JP2012210337A - Photoacoustic imaging apparatus and method for detecting failure in the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a failure in an optical fiber that propagates light such as a laser beam toward an object to be inspected in a photoacoustic imaging apparatus.SOLUTION: In the photoacoustic imaging apparatus including a probe having a light source 2 for emitting light L to be irradiated to the object to be inspected, and the optical fiber 30B for propagating the light L to the object to be inspected, a return light RL returning to the light source 2 after entering the optical fiber 30B is branched off from a light path of a light heading for the optical fiber 30B from the light source, the branched return light RL is detected by a light detector 20, and the failure in the optical fiber 30B is detected based on a light quantity of the detected return light RL.

Description

  The present invention relates to a photoacoustic imaging apparatus, that is, an apparatus for irradiating a subject such as a living tissue with light and imaging the subject based on an acoustic wave generated by the light irradiation.

  The present invention also relates to a method for detecting a failure of such a photoacoustic imaging apparatus, and more specifically, a failure of an optical fiber constituting a probe of the apparatus.

  Conventionally, as shown in Patent Document 1 and Non-Patent Document 1, for example, a photoacoustic imaging apparatus that images the inside of a living body using a photoacoustic effect is known. In this photoacoustic imaging apparatus, pulsed light such as pulsed laser light is irradiated into the living body. Inside the living body that has been irradiated with the pulsed light, the living tissue that has absorbed the energy of the pulsed light undergoes volume expansion due to heat and generates an acoustic wave (acoustic signal). Therefore, this acoustic wave is detected by a piezoelectric element or the like, and the inside of the living body can be visualized based on the detection signal.

  In such a photoacoustic imaging apparatus, as described in Patent Document 1, the tip portions of a plurality of optical fibers that propagate light and the piezoelectric elements that detect acoustic waves are one-dimensional or two-dimensional. Many arranged probes (probes) are used. In this type of probe, light such as laser light is emitted from the tips of a plurality of optical fibers toward the subject, and acoustic waves generated from the subject receiving the light are detected by a plurality of piezoelectric elements. It is like that.

JP 2005-21380 A

A High-Speed Photoacoustic Tomography System based on a Commercial Ultrasound and a Custom Transducer Array, Xueding Wang, Jonathan Cannata, Derek DeBusschere, Changhong Hu, J. Brian Fowlkes, and Paul Carson, Proc.SPIE Vol. 7564, 756424 (Feb. 23, 2010)

  The above-described optical fiber propagates light from a light source such as a laser light source to the probe. However, the optical fiber may be broken or broken while the probe is used. When a photoacoustic image is acquired while the optical fiber is in such a state, the amount of light applied to the subject is reduced in the vicinity of the broken or broken optical fiber as compared with other parts. The state of the living tissue is illegally indicated. However, the conventional photoacoustic imaging apparatus has not taken measures to accurately detect such a failure (disconnection or breakage) of the optical fiber.

  The present invention has been made in view of the above circumstances, and provides a failure detection method for a photoacoustic imaging apparatus capable of accurately detecting a failure in an optical fiber that propagates light such as laser light toward a subject. The purpose is to provide.

  Another object of the present invention is to provide a photoacoustic imaging apparatus that can carry out the failure detection method.

The failure detection method of the photoacoustic imaging apparatus according to the present invention includes:
Method for detecting failure such as disconnection or breakage of optical fiber in photoacoustic imaging apparatus provided with light source for emitting light to irradiate subject and probe having optical fiber for propagating light toward subject Because
Return light returning to the light source side after entering the optical fiber is branched from the optical path of light from the light source toward the optical fiber,
The branched return light is detected by a photodetector,
A failure of the optical fiber is detected based on the detected amount of return light.

  More specifically, in this method, when the amount of return light exceeds a predetermined reference value, it is determined that the optical fiber is broken. In addition, it is preferable to use what was defined for each photoacoustic imaging apparatus as such a reference value.

