WO2009150653A1

WO2009150653A1 - Optical system for use in an endoscope

Info

Publication number: WO2009150653A1
Application number: PCT/IL2009/000586
Authority: WO
Inventors: Tzvi Phillip
Original assignee: GI View Ltd
Current assignee: GI View Ltd
Priority date: 2008-06-12
Filing date: 2009-06-14
Publication date: 2009-12-17
Anticipated expiration: 2010-12-12

Abstract

An optical system is presented suitable to be used with an endoscope for insertion into a body lumen of a subject. The optical system comprises a light collecting and focusing lens unit configured to collect light from a region of interest and to focus said light onto a focal spot; said light collecting and focusing lens unit comprises a plurality of separate lens elements defining together an arrangement of spaced-apart substantially refractive interfaces accommodated along an optical axis of the system and defining together a predetermined refractive index profile along said optical axis to appropriately bend a light propagation path through said lens unit, said arrangement of interfaces comprising a light collection surface configured with a predetermined curvature capable of collecting light from the region of interest to which it is exposed with a field of view of 180 and higher degrees, and light conveying surfaces,.

Description

OPTICAL SYSTEM FOR USE IN AN ENDOSCOPE

FIELD OF THE INVENTION

The present invention is generally in the field of medical devices, and relates to an optical system and method for use in an endoscope. Specifically, the present invention relates to enhancing viewing through an endoscope.

REFERENCES

The following references are considered to be pertinent for the purpose of understanding the background of the present invention:

US Patent 6,449,103 to Charles US Patent 5,017,783 to Mousavi

Chalam et al., "Optics of wide-angle panoramic viewing system-assisted vitreous surgery," Surv Ophthalmol. 2004 Jul-Aug;49(4):437-45.

BACKGROUND OF THE INVENTION Endoscopes are used to view internal organs in a minimally invasive way.

They are utilized in many parts of the body, including the GI tract, the urinary tract and the respiratory tract. Generally, endoscopes incorporate a system of lenses for transmitting an image of the organ under inspection, to the viewer.

PCT Publication WO 05/065044 to Cabiri et al. assigned to the assignee of the present patent application,, describes apparatus for use with a biologically- compatible-fluid pressure source, the apparatus including an elongate carrier, adapted to be inserted through a proximal opening of a body lumen, and a piston head coupled to a distal portion of the carrier. The piston head is adapted to form a pressure seal with a wall of the lumen after the carrier has been inserted into the lumen, and to be advanced distally through the body lumen in response to pressure from the fluid pressure source. The apparatus is configured to facilitate distal advancement of the piston head by facilitating passage of fluid out of the lumen from a site within the lumen distal to the piston head. The apparatus additionally includes an optical system, coupled to the carrier in a vicinity of the distal portion, the optical system having distal and proximal ends. US Patent Application Publication 2008/0097292 to Cabiri et al. assigned to the assignee of the present patent application, , describes apparatus for use with a biologically-compatible-fluid pressure source, the apparatus including an elongate carrier, adapted to be inserted through a proximal opening of a body lumen, and a piston head coupled to a distal portion of the carrier. The apparatus is described as additionally including an optical system, coupled to the carrier in a vicinity of the distal portion, the optical system having distal and proximal ends. The optical system includes an image sensor, positioned at the proximal end of the optical system; an optical member having distal and proximal ends, and shaped so as to define a lateral surface, at least a distal portion of which is curved, configured to provide omnidirectional lateral viewing; and a convex mirror, coupled to the distal end of the optical member, wherein the optical member and the mirror have respective rotational shapes about a common rotation axis.

