WO2012114730A1 - Photoacoustic measurement device and photoacoustic signal detection method - Google Patents

Abstract

To improve the accuracy with which a subject is detected by a photoacoustic image generating device, wherein first light is radiated to the subject, and photoacoustic signals generated inside the subject by irradiating the subject with the first light are detected. Prior to radiating the first light, second light for measuring distance is emitted, and reflected light of the emitted second light is detected. The time from emission of the second light to detection of the reflected light is measured, and radiation of the first light is controlled based on the measured time.

Description

Photoacoustic measurement apparatus and photoacoustic signal detection method

The present invention relates to a photoacoustic measurement apparatus and a photoacoustic signal detection method, and more specifically, a photoacoustic measurement apparatus and a photoacoustic signal for irradiating a subject with light and detecting ultrasonic waves generated in the subject by the light irradiation. It relates to a detection method.

An ultrasonic inspection method is known as a kind of image inspection method capable of non-invasively examining the state inside a living body. In the ultrasonic inspection, an ultrasonic probe capable of transmitting and receiving ultrasonic waves is used. When ultrasonic waves are transmitted from the ultrasonic probe to the subject (living body), the ultrasonic waves travel inside the living body and are reflected at the tissue interface. By receiving the reflected sound wave with the ultrasonic probe and calculating the distance based on the time until the reflected ultrasonic wave returns to the ultrasonic probe, the internal state can be imaged.

Also, photoacoustic imaging is known in which the inside of a living body is imaged using the photoacoustic effect. In general, in photoacoustic imaging, a living body is irradiated with pulsed laser light. Inside the living body, the living tissue absorbs the energy of the pulsed laser light, and ultrasonic waves (photoacoustic signals) are generated by adiabatic expansion due to the energy. By detecting this photoacoustic signal with an ultrasonic probe or the like and constructing a photoacoustic image based on the detection signal, in-vivo visualization based on the photoacoustic signal is possible.

Here, in photoacoustic imaging, it is necessary to irradiate a living body with a laser beam having a relatively high output. From the viewpoint of safety, it is preferable to suppress emission of pulsed laser light when the probe is not in contact with the living body. In this regard, Patent Document 1 includes an object detection unit that detects an object placed on the optical path, and performs light irradiation when the object detection unit detects the object to be measured. Is described. For detection of an object to be measured, identification of the object to be measured can be used. Specifically, the light shielding property, reflectivity, inherent temperature, weight, and capacitance of the object to be measured can be used.

JP 2009-142320 A

In Patent Document 1, when detecting the object to be measured using the reflectivity of the object to be measured, the object measuring means includes a light emitter that emits light and a light receiver that is disposed on the same side as the light projector. Composed. When the object to be measured is arranged on the optical path, the light emitted from the projector is reflected by the object to be measured and received by the light receiver. On the other hand, when the object to be measured is not arranged on the optical path, the light emitted from the projector proceeds as it is without being reflected, and the light receiver cannot detect the reflected light.

In the case of the above configuration, the presence / absence of the object to be measured can be determined based on the detection result of light by the light receiver. However, in the above configuration, it is merely determined that the object to be measured is correctly arranged when light is detected by the light receiver. Therefore, the accuracy of detection of the object to be measured is low.

In view of the above, an object of the present invention is to provide a photoacoustic measurement device and a photoacoustic signal detection method with improved detection accuracy of a subject.

In order to achieve the above object, the present invention detects a first light source that generates first light to be irradiated to a subject, and a photoacoustic signal generated in the subject by the irradiation of the first light. A photoacoustic signal detection means; a second light source for generating second light for distance measurement; a reflected light detection means for detecting reflected light with respect to the second light emitted from the second light source; It is characterized by comprising a time measuring means for measuring the time between emission of light and detection of reflected light, and a light irradiation control means for controlling the emission of the first light based on the measured time. A photoacoustic measuring device is provided.