On the other hand, the photoacoustic imaging apparatus according to the present invention is:
In a photoacoustic imaging apparatus comprising a light source that emits light to irradiate a subject, and a probe having an optical fiber that propagates the light toward the subject.
A branching optical system for branching the return light that enters the optical fiber and returns to the light source side from the optical path of the light from the light source toward the optical fiber;
A photodetector for detecting return light branched from the optical path by the branching optical system;
Failure detection means for detecting failure of the optical fiber based on the amount of return light detected by the photodetector is provided.

  The failure detection means is preferably configured to determine that the optical fiber is broken when the amount of return light exceeds a predetermined reference value. In that case, as the reference value, a reference value determined for each photoacoustic imaging apparatus and stored in the storage means is preferably used.

  In the photoacoustic imaging apparatus of the present invention, it is preferable that a display means for displaying a failure when the failure detection means detects a failure of the optical fiber is further provided.

  Alternatively, when the failure detection means detects a failure of the optical fiber, an alarm means for issuing an alarm by sound or light indicating the failure may be provided. Such alarm means can be provided together with the display means or in place of the display means.

  The photoacoustic imaging apparatus of the present invention is preferably configured on the assumption that a plurality of optical fibers are provided to form a bundle fiber.

  On the other hand, as the branching optical system, an optical system including a beam splitter inserted in the optical path of light from the light source toward the optical fiber is preferably used.

  Alternatively, particularly when the light source emits linearly polarized light, the branching optical system is inserted into the optical path with the transmission axis parallel to the linear polarization direction of the light traveling toward the optical fiber. A polarizing beam splitter and a λ / 4 plate inserted in the optical path between the polarizing beam splitter and the optical fiber are preferably used.

  Further, as the branching optical system, an optical system including a prism that is inserted in an optical path of light from the light source toward the optical fiber and reflects a part of the return light is also preferably used.

  Also, when there are a plurality of optical fibers and the end faces from which the return lights are emitted are arranged in a line, when the return lights are emitted from the plurality of optical fibers as the photodetectors, It is desirable to use a line sensor in which the light detection part extends along the direction in which the return lights are arranged.

  When the optical fiber constituting the probe is not broken or broken, the light emitted from the light source and incident thereon hardly returns to the light source side. On the other hand, if the optical fiber has a broken or broken part, the incident light is reflected by that part and returns to the light source side as return light. The failure detection method of the photoacoustic imaging apparatus according to the present invention pays attention to this point, and splits the return light that enters the optical fiber and then returns to the light source side from the optical path of the light from the light source toward the optical fiber. Since the return light is detected by the photodetector and the failure of the optical fiber is detected on the basis of the detected amount of the return light, it is possible to accurately detect the disconnection or breakage failure in the optical fiber.

  In addition, if the point of whether or not the amount of return light exceeds a predetermined reference value is used as a failure determination criterion, failure detection can be performed with a simpler configuration.

  In such a case, if the reference value determined for each photoacoustic imaging apparatus is used, the presence or absence of a failure can be accurately detected even when the characteristics of the probe differ from apparatus to apparatus. Become.

  A photoacoustic imaging apparatus according to the present invention is branched by a branching optical system for branching return light that enters the optical fiber and then returns to the light source side from the optical path of the light from the light source toward the optical fiber. And a failure detection means for detecting a failure of the optical fiber based on the amount of the return light detected by the photodetector. Therefore, the failure detection method according to the present invention described above is provided. Can be implemented.

  In the photoacoustic imaging apparatus of the present invention, when the failure detection means detects a failure of the optical fiber, if the display means for displaying the failure and the alarm means for issuing an alarm are provided, the user of the apparatus It is possible to immediately know that a failure has occurred.

