at a given rotational speed, an optional deflection counterweight 128 can be added to the deformable element or to other elements mounted at the free end of the deformable element 124, such as the deflection element 122. While the imaging angle in this particular embodiment may be derived from the OCT imaging circuit, a strain gauge 130 and a connection 132 for the strain gauge are also shown. The strain gauge 130 is an alternative mechanism for estimating the imaging angle. At high rotational speeds, the deformable element 124 will tend to bend, as shown in FIG10b.

FIG11a illustrates another embodiment of an imaging probe 100, which is used to cause rotational speed to affect imaging angle via one or more hydrofoil elements (e.g., wings) on a deflectable or tiltable member. The mechanism 100, much like the probe 31 in FIG5a , features three wings 102 secured to the distal edge of a disc-shaped deflectable member. As rotational speed increases in the direction 981 shown, the wings create a pressure gradient that, in this example, causes the imaging angle to increase. Also note in this figure how the imaging assembly need not have a housing that completely surrounds the components of the imaging assembly. Removing the housing or a portion of the housing minimizes the volume of the imaging assembly 30. Furthermore, when one or more hydrofoil elements are incorporated into the design, it is advantageous to place the fluid traveling through the hydrofoil in direct fluid communication with a non-rotating surface, such as a jacket. By placing this fluid in direct fluid communication with the jacket, the fluid generally develops a flow pattern in which the fluid velocity in this region is reduced due to the drag of the jacket relative to the static surface. This increases the relative velocity of the "wing" traveling through the fluid and, thereby, increases the lift generated by the wing.

Similarly, FIG. 12 shows at 110 an embodiment of a probe similar to the probe 120 in FIG. 10 a , wherein the deflection member 122 comprises wings 112 which bring about the same effect as the probe 100 with wings on the tiltable element 70 .

In some applications, the rotational speed will be varied in a stepwise manner, while in other cases, the rotational speed will be swept across a range of speeds. The desired scan patterns and the associated function of the rotational speeds required to achieve these scan patterns will depend strongly on the application. For example, if the desired scan pattern is to scan a space close to the surface of a cone, a specific rotational speed can be activated by rotating the motor. The slope of the cone can be changed by varying the rotational speed. If it is desired to scan the entire space, multiple cones can be imaged by gradually varying the rotational speed, or the scanned space can include a spiral path by sweeping across a range of rotational speeds. A variety of other scan patterns can be obtained by varying the rotational speed over time.

FIG13 a shows an example of one of a variety of scanning patterns that can be obtained by various embodiments of the present invention. The imaging assembly 12 is shown along Cartesian coordinate axes. The volume of interest can be imaged by rotating the imaging catheter and the imaging assembly. By changing the imaging angle in a stepwise manner and acquiring imaging data in one or more revolutions at different imaging angles, the imaging data is collected along the surface of a series of concentric cones 991. This scanning pattern is simpler for image reconstruction, but is not ideal in terms of the time it takes to acquire the imaging data. FIG13 b shows an example of a scanning pattern in which the imaging beam follows a more spiral path 992 by causing the imaging angle to change continuously as the imaging probe rotates. This scanning pattern can increase the complexity of the algorithm for reconstructing the 3D imaging data, but is more time-efficient in data acquisition than the pattern in FIG13 a.

Current intravascular imaging methods generally assess rotation angles by assuming that the rotational velocity at the proximal end of the imaging catheter is a good approximation of the rotational velocity at the distal end. As imaging catheters become smaller to access smaller vessels and are incorporated into guidewires, they are also more susceptible to deformation, and the problem of uneven rotational distortion is exacerbated.

Meanwhile, many intravascular imaging systems use a constant rotational speed over a sufficiently long period of time, whereby the system exhibits a steady state in which the average rotational speed of the distal end of the imaging catheter is close to the average rotational speed of the proximal end of the imaging catheter. In the context of the present invention, many embodiments involve frequently or continuously varying the rotational speed, and the presentation of a steady state between the rotational speeds of the proximal and distal ends of the imaging catheter may be unreliable. To this end, a rotary encoder near the distal end of the imaging catheter or incorporated into the imaging assembly may be beneficial. Optical, impedance, or other rotary encoders may be used herein.

An optical pattern on a non-rotating component near the rotating component can be observed by an optical receiver on the rotating component. This optical pattern can be as simple as a pattern of lines extending around the perimeter of the non-rotating component, with the optical receiver generating an optical or electrical signal each time a line is passed, indicating that the line has been passed. The spacing between the lines represents a known degree of rotation. Alternatively, two receivers can be used to achieve quadrature encoding, providing directional information in addition to information about the increment of rotational displacement.

