WO2019044212A1

WO2019044212A1 - Photoacoustic image generation device and image acquisition method

Info

Publication number: WO2019044212A1
Application number: PCT/JP2018/026597
Authority: WO
Inventors: 温之橋本; 山本　勝也
Original assignee: 富士フイルム株式会社
Priority date: 2017-08-29
Filing date: 2018-07-13
Publication date: 2019-03-07

Abstract

Provided is a photoacoustic image generation device offering improved visible depth of photoacoustic images in photoacoustic imaging using an inserted article comprising a photoacoustic wave generation unit provided near the distal end thereof. Also provided is an image acquisition method for use with the photoacoustic image generation device. A control unit of the photoacoustic image generation device performs a control for adjusting excitation light generation conditions for a light source that irradiates the photoacoustic wave generation unit disposed on the distal end section of the inserted article with excitation light, said conditions being based on the pulse width and multiple pulse counts for the excitation light generated by the light source, on the basis of the reception frequency properties of an acoustic wave detection means.

Description

Photoacoustic image generating apparatus and image acquiring method

According to the present invention, the photoacoustic wave generation unit disposed at the tip of the insert inserted in the subject detects the photoacoustic wave generated by receiving the excitation light emitted from the light source by the acoustic wave detection means. The present invention relates to a photoacoustic image generation device that generates a photoacoustic image based on a signal obtained by the above-described method, and an image acquisition method in the photoacoustic image generation device.

Ultrasonography is known as a type of imaging that can noninvasively inspect the internal condition of a living body. In ultrasonic examination, an ultrasonic probe capable of transmitting and receiving ultrasonic waves is used. When ultrasonic waves are transmitted from the ultrasonic probe to a subject (living body), the ultrasonic waves travel inside the living body and are reflected at the tissue interface. The internal appearance can be imaged by receiving the reflected ultrasound by the ultrasound probe and calculating the distance based on the time until the reflected ultrasound returns to the ultrasound probe.

Moreover, photoacoustic imaging which image-forms the inside of a biological body using a photoacoustic effect is known. In general, in photoacoustic imaging, pulsed laser light is applied to the inside of a living body. Inside the living body, living tissue absorbs the energy of the pulsed laser light, and adiabatic expansion by the energy generates an ultrasonic wave (photoacoustic wave). Visualization of the inside of the living body based on the photoacoustic wave is possible by detecting the photoacoustic wave with an ultrasonic probe or the like and constructing a photoacoustic image based on the detection signal.

Further, with regard to photoacoustic imaging, there has been proposed a puncture needle in which a photoacoustic wave generating unit for absorbing light and generating a photoacoustic wave is provided in the vicinity of the tip. In this puncture needle, an optical fiber is provided up to the tip of the puncture needle, and the light guided by the optical fiber is irradiated to the photoacoustic wave generation unit. The photoacoustic wave generated in the photoacoustic wave generation unit is detected by the ultrasonic probe, and a photoacoustic image is generated based on the detection signal. In the photoacoustic image, a portion of the photoacoustic wave generation unit appears as a bright spot, and the position of the puncture needle can be confirmed using the photoacoustic image.

JP, 2016-47232, A JP, 2016-47077, A

In the photoacoustic imaging as described above, in order to improve the visible depth in the photoacoustic image, (1) increase the energy of the photoacoustic wave generated in the object, (2) the generated photoacoustic wave There are three possible ways to improve the receiving efficiency of the ultrasonic probe that detects the (3) reduce the background noise of the image.

In order to increase the energy of the photoacoustic wave generated in the object in (1), it is conceivable to increase the energy of the excitation light irradiated in the object, but due to the hardware limitation of the light source There is a limit to increasing the peak energy of one pulse of excitation light. Moreover, in order to reduce the background noise of the image of (3), one image may be configured using a plurality of photoacoustic images, or one line may be used using reception data of a plurality of waves. In this case, there is a problem that the frame rate decreases.

Therefore, in order to improve the viewable depth in the photoacoustic image, it is preferable to improve the reception efficiency of the ultrasonic probe that detects the generated photoacoustic wave in (2).