The block diagram which shows the basic composition of the photoacoustic imaging device by one Embodiment of this invention. The perspective view which shows schematic structure of the probe used for the apparatus of FIG. The schematic front view which shows the optical fiber which the probe of FIG. 2 has Block diagram showing an example of connection between the probe and the signal acquisition unit 1 is a schematic side view showing a branching optical system of a probe used in the apparatus of FIG. Explanatory drawing explaining the state of the return light radiate | emitted from an optical fiber The schematic side view which shows another example of the branch optical system used for the photoacoustic imaging device of this invention The schematic side view which shows another example of the branch optical system used for the photoacoustic imaging device of this invention The schematic side view which shows another example of the photodetector used for the photoacoustic imaging device of this invention. Schematic front view showing a part of the configuration of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of a photoacoustic imaging apparatus according to an embodiment of the present invention. The photoacoustic imaging apparatus 100 includes a laser driver 1, a laser light source 2, an ultrasonic probe (probe) 3, a region selection unit 4, a light irradiation detection unit 5, a synchronization correction processing unit 6, a signal capturing unit 7, and an element. A data memory 8, an image construction unit 9, an image memory 10, an image display unit 11, a photodetector 20, a failure detection unit 21, and a branching optical system 40 are included.

  The laser light source 2 emits laser light that irradiates a living tissue that is a subject. In the present embodiment, a laser light source 2 that emits pulsed laser light L is used. The laser driver 1 drives the laser light source 2.

  As shown in FIG. 2, the probe 3 includes a plurality of channels (channels) of piezoelectric elements 31. For example, 192 piezoelectric elements 31 are provided side by side so as to correspond to a range in which a biological tissue is imaged. The probe 3 detects an acoustic signal (ultrasonic wave) generated from the living tissue when the pulsed laser light L is irradiated from the laser light source 2 to the living tissue, and converts the acoustic signal into an electrical signal. Output.

  In many cases, the photoacoustic imaging apparatus irradiates the living tissue with ultrasonic waves from the piezoelectric element 31 and receives the ultrasonic waves reflected by the living tissue by the piezoelectric element 31 so that an ultrasonic image can also be acquired. However, since this point is not directly related to the present invention, description thereof is omitted.

  A range corresponding to the plurality of piezoelectric elements 31 of the probe 3, that is, a range in which a biological tissue is imaged is divided into a plurality of partial regions that do not overlap each other. In this embodiment, there are three partial regions, for example, region A, region B, and region C, as will be described in detail later. The width of each partial region corresponds to the same number of piezoelectric elements as the number of signals that can be sampled in parallel by the signal capturing unit 7. In this example, the signal capturing unit 7 can sample data for 64 channels in parallel. Therefore, each of the regions A, B, and C has a width corresponding to 64 piezoelectric elements.

  The region selection unit 4 selects one of the three partial regions, and notifies the laser driver 1 and the probe 3 of the selection information. The laser driver 1 drives the laser light source 2 so as to irradiate a pulse laser beam in a range including at least a selected partial region. On the other hand, the probe 3 uses a multiplexer or the like to connect the piezoelectric element 31 corresponding to the selected partial region to the signal capturing unit 7. The signal capturing unit 7 samples the electrical signal (acoustic signal data) output from the connected piezoelectric element 31 a plurality of times over a predetermined measurement period after the partial region is irradiated with the pulse laser beam, and the sampled data is the element Store in the data memory 8.

  When the acoustic signal data from the piezoelectric element 31 corresponding to the selected partial region is stored in the element data memory 8, the region selection unit 4 selects the next partial region. Thus, the region selection unit 4 sequentially selects the partial regions until the entire range to be imaged of the living tissue is selected. As the region selection unit 4 sequentially selects the partial regions, acoustic signal data from all the piezoelectric elements 31 of the probe 3 is stored in the element data memory 8 in the element data memory 8. That is, if the region selection unit 4 sequentially selects the region A, the region B, and the region C and the signal capturing unit 7 samples N times for each region, the element data memory 8 stores a total of (192 × N) ch of sounds. Signal data is stored.