Alternatively, the encoder can encode position by using multiple receivers and an optical pattern (such as Gray coding, commonly used in larger-scale rotary encoders). Alternatively, the wavelength spectrum of light absorbed, reflected, or otherwise emitted from the optical pattern can represent absolute position. Thin films, diffraction gratings, and other optical surfaces or components can be used for this purpose. Alternatively, the optical pattern can be on the rotating component and the optical receiver can be on the non-rotating component.

Other implementations of rotary encoders may include an impedance rotary encoder, one or more accelerometers near the distal end of the imaging catheter, and identification of fiduciary landmarks or features within the catheter. For example, the thickness of an imaging cuff may vary as a function of angle about the longitudinal axis.

FIG14a illustrates an embodiment of an imaging probe at 150 that includes an encoding pattern 156 contained within a sleeve 152 positioned behind the imaging assembly 160 for encoding the rotational position of the imaging assembly 160. A non-rotating encoding pattern 156 is positioned adjacent to or within the imaging assembly 160, allowing it to freely travel along a portion of the length of the imaging probe. Thus, while the imaging catheter 34 and the imaging assembly 160 can rotate, the optical encoding pattern 156 does not. In this example, the encoding pattern includes a protruding structure 158 that is accommodated by a similarly shaped channel along the length of the sleeve. The one or more protruding structures prevent the optical encoder from rotating when the adjacent imaging assembly 160 and the imaging catheter 34 rotate.

The signal lines within the rotating portion of the imaging probe are directed to the encoder to facilitate reading the rotational position. In this example, a non-imaging optical fiber 164 is introduced to illuminate the optical encoder element 156. The illuminated light interacts with the optical encoder in a manner that depends on the angle of rotation. The light then travels from the optical encoder element 156 back through the non-imaging optical fiber 164. The proximal end of the optical fiber 164 can be connected to a light detector or other optical sensor at the proximal end of the imaging probe and convert the optical signal into one or more electrical signals that can then be transmitted to the imaging system through an adapter. The advantage of this configuration is that the imaging assembly can be translated within the outer shell without affecting the ability to detect the rotational position.

Further details of embodiments of the encoding pattern 156 and other embodiments for encoding on imaging probes are disclosed in U.S. Patent No. 9,357,923, entitled “MEDICAL IMAGING PROBE WITH ROTARY ENCODER,” filed concurrently with the present application, which is hereby incorporated by reference in its entirety.

The performance of a deformable or tiltable component in achieving a desired imaging angle can be improved by mechanically connecting the deformable or tiltable component to another deformable or tiltable component. Figure 15 shows an example of a distal tiltable component 650 that includes an energy deflection component. The distal energy deflection component is mechanically connected to a second, more proximal tiltable component 651 via a connector 652 having a connection point 653 at each end, wherein the connector is connected to each of the two tiltable components. Compared to being designed into the first tiltable component (for example, made of a denser material), the second tiltable component can have better characteristics for achieving the desired imaging angle. Alternatively, the second tiltable component can provide advantages by providing a strain gauge or other component for measuring the imaging angle.

Referring to Figure 16a, in order to allow imaging in the same direction by ultrasound and optical means, an ultrasonic sensor is provided that allows light energy to travel through a conduit in the sensor. Basically, the piezoelectric material is altered so as to have an opening, such as a hole, through its substrate. Electrical contacts 400 are directed to a conductive layer 401 on either side of the acoustic substrate 402 of the sensor. Optical fibers 403 provide an optical conduit for optical imaging. Optional optical isolators 780 and GRIN lenses 405 or other optical components can be in the opening 407 of the acoustic substrate 402, as shown in Figure 16a. The optical imaging energy from the optical fiber is directed to a tiltable component 70 that can be tilted about a pivot axis 626. The tiltable component includes a reflective surface. Conductive layers 401 on either side of the piezoelectric material are incorporated as needed to apply voltage to the piezoelectric.

Stop 781 and magnet 782 are shown as part of the imaging assembly. A second magnet 784 is also present on the tiltable member 70. The magnet serves as one of several possible sources of restoring force tending to bring the tiltable member into contact with stop 781. At higher rotational speeds, the tiltable member 70 will tilt about its pivot axis 626 away from stop 781, resulting in a change in imaging angle. Thus, FIG16 a illustrates an embodiment of an imaging probe 10 adapted for use with a scanning mechanism capable of lateral viewing at multiple imaging angles.

FIG16b depicts a similar embodiment, except that magnet 782 is an electromagnet 785, wherein a conductive loop 786 extends from the proximal end of the imaging probe to the electromagnet 785, thereby providing current to the electromagnet. By varying the strength and direction of the magnetic field generated by electromagnet 785, the restoring force of the tiltable member 70 can be adjusted, as may be desired during use. The tilt mechanism in this particular embodiment does not depend on centripetal acceleration. Therefore, by using an electromagnet and a tiltable member influenced by the electromagnet, for example by including a second magnet on the tiltable member, a scanning pattern can also be generated independently of rotational motion. The use of magnetic force can be applied to embodiments for forward viewing imaging (as shown in FIG5a through 5i) as well as embodiments using a deformable member (as shown in FIG10a and 10b) to change the imaging angle. Similarly, if the tiltable or deformable member does not include a magnet, the force causing the tiltable or deformable member to twist in a first direction can be provided by other means, such as a spring, a cantilever, or other means described above for restoring force. The tiltable or deformable member can then be twisted in the opposite direction using an electrically controllable electromagnetic force.