In the photoacoustic measurement apparatus of the present invention, the control means calculates the distance to the subject based on the measured time, and when the calculated distance is equal to or less than a predetermined threshold, the first light is It can be configured to irradiate the subject.

The photoacoustic measurement apparatus of the present invention can employ a configuration further comprising photoacoustic image generation means for generating a photoacoustic image based on a photoacoustic signal.

The second light may be pulsed laser light.

In the photoacoustic measurement apparatus of the present invention, a configuration in which the first light source also serves as the second light source can be employed.

The light intensity of the second light is preferably lower than the light intensity of the first light.

The present invention also includes a step of irradiating the subject with the first light, a step of detecting a photoacoustic signal generated in the subject by the irradiated first light, and prior to the irradiation of the first light. The step of emitting the second light for distance measurement, the step of detecting the reflected light with respect to the emitted second light, and the time between the emission of the second light and the detection of the reflected light are measured. There is provided a photoacoustic signal detection method comprising: a step; and a step of controlling the emission of the first light based on the measured time.

The photoacoustic measurement device and the photoacoustic signal detection method of the present invention emit the second light for distance measurement and measure the time until the reflected light with respect to the second light is detected. The shorter the distance to the subject, the shorter the time required until the reflected light is detected, and the distance to the subject can be determined based on the detected time. For this reason, the detection accuracy of the subject can be improved as compared with the case where the subject is detected simply based on the presence or absence of reflected light. Based on the measured time, for example, the first light irradiation is performed when the measured time is shorter than a predetermined time, so that the first light is sufficiently close to the subject. Can irradiate light.

The block diagram which shows the photoacoustic measuring device of 1st Embodiment of this invention. The figure which shows an ultrasonic probe and a test object. The figure which shows the principle of the distance measurement using a pulse laser beam. The flowchart which shows an operation | movement procedure. The block diagram which shows the photoacoustic measuring device of 2nd Embodiment of this invention. The flowchart which shows the operation | movement procedure in 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a photoacoustic measuring apparatus according to a first embodiment of the present invention. The photoacoustic measurement apparatus 10 is configured as a photoacoustic image diagnostic apparatus (photoacoustic image generation apparatus), and includes an ultrasonic unit 11, an ultrasonic probe 12, and a laser unit 13. The photoacoustic image diagnostic apparatus 10 generates at least a photoacoustic image. The photoacoustic image diagnostic apparatus 10 may generate an ultrasonic image in addition to the photoacoustic image. The laser unit 13 includes a laser light source (first light source) 22 that generates light (first light) to be irradiated onto the subject. The laser light source 22 generates pulsed laser light (first pulsed laser light) to be irradiated on the subject when generating the photoacoustic image. The wavelength of the first pulse laser beam may be set as appropriate according to the observation object.

The ultrasonic probe 12 includes an ultrasonic sensor 18, a laser light source (second laser light source) 19, reflected light detection means 20, and a light irradiation unit 21. The first pulse laser beam emitted from the laser unit 13 is guided to the ultrasonic probe 11 using a light guide means such as an optical fiber. The light irradiation unit 21 emits the guided first pulse laser beam toward the subject. The ultrasonic sensor 18 is a photoacoustic signal detection unit, and includes, for example, a plurality of ultrasonic transducers arranged one-dimensionally. The ultrasonic sensor 18 detects ultrasonic waves (photoacoustic signals) generated on the observation target in the subject by being irradiated with the first pulse laser beam.

The laser light source 19 corresponds to a second light source that generates light for distance measurement (second light). The laser light source 19 is a pulse laser and generates a pulse laser beam (second pulse laser beam) for distance measurement. As the laser light source 19, a laser diode (LD: laser diode) or the like can be used. The laser power (light intensity) of the second pulse laser light is lower than the laser power of the first pulse laser light for excitation. The reflected light detection means 20 detects reflected light with respect to the second pulsed laser light emitted from the laser light source 19. As the reflected light detection means 20, a photodiode (PD: photo ： diode) or the like can be used.