US Patent Application Publication 2004/0249247 to Iddan, describes an endoscope capable of capturing images of an in-vivo area behind a distal end of the endoscope's tube. The endoscope is described as having an imaging unit that may, for example, include a reflective surface that reflects an image of an area surrounding such tube onto an image sensor. Other optical systems are described for imaging behind one end of an endoscope or imaging device. US Patent 5,313,306 to Kuban et al., describes an endoscopic-type device for omnidirectional image viewing providing electronic pan-and-tilt orientation, rotation, and magnification within a selected field-of-view for use in applications in various environments such as in internal medicine inspection, monitoring, and surgery. The imaging device (using optical or infrared images) is based on the effect that the image from a wide angle lens, which produces a circular image of an entire field-of-view, can be mathematically corrected using high speed electronic circuitry. More specifically, an incoming image from an endoscope image acquisition source, including a wide angle lens, is transmitted through an image conduit and captured by a camera that produces output signals according to that image. A transformation of these output signals is performed for the viewing region of interest and viewing direction, and a corrected image is output as a video image signal for viewing, recording, or analysis. Multiple simultaneous images are described as being output from a single input image.

GENERAL DESCRIPTION

There is a need in the art in a novel optical system to be used with an endoscope. Such optical system should enable high-quality imaging a region of interest with a more than 180 degree field of view, while being sufficiently small in size and defining a sufficiently short optical path of the collected light propagating through the system to an imaging detector.

Generally, lenses capable of collecting light with more than 180 degree numerical aperture are known and used in photography equipment, for example Nikon produces the 6 mm Nikkor fisheye lens; the lens is described as having a picture angle of 220 degrees. IPIX corporation produces the IPIX 4.88 mm fisheye lens, which is described as providing 185 degrees of coverage. However such fisheye lens are inappropriate in endoscopic systems, because of their too large sizes. Also, a problem with the conventional systems of the kind specified is the typical use of mirrors. This unavoidably increases the system size. The size of the optical system is a critical parameter for various applications, especially medical ones, for example endoscopic imaging.

The present invention provides a small-size optical system for use with an endoscope. The optical system collects light and focuses it onto an imaging sensor. An endoscope tube is coupled to the image sensor. The optical system comprises a light collecting and focusing lens unit located inside the endoscope tube and formed by a plurality of lenses accommodated along the endoscope. A - A - collection surface of the lens unit is configured for collecting light with more than 180-degree collection angle (field of view) and protrudes from a distal end of the endoscope to be exposed to light coming from the region of interest. Light collected through the collecting surface is conveyed by the optical system onto a focal spot on the image sensor.

In the context of the present application, and in the appended claims, the terms "proximal" and "distal" should be understood as being with respect to the physician.

According to the invention, the optical system is configured for "direct imaging" of the collected light onto a focal spot, which means that there is no transfer of a virtual image onto intermediate imaging plane(s), as for example in relay optics. The optical system of the present invention is configured to define multiple spaced-apart substantially refractive interfaces (with substantially no reflection of light therefrom, i.e. mirrorless arrangement) configured and arranged to define together a predetermined refractive index profile along an optical axis of the optical system. The arrangement of refractive interfaces is selected so as to provide direct imaging of light collected with a predetermined field of view, being higher than 180 degrees, onto a desirably small, high quality (reduced aberrations and image blur), focal spot on the imaging sensor, with the fixed focal plane location and with no need for moving any of said refractive interfaces. Thus, the optical system of the present invention is configured with a fixed focus configuration.

These refractive interfaces arranged in a spaced-apart relationship in the optical path of light are formed by surfaces of a plurality of separate lens elements (i.e. single-lens elements, no doublets). The use of separate lens elements eliminates a need for any adhesive material in the optical path of light, thus improving the image quality.

A number of the lens elements, their geometry (shape), spaces between the lens element, as well as material(s) from which the lens elements are made define together the arrangement of the refractive interfaces along the collecting and focusing lens unit. All these parameters are appropriately selected to ensure that the refractive interfaces operate together to provide a predetermined refractive index profile along the optical path defined by the arrangement of said lens elements and accordingly the refractive interfaces and an incident angle of light on each of the interfaces during the light propagation through the optical system, i.e. appropriately bend the light propagation path through the lens unit. The outer surface of the lens unit through which light is collected has a curved geometry thus collecting light from surroundings with a solid collection angle of about 180 degree and higher, generally about 180-220-degree solid angle of light collection. It should be understood, that for a given optical system, the larger field of view corresponds to the higher F# of the system (due to the larger angular region from which the light is being collected). Considering the field of view of 180-220 degrees, the F# is about 7.4.

