JP2012183295A - Optoacoustic imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent noises from generating in an image signal in an optoacoustic imaging device in which a semiconductor laser is used as a pulsed light source for irradiation of pulsed light.SOLUTION: The optoacoustic imaging device is configured by using the semiconductor laser 102 as the pulsed light source for irradiating a subject with the pulsed light. Particularly in the optoacoustic imaging device 200 configured to constantly supply a low electric current less than an oscillation threshold to the semiconductor laser 102 during the operation of the device, a time filter 250 for cutting the light from the semiconductor laser 102 is arranged between the semiconductor laser 102 and the subject while the electric current less than the oscillation threshold is supplied to the semiconductor laser 102.

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.

  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, it is possible to detect this acoustic wave with an ultrasonic probe or the like and visualize the inside of the living body based on the detection signal.

  In the photoacoustic imaging apparatus as described above, as described in Patent Document 1, a semiconductor laser (laser diode) is often used as a light source that emits pulsed light. This semiconductor laser is advantageous in reducing the size and weight of the photoacoustic imaging apparatus and forming it at a lower cost than other solid-state lasers and the like. In addition, if the energy required for photoacoustic imaging cannot be reached with a single semiconductor laser, a semiconductor laser is used as a seed light source, and the light from there is used as a fiber amplifier or semiconductor light comprising an optical fiber to which a rare earth is added. It is also considered to use an optical amplification type laser light source that is amplified by an amplifier (may be provided in a plurality of stages if necessary) (see Non-Patent Document 2).

  In the case of using the semiconductor laser described above, in order to improve the rise of pulse driving, it is considered that a low current less than the oscillation threshold is always supplied to the semiconductor laser during operation of the photoacoustic imaging apparatus. When an optical amplification laser light source using a pulsed semiconductor laser as a seed light source is used, amplified spontaneous emission (ASE) of the optical amplifier is used in the time zone between the seed light pulses, that is, the non-light emission time zone. The phenomenon that light is emitted as a continuous wave in terms of time with a spectral width much wider than that of a semiconductor laser is observed.

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) Development of all-polarization-maintaining high-power Yb fiber MOPA system, Kazuhiko Sumimura, Eiji Yoshida, Naoto Fujita, Masahiro Nakatsuka, IEICE Transactions C vol.J91-C, No.4, pp.244-250 , 2008

  However, in the conventional photoacoustic imaging apparatus in which a semiconductor laser or a light amplification type laser light source using a semiconductor laser as a seed light source is applied as a pulse light source, there is a problem that noise is easily included in the obtained image signal. ing. As described above, this problem is particularly noticeable in the photoacoustic imaging apparatus in which a low current is constantly supplied to the semiconductor laser when the apparatus is in operation.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a photoacoustic imaging apparatus capable of obtaining an image signal with little noise even when a semiconductor laser is applied as a pulse light source.

A first photoacoustic imaging apparatus according to the present invention includes:
In a photoacoustic imaging apparatus using a semiconductor laser as a pulse light source for irradiating a subject such as a biological tissue with pulse light, or an optically amplified laser light source using a semiconductor laser as a seed light source,
A spectral filter is provided at a position between the pulse light source and the subject so as to allow the laser light emitted from the pulse light source to pass therethrough and cut off spontaneous emission light having a wavelength different from that of the laser light. Is.

  In the case where the pulse light source has a ring resonator, it is desirable that the spectral filter is disposed in the ring resonator.

  Further, when a plurality of pulse light sources that emit laser beams having different wavelengths are provided as the pulse light sources, it is desirable that the spectral filter is disposed corresponding to each of the pulse light sources.

Moreover, the second photoacoustic imaging apparatus according to the present invention includes:
In a photoacoustic imaging apparatus using a semiconductor laser as a pulse light source for irradiating a subject such as a biological tissue with pulse light, or an optically amplified laser light source using a semiconductor laser as a seed light source,
The period during which the current less than the oscillation threshold is supplied to the semiconductor laser (one used alone or one used as a seed light source of an optical amplification type laser light source) at a position between the pulse light source and the subject is: A time filter for cutting light from the pulse light source is provided.

  Also in this second photoacoustic imaging apparatus, when the pulse light source has a ring resonator, it is desirable that the time filter is disposed in the ring resonator.

  Also in this second photoacoustic imaging apparatus, when a plurality of pulse light sources emitting laser beams having different wavelengths are provided as the pulse light source, the time filter is arranged corresponding to each of the pulse light sources. It is desirable that

  In the second photoacoustic imaging apparatus, a spectral filter similar to that provided in the first photoacoustic imaging apparatus, that is, a laser emitted from the pulsed light source, is disposed between the pulsed light source and the subject. It is desirable to further provide a spectral filter that cuts spontaneous emission light having a wavelength different from that of the laser light while allowing the light to pass therethrough.