An alternative embodiment for side viewing is shown in FIG16 c, which uses a non-magnetic restoring force in combination with a centripetal force to enable side viewing imaging. Stops 80 and 82 limit the range of motion of the tiltable member 70. The cantilever wire 640 is mounted on a post 787 and contacts the surface of the tiltable member 70.

At higher rotational speeds, the tiltable member will pivot (counter-clockwise in FIG. 16 c ) and cause a change in the imaging angle.

As shown in some embodiments of the present invention, it may be desirable to combine ultrasound with one or more optical imaging devices used in conjunction with the scanning mechanism of the present invention. Figures 16a to 16c depict examples of how ultrasound sensors can be combined with optical imaging transmitters and/or receivers.

17a to 17g also depict various embodiments for combining an ultrasound sensor with an optical imaging transmitter and/or receiver. These embodiments include a deflection mechanism for the optical imaging transmitter and/or receiver, such as a mirror or prism.

Referring to FIG17a , an imaging subassembly 399 is provided that is configured to allow imaging in the same direction by acoustic and optical means, thereby utilizing an acoustic sensor that allows light energy to travel through a conduit in the sensor. Importantly, probe 399 utilizes an acoustic sensor 402 that has been modified to include an optical transmission channel through its substrate. Acoustic sensor 402 can be any type of ultrasonic sensor known in the art, such as a piezoelectric component (e.g., PZT or PVDF), a composite sensor, or a single crystal sensor.

Electrical contacts 400 are directed to a conductive layer 401 on either side of the sensor's acoustic substrate 402. Optical fibers 403 provide an optical conduit for enabling optical imaging. One or more matching layers can be added to the sensor's emitting surface, such as an epoxy layer (e.g., a silver or copper conductive epoxy layer, which can also functionally serve as one or both electrodes to drive the sensor), or a polymer (e.g., parylene or PVDF).

The optical transmission channel 407 is made by any of a variety of techniques, such as precision drilling, laser ablation, photolithography, including structures in a mold to create openings, and other means.

Conductive layers 401 are optionally incorporated on either side of piezoelectric material 402 for applying voltage to the piezoelectric. Opening 407 is connected to the optical waveguide 403 directly or through one or more mirrors 404 or prisms and one or more lenses 405.

As shown in FIG17b, light from an optical fiber can be directed toward a reflector (or prism) 404, which deflects the light from the optical fiber and passes it through an optical transmission channel 407. Alternatively, as shown in FIG17c, a prism 397 can be used to deflect the light and pass it through the optical transmission channel. Prism 397 can deflect the light as a result of total internal reflection or with the help of a reflective coating on its deflecting surface. Prism 397 can be a separate optical component fixed to an appropriate position along the optical path. For example, it can be glued to an appropriate position on the end of the optical fiber, on a lens, or on a spacer using a bonding method (e.g., UV curing glue). Alternatively, a segment of unclad optical fiber connected along the optical path and cut off at a desired length can be used to make the prism. The segment of clad optical fiber can be cut and/or polished to obtain the desired angle. Mao describes this method in the reference cited above.

Referring also to FIG17c, an optically transparent window 409 is optionally provided at the end of the optical transmission channel 407, and any unoccupied space within the channel is filled with a gas, a fluid, or an optically transparent material, such as glass or any of a variety of transparent polymers known in the art. The purpose of the window 409 is to prevent the generation or retention of unwanted bubbles in the channel 407 and to protect the components within the optical transmission channel 407.

As shown in FIG. 17 d , it is desirable to have gas rather than fluid or solid material in the channel 407 in order to improve the refractive power of certain optical components such as the curved lens 424 (which may be a spherical lens).

As shown in Figures 4e to 4g, a GRIN lens 405 or other optical component can be located adjacent to the distal end of the optical fiber 403, between the optical fiber 403 and the deflecting mirror or prism 404 along the optical path. In this case, the opening in the acoustic substrate 402 can be free of any optical components and simply contain optically transparent material or be covered by a window 409.

17f, an optical isolator 433 is positioned between the distal end of the optical fiber 403 and the GRIN lens 405. The optical isolator element 433 may comprise an optically transparent medium, such as an unclad optical fiber, glass, plastic, a gas-filled gap, or a fluid-filled gap. The use of the optical isolator element 433 helps reduce the precision required for alignment and sizing of optical components to achieve a desired focal length.