It should be understood that in order to be used for endoscopic applications, the optical system configuration of the present invention is selected such that the total track of the optical system is about a few tens of millimeters, e.g. 26 mm length and about 12 mm to 30 mm cross-section.

In some embodiments, the lens elements of the optical system of the present invention are made of glass materials. This enables sterilization thereof (at temperature of about 130°C) and therefore the optical system can be reused, rather than being disposable as typically in conventional endoscopic systems.

There is thus provided according to one aspect of the invention, an optical system to be used with an endoscope for insertion into a body lumen of a subject; said optical system comprising a light collecting and focusing lens unit configured to collect light from a region of interest and to focus said light onto a focal spot; said light collecting and focusing lens unit comprises a plurality of separate lens elements defining together an arrangement of spaced-apart substantially refractive interfaces accommodated along an optical axis of the system, said arrangement of interfaces comprising a light collection surface configured with a predetermined curvature capable of collecting light from the region of interest to which it is exposed with a field of view of 180 and higher degrees.

The interfaces arrangement includes substantially refractive interfaces configured and arranged to define together a predetermined refractive index profile along said optical axis to appropriately bend a light propagation path through said lens unit.

The predetermined refractive index profile along the optical path is defined by a selected number of the refractive interfaces; a distance (air space) between them; the geometry of the lens elements defining said interfaces; and a material from which the lens elements are made.

Preferably, the interfaces arrangement is configured for direct imaging of light collected with more than 180 degrees field of view onto said focal spot. As mentioned above, this means that there is no transfer of a virtual image onto intermediate imaging plane(s), as for example in relay optics. Preferably, the lens unit is configured to define the focal spot at a fixed focal plane location with the predetermined field of view.

The lens elements may be made of at least one transparent material selected from plastic, acrylic resin, polystyrene, cycloolefin, cycloolefin copolymer, polysulfone, and a polycarbonate. Preferably however, the lens elements are made of glass. This allows reusage of the lens unit, after sterilization.

The lens element defining the light collection surface may for example have a cross sectional dimension substantially not exceeding 30 mm, more preferably, not exceeding 20 mm. The curvature of the collection surface may be characterized by a radius in a range of about 10 mm to 20 mm, more preferably in a range of 12 mm to 17 mm. The surface area of the collection surface exposed to the region of interest may be in a range of about 600 mm to 1000 mm , more preferably in a range of about 750 mm to 850 mm .

The lens unit is preferably configured to define a length of the optical path from the collection surface to the focal plane of about a few tens of millimeters. For example, the optical system may have the optical path length of about 26 mm and a cross-sectional dimension in a range of about 12 mm to 30 mm.

It is important to note that the above configuration of the optical system, enables it to be used as the single optical system in an endoscope, i.e. the system capable of imaging a region in front of the distal end of the endoscope and also implementing a so-called "back-imaging".

According to another broad aspect of the invention, there is provided an apparatus, comprising: an endoscope configured for insertion into a body lumen of a subject to be exposed to light coming from a region of interest; an image sensor to be coupled to said endoscope; and a single optical system comprising a light collecting and focusing lens unit configured to collect light from the region of interest and to focus said light onto a focal spot on the image sensor; said light collecting and focusing lens unit comprises a plurality of separate lens elements defining together an arrangement of spaced-apart substantially refractive interfaces accommodated along an optical axis of the system, said arrangement of interfaces comprising a light collection surface configured with a predetermined curvature capable of collecting light from the region of interest to which it is exposed with a field of view of 180 and higher degrees.