  The present invention is a photoacoustic image having a configuration in which a low current less than the oscillation threshold is constantly supplied to a semiconductor laser (used alone or used as a seed light source of an optical amplification type laser light source) when the apparatus is in operation. It is particularly desirable to be applied to a conversion apparatus.

  The “current below the oscillation threshold” in the second photoacoustic imaging apparatus of the present invention includes “low current” that is constantly supplied when the apparatus is in operation, but is not limited thereto, and the semiconductor laser is pulsed. It also includes a relatively low current that flows transiently through the semiconductor laser when it is driven.

  According to the inventor's research, it has been found that noise is likely to occur in an image signal when a semiconductor laser is used as a pulsed light source in a conventional photoacoustic imaging apparatus for the following reason.

  As is well known, a semiconductor laser emits spontaneously emitted light when supplied with a low current less than an oscillation threshold, and the wavelength range of spontaneously emitted light is generally wider than the wavelength range of oscillated laser light. Is. As the semiconductor laser constituting the pulse light source of the photoacoustic imaging apparatus, one having an oscillation wavelength that is originally in a wavelength region to be irradiated on the subject is selected and used, but spontaneous emission light having a wavelength different from the oscillation wavelength is used. When the subject is irradiated, the spontaneously emitted light is absorbed by a part other than the part to be imaged, and a weak acoustic wave is emitted therefrom. Since the weak acoustic wave is detected by being superimposed on the acoustic wave that should be detected, the spatial resolution of the photoacoustic image is lowered, and as a result, noise is generated in the image.

  The spontaneous emission light is generated when a current less than the oscillation threshold flows transiently in the semiconductor laser when the semiconductor laser rises from a state where the supply current is zero and is pulse-driven. If it is irradiated to a subject such as, it will lead to the generation of the noise.

  In particular, when the photoacoustic imaging apparatus is in operation, when the semiconductor laser is constantly supplied with a low current less than its oscillation threshold, as described above, the spontaneous emission light generated transiently within the pulse drive period is generated. In addition, the spontaneous emission light generated by the constant supply of a low current is also irradiated on the subject, so that more noticeable noise is generated. On the other hand, when an optical amplification type laser light source is used, amplified spontaneous emission light is continuously emitted from the optical amplifier itself in addition to the above spontaneous emission light. Such spontaneously emitted light also heats the subject as a broadband component of continuous wave, so the extra heating affects the thermal expansion of the subject you really want to know, and the level of the photoacoustic signal This leads to a reduction, and consequently, a reduction in the image quality of the photoacoustic image.

  Based on the above knowledge, in the first photoacoustic imaging apparatus according to the present invention, the laser light emitted from the pulsed light source passes through the position between the pulsed light source and the subject, and the wavelength of the laser light is A spectral filter that cuts different spontaneous emission light is installed, so that the subject is not irradiated with spontaneous emission light having a wavelength different from the wavelength that should be irradiated, and noise is prevented from occurring in the image signal. It becomes possible.

  Moreover, in the second photoacoustic imaging apparatus according to the present invention based on the above knowledge, a period during which a current less than the oscillation threshold is supplied to the semiconductor laser at a position between the pulse light source and the subject is Since a time filter that cuts off the light from the pulsed light source is provided, in this case as well, the subject is irradiated with spontaneously emitted light emitted from the semiconductor laser or the optical amplifier outside the predetermined light irradiation period. This eliminates the occurrence of noise in the image signal.

  When the present invention is applied to a photoacoustic imaging apparatus having a configuration in which a low current below the oscillation threshold is constantly supplied to the semiconductor laser when the apparatus is in operation, as described above, when the semiconductor laser is started up, In addition to the spontaneous emission light generated in step 1, the spontaneous emission light generated by supplying the low current to the semiconductor laser can also be cut off.

The block diagram which shows schematic structure of the photoacoustic imaging device by 1st Embodiment of this invention. The perspective view which shows the structural example of an ultrasound probe Block diagram showing an example of connection between an ultrasound probe and a signal acquisition unit 1 is a graph showing a light irradiation period of a semiconductor laser in the apparatus of FIG. The block diagram which shows schematic structure of the photoacoustic imaging device by 2nd Embodiment of this invention. The graph which shows the light emission period of the semiconductor laser in the apparatus of FIG. 5, and the light passage / blocking period by a time filter The block diagram which shows schematic structure of the photoacoustic imaging device by 3rd Embodiment of this invention. Schematic side view showing an optical amplification type laser light source used in the apparatus of FIG. FIG. 8 is a graph schematically showing light waveforms before and after the optical amplifier in the optical amplification laser light source of FIG. The block diagram which shows schematic structure of the photoacoustic imaging device by 4th Embodiment of this invention. Schematic which shows the example of the semiconductor laser light source which can be used for the photoacoustic imaging device of this invention. The figure explaining the drive state of the semiconductor laser apparatus of FIG. Schematic which shows another example of the semiconductor laser light source which can be used for the photoacoustic imaging device of this invention.