The ultrasonic unit 11 includes a receiving circuit 14, an image generating unit 15, a time measuring unit 16, and a light irradiation control unit 17. The receiving circuit 14 receives a photoacoustic signal detected by the ultrasonic sensor 18 of the ultrasonic probe 12. The image generating unit 15 generates a photoacoustic image based on the photoacoustic signal received by the receiving circuit 14. The generated photoacoustic image is displayed on a display screen such as a display unit (not shown). Some signal processing may be performed on the photoacoustic signal without imaging the photoacoustic signal.

The time measuring means 16 receives notification of the timing of reflected light detection from the reflected light detecting means 20 of the ultrasonic probe 12. The time measuring means 16 measures the time between the emission of the second pulse laser beam and the detection of the reflected light. The light irradiation control means 17 controls the emission of the first pulse laser beam based on the measured time. For example, the light irradiation control means 17 calculates the distance between the ultrasonic probe 12 and the subject based on the measured time. The light irradiation control means 17 irradiates the subject with the first pulse laser beam only when the calculated distance is equal to or less than a predetermined threshold value.

FIG. 2 shows the ultrasonic probe 12. The ultrasonic probe 12 is connected to the ultrasonic unit 11 and the laser unit 13 using an optical fiber or an electric cable. The light irradiation unit 21 irradiates the subject 30 with a first pulsed laser beam, which is excitation light, guided from the laser unit 13 using an optical fiber. The observation object 31 in the subject absorbs the energy of the first pulse laser beam and generates a photoacoustic signal by adiabatic expansion due to the energy. The ultrasonic sensor 18 detects a photoacoustic signal generated at the observation object 31.

The second pulse laser beam emitted from the laser light source 19 is reflected by the surface of the subject 30. The reflected light detection means 20 detects the reflected light reflected by the surface of the subject 30. The time from when the laser light source 19 emits the second pulse laser light to when the reflected light is detected by the reflected light detection means 20 depends on the distance D between the ultrasonic probe 12 and the subject 30. Change. The drive circuit 23 is a drive power supply circuit for the laser light source 19 and the reflected light detection means 20. The drive circuit 23 does not have to be provided in the ultrasonic probe 12 and may be provided in the ultrasonic unit 11.

FIG. 3 shows the principle of distance measurement using pulsed laser light. The pulse laser 50 in FIG. 3 corresponds to the laser light source 19 in FIG. 1, and the photodetector 55 corresponds to the reflected light detection means 20. First, the emission timing of the pulse laser is defined as time t = 0. For example, the light emitted from the pulse laser 50 is branched in the direction of the photodetector 52 by the beam splitter 51, and the timing at which the photodetector 52 detects the light is defined as t = 0. The pulse laser beam is reflected by the subject 53. The beam splitter 54 is placed on the optical path of the reflected light, and the time when the reflected light branched by the beam splitter 54 is detected by the photodetector 55 is checked. When the detection time of the reflected light is t = T, the distance L to the subject 53 is obtained by L = cT / 2 where c is the speed of light.

In the distance measuring technique using the pulse laser as described above, a pulse laser beam having a pulse width of n seconds to p seconds has been reported. When pulsed laser light having a pulse width of several tens of nanoseconds is used, an electric wire having a length of 1 cm or less can be detected. According to Topcon's report, a distance resolution of 1 mm or less is possible in a semiconductor laser having a pulse width of 8 ns, a repetition frequency of 8.5 kHz, and a peak power of 40 W. The wavelength of the pulse laser is selected according to the transmittance of the space for measuring the distance. In the case of long distances such as atmospheric observation, a wavelength having a high atmospheric transmittance is selected in consideration of safety to the eyes. For example, in-vehicle use, pulsed laser light with a wavelength of 800 nm to 900 nm is used. Also in this embodiment, pulse laser light with a wavelength of 800 nm to 900 nm is used as the second pulse laser light for distance measurement.