  The signal capturing unit 7 stores the electrical signal from the probe 3 in the element data memory 8. The signal acquisition unit 7 samples the electric signal output from the probe 3 a plurality of times over a predetermined measurement period, and stores the sampling data obtained thereby in the element data memory 8. The signal capturing unit 7 includes, for example, a preamplifier that amplifies a minute signal and an AD converter that converts an analog signal into a digital signal. The number of signals that the signal capturing unit 7 can capture in parallel, that is, the number of channels (ch), is smaller than the total number of piezoelectric elements that the probe 3 has. For example, in the present embodiment, the probe 3 includes 192 piezoelectric elements 31 as an example, whereas the number of channels that can be captured in parallel by the signal capturing unit 7 is 64.

  Next, the above configuration will be described in more detail with reference to FIGS. The laser light source 2 shown in FIG. 1 uses, for example, an Nd: YAG / SHG laser that converts a laser beam having a wavelength of 1064 nm into a laser beam having a second harmonic, that is, a wavelength of 532 nm, and the laser beam having the wavelength of 532 nm. It is composed of two solid-state lasers of Ti: sapphire laser that are excited to emit laser light having a wavelength of about 700 to 900 nm. When the photoacoustic image is acquired, the Nd: YAG / SHG laser is pulse-driven when receiving a trigger signal T instructing light irradiation, and finally a pulse laser beam L having a wavelength of about 700 to 900 nm is emitted from the laser light source 2. It is done.

  The pulse laser beam L is supplied to the bundle fiber of the probe 3 shown in FIG. 2 via the branch optical system 40 shown in FIG. 1 which also serves as a fiber input optical system (this will be described in detail later with reference to FIG. 5). 30B. As shown in FIG. 3, the bundle fiber 30 </ b> B is formed by bundling a large number of multi-mode optical fibers 30, and the pulsed laser light L is input to each optical fiber 30 in approximately equal amounts of light. .

  The piezoelectric elements 31 shown in FIG. 2 are arranged one-dimensionally along a predetermined direction. The tip of each optical fiber 30 of the bundle fiber 30B is arranged along the direction in which the elements 31 are arranged on both sides of the arranged piezoelectric elements 31, and the pulse laser light L propagated through the optical fiber 30 is transmitted. The living tissue is irradiated from both sides of the piezoelectric element 31. That is, the end portions of the optical fibers 30 arranged side by side constitute a light irradiation unit. In FIG. 2, the numbers of optical fibers 30 and piezoelectric elements 31 are schematically shown, and examples of actual numbers are as described above.

  In the present embodiment, the light irradiation unit includes a plurality of optical fibers 30 corresponding to, for example, each of the three regions A, B, and C of the living tissue. That is, the light irradiation unit including a plurality of optical fibers 30 corresponding to the region A irradiates at least the region A with the pulsed laser light L when the region A is selected. The light irradiating unit composed of the plurality of optical fibers 30 corresponding to the region B irradiates at least the region B with the pulsed laser light L when the region B is selected, and the light irradiating unit composed of the plurality of optical fibers 30 corresponding to the region C. Irradiates at least the region C with the pulse laser beam L when the region C is selected.

  The probe 3 is provided with three photodetectors 33a, 33b and 33c. These photodetectors 33a to 33c are included in the light irradiation detection unit 5 shown in FIG. The photodetectors 33a to 33c detect that the pulsed laser light L has been applied to the living tissue, and when receiving the pulsed laser light L, output a light detection signal. The photodetectors 33a, 33b, and 33c are provided corresponding to the regions A, B, and C, respectively. The light detector 33a corresponding to the region A detects that the region A is irradiated with the pulsed laser light L when the region A is selected. The same applies to the photodetectors 33b and 33c corresponding to the regions B and C, and when each region is selected, it is detected that the pulsed laser light L has been irradiated to each region.

  FIG. 4 shows an example of connection between the probe 3 and the signal capturing unit 7. As described above, the probe 3 has a 192ch piezoelectric element 31 (see FIG. 2). The region of the biological tissue corresponding to the 192ch piezoelectric element 31 is considered to be composed of three partial regions (regions A to C) as described above. In other words, if the width of the living tissue corresponding to the 192ch piezoelectric element 31 is 60 mm, the width of each partial region is 20 mm. The photoacoustic imaging apparatus 100 sequentially performs light irradiation and data collection on the partial region having a width of 20 mm to acquire data for all 192 channels.