  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 the photoacoustic imaging apparatus according to the first embodiment of the present invention. The photoacoustic imaging apparatus 100 includes a laser driver 101, a laser light source 102, an ultrasonic probe 103, a region selection unit 104, a light irradiation detection unit 105, a synchronization correction processing unit 106, a signal capturing unit 107, and an element data memory 108. An image construction unit 109, an image memory 110, an image display unit 111, and a spectrum filter 150.

  The laser light source 102 emits pulsed laser light that irradiates a living tissue that is a subject, and a semiconductor laser is used in this embodiment. The laser driver 101 drives the laser light source (hereinafter referred to as a semiconductor laser) 102. When a trigger signal is input, the semiconductor laser 102 is pulse-driven in response thereto.

  The ultrasonic probe 103 includes a plurality of channels of ultrasonic probe elements (probe elements). For example, 192 probe elements are provided so as to correspond to the range in which the biological tissue is imaged. The ultrasonic probe 103 detects an acoustic signal (ultrasound) generated from the living tissue when the semiconductor laser 102 irradiates the living tissue with pulsed laser light, and converts the acoustic signal into an electrical signal. Output.

  A range corresponding to a plurality of probe elements of the ultrasound probe 103, 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 probe elements as the number of signals that can be sampled in parallel by the signal capturing unit 107. In this example, the signal capturing unit 107 can sample data for 64 channels in parallel. Therefore, each of the regions A, B, and C has a width corresponding to 64 probe elements.

  The area selection unit 104 selects one of the three partial areas, and notifies the laser driver 101 and the ultrasound probe 103 of the selection information. The laser driver 101 drives the semiconductor laser 102 so as to irradiate a pulse laser beam in a range including at least a selected partial region. On the other hand, the ultrasound probe 103 connects the probe element corresponding to the selected partial region to the signal capturing unit 107 using a multiplexer (not shown) or the like. The signal capturing unit 107 samples the electrical signal (acoustic signal data) output from the connected probe element a plurality of times over a predetermined measurement period after the partial region is irradiated with light, and the sampled data is transmitted to the element data memory 108. To store.

  When the acoustic signal data from the probe element corresponding to the selected partial area is stored in the element data memory 108, the area selection unit 104 selects the next partial area. Thus, the region selection unit 104 sequentially selects the partial regions until the entire range to be imaged of the living tissue is selected. As the region selection unit 104 sequentially selects partial regions, acoustic signal data from all probe elements of the ultrasound probe 103 is stored in the element data memory 108 in the element data memory 108. That is, if the region selection unit 104 sequentially selects the region A, the region B, and the region C, and the signal capturing unit 107 samples N times for each region, the element data memory 108 stores a total of (192 × N) ch of sounds. Signal data is stored.

  The signal capturing unit 107 stores the electrical signal from the ultrasound probe 103 in the element data memory 108. The signal acquisition unit 107 samples the electrical signal output from the ultrasound probe 103 a plurality of times over a predetermined measurement period, and stores the sampling data obtained thereby in the element data memory 108. The signal capturing unit 107 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 acquisition unit 107 can acquire in parallel, that is, the number of channels (ch), is smaller than the total number of probe elements that the ultrasonic probe 103 has. For example, in the present embodiment, the ultrasonic probe 103 has 192 probe elements as an example, whereas the number of channels that can be captured in parallel by the signal capturing unit 107 is 64.

  Next, the above configuration will be described in more detail. FIG. 2 shows the ultrasonic probe 103 in detail. The probe element 131 is shown here. For example, the probe elements 131 are arranged one-dimensionally along a predetermined direction. The optical fiber 134 guides pulsed laser light emitted from the semiconductor laser 102 (see FIG. 1) to a light irradiation unit 132 provided in the ultrasonic probe 103. The light irradiation unit 132 irradiates the living tissue with the pulse laser beam. In this embodiment, the light irradiation part 132 is provided corresponding to each of the three area | region A of the biological tissue, the area | region B, and the area | region C, for example. That is, the light irradiation unit 132 corresponding to the region A irradiates at least the region A with pulsed laser light when the region A is selected. Further, the light irradiation unit 132 corresponding to the region B irradiates at least the region B with the pulse laser light when the region B is selected, and the light irradiation unit 132 corresponding to the region C applies at least the pulse laser light when the region C is selected. Irradiate.