FIG. 4 shows the operation procedure. When generating the photoacoustic image, the laser light source 19 emits a second pulse laser beam for distance measurement (step A1). In the ultrasonic probe 12, the light emission surface of the second pulse laser beam is assumed to be on the same surface as the surface on which the ultrasonic sensor 18 in contact with the subject 30 (FIG. 2) is disposed. The reflected light detection means 20 detects reflected light with respect to the second pulse laser beam (step A2). The time measuring means 16 measures the time between the emission of the second pulse laser beam and the detection of the reflected light (step A3).

The light irradiation control unit 17 calculates a distance D from the ultrasonic probe 12 (second pulse laser beam emission surface) to the surface of the subject 30 based on the time measured by the time measurement unit 16. (Step A4). The light irradiation control unit 17 determines whether or not the calculated distance D is equal to or less than a predetermined threshold value (step A5). When the calculated distance D is less than or equal to the threshold value, the surface of the ultrasonic probe 12 on which the ultrasonic sensor 18 is disposed is in contact with the surface of the subject 30 or sufficiently close to the surface of the subject 30. It can be judged that The light irradiation control means 17 gives a light emission signal (laser trigger signal) to the laser unit 13 when the distance D is less than or equal to the threshold value (step A6).

The light irradiation control means 17 does not give a light emission signal to the laser unit 13 when determining that the distance D is larger than the threshold value in step A5. In that case, it returns to step A1, and it repeats from emission of the 2nd pulse laser beam to calculation of distance D. When the calculated distance D is equal to or smaller than the threshold value, the process proceeds to step A6, and a light emission signal is given to the laser unit 13. Since the distance D is proportional to the time until the reflected light is detected, step A4, which is a step for calculating the distance D from the time until the reflected light is detected, is omitted. In step A5, the time measured in step A3 may be subjected to threshold processing as it is.

When the light irradiation control means 17 outputs a light emission signal, the laser light source 22 emits a first pulse laser beam (step A7). The first pulse laser beam emitted from the laser light source 22 is guided to the probe 11 and is irradiated onto the subject 30 from the light irradiation unit 21. By this light irradiation, a photoacoustic signal is generated in the observation object 31 in the subject 30. The ultrasonic sensor 18 detects a photoacoustic signal from the observation object 31 (step A8). The image generation means 15 inputs a photoacoustic signal via the receiving circuit 14 and generates a photoacoustic image (step A9). The generated photoacoustic image is displayed on a display device or the like.

In this embodiment, when generating a photoacoustic image, the subject is irradiated with the second pulse laser beam. The reflected light with respect to the second pulse laser beam is detected, and the time from the irradiation of the second pulse laser beam to the detection of the reflected light is measured. Based on the measured time, the distance from the ultrasonic probe 12 to the surface of the subject can be determined. In the present embodiment, the distance measurement technique using a pulse laser is applied to determine the distance to the subject, so that the subject is in contact with the ultrasonic probe 12 or the subject is super Whether or not the acoustic probe 12 is sufficiently close can be accurately determined. Thus, in this embodiment, the detection accuracy of the subject can be improved. When the subject is away from the ultrasound probe 12, safety can be improved by suppressing the first pulse laser beam generated by the laser unit 13 from being emitted from the light irradiation unit 21.

Subsequently, a second embodiment of the present invention will be described. FIG. 5 shows a photoacoustic image generation apparatus according to the second embodiment of the present invention. In the photoacoustic image generation apparatus (photoacoustic image diagnostic apparatus) 10 a according to the present embodiment, the ultrasonic probe 12 a includes an ultrasonic sensor 18, reflected light detection means 20, and a light irradiation unit 21. The configuration of the ultrasonic probe 12a in the photoacoustic image diagnostic apparatus 10a of the present embodiment is a configuration in which the laser light source 19 is omitted from the configuration of the ultrasonic probe 12 in the photoacoustic image diagnostic apparatus 10 of the first embodiment shown in FIG. It is. In the present embodiment, the laser light source 22 of the laser unit 13 also serves as a second laser light source that generates a second pulse laser beam for distance measurement.