  The signal capturing unit 7 includes, for example, an AD converter that can sample data for 64 channels in parallel. The multiplexer 12 selectively connects the piezoelectric element 31 of the probe 3 and the signal capturing unit 7. The multiplexer 12 is connected to, for example, 192 ch piezoelectric elements, and 64 ch of them are selectively connected to the AD converter of the signal capturing unit 7. For example, when the region A is selected, the multiplexer 12 connects the 64 ch piezoelectric elements 31 corresponding to the region A to the AD converter of the signal capturing unit 7. Further, when the region B is selected, the multiplexer 12 connects the 64 ch piezoelectric element 31 corresponding to the region B to the AD converter of the signal capturing unit 7, and when the region C is selected. The 64 ch piezoelectric elements 31 corresponding to the region C are connected to the AD converter of the signal capturing unit 7.

  When the region A is selected and the light irradiating unit including the plurality of optical fibers 30 irradiates the region A of the living tissue with the pulsed laser light L, the pulsed laser light L has a certain extent due to scattering in the living tissue. proceed. An absorber such as blood existing in the living tissue absorbs the energy of the pulsed laser light L and generates an acoustic signal (acoustic wave). The time required for this acoustic signal to be detected by each piezoelectric element 31 depends on the positional relationship in the X direction between the acoustic signal generation point and each piezoelectric element 31 and the position in the Z direction of the acoustic signal generation point. .

  In order to detect the acoustic signal, the electric signal output from the piezoelectric element 31 selected by the multiplexer 12 is sampled a plurality of times over a predetermined measurement period by the AD converter. The same applies to the other regions B and C. The pulse laser beam L is irradiated to each region, and the electric signal output from the piezoelectric element 31 corresponding to each region is sampled a plurality of times over a predetermined measurement period. And an acoustic signal is detected.

  Here, considering the flow of processing related to each partial area, selection of the partial area, generation of the trigger signal T, irradiation of pulsed laser light to the living tissue, detection of acoustic signals from the living tissue, storage of data in the element data memory It becomes the flow. The electric signal acquisition start timing, that is, the sampling start timing in the signal acquisition unit 7 is set in accordance with the timing at which the pulsed laser light L is irradiated onto the living tissue.

  When the time from the generation of the trigger signal to the actual irradiation of the pulsed laser light L on the living tissue is different for each partial area, the acoustic signal data obtained for each partial area is synthesized and generated. This causes a problem that the quality of the generated image is degraded. The light irradiation detection unit 5 and the synchronization correction processing unit 6 are provided to prevent this problem. That is, the light irradiation detection unit 5 detects that the living tissue is irradiated with light from the laser light source 2, and the synchronization correction processing unit 6 calculates the difference in light irradiation timing detected by the light irradiation detection unit 5 between the partial regions. The time axis of the sampling data in the element data memory 8 is corrected between the partial areas based on the timing difference.

  When the region selection unit 4 selects all the partial regions and a plurality of sampling data output from each of the 192ch piezoelectric elements 31 of the probe 3 are stored in the element data memory 8, the image construction unit 9 Sampling data is read from the memory 8, and a tomographic image of the living tissue is constructed based on the read data. The image construction unit 9 typically includes a signal processing unit, a phase matching addition unit, and an image processing unit. Although a detailed description of a detailed image construction procedure in the image construction unit 9 is omitted, the function can be realized by a computer operating according to a predetermined program, for example. Alternatively, the function of the image construction unit 9 may be realized by a digital signal processor (DSP), a field programmable gate array (FPGA), or the like.

  The image construction unit 9 stores image data indicating the constructed tomographic image in the image memory 10. The image display unit 11 displays the tomographic image on, for example, a liquid crystal display screen based on the image data stored in the image memory 10.