  The photodetector 133 is included in the light irradiation detection unit 105 shown in FIG. The photodetector 133 detects that the living tissue has been irradiated with the pulsed laser light from the light irradiation unit 132, and outputs a light detection signal when receiving the pulsed laser light. The photodetector 133 is provided corresponding to each of the region A, the region B, and the region C. The photodetector 133 corresponding to the region A detects that the region A is irradiated with the pulse laser beam when the region A is selected. The same applies to the photodetectors 133 corresponding to the regions B and C. When each region is selected, it is detected that each region has been irradiated with pulsed laser light.

  FIG. 3 shows an example of connection between the ultrasound probe 103 and the signal capturing unit 107. As described above, the ultrasonic probe 103 has the 192ch probe element 131 (see FIG. 2). The region of the biological tissue corresponding to the 192ch probe element 131 is considered to be composed of three partial regions (regions A to C) as described above. That is, assuming that the width of the living tissue corresponding to the 192ch probe element 131 is 57.6 mm, the width of each partial region is 19.2 mm. The photoacoustic imaging apparatus 100 sequentially performs light irradiation and data collection on the partial region having the width of 19.2 mm to acquire data for all 192 channels.

  The signal acquisition unit 107 includes, for example, an AD converter that can sample data for 64 channels in parallel. The multiplexer 112 selectively connects the probe element of the ultrasonic probe 103 and the signal capturing unit 107. The multiplexer 112 is connected to, for example, 192 ch probe elements, and 64 ch of them are selectively connected to the AD converter of the signal capturing unit 107. For example, when the region A is selected, the multiplexer 112 connects the 64 ch probe elements corresponding to the region A to the AD converter of the signal capturing unit 107. The multiplexer 112 connects the 64 ch probe element corresponding to the region B to the AD converter of the signal capturing unit 107 when the region B is selected, and when the region C is selected, The 64 ch probe elements corresponding to the region C are connected to the AD converter of the signal capturing unit 107.

  When the region A is selected and the light irradiation unit 132 (see FIG. 2) irradiates the region A of the living tissue with the pulsed laser light, the pulsed laser light travels with a certain extent due to scattering in the living tissue. An absorber such as blood existing in the living tissue absorbs the energy of the pulsed laser beam and generates an acoustic signal. The time required for this acoustic signal to be detected by each probe element depends on the positional relationship between the acoustic signal generation point and each probe element in the X direction and the position of the acoustic signal generation point in the Z direction.

  In order to detect the acoustic signal, the electrical signal output from the probe element 131 selected by the multiplexer 112 is sampled a plurality of times over a predetermined measurement period by the AD converter. This is the same for the other regions B and C, where each region is irradiated with pulsed laser light, and the electrical signal output by the probe element corresponding to each region is sampled multiple times over a predetermined measurement period, An acoustic signal is detected.

  Here, considering the flow of processing related to each partial area, selection of the partial area, generation of a trigger signal, driving of the laser light source, irradiation of pulsed laser light to the living tissue, detection of acoustic signals from the living tissue, data to the element data memory The flow is storage. The electric signal acquisition start timing, that is, the sampling start timing in the signal acquisition unit 107 is set in advance in accordance with the timing at which the living tissue is irradiated with the pulsed laser light.

  If the time from the generation of the trigger signal to the actual irradiation of the pulsed laser light on the living tissue is different for each partial area, it is generated by synthesizing the acoustic signal data obtained for each partial area. This causes a problem that the quality of the image is degraded. The light irradiation detection unit 105 and the synchronization correction processing unit 106 are provided to prevent this problem. That is, the light irradiation detection unit 105 detects that the living tissue is irradiated with light from the semiconductor laser 102, and the synchronization correction processing unit 106 calculates the difference in light irradiation timing detected by the light irradiation detection unit 105 between the partial regions. Based on the timing difference, the time axis of the sampling data in the element data memory 108 is corrected between the partial areas.

  When the region selection unit 104 selects all the partial regions and the sampling data of a plurality of times output from each of the 192ch probe elements included in the ultrasound probe 103 is stored in the element data memory 108, the image construction unit 109 Sampling data is read from the element data memory 108, and a tomographic image of the living tissue is constructed based on the read data. The image construction unit 109 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 109 is omitted, the function can be realized by, for example, a computer operating according to a predetermined program. Alternatively, the function of the image construction unit 109 may be realized by a digital signal processor (DSP), a field programmable gate array (FPGA), or the like.

  The image construction unit 109 stores image data indicating the constructed tomographic image in the image memory 110. The image display unit 111 displays the tomographic image on a display monitor or the like based on the image data stored in the image memory 110.