Alternatively, referring to FIG17g, the path length of the prism or reflector 404 can serve as all or part of the optical spacer between the distal end of the optical fiber and the lens. The advantage of replacing a portion of the functional optical spacer with the distance that light must travel through the reflector or prism 404 is that the focusing element (e.g., GRIN lens 405 or other lens) is closer to the area being imaged, thereby increasing the effective working distance of the optical imaging system. In some cases, the lens 405 can be offset from either edge of the optical transmission channel to achieve a desired depth of focus, as shown in FIG17g.

Additional details of various combined IVUS/OCT devices that may be used with the scanning mechanisms disclosed herein are disclosed in U.S. Patent No. 9,357,923, entitled “IMAGING PROBE WITH COMBINED ULTRASOUND AND OPTICALMEANS OF IMAGING,” filed concurrently with the present application, which is hereby incorporated by reference in its entirety.

Figures 18a to 18d depict a tiltable deflector member having an optically reflective surface as distinct from an acoustically reflective surface. Figure 18a is a perspective view of a deflector member having a hole in the side thereof for receiving a pin about which the deflector member can pivot within the imaging assembly.

Figure 18b shows a cross-section through the deflector near its center. The hole for accommodating the pin 465 can be seen. The top layer is a flat, optically reflective layer 461. Beneath this optically reflective layer is a substantially acoustically transparent layer 462, located between the optically reflective layer and an acoustically reflective substrate 463. This device can be constructed by using a disk of acoustically reflective material (e.g., stainless steel) and drilling the necessary holes or recesses to allow the deflector to be ultimately mounted in the imaging assembly. Parabolic or spherical recesses can be made on one face of the disk. The jagged surface can then be filled with an acoustically transparent medium, such as TPX. An optically reflective film, such as a thin gold film, can then be added to the top surface of the acoustically transparent medium. Figures 18c and 18d show cross-sectional views of such a deflector at different points from the center of the disk.

Figures 19a to 19h show the use of an imaging probe of the present invention in conjunction with one or more steerable components. Steerable guidewires, such as the STEER-IT guidewire from CORDIS, are available, in which the distal portion of the wire can be controllably deflected by an operator. Similarly, steerable catheters, such as those using the mechanism described by Badger (U.S. Patent No. 4,898,577), are available, in which the operator controllably deflects the distal tip of the catheter. Figure 19a shows the distal portion of a flexible embodiment of an imaging probe 440 having a guidewire lumen, in which a steerable guidewire 441 is substantially within the guidewire lumen of the outer jacket of the imaging probe. Figure 19b shows how deflection of the steerable guidewire causes deflection of the distal region of the imaging probe.

FIG19 c shows the distal portion of the imaging probe 440 substantially within the steerable catheter 442. A guide wire 443 may also extend through the imaging probe. The guide wire may be steerable or may be a conventional non-steerable guide wire. FIG19 d shows how deflection of the steerable catheter causes deflection of the distal region of the imaging probe.

Alternatively, the same mechanisms that allow steering in a steerable guidewire or steerable catheter may be incorporated directly into the imaging probe.

Figures 19e through 19h further illustrate how a steerable component can be used in conjunction with an imaging probe to facilitate passage through an obstructed lumen in a blood vessel. In Figure 19e, a steerable guidewire 441 is positioned substantially within an imaging probe 440. When the imaging probe is advanced near an obstructed segment of a blood vessel 445, the imaging device has a field of view determined by the limits of the range of imaging angles 446 achievable by the imaging probe. The steerable guidewire can be controlled to deflect the imaging probe and guidewire to a desired orientation, as shown in Figure 19f. The guidewire can then be advanced into the obstructed segment under image guidance. If desired, image guidance of the wire's advancement can help ensure that the wire remains within the vessel wall boundary 447 during advancement. The guidewire can have properties such as a hydrophilic coating or sufficient stiffness to facilitate initial penetration of the obstructed segment. The imaging probe 440 can then be advanced into the obstructed segment 445 over the guidewire 441. This iterative process of imaging, steering the wire, advancing the wire, and/or advancing the imaging probe can be used to facilitate penetration of the obstructed segment.

Alternatively, as shown in FIG19g, the guidewire may include an expandable component, such as an expandable balloon 448 and an expansion lumen (not visible), to facilitate creating an area in the blockage into which a larger imaging probe can be more easily advanced. The iterative process of imaging, steering the wire, advancing the wire, and/or advancing the imaging probe can be used to help puncture the blockage. FIG19h shows that the imaging probe has been advanced into the blockage, and the next iteration point can be started from this point.