  Here, the plurality of optical fibers 30 shown in FIG. 2 may be broken or broken while the probe 3 is used. If the photoacoustic imaging apparatus 100 is used in this state, the above-described problems are caused. Hereinafter, the point of detecting disconnection or breakage of the optical fiber 30 will be described.

  FIG. 5 shows in detail the configuration of the branching optical system 40 shown in FIG. 1 and its surroundings. As shown here, the branching optical system 40 is arranged in a collimator lens 41 that collimates the pulse laser light L emitted from the laser light source 2 as divergent light, and an optical path of the pulse laser light L that has become parallel light. And a condensing lens 43 that condenses the pulsed laser light L that has passed through the beam splitter 42 and inputs it to each optical fiber 30 of the bundle fiber 30B.

  When the pulsed laser light L incident on the optical fiber 30 becomes the return light RL and travels toward the laser light source 2, the return light RL is transmitted to the optical fiber 30 from the laser light source 2 by the beam splitter 42. It is branched from the optical path and proceeds downward in FIG. The branched return light RL is passed through the imaging lens 44, and the imaging lens 44 forms an image of the incident end face (outgoing end face for the return light RL) of the bundle fiber 30 </ b> B on the photodetector 20. The As the photodetector 20, for example, a CCD area sensor or the like is preferably used. Further, as the beam splitter 42, the ratio of the transmitted light amount and the reflected light amount is, for example, 50:50. As long as the return light RL is observed by the photodetector 20, the ratio is, for example, 90:10. May be.

  FIG. 6 schematically shows an image of the incident end face (see FIG. 3) of the bundle fiber 30B, which is imaged on the photodetector 20. As shown in FIG. If there is no disconnection or breakage in each optical fiber 30 shown in FIG. 3, the portion is dark as indicated by F in FIG. On the other hand, in the portion of the optical fiber 30 where the disconnection or breakage occurs, the return light RL is emitted, so that it is brightly observed as indicated by F ′ in FIG. Therefore, the amount of light detected by the photodetector 20 is larger when some of the optical fibers 30 are disconnected or broken compared to when all the optical fibers 30 are normal.

  The photodetector 20 outputs a signal indicating the detected total light amount. This output signal is input to the failure detection unit 21 shown in FIG. The failure detection unit 21 compares the output signal with a signal indicating a light quantity reference value stored in an internal memory (not shown). If the former exceeds the latter, a failure detection signal indicating a failure of the optical fiber 30. SD is output. The failure detection signal SD is input to the pixel display unit 11. When the pixel display unit 11 receives the failure detection signal SD, the pixel display unit 11 performs a display notifying of a failure such as “There is an abnormality in the optical fiber of the probe”.

  The device operator can know the failure of the optical fiber 30 from this display, and can repair or replace the probe 3, so that the probe 3 including the failed optical fiber 30 can be used for illegal photoacoustics. It is possible to prevent an image from being acquired. Note that alarm means for making a buzzer sound or blinking an alarm lamp may be provided instead of displaying the optical fiber failure as described above.

  The above-mentioned light quantity reference value may be determined for each photoacoustic imaging apparatus 100 or, for example, for each photoacoustic imaging apparatus provided with a common specification or type of probe 3. A common value may be used.

  Next, another example of the branching optical system that can be used in the photoacoustic imaging apparatus of the present invention will be described with reference to FIGS. In these drawings, the same elements as those in FIGS. 1 to 6 are denoted by the same reference numerals, and description thereof will be omitted unless necessary (the same applies hereinafter).

  First, in contrast to the branching optical system 40 shown in FIG. 5, the branching optical system 50 shown in FIG. 7 is provided with a polarizing beam splitter 51 instead of the beam splitter 42, and the polarizing beam splitter 51 and the condenser lens 43. The point that the λ / 4 plate 52 is inserted in the optical path of the pulsed laser light L is different from that in FIG.