  Next, the spectral filter 150 shown in FIG. 1 and its operation will be described. The semiconductor laser 102 applied as a pulse light source in the present embodiment emits spontaneous emission light when a current having a value less than the oscillation threshold value is supplied. FIG. 4 shows this. In the figure, Ps is a predetermined optical output required for the semiconductor laser 102, and the laser driver 101 shown in FIG. In the present embodiment, during the operation of the photoacoustic imaging apparatus 100, no current is supplied to the semiconductor laser 102 during a period in which the semiconductor laser 102 is not driven. Therefore, in the light irradiation period in which the driving current is supplied to the semiconductor laser 102, the optical output of the semiconductor laser 102 rises from a zero state, but when the driving current is less than the oscillation threshold, spontaneous emission light is emitted and the driving current is emitted. When is equal to or greater than the oscillation threshold, oscillated laser light is emitted. In FIG. 4, the spontaneous emission region is indicated as P1, and the laser oscillation region is indicated as P2.

  As is well known, spontaneous emission light has a wider wavelength range than oscillated laser light. When such a spontaneous emission light is irradiated onto a living tissue, light having a wavelength different from the wavelength of the light that should originally be irradiated onto the living tissue is irradiated, and as described above, it is constructed. It causes image quality degradation. The spectral filter 150 is for preventing this problem, and is disposed so as to be positioned between the semiconductor laser 102 and the living tissue. The spectral filter 150 allows a laser beam having a wavelength of 799.5 nm to 800.5 nm emitted from the semiconductor laser 102 (for example, an oscillation center wavelength of 800 nm and a spectral width of 1 nm) to pass well, but has a different wavelength range, for example, 750 nm or more. Spontaneous emission light included in a range of less than 799.5 nm and more than 800.5 nm and 850 nm or less has a characteristic of cutting. That is, the spectral filter 150 functions as a bandpass filter having a bandwidth of 1 nm.

  Since the spectral filter 150 as described above is provided, the spontaneous emission light having a wavelength different from the wavelength of the light to be originally irradiated is not irradiated on the living tissue. Increase and image quality degradation can be prevented.

  Next, a photoacoustic imaging apparatus 200 according to the second embodiment of the present invention will be described with reference to FIG. In FIG. 5, the same elements as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted unless necessary (the same applies hereinafter).

The photoacoustic imaging apparatus 200 according to the second embodiment is different from the photoacoustic imaging apparatus 100 according to the first embodiment shown in FIG. The difference is that a low current less than the oscillation threshold is always supplied from the driver 101 and a time filter 250 is provided in place of the spectrum filter 150. This time filter 250 is also arranged in a state located between the semiconductor laser 102 and the living tissue. When the apparatus is in operation, the low current is constantly supplied to the semiconductor laser 102, so that the rising characteristic when the semiconductor laser 102 is pulse-driven becomes good. Incidentally, while the low current is always supplied, i.e. before and after the irradiation period, the semiconductor laser 102 continues emit spontaneous emission light of a low output P _L.

  The time filter 250 is configured by combining an electro-optic element and a polarizer. The time filter 250 is opened only for a set period and allows light emitted from the semiconductor laser 102 to pass therethrough. More specifically, when the time filter 250 is in a closed state, a driving voltage that gives a half-wave phase difference to the passing light is applied to the electro-optic element to rotate the polarization direction of the laser light by 90 degrees, and this is applied to the polarizer. On the other hand, when the open state is set, the laser light is allowed to pass by cutting the drive voltage. The light passing period in the time filter 250 is set as shown in FIG. 6, for example, based on the output timing of the pulse wave driving current supplied from the laser driver 101 to the semiconductor laser 102. That is, a period during which the current less than the oscillation threshold flows while the low current is supplied and when the pulse-driven semiconductor laser 102 rises and falls transiently is defined as a cutoff period by the time filter 250. A period during which a current equal to or greater than the oscillation threshold is supplied to 102 is a filter passing period.

  By providing the time filter 250 that operates in this manner, in this embodiment, the spontaneous emission light having a wavelength different from the wavelength of the light that should be irradiated is not irradiated on the living tissue. It is possible to prevent image quality degradation of the image to be displayed.

  As described above, the spectral filter 150 used in the first embodiment may be provided in the photoacoustic imaging apparatus having a configuration in which the above-described low current is constantly supplied to the semiconductor laser when the apparatus is in operation. Even in such a case, the same effect as in the first embodiment can be obtained. In that case, the time filter 250 is basically unnecessary, but the time filter 250 may be provided together in order to more reliably prevent image quality deterioration.

  Contrary to the above, a time filter is provided in the photoacoustic imaging apparatus in which the aforementioned low current is not constantly supplied to the semiconductor laser when the apparatus is in operation, thereby achieving the same effect as in the second embodiment. It can also be obtained. In other words, in this case, the time during which the current less than the oscillation threshold flows transiently at the rise and fall of the pulse-driven semiconductor laser is set as the cutoff period by the time filter, and current exceeding the oscillation threshold is supplied to the semiconductor laser. The period is set as a filter passing period. In that case, the semiconductor laser naturally does not emit light before and after the period during which the pulse wave drive current is supplied to the semiconductor laser, and therefore it is basically unnecessary to block the light with a time filter during the non-emission period.