Figure 20a depicts another embodiment for enabling a tiltable component to affect a change in imaging angle as a function of the rotational speed of the imaging assembly. A tiltable deflection component 501 is mounted on a pin 502. An acoustic sensor 503 and an optical transmitter/receiver 504 are included, as well as a first stop 505 for the maximum imaging angle and a second stop 506 for the minimum imaging angle. A weighted elastic component is connected to the tiltable component and to the imaging assembly or imaging catheter. The weighted elastic component may include a nitinol rod 507 to which a stainless steel counterweight 508 is attached, or is made of another suitable material. At low rotational speeds, the elastic component exhibits a relatively straight profile as shown in Figure 20a. As the rotational speed increases, the centripetal force of the weighted elastic component causes the counterweight to move toward the wall of the imaging assembly. Subsequently, the elastic component will deform and cause the deflection component to change its tilt angle, as shown in Figure 20b. This configuration enhances the ability of the present invention to reliably achieve the desired imaging angle.

Image reconstruction

While various embodiments for varying the imaging angle have been described above, it may be helpful to assume, estimate, measure (directly or indirectly), or otherwise derive the imaging angle and rotation angle associated with the acquired imaging data. Each pixel or sample of the imaging data may be associated with: 1) an angle about an axis of rotation, referred to as the rotation angle; 2) an angle from the axis of rotation, referred to as the imaging angle; and optionally, 3) a distance from a reference point within or near the imaging assembly, such as an imaging receptor or an imaging deflection element. These two angles and the optional distance measurements may be used to help reconstruct the 3D geometry of the imaged object/tissue.

In ultrasound, the distance to the sensor or deflection element is estimated based on the transmission time of the ultrasound signal combined with the speed of sound. In optical coherence tomography, the distance to the receiving end of the optical circuit or deflection surface is measured using interferometry or a technique called optical frequency field imaging (OFDI). For optical coherence tomography, the depth range or "window" imaged is generally selected to optimize the performance of the system. The window size can range from as small as 4 microns to as large as several millimeters and is selected based on the performance requirements of the system, such as the number of pixels or vectors acquired per time interval and the optical properties of the medium (e.g., blood, tissue, air and/or serum) through which imaging occurs. For angioscopy and the infrared imaging method described by Amundson, although the ability to achieve stereoscopic vision using two sets of optical transmitters and/or receivers in the present invention will facilitate some depth perception, there is no distance information.

In the simplest embodiment, the imaging angle or the rotation angle may not be of concern and the ability to change the imaging angle without actually knowing the imaging angle would be a substantial improvement over the prior art.

However, in many cases, the imaging angle is of interest for generating an adequate 2D or 3D representation of the imaging region and/or for performing measurements within the imaging region. Various methods can be used to derive the imaging angle. In the simplest case, the imaging angle can be a function of rotational velocity. Thus, an estimate or measurement of the imaging assembly's rotational velocity can be mapped to an estimate of the imaging angle based on a function or lookup table derived from experiments or first principles. In many cases, the rotational velocity is a function that varies over time, and the mechanism for mapping the rotational velocity to the imaging angle can use not only the instantaneous rotational velocity as input to the mapping scheme but also incorporate rotational velocities that have occurred or are projected to occur around that time. This simple mapping of rotational velocity to imaging angle is most suitable when the tiltable or bendable component is not significantly affected by external forces applied to the imaging component. For example, unless the tiltable component's axis of rotation passes through its approximate center of mass, the effects of gravity on the tiltable component will significantly affect the actual imaging angle, thereby distorting the image or any measurements based on the assumed imaging angle.

The variation of the tilt angle over time can be appropriately assumed to approximate a preselected parametric function or a random function, which can be used as an input to the imaging reconstruction process. The preselected imaging angle function may depend on the probe type and the rotational motion control sequence applied to the motor controller. The user can adjust the imaging function and thereby adjust the reconstructed image by changing one or more parameters of the parametric function or by adjusting the random points of the random function.

A more direct assessment of the imaging angle is also possible. Strain gauges can be added to assess the rotation or deformation of the bendable or tiltable component. Alternatively, an optical tilt encoding interface can be incorporated into the tiltable or bendable component and monitored through a separate fiber channel or using a local LED and light detector. For example, an optical fiber can direct light to the surface of the tiltable or bendable component, and the intensity of the light reflected back into the fiber can change as a function of the tilt angle. This intensity can be detected using a light detector at the proximal end of the fiber of the encoder.

Impedance, capacitive, magnetic, and inductive encoders can be used. Alternatively, information acquired from the imaging energy can be used to provide an assessment of the imaging angle. For example, where the imaging assembly includes an energy deflecting surface for ultrasound or optical coherence tomography, most of the imaging energy will be reflected in the direction of the imaging angle. However, a small amount of imaging energy will also be reflected toward the imaging energy receiver. By making small changes in the smoothness or texture of the reflective surface, thereby making it an imperfect optical reflector, the amount of imaging energy reflected back can be increased.

Using conventional distance measurement techniques used in ultrasound or OCT imaging, the distance between the range receptor and the deflection member can be determined. Thus, if the deflection surface area, on which the imaging energy is deflected, changes distance from the imaging receptor due to tilt or curvature, this distance can be used to determine the imaging angle using trigonometric principles.