  As the laser light source 2, one that emits linearly polarized pulsed laser light L is used. The polarization beam splitter 51 is arranged such that its transmission axis coincides with the direction of linear polarization of the pulsed laser light L traveling from the laser light source 2 toward the bundle fiber 30B. Therefore, the pulsed laser light L emitted from the laser light source 2 and incident on the polarization beam splitter 51 is transmitted through the polarization beam splitter 51 with high transmittance. The pulsed laser light L that has passed therethrough is then converted from a linearly polarized state to a circularly polarized state by the λ / 4 plate 52 and is incident on the bundle fiber 30B.

  Also in the above configuration, if there is a broken or broken portion in the optical fiber 30 of the bundle fiber 30B, a part of the pulsed laser light L is reflected by those portions and returns to the laser light source 2 side as return light RL. . When the return light RL is reflected as described above, the direction of the circularly polarized light is opposite. Therefore, when the return light RL passes through the λ / 4 plate 52, the return light RL is in a direction perpendicular to the linear polarization direction of the pulsed laser light L toward the bundle fiber 30B. It will be linearly polarized. Therefore, the return light RL is reflected downward in the drawing by the polarization beam splitter 51 and enters the imaging lens 44. Subsequent detection of the return light RL, failure detection of the optical fiber 30 based on the detected light amount, and display thereof are performed in this example as described above.

  According to the branching optical system 50 including the polarizing beam splitter 51 and the λ / 4 plate 52 as described above, it is possible to prevent light loss at the beam splitter 42 that may occur in the branching optical system 40 shown in FIG. Can do.

  Next, in contrast to the branching optical system 40 shown in FIG. 5, the branching optical system 60 shown in FIG. 8 is provided with a prism 61 instead of the beam splitter 42, and the laser light source 2 is shown in the drawing of the lenses 41 and 42. The difference is that the pulse laser beam L is arranged so that the upper half of the laser beam L travels. The prism 61 is disposed so as to reflect the return light RL that passes through the lower half of the lenses 41 and 43 in the figure downward.

  The return light RL reflected by the prism 61 enters the imaging lens 44. Subsequent detection of the return light RL, failure detection of the optical fiber 30 based on the detected light amount, and display thereof are performed in this example as described above.

  By applying the branching optical system 60 including the prism 61 as described above, it is possible to prevent light loss at the beam splitter 42 that may occur in the branching optical system 40 shown in FIG. it can.

  Next, another example of the photodetector that can be used in the photoacoustic imaging apparatus of the present invention will be described with reference to FIGS. In this example, as shown in FIG. 9, the same branching optical system 40 as that shown in FIG. 5 is used. On the other hand, in the bundle fiber 30B, as shown in the front shape in FIG. 10, a plurality of optical fibers 30 are arranged with the end faces from which the pulse laser light L is incident and the return light RL is emitted aligned. ing.

  Therefore, the image of the end face of the bundle fiber 30B formed by the imaging lens 44 is obtained by arranging the end faces of the plurality of optical fibers 30 in a line. That is, if the return lights RL are emitted from the end faces, the return lights RL are arranged in a line. As the photodetector 70, a line sensor is used in which the photodetector is extended along the direction in which the return lights RL are arranged (for example, in the horizontal direction in FIG. 9).

  As the above-described line sensor, for example, a photodiode array can be preferably used. Such a line sensor is less expensive than the CCD area sensor described above, and is advantageous in reducing the cost for detecting a failure.

  In the photoacoustic imaging apparatus 100 according to the embodiment described above, the probe 3 having a plurality of optical fibers 30 is used, but the present invention is a photoacoustic having a probe having only one optical fiber. The present invention can also be applied to an imaging apparatus. Even in that case, according to the present invention, it is possible to accurately detect the breakage or breakage of the one optical fiber.

  As the laser light source, in addition to the solid-state laser used in the above embodiment, other solid-state lasers such as an alexandrite laser, an AlGaAs semiconductor laser with an oscillation wavelength of about 800 nm at the maximum, and an InGaAs semiconductor with an oscillation wavelength of about 900 nm at the maximum A laser or the like is also applicable. Further, a combination of an optical amplification type laser light source that uses a semiconductor laser as a seed light source and an optical wavelength conversion element, more specifically, a semiconductor laser that emits laser light having a wavelength of about 1560 nm, and the laser light is amplified. A fiber amplifier composed of a polarization-maintaining Er (erbium) -doped optical fiber, and an SHG (second harmonic generation) element that converts the laser light amplified there into a second harmonic having a wavelength of about 780 nm Etc. are also applicable.