  Next, with reference to FIG. 7, a photoacoustic imaging apparatus 300 according to a third embodiment of the present invention will be described. The photoacoustic imaging apparatus 300 of the third embodiment is basically an optical amplification type instead of the laser light source 102 made of a semiconductor laser, as compared with the photoacoustic imaging apparatus 100 of the first embodiment shown in FIG. The difference is that a laser light source 302 is used and a spectral filter 350 having a different pass band from the spectral filter 150 is applied.

  As shown in the block diagram of FIG. 8, the optical amplification type laser light source 302 has a semiconductor laser 351 that emits a pulse laser beam 360 as seed light, an excitation semiconductor laser 353 that emits an excitation laser beam 352, a pulse A multiplexer 354 for multiplexing the laser beam 360 and the pumping laser beam 352, a fiber optical amplifier 355 having a core doped with, for example, Er (erbium), connected to the multiplexer 354, and the fiber An optical isolator 356 for preventing oscillation connected to the optical amplifier 355, and an optical wavelength conversion element 358 for converting the pulse laser light 370 output from the optical isolator 356 into a second harmonic having a wavelength of ½. It is configured.

  At the time of acquiring a photoacoustic image, in the light amplification type laser light source 302, the semiconductor laser 351 which is a seed light source is pulse-driven based on the trigger signal shown in FIG. 7, and pulse laser light having a wavelength of 1560 nm, for example, is emitted therefrom. 360 is input to the fiber optical amplifier 355. This pulse laser beam 360 propagates through the core of the fiber optical amplifier 355, and at that time, for example, the pulse laser beam 360 is amplified by receiving energy from erbium ions excited by the excitation laser beam 352 having a wavelength of 980 nm. The amplified pulsed laser beam 370 is emitted from the fiber optical amplifier 355, and then converted into a pulsed laser beam 380 that is a second harmonic of a wavelength of 780 nm by the optical wavelength conversion element 358. Finally, the pulsed laser beam 380 Is irradiated to the living tissue from the ultrasonic probe 103 as shown in FIG.

  FIG. 9 schematically shows the waveforms of light before and after being input to the fiber optical amplifier 355. The fiber optical amplifier 355 is compared with the pulse laser light 360 before input shown in FIG. The pulsed laser beam 370 after being amplified in (1) has a higher output as shown in FIG. However, here, in the fiber optical amplifier 355, the spontaneous emission light emitted by the erbium ions is amplified when passing through the optical amplifier itself, and this amplified spontaneous emission light is pulsed as indicated by 390 in FIG. The laser beam 370 is superimposed and output. The spontaneous emission light 390 extends over a wide wavelength range centering on 1560 nm, and is emitted continuously in time, that is, through a period in which the pulse laser beam 360 is not input. When the spontaneous emission light 390 over such a wavelength range passes through the light wavelength conversion element 358 and is irradiated to the living tissue in the process of photoacoustic imaging, the noise increase in the photoacoustic image and the image quality as described above. Incurs a decline.

  In order to prevent this problem, the pulsed laser light 380 output from the light wavelength conversion element 358 is irradiated to the living tissue through the spectral filter 350 shown in FIG. As an example, the spectral filter 350 has a characteristic of allowing pulsed laser light 380 having a wavelength of 779.5 nm to 780.5 nm to pass through satisfactorily while cutting spontaneous emission light having a different wavelength range, that is, 1450 nm to 1650 nm. It is. That is, the spectral filter 350 functions as a bandpass filter having a bandwidth of 1 nm.

  Since the spectral filter 350 as described above is provided, in this embodiment, the spontaneous emission light having a wavelength different from the wavelength of the light to be irradiated is not irradiated on the living tissue. Noise increase and image quality deterioration of the photoacoustic image can be prevented.

  Next, a photoacoustic imaging apparatus 400 according to a fourth embodiment of the present invention will be described with reference to FIG. Compared with the photoacoustic imaging apparatus 200 of the second embodiment shown in FIG. 5, the photoacoustic imaging apparatus 400 of the fourth embodiment is basically replaced with the laser light source 102 made of a semiconductor laser. The difference is that an optical amplification laser light source 302 similar to that shown in FIGS.