The apparatus preferably includes an illumination system, which may include a plurality of light sources, e.g. including one or more light emitting diodes.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic illustration of an optical system that protrudes from a distal end of an endoscope, in accordance with an embodiment of the present invention;

Fig. 2 is a schematic illustration of the optical system of Fig. 1, in accordance with an embodiment of the present invention;

Fig. 3 is a graph showing the modulus of the optical transfer function of the optical system of Fig. 2, as a function of frequency, the optical system being in accordance with an embodiment of the present invention;

Fig. 4 is a schematic illustration of the optical system of Fig. 1, in accordance with an alternative embodiment of the present invention; and

Fig. 5 is a graph showing the modulus of the optical transfer function of the optical system of Fig. 4, as a function of frequency, the optical system being in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is made to Fig. 1, which is a schematic illustration of an example of an apparatus, generally designated 100, including an endoscope 22 configured for insertion into a body lumen of a subject to be exposed to light coming from a region of interest, an optical system 20 of the present invention accommodated inside the endoscopic tube, and an image sensor 26 coupled to the endoscope.

More specifically, the present invention is used in a colonoscope- endoscope and is therefore described below with respect to this specific application. It should however be understood that the invention is not limited to this specific example, and the principles of the invention may be used in other type endoscopes and in generally in any imaging system. Such colonoscope- endoscope may for example be configured and operable as described in WO 05/065044 to the assignee of the present patent application, incorporated by reference herein with respect to this specific example. A piston head 32 of an endoscope as described in the above-mentioned PCT application is advanced into a subject's colon 35. For some applications, optical system 20 is coupled to a distal end of the piston head 32.

As shown, the optical system 20, by its light collection surface (interface) 28A protrudes from the distal end of endoscope 22 and is thus exposed to the region of interest. The light collection surface 28A is an external surface of a ray- capturing lens 28 which is appropriately configured (i.e. has a predetermined curvature) to define a field of view greater than 180 degrees (generally of about 180 degrees or higher but preferably not less than 220 degrees).

As will be described more specifically further below, optical system 20 is configured to convey light from the region of interest, collected by surface 28 A, to image sensor 26, by using substantially refractive interfaces, i.e. without utilizing reflection of the light by any element of the optical system 20. Image sensor 26 may be of any known suitable type capable of receiving light and generating output data indicative of a detected image. This output data is transmitted to a viewing station outside the subject's body, via a cable 30, or wireless signal transmission as the case may be.

In some embodiments, optical system 20 and image sensor 26 are housed in a housing 24. As will be described below, the optical system is configured to be reusable by sterilization between uses (e.g. at 130⁰C temperature); and may be detachable from the endoscope, as well as may be e.g. together with the image sensor, be removed from the housing.

For some applications, endoscope 22 includes an illumination system 34.The illumination system may comprise a plurality of light sources 36, which are configured to illuminate the entire field of view of lens 28. In some embodiments, the light sources include one or more light emitting diodes. For example, the light emitting diodes are arranged upon a printed circuit board 38 in a circular array so as to be around the region of interest.

Reference is now made to Fig. 2, which is a more specific illustration of a non-limiting example of the configuration of optical system 20, in accordance with an embodiment of the present invention. Optical system 20 includes a light collecting and focusing lens unit formed by a plurality of separate (not attached to one another) lens elements, which are configured and arranged to define a predetermined arrangement of spaced-apart refractive interfaces accommodated along the optical axis OA of the system. The lens units include ray-capturing lens 28, a set 40 of correction and scaling lenses (42, 44, 46, 48 and 50), and an aperture stop 52 in between the scaling lenses 46 and 48. As also shown in the figure, there is preferably provided a cover glass 54 that covers an image sensor it is located on the last surface of 54

Ray-capturing lens 28 has a geometry defining an input, light collection surface 28 A (distal surface) and an output surface 28B (proximal surface) both being appropriately curved. The curvature of light collection surface 28A (defined by its cross sectional dimension D, and a radius of curvature), which in turn defines a surface area of the surface exposed to the region of interest, is selected to collect light with 180 degrees solid angle (field of view) or higher In some embodiments, the field of view is up to 220 degrees. The surface area (i.e. total area of the exposed optic surface) of ray- capturing lens 28 is in the range of about 600 mm² to 1000 mm², in particular in the range of about 750 mm² and 850 mm².