The laser unit 13 operates in two operation modes: a mode for generating a first pulsed laser beam for excitation and a mode for generating a second pulsed laser beam for distance measurement. The laser light source 22 generates a first pulse laser beam and a second pulse laser beam according to the mode. The laser wavelength, pulse width, and repetition period of the pulse laser beam may be the same for the first pulse laser beam and the second pulse laser beam. The peak power of the second pulse laser beam is preferably lower than the peak power of the first pulse laser beam.

The second pulsed laser light generated by the laser light source 22 is guided from the laser unit 13 to the ultrasonic probe 12a, and irradiated from the light irradiation unit 21 of the ultrasonic probe 12a toward the subject. When the subject 30 (FIG. 2) exists before the second pulse laser beam travels, a part of the reflected light of the light emitted from the light irradiation unit 21 enters the reflected light detection means 20 and is reflected. The light detection means 20 detects reflected light. The operations from the detection of the reflected light to the calculation of the distance D between the subject 30 and the ultrasonic probe are the same as in the first embodiment.

The light irradiation control means 17 sends a light emission signal of the first pulse laser light to the laser unit 13 when the calculated distance D is not more than a predetermined threshold value. When a light emission signal is input, the laser light source 22 generates a first pulse laser beam for excitation. The first pulsed laser light is guided from the laser unit 13 to the ultrasonic probe 12a and irradiated from the light irradiation unit 21 toward the subject 30. In the observation target in the subject 30, a photoacoustic signal is generated by the irradiated first pulse laser beam. The operations from the detection of the photoacoustic signal to the generation of the photoacoustic image are the same as those in the first embodiment.

FIG. 6 shows an operation procedure in the second embodiment. First, the laser light source 22 operates in a mode for generating a second pulse laser beam for distance measurement. When generating the photoacoustic image, the laser light source 22 generates a second pulse laser beam (step B1). The second pulse laser beam is guided to the ultrasonic probe 12a by an optical fiber or the like and emitted from the light irradiation unit 21 (step B2). The reflected light detection means 20 detects reflected light with respect to the second pulse laser beam (step B3). The time measuring means 16 measures the time between the emission of the second pulse laser beam and the detection of the reflected light (step B4).

The light irradiation control unit 17 calculates a distance D from the ultrasonic probe 12a (the emission surface of the light irradiation unit 21) to the surface of the subject 30 based on the time measured by the time measurement unit 16 (step) B5). The light irradiation control means 17 determines whether or not the calculated distance D is equal to or less than a predetermined threshold value (step B6). When the calculated distance D is less than or equal to the threshold value, the surface of the ultrasonic probe 12a on which the ultrasonic sensor 18 is disposed contacts the surface of the subject 30 or is sufficiently close to the surface of the subject 30. Can be judged. When the distance D is equal to or less than the threshold value, the light irradiation control means 17 gives a light emission signal (main irradiation trigger signal) of excitation light to the laser unit 13 (step B6).

When the light irradiation control means 17 determines that the distance D is larger than the threshold value in step B6, the light irradiation control means 17 does not give a light emission signal of excitation light to the laser unit 13. In that case, the process returns to step B1, and the process from the emission of the second pulse laser beam to the calculation of the distance D is repeated until the calculated distance D becomes equal to or less than the threshold value. When the calculated distance D is equal to or smaller than the threshold value, the process proceeds to step B7, and a light emission signal of excitation light is given to the laser unit 13. Similar to the first embodiment, the measured time may be subjected to threshold processing without calculating the distance D.