  The time filter 250 used in the photoacoustic imager 400 is basically the same as the time filter 250 in the photoacoustic imager 200 of FIG. 5, and its light passing / blocking characteristics are shown in FIG. As shown. A pulse laser beam 380 having a center wavelength of 780 nm emitted from the optical amplification type laser light source 302 is irradiated to the living tissue through the time filter 250. Therefore, the spontaneous emission light 390 (see FIG. 9) continuously emitted from the fiber optical amplifier 355 is prevented from being applied to the living tissue outside the irradiation period of the pulsed laser light 380. It is possible to prevent noise increase and image quality deterioration of the photoacoustic image.

  In the present embodiment, it is impossible to prevent the living tissue from being irradiated with the spontaneous emission light 390 during the irradiation period of the pulsed laser light 380. Therefore, when configured as in the present embodiment, it is more preferable to install the spectral filter 350 shown in FIG.

  In the present embodiment, the semiconductor laser 351 (see FIG. 8) as a seed light source of the optical amplification type laser light source 302 is not always supplied with a low current less than the oscillation threshold when the apparatus is in operation. In order to improve the rising characteristics, the low current may be supplied. In such a case, the spontaneous emission light having a wavelength of around 1560 nm is emitted from the semiconductor laser 351 outside the pulse driving period of the semiconductor laser 351 (this is the irradiation period of the pulsed laser light 380). This spontaneously emitted light is emitted from the optical wavelength conversion element 358 via the fiber optical amplifier 355 and the optical isolator 356 shown in FIG. 8, and since this spontaneously emitted light is also cut by the time filter 250, the spontaneously emitted light is The tissue is prevented from being irradiated.

  Here, another example of a laser light source that can be used in the photoacoustic imaging apparatus of the present invention will be described. The photoacoustic imaging apparatus is often used for acquiring blood vessel images (venous images and arterial images) of the human body. In this case, for example, pulse laser light having a wavelength of 750 nm that is well absorbed by the veins and arterial images For example, it is necessary to irradiate the blood vessel portion of the human body alternately with a pulsed laser beam having a wavelength of 800 nm that is well absorbed at short time intervals. The laser light source shown in FIGS. 11 and 13 has a configuration that meets such a requirement.

  First, the laser light source 500 shown in FIG. 11 will be described. This laser light source 500 is an optical amplification type laser light source having one light emitting unit, and includes one semiconductor optical amplifier (SOA) 501, an isolator 502 that sets the traveling direction of light to only one direction, a tap coupler 503, A wavelength tunable element 504, an isolator 505 similar to the isolator 502, a time filter 507, and a waveguide means 506 such as an optical fiber that forms a ring resonator by coupling the above elements so that light circulates. It is composed of

  The semiconductor optical amplifier 501 has almost the same structure as that of the semiconductor laser, but is not provided with a resonator alone, and light emitted therefrom is oscillated by the ring resonator. The wavelength band of this semiconductor optical amplifier 501 is 750 to 800 nm. The semiconductor optical amplifier 501 is supplied with a drive current in a pulse form as shown in (1) of FIG. 12. Therefore, the laser light oscillated as described above becomes a pulsed laser light.

  On the other hand, the tap coupler 503 returns incident light to the ring resonator at a predetermined ratio (for example, 20%), and outputs the remainder from the resonator.

  The wavelength tunable element 504 includes, for example, a diffraction grating, a Fabry-Perot tunable filter, and the like, and a drive voltage having a waveform as shown in FIG. The wavelength variable element 504 selectively transmits light having a wavelength corresponding to the value of the applied drive voltage, and the relationship between the drive voltage and the selected wavelength is linear. Therefore, if a drive current is supplied to the semiconductor optical amplifier 501 when the selected wavelength of the wavelength tunable element 504 reaches 750 nm and 800 nm, a pulse laser beam with a wavelength of 750 nm and a pulse with a wavelength of 800 nm are supplied from the tap coupler 503. Laser beams are alternately output at regular time intervals.

  Similar to the time filter 250 shown in FIG. 5, the time filter 507 cuts light passing therethrough during a transient period in which the drive current supplied to the semiconductor optical amplifier 501 is less than the oscillation threshold. By providing the time filter 507 that operates in this way, in this embodiment as well, the spontaneous emission light having a wavelength different from the wavelength of the light that should be irradiated is not irradiated on the living tissue. It is possible to prevent image quality degradation of the image to be displayed.

  Also in the configuration shown in FIG. 5, the waveguide unit 506 includes a spectral filter that cuts light having a wavelength different from the pulse laser light having a wavelength of 750 nm and the pulse laser light having a wavelength of 800 nm in conjunction with the operation of the wavelength variable element 504. If it is interposed, it is possible to prevent the body tissue from being irradiated with spontaneously emitted light having a wavelength different from the wavelength of the light to be irradiated.