DESCRIPTION OF SYMBOLS 1 Laser driver 2 Laser light source 3 Probe 4 Area | region selection part 5 Light irradiation detection part 6 Synchronization correction process part 7 Signal acquisition part 8 Element data memory 9 Image construction part 10 Image memory 11 Image display part 12 Multiplexer 20, 70 Photo detector 21 Failure detection unit 30 Optical fiber 30B Bundle fiber 31 Piezoelectric element 40, 50, 60 Branch optical system 41 Collimator lens 42 Beam splitter 43 Condensing lens 44 Imaging lens 51 Polarizing beam splitter 52 λ / 4 plate 61 Prism 100 Photoacoustic image Device

Claims (13)

In a photoacoustic imaging apparatus comprising a light source that emits light that irradiates a subject and a probe that has an optical fiber that propagates the light toward the subject, a method for detecting a failure of the optical fiber,
Return light returning to the light source side after entering the optical fiber is branched from the optical path of light from the light source toward the optical fiber,
The branched return light is detected by a photodetector,
A failure detection method for a photoacoustic imaging apparatus, wherein a failure of the optical fiber is detected based on the detected amount of return light.   2. The failure detection method for a photoacoustic imaging apparatus according to claim 1, wherein when the amount of the return light exceeds a predetermined reference value, it is determined that the optical fiber is broken.   3. The photoacoustic imaging apparatus failure detection method according to claim 2, wherein the reference value is determined for each photoacoustic imaging apparatus. In a photoacoustic imaging apparatus comprising a light source that emits light to irradiate a subject, and a probe having an optical fiber that propagates the light toward the subject.
A branching optical system for branching the return light that enters the optical fiber and then returns to the light source side from the optical path of the light from the light source toward the optical fiber;
A photodetector for detecting return light branched from the optical path by the branching optical system;
A photoacoustic imaging apparatus, comprising: failure detection means for detecting failure of the optical fiber based on the amount of return light detected by the photodetector.   5. The photoacoustic imaging apparatus according to claim 4, wherein the failure detection means determines that the optical fiber is broken when the amount of the return light exceeds a predetermined reference value.   6. The photoacoustic imaging according to claim 5, wherein the failure detection means uses, as the reference value, a reference value determined for each individual photoacoustic imaging apparatus and stored in a storage means. apparatus.   The photoacoustic imaging apparatus according to any one of claims 4 to 6, further comprising display means for displaying an indication of the failure when the failure detection means detects a failure of the optical fiber.   The photoacoustic imaging apparatus according to any one of claims 4 to 6, further comprising an alarm unit that issues an alarm indicating the failure when the failure detection unit detects a failure of the optical fiber.   The photoacoustic imaging apparatus according to claim 4, wherein a plurality of the optical fibers are provided to constitute a bundle fiber.   The photoacoustic imaging apparatus according to claim 4, wherein the branching optical system includes a beam splitter inserted in the optical path. The light source emits linearly polarized light;
A polarization beam splitter inserted into the optical path in a direction in which a transmission axis is parallel to a linear polarization direction of light traveling toward the optical fiber, and the polarization beam splitter and the optical fiber; The photoacoustic imaging apparatus according to claim 4, further comprising a λ / 4 plate inserted in the optical path between the first and second optical paths.   The photoacoustic imaging apparatus according to claim 4, wherein the branching optical system includes a prism that is inserted into the optical path and reflects a part of the return light. A plurality of the optical fibers, the end faces from which the return light is emitted are arranged in a line,
The line detector, wherein when the return light is emitted from each of the plurality of optical fibers, a light detection unit extends along the alignment direction of the return lights. The photoacoustic imaging apparatus of any one of 4-12.