Each lens unit defines distal and proximal surfaces (e.g. lens 28 defines surfaces 28A, 28B, lens 42 defines surfaces 42A, 42B, etc.), and the lenses are made of selected material(s) such that these surface act as the refractive interfaces. As indicated above, the lens elements are selected to provide the arrangement of the refractive interfaces defining together a predetermined refractive index profile along the optical axis OA to appropriately bend the light propagation path through the lens unit. Also, the configuration of the elements is preferably selected to reduce aberrations of light propagating through the lens unit. The following is a Table 1 providing the properties of the surfaces of the lenses according to a specific but not limiting example of the invention. Table 1:

In some embodiments, one or more lenses of optical system 20 are made of one or more materials from the following plastic, an acrylic resin, polystyrene, cycloolefin, cycloolefin copolymer, polysulfone, and/or a polycarbonate. In some embodiments, one or more of the lenses are made of glass. As indicated above, this facilitates sterilization of the lens unit, thus enabling its reusage.

For some applications, a cross sectional dimension (termed herein below as diameter) D of ray-capturing lens 28 is less than 30 mm, e.g., less than 20 mm. The radius of curvature of light collection surface 28A is in the range of about 10 mm to 20 mm, e.g., 12 mm to 17 mm.

It should be understood, that the appropriate selection of the above parameters for given conditions of the field of view, spot size and its location, result in such optical system characteristic as Modulation Transfer Function (MTF), being the absolute value (modulus) of the optical transfer function (OTF). In this connection, reference is made to Fig. 3, representing a graph showing the MTF of optical system 20, as a function of frequency. Here, the configuration of the optical system 20 as per specified in Table 1 is considered. As shown, the system collects spatially separated light components incident onto the light collection surface with solid angles of collection within a range of 180- 220 degrees (represented respectively by curves TS 90 and TS 110, i.e. angles in the TS-plane, being the tangential-sagita plane perpendicular to the optical axis). - o -

The graph shows the optical performance of the system as a function of increasing frequency, i.e. resolution. The performance decreases (becomes poorer) at higher resolution values as is common in all real optical systems.

Reference is now made to Fig. 4, showing optical system 20, in accordance with another embodiment of the present invention. In this example, similar to that of Fig. 2, optical system 20 includes ray-capturing lens 28 collecting light with up to about 220 degrees collection angle , a set 64 of correction and scaling lenses (66, 68, 70, 72, and 74), and an aperture stop 76; also a cover glass 78 associated with an image sensor (not shown) is provided.

As shown, in the present example, planar-surfaces lens elements 48 and 50 of Fig. 2 are replaced by lens elements 72 and 74 defining two (or more) aspheric surfaces 80 and 82. Table 2 below specifies the parameters and properties of the lenses of optical system 20 in the example of Fig. 4. In all other aspects, optical system 20, as shown in Fig. 4, is generally similar to that shown in Fig. 2.

Table 2 :

Fig. 5 is a graph showing the MTF of optical system 20 of Fig. 4 with the parameters as provided in Table 2. The graphs in Figs. 3 and 5 are slightly different as they correspond to the use of different lens elements' materials, plastic in Fig. 3 and glass in Fig. 5 and different lens shape and lens spacing so the performances of the systems are different as well.

Claims

CLAIMS:

1. An optical system to be used with an endoscope for insertion into a body lumen of a subject; said optical system comprising a light collecting and focusing lens unit configured to collect light from a region of interest and to focus said light onto a focal spot; said light collecting and focusing lens unit comprises a plurality of separate lens elements defining together an arrangement of spaced-apart substantially refractive interfaces accommodated along an optical axis of the system and defining together a predetermined refractive index profile along said optical axis to appropriately bend a light propagation path through said lens unit, said arrangement of interfaces comprising a light collection surface configured with a predetermined curvature capable of collecting light from the region of interest to which it is exposed with a field of view of 180 and higher degrees, and light conveying surfaces,.