  Next, another example of a laser light source that can be applied to the photoacoustic imaging apparatus of the present invention will be described with reference to FIG. The laser light source 600 of FIG. 13 combines a pulse driving circuit 601, two semiconductor lasers 602 and 603 driven by the pulse driving circuit 601, and pulse laser beams emitted from these semiconductor lasers 602 and 603, respectively. And an optical coupler 604 for wave generation. The semiconductor laser 602 and the optical coupler 604 are connected by a waveguide unit 605 such as an optical fiber. The semiconductor laser 603 and the optical coupler 604 are connected by a similar waveguide unit 606. A pulsed laser beam is output through a waveguide means 607 such as a fiber.

  A spectral filter 608 is interposed in the waveguide unit 605 between the semiconductor laser 602 and the optical coupler 604, and a spectral filter 609 is interposed in the waveguide unit 606 between the semiconductor laser 603 and the optical coupler 604. ing.

  For example, the oscillation wavelength of one semiconductor laser 602 is 750 nm, and the oscillation wavelength of the other semiconductor laser 603 is 800 nm. The pulse driving circuit 601 alternately drives these semiconductor lasers 602 and 603 at a predetermined time interval ΔT. Therefore, the optical coupler 604 alternately outputs a pulse laser beam having a wavelength of 750 nm and a pulse laser beam having a wavelength of 800 nm with a time interval ΔT.

  The spectral filter 608 allows pulsed laser light having a wavelength of 750 nm to pass therethrough, while cutting spontaneously emitted light having a wavelength different from that. The spectral filter 609 allows pulsed laser light having a wavelength of 800 nm to pass through, but cuts spontaneously emitted light having a wavelength different from that. Since such spectral filters 608 and 609 are provided, in this embodiment, the spontaneous emission light having a wavelength different from the wavelength of the light to be originally irradiated is not irradiated on the living tissue. It is possible to prevent image quality degradation of the image to be displayed.

  In place of the spectral filters 608 and 609, time filters may be provided. Further, such a time filter and the spectral filter 608 may be arranged in series, or such a time filter and the spectral filter 609 may be arranged in series so as to cut the spontaneous emission light more reliably. . Further, a time filter and / or a spectral filter may be arranged after the optical coupler 604.

100, 200, 300, 400 Photoacoustic imaging apparatus 101 Laser driver 102 Laser light source (semiconductor laser)
DESCRIPTION OF SYMBOLS 103 Ultrasonic probe 104 Area | region selection part 105 Light irradiation detection part 106 Synchronization correction process part 107 Signal acquisition part 108 Element data memory 109 Image construction part 110 Image memory 111 Image display part 112 Multiplexer 131 Probe element 132 Light irradiation part 133 Light Detector 134 Optical fiber 150, 608, 609 Spectral filter 250, 507 Time filter 302 Laser light source (light amplification type laser light source)
500 Laser light source (optical amplification type laser light source)
600 Laser light source (semiconductor laser)

Claims (8)

In a photoacoustic imaging apparatus in which a semiconductor laser or a light amplification type laser light source using a semiconductor laser as a seed light source is used as a pulse light source for irradiating a subject with pulsed light,
A spectral filter is provided at a position between the pulsed light source and the subject to cut the spontaneously emitted light having a wavelength different from that of the laser light while passing the laser light emitted from the pulsed light source. A photoacoustic imaging device.   2. The photoacoustic imaging apparatus according to claim 1, wherein the pulse light source has a ring resonator, and the spectral filter is disposed in the ring resonator.   2. The light according to claim 1, wherein a plurality of pulse light sources that emit laser beams having different wavelengths are provided as the pulse light source, and the spectral filter is disposed corresponding to each of the pulse light sources. Acoustic imaging device. In a photoacoustic imaging apparatus in which a semiconductor laser or a light amplification type laser light source using a semiconductor laser as a seed light source is used as a pulse light source for irradiating a subject with pulsed light,
A time filter for cutting light from the pulsed light source is disposed at a position between the pulsed light source and a subject during a period in which a current less than an oscillation threshold is supplied to the semiconductor laser. A photoacoustic imaging device.   5. The photoacoustic imaging apparatus according to claim 4, wherein the pulse light source has a ring resonator, and the time filter is disposed in the ring resonator.   5. The light according to claim 4, wherein a plurality of pulse light sources that emit laser beams having different wavelengths are provided as the pulse light sources, and the time filter is disposed corresponding to each of the pulse light sources. Acoustic imaging device.   A spectral filter is further disposed at a position between the pulse light source and the subject to cut the spontaneous emission light having a wavelength different from that of the laser light while passing the laser light emitted from the pulse light source. The photoacoustic imager according to any one of claims 4 to 6.   8. The photoacoustic imaging apparatus according to claim 1, wherein the apparatus is configured to always supply a low current less than an oscillation threshold value to the semiconductor laser when the apparatus is in operation.