OCT imaging has a much higher resolution than ultrasound imaging, so in many cases it is preferable to use an OCT receiver to measure changes in distance as a surrogate marker for changes in imaging angle. Alternatively, the housing of the imaging assembly or other structures of the imaging assembly can serve as an interface that produces reflections that can be detected by acoustic or optical means. Such an interface thus provides an intrinsic landmark that can be used. Thus, the distance, which is the path length, between the receiver and the interface or between the deflector and the interface can be measured. If this path length changes as a function of imaging angle (due to the morphology of the housing), then the imaging angle can then be derived.

A signal detection mechanism incorporated into the imaging system can be used to automatically detect reflections generated by deflecting surfaces or by intrinsic landmark interfaces and provide information about the imaging angle to other components of the imaging system. Such a signal detection system can be implemented as a hardware or software detection system, or a combination of both.

Displaying 3D data on a conventional 2D display screen can be implemented in a variety of ways, including continuous 2D images and other methods known in the medical imaging field. For example, a 2D image can represent an arbitrary plane cutting through 3D space, a maximum intensity projection image, a multi-plane reformatted image, and a variety of other forms. Data can also be represented in polar coordinates, for example using coordinates (rotation angle, imaging angle, distance). Any surface in 3D space based on polar coordinates can be selected for display. For example, data corresponding to a single imaging angle within a range of rotation angles and a range of distances can be displayed.

Embodiments of the present invention may be used with or incorporated into devices for interventional procedures, such as cardiovascular interventional procedures such as angioplasty balloons, atherectomy devices, stent delivery systems, or local drug delivery systems. Embodiments may also be used with or incorporated into devices that facilitate biopsy, radiofrequency ablation, resection, cauterization, local brachytherapy, cryotherapy, laser ablation, or sonic ablation.

In particular, laser or acoustic ablation of tissue using the present device can be facilitated by using an image scanning mechanism to direct higher power optical or acoustic energy to a target area. For example, while imaging a vascular region using OCT or an ultrasound embodiment of the imaging probe described herein, the area to which treatment is to be delivered can be selected through a user interface. Subsequently, powerful pulses of energy can be delivered from time to time as the scanning mechanism is oriented to carry energy in a desired direction. For example, pulses of laser energy can be transmitted along the same optical fiber used for optical imaging, deflected by a deflection member in those embodiments that include a deflection member, and directed toward the target tissue to achieve the desired effect. The pulses of laser energy are timed to coordinate with the scanning pattern achieved by the imaging probe to direct the energy to the target area.

As previously mentioned, combining OCT with IVUS is useful for imaging probes because one of the two modalities (preferably OCT due to its higher resolution) can be used to assess the imaging angle. Furthermore, combining OCT with IVUS is particularly useful because the two modalities often provide complementary information to each other, such as when assessing blood spot structure and function. When images from the two modalities are correctly mapped to each other, they can help provide a composite image that provides valuable information about the tissue being assessed. Indeed, any imaging data generated by the various acoustic and optical imaging modalities described herein can potentially be combined to improve the assessment of the tissue being assessed.

In addition, the ability to manufacture forward viewing imaging probes with the ability to adjust their imaging angles increases the possibility of using forward viewing imaging instead of fluorescence imaging for visualizing vascular trees or other sets of anatomical spaces. As the probe advances into the body, a 3D space of imaging data is obtained. If successive 3D spaces of imaging data overlap sufficiently, the possibility of combining a series of 3D images together to form an extended set of 3D imaging data becomes attractive. For example, if space (i) is obtained and then space (i+1) is obtained, then the imaging data from both spaces can be subjected to a series of transformations, such as translation, rotation, and stretching, where features in the overlapping region of the two spaces match each other. This can be facilitated by using autocorrelation techniques and other well-known techniques for stitching 2D or 3D imaging data together.

Angioscopy and infrared imaging can also gain specific advantages based on the present invention. Typically, angioscopy and infrared imaging rely on the use of fiber optic bundles to produce images. The space or surface being imaged is illuminated by light spanning the desired wavelength range, and the back-reflected light provides an image of the interface in the field of view. For angioscopy, the wavelength range essentially spans the visible spectrum, while for infrared imaging, a more selective longer wavelength range described by Amundson is used to improve penetration into blood. For traditional angioscopy and infrared imaging, the number of optical fibers in the bundle affects the system resolution and the size of the field of view. However, adding more optical fibers to the bundle increases the size of the bundle and reduces the flexibility of the bundle.