2. The optical system of claim 1, wherein said predetermined refractive index profile along the optical path is defined by a selected number of the refractive interfaces; a distance between them; the geometry of the lens elements defining said interfaces; and a material from which the lens elements are made.

3. The optical system of claim 1 or 2, wherein said interfaces arrangement is configured for direct imaging of light collected with more than

180 degrees field of view onto said focal spot.

4. The optical system of any one of claims 1 to 3, wherein said lens unit is configured to define the focal spot at a fixed focal plane location.

5. The optical system according to any one of claims 1 to 4, wherein the lens unit collects light with a solid angle of collection in the range of about

180 degrees to 220 degrees.

6. The optical system of any one of claims 1 to 5, wherein said lens elements are made of at least one transparent material selected from plastic, acrylic resin, polystyrene, cycloolefin, cycloolefϊn copolymer, polysulfone, and a polycarbonate.

7. The optical system of any one of claims 1 to 5, wherein said lens elements are made of glass.

8. The optical system of claim 7, configured to be reusable by sterilization.

9. The optical system according to any one of claims 1 to 8, wherein the lens element defining said light collection surface has a cross sectional dimension substantially not exceeding 30 mm.

10. The optical system according to claim 9, wherein the collection surface has the cross sectional dimension not exceeding 20 mm.

11. The optical system according to any one of claims 1 to 10, wherein a radius of the curvature of the collection surface is in a range of about 10 mm to 20 mm.

12. The optical system according to claim 11, wherein the radius of the curvature of the collection surface is in a range of 12 mm to 17 mm.

13. The optical system according to any one of claims 1 to 12, wherein a surface area of the collection surface exposed to the region of interest is in a range of about 600 mm² to 1000 mm².

14. The optical system according to claim 13, wherein the surface area of the collection surface is in a range of about 750 mm² to 850 mm².

15. The optical system according to any one of claims 1 to 14, wherein the lens unit is configured to define a length of the optical path from the collection surface to the focal plane to be about a few tens of millimeters.

16. The optical system according to claim 15, wherein said optical path length is about 26 mm and a cross-sectional dimension of the lens unit is in a range of about 12 mm to 30 mm.

17. An endoscopic apparatus comprising the single optical system of any one of claims 1 to 16.

18. An apparatus, comprising: an endoscope configured for insertion into a body lumen of a subject to be exposed to light coming from a region of interest; an image sensor to be coupled to said endoscope; and a single optical system comprising a light collecting and focusing lens unit configured to collect light from the region of interest and to focus said light onto a focal spot on the image sensor; said light collecting and focusing lens unit comprises a plurality of separate lens elements defining together an arrangement of spaced-apart substantially refractive interfaces accommodated along an optical axis of the system and defining together a predetermined refractive index profile along said optical axis to appropriately bend a light propagation path through said lens unit, said arrangement of interfaces comprising a light collection surface configured with a predetermined curvature capable of collecting light from the region of interest to which it is exposed with a field of view of 180 and higher degrees, and light conveying surfaces,.

19. The apparatus according to claim 18, wherein the lens unit collects light with a collection angle in the range of about 180 degrees to 220 degrees.

20. The apparatus according to claim 18 or 19, wherein said spaced- apart interfaces are made of glass.

21. The apparatus according to any one of claims 18 to 20, wherein said optical system is configured to be detached from the endoscope.

22. The apparatus according to claim 20 or 21, wherein said optical system is configured to be reusable by sterilization .

23. The apparatus according to any one of claims 18 to 22, wherein the endoscope comprises an illumination system.

24. The apparatus according to claim 23, wherein the illumination system comprises a plurality of light sources.

25. The apparatus according to claim 24, wherein the plurality of light sources comprise at least one light emitting diode.

26. The apparatus according to claim 25, comprising a printed circuit board comprising a plurality of the light emitting diodes arranged in a substantially circular array upon the printed circuit board.

27. The apparatus according to any one of claims 18 to 26, wherein the endoscope comprises a colonoscope.