When the light irradiation control means 17 outputs the emission signal of the excitation light, the laser unit 13 switches the operation mode of the laser light source 22 to a mode for generating the first pulse laser light for excitation, and the first pulse laser light. Is generated (step B8). The generated first pulse laser beam is guided from the laser unit 13 to the ultrasonic probe 12a, and irradiated from the light irradiation unit 21 toward the subject 30 (step B9). By irradiating the first pulse laser beam, a photoacoustic signal is generated in the observation object 31 in the subject 30, and the ultrasonic sensor 18 detects the photoacoustic signal from the observation object 31 (step). B10). The image generation means 15 inputs a photoacoustic signal via the receiving circuit 14 and generates a photoacoustic image (step B11). The generated photoacoustic image is displayed on a display device or the like.

In the present embodiment, the laser light source 22 that generates the first pulse laser light for excitation also serves as the second laser light source that generates the second pulse laser light for distance measurement. In the present embodiment, a single laser light source 22 is used to generate a first pulse laser beam for excitation and a second pulse laser beam for distance measurement. The configuration of the ultrasonic probe can be simplified as compared with the first embodiment in which is separately provided. Moreover, it is not necessary to provide a driving power supply circuit for driving the laser light source in the ultrasonic probe. Other effects are the same as those of the first embodiment.

In the first embodiment, the ultrasonic probe 12 is provided with the laser light source 19 that generates the second pulse laser light for distance measurement. However, the second laser light source that generates the second pulse laser light is super There is no need to be provided in the acoustic probe 12. For example, the laser unit 13 is provided with a second laser light source in addition to the laser light source 22 that generates the first pulse laser light for excitation, and the light generated by the second laser light source is used using an optical fiber or the like. Then, the light may be guided to the ultrasonic probe 12 and irradiated with the second pulse laser beam from the ultrasonic probe 12.

As mentioned above, although this invention was demonstrated based on the suitable embodiment, the photoacoustic measuring device and photoacoustic signal detection method of this invention are not limited only to the said embodiment, From the structure of the said embodiment. Various modifications and changes are also included in the scope of the present invention.

Claims (12)

A first light source for generating first light to be irradiated on the subject;
Photoacoustic signal detection means for detecting a photoacoustic signal generated in the subject by the irradiation of the first light;
A second light source for generating second light for distance measurement;
Reflected light detection means for detecting reflected light with respect to the second light emitted from the second light source;
A time measuring means for measuring a time from emission of the second light to detection of the reflected light;
A photoacoustic measurement device comprising: a light irradiation control unit that controls the emission of the first light based on the measured time. The control means calculates a distance to the subject based on the measured time, and irradiates the subject with the first light when the calculated distance is equal to or less than a predetermined threshold value. The photoacoustic measuring device according to claim 1, wherein The photoacoustic measuring apparatus according to claim 1, wherein the first light source also serves as the second light source. The photoacoustic measuring device according to claim 1, further comprising photoacoustic image generation means for generating a photoacoustic image based on the photoacoustic signal. The photoacoustic measuring device according to claim 1, wherein the second light is a pulsed laser beam. The photoacoustic measuring device according to claim 1, wherein the light intensity of the second light is lower than the light intensity of the first light. Irradiating the subject with the first light;
Detecting a photoacoustic signal generated in the subject by the irradiated first light;
Emitting a second light for distance measurement prior to the irradiation with the first light;
Detecting reflected light with respect to the emitted second light;
Measuring the time between the emission of the second light and the detection of the reflected light;
And a step of controlling the emission of the first light based on the measured time. In the step of controlling the emission of the first light, a distance between the probe and the subject is calculated based on the measured time, and when the calculated distance is a predetermined threshold value or less, The photoacoustic signal detection method according to claim 7, wherein the subject is irradiated with the first light. The photoacoustic signal detection method according to claim 7, wherein the first light and the second light are emitted from the same light source. The photoacoustic signal detection method according to claim 7, further comprising a step of generating a photoacoustic image based on the photoacoustic signal. The photoacoustic signal detection method according to claim 7, wherein the second light is a pulsed laser beam. The photoacoustic signal detection method according to claim 7, wherein the light intensity of the second light is lower than the light intensity of the first light.

Images