The present invention is able to overcome these limitations by requiring fewer optical fibers to perform the desired imaging. In the simplest case, a single optical fiber is used. The ability to scan an area with a single optical receiver using a tiltable or bendable component provides the ability to reduce the number of optical fibers used to scan the same area of interest. In this case, illumination light within the desired wavelength range is delivered to the area to be imaged, such as by a separate optical fiber connected to a light source, an LED illuminator located near the imaging assembly, or by receiving the same optical fiber that reflects back light. The advantages of not requiring a fiber bundle to perform such imaging may include a more flexible imaging probe, a smaller imaging probe, a reduction in the number of required photodetectors (where photodetector arrays for infrared imaging are expensive), and the use of a small number (e.g., one to ten) of highly specialized photodetectors rather than large arrays of less specialized photodetectors (e.g., arrays of more than 64*64 elements).

The photodetectors can be varied for their wavelength characteristics as well as their sensitivity. Disadvantages of such systems compared to fiber bundle systems include the need to reconstruct the image from the scan data, a potentially lower signal-to-noise ratio, and image distortion due to possible fidelity flaws in the scanning mechanism used to obtain the desired scan pattern.

The signal-to-noise ratio of single-fiber embodiments in angioscopy or infrared imaging can be improved by focusing the illumination light into a narrow beam in the direction in which imaging occurs. This can be accomplished by transmitting the illumination light along the same fiber and passing through the same lens in the imaging assembly that receives the imaging light. This is particularly advantageous when imaging through scattering media, such as blood, because the light received by the lens and fiber is substantially free of light that would otherwise be scattered from adjacent spaces when using a more diffuse illuminator.

Gastrointestinal endoscopy, colposcopy, bronchoscopy, laparoscopy, laryngoscopy, cystoscopy, otoscopy, and funduscopy are examples of applications in which the scanning mechanism described herein may be used in a manner similar to angioscopy or infrared imaging. There are a variety of non-medical uses for flexible and/or miniaturized imaging probes in which the scanning mechanism described herein is used to produce images, such as images in the visible or infrared spectrum.

The imaging probe 12 and its components can have a variety of sizes and characteristics depending on the anatomical location and the purpose of the imaging to be performed by the imaging probe 12. For example, for use in the cardiovascular system (including the heart chambers), the imaging probe 12 is preferably elongated and flexible, with a length ranging from 5 to 3000 mm, preferably from 300 mm to 1600 mm. The imaging catheter 34 and the imaging assembly 30 can have a maximum cross-sectional dimension ranging from 200 microns to 10 mm, preferably from 500 microns to 8 mm. Both the imaging catheter 34 and the imaging assembly 30 can be surrounded by an outer sleeve 48. This allows the imaging catheter 34 and the imaging assembly 30 to rotate within the outer sleeve while mechanically isolating the rotational motion of the two components from the surrounding tissue.

In some cases, embodiments of the present invention can be used where the imaging catheter is very short or not strictly necessary. For example, the imaging assembly can be directly connected to a micromotor, turbine, or shaft with rapid reciprocating motion. Using centripetal acceleration to cause changes in imaging angle in acoustic or optical imaging devices can be incorporated into such embodiments.

In yet another embodiment, the imaging probe 12 for use in the gastrointestinal system generally has an elongated and flexible imaging probe 12 with a length ranging from 50 mm to 6000 mm, preferably from 300 mm to 2000 mm, and a maximum cross-sectional dimension ranging from 3 mm to 20 mm.

In yet another embodiment, the use of the imaging probe 12 for imaging soft tissue via percutaneous means results in an imaging probe having a rigid shaft. The outer sheath may be replaced by a rigid hollow shaft, such as a stainless steel tube, although a variety of other polymers, metals, and even ceramics are functionally suitable.

As used herein, the terms "comprises" and "comprising" are to be interpreted as inclusive and open-ended rather than exclusive. Specifically, when used in this specification, including in the claims, the terms "comprises," "comprising," and variations thereof mean that the specified features, steps, or components are included. These terms are not to be interpreted as excluding other features, steps, or components.

The foregoing description of the preferred embodiments of the present invention is provided to explain the principles of the present invention and is not intended to limit the present invention to the specific embodiments shown. It is intended that the scope of the present invention be defined by all embodiments encompassed within the scope of the claims and their equivalents.

Claims (17)

1. An imaging probe, comprising: Hollow shaft; An imaging conduit extending through the hollow axis, the imaging conduit defining a longitudinal axis; A scanning mechanism attached to the imaging conduit at a proximal position remote from the imaging conduit, the scanning mechanism including a tiltable member configured to control the direction of an imaging beam emitted from the scanning mechanism, wherein the tiltable member is tiltable such that the tilt angle of the tiltable member is variable relative to the longitudinal axis; and An imaging angle encoder connected to the scanning mechanism, wherein the imaging angle encoder is configured to generate a signal that depends on the tilt angle of the tiltable component. The imaging angle encoder is characterized in that it is configured to guide an incident optical energy beam or ultrasonic energy beam onto a surface associated with the tiltable member and to receive reflected optical energy beams or ultrasonic energy beams from the surface, such that a change in the tilt angle of the tiltable member produces a corresponding change in the reflected optical energy beams or ultrasonic energy beams. 2. The imaging probe of claim 1, wherein the reflected optical energy beam or ultrasonic energy beam is a reflected beam, and wherein the imaging angle encoder is configured such that changes in the reflected beam include changes in the intensity of the reflected beam. 3. The imaging probe of claim 1, wherein the imaging angle encoder is configured such that the path lengths of the incident optical energy beam or ultrasonic energy beam and the reflected optical energy beam or ultrasonic energy beam depend on the tilt angle of the tiltable component. 4. The imaging probe according to any one of claims 1 to 3, wherein the imaging angle encoder is an optical imaging angle encoder configured to guide an incident light beam onto a surface associated with the tiltable member and to receive a reflected light beam from the surface, such that a change in the tilt angle of the tiltable member produces a corresponding change in the reflected light beam. 5. The imaging probe of claim 4, wherein the imaging conduit comprises an optical fiber, and wherein the signal is a reflected light beam. 6. The imaging probe of claim 5, wherein the optical fiber is configured for transmission of the incident light beam to the imaging angle encoder. 7. The imaging probe of claim 4, wherein the imaging angle encoder includes a photodetector for detecting the reflected beam. 8. The imaging probe of claim 4, wherein the surface includes a surface profile having a smoothness or texture configured to produce an intensity variation of the reflected light beam in response to a change in the tilt angle of the tiltable member. 9. The imaging probe of claim 4, wherein the imaging conduit includes an optical fiber adapted for optical coherence tomography (OCT), wherein the imaging angle encoder includes a distal optical component for guiding an incident OCT beam onto a surface associated with the tiltable component and receiving a reflected OCT beam from the surface, and wherein the optical imaging angle encoder is configured such that the path lengths of the incident OCT beam and the reflected OCT beam depend on the tilt angle of the tiltable component. 10. The imaging probe according to any one of claims 1 to 3, wherein the imaging angle encoder is an ultrasonic imaging angle encoder configured to detect acoustic reflections associated with a tilt angle. 11. The imaging probe according to claim 1, wherein the imaging angle encoder includes a strain gauge encoding mechanism. 12. The imaging probe of claim 1, wherein the imaging angle encoder comprises an encoding mechanism selected from the group consisting of an impedance encoding mechanism, a capacitive encoding mechanism, a magnetic encoding mechanism, and an inductive encoding mechanism. 13. The imaging probe according to any one of claims 1 to 3, wherein the tiltable component is mounted such that the tilt angle can be changed by adjusting the angular velocity of the imaging conduit. 14. The imaging probe of claim 13, further comprising a return mechanism configured to apply a torque to the tiltable member to push the tiltable member away from the preferred orientation. 15. The imaging probe of claim 1, wherein the imaging angle encoder is configured to receive a reflected optical energy beam or ultrasonic energy beam generated by reflection of an optical energy beam or ultrasonic energy beam from the surface of the scanning mechanism, such that a change in the tilt angle of the tiltable member produces a corresponding change in the reflected energy. 16. An imaging probe, comprising: Hollow shaft; An imaging conduit extending through the hollow axis, the imaging conduit defining a longitudinal axis; A scanning mechanism attached to the imaging conduit at a proximal position remote from the imaging conduit, the scanning mechanism including a deflectable member configured to control the direction of an imaging beam emitted from the scanning mechanism, wherein the deflectable member is deflectable such that the deflection angle of the deflectable member is variable relative to the longitudinal axis; and An imaging angle encoder connected to the scanning mechanism, wherein the imaging angle encoder is configured to generate a signal that depends on the deflection angle of the deflectable member. The imaging angle encoder is characterized in that it is configured to guide an incident optical energy beam or ultrasonic energy beam onto a surface associated with the deflectable member and to receive reflected optical energy beams or ultrasonic energy beams from the surface, such that a change in the deflection angle of the deflectable member produces a corresponding change in the reflected optical energy beam or ultrasonic energy beam. 17. A medical probe, comprising: Hollow shaft; A conduit extending through the hollow shaft, the conduit defining a longitudinal axis; A scanning mechanism attached to the conduit at a proximal position remote from the conduit, the scanning mechanism including a tiltable member configured to control the scanning direction of the scanning mechanism, wherein the tiltable member is tiltable such that the tilt angle of the tiltable member is variable relative to the longitudinal axis; and An angle encoder connected to the scanning mechanism, wherein the angle encoder is configured to generate a signal that depends on the tilt angle of the tiltable component. The feature is that the angle encoder is configured to guide an incident optical energy beam or ultrasonic energy beam onto a surface associated with the tiltable member and to receive reflected optical energy beams or ultrasonic energy beams from the surface, such that a change in the tilt angle of the tiltable member produces a corresponding change in the reflected optical energy beam or ultrasonic energy beam.