In this regard, in Patent Document 1, the photoacoustic wave can be efficiently received by the ultrasonic probe by optimizing the pulse width of the excitation light for generating the photoacoustic wave according to the ultrasonic probe. Is disclosed. However, in the method of Patent Document 1, efficiency improvement is insufficient such that many acoustic waves of frequency components that do not contribute to imaging still occur.

Further, Patent Document 2 discloses that the photoacoustic wave can be efficiently received by the ultrasonic probe by determining the pulse width and the number of pulses of the excitation light according to the reception frequency characteristic of the ultrasonic probe. ing. Further, in Patent Document 2, after the pulse width and the number of pulses of excitation light are determined according to the reception frequency characteristic of the ultrasonic probe, the resolution can be improved by changing the pulse repetition period while keeping the pulse width constant. It is stated that it can. However, if the pulse repetition period is changed after determining the pulse width of the excitation light, the band of the generated photoacoustic wave changes, and the reception frequency characteristic of the ultrasonic probe does not match, and the reception efficiency of the ultrasonic probe becomes There is a problem of falling.

Moreover, neither patent document 1 nor 2 mentions at all about inserts, such as a puncture needle which provided the photoacoustic wave generation part in the tip vicinity.

The present invention, in view of the above circumstances, in photoacoustic imaging using an insert provided with a photoacoustic wave generation unit in the vicinity of the tip, a photoacoustic image generation device with improved visible depth in a photoacoustic image, and light An object of the present invention is to provide an image acquisition method in an acoustic image generation device.

In the photoacoustic image generation apparatus according to the present invention, the photoacoustic wave generation unit disposed at the tip of the insert inserted in the subject receives the excitation light emitted from the light source and the photoacoustic wave is generated. In a photoacoustic image generation apparatus including a photoacoustic image generation unit that generates a photoacoustic image based on a signal obtained by detection by an acoustic wave detection unit, a light source is based on a reception frequency characteristic of the acoustic wave detection unit. And a control unit that performs control to adjust the excitation light generation condition based on the pulse width of the excitation light generated in the light source and the number of pulses.

In the photoacoustic image generating apparatus according to the present invention, the control unit adjusts the excitation light generation condition to approximate the frequency characteristic of the photoacoustic wave detected by the acoustic wave detection unit and the reception frequency characteristic of the acoustic wave detection unit. Control may be performed.

Further, the control unit stores a plurality of excitation light generation conditions having different frequency characteristics of the photoacoustic wave generated in the object, and the excitation light generation condition selected from among the plurality of stored excitation light generation conditions The light source may be controlled based on

In this case, the control unit stores a plurality of excitation light generation conditions for each type of acoustic wave detection means having different reception frequency characteristics, and the excitation light selected by the user from among the plurality of stored excitation light generation conditions The light source may be controlled based on the generation condition.

In addition, the control unit may adjust the excitation light generation condition based on the position of the distal end portion of the insert in the photoacoustic image.

The control unit may adjust the excitation light generation condition based on the image depth of the photoacoustic image.

In addition, the control unit may adjust the excitation light generation condition based on the focal depth of the photoacoustic image.

The photoacoustic image generation unit may perform correction processing on the photoacoustic image based on the excitation light generation condition.

In the image acquisition method of the present invention, the photoacoustic wave generated when the photoacoustic wave generation unit disposed at the tip of the insert inserted into the subject receives the excitation light emitted from the light source is an acoustic wave. It is an image acquisition method in a photoacoustic image generation apparatus provided with the photoacoustic image generation part which produces a photoacoustic image based on the signal obtained by detecting by detection means, and the light source receives the acoustic wave detection means Based on the frequency characteristics, control is performed to adjust the excitation light generation conditions based on the pulse width of the excitation light generated in the light source and the number of pulses.

In the image acquisition method of the present invention, the excitation light generation condition is adjusted to perform control to make the frequency characteristic of the photoacoustic wave detected by the acoustic wave detection means closer to the reception frequency characteristic of the acoustic wave detection means. May be

Further, a plurality of excitation light generation conditions having different frequency characteristics of the photoacoustic wave generated in the object are stored, and the light source is selected based on the excitation light generation conditions selected from among the plurality of stored excitation light generation conditions. May be controlled.

In this case, a plurality of excitation light generation conditions are stored for each type of reception frequency characteristics of the acoustic wave detection means different, and based on the excitation light generation conditions selected by the user from among the plurality of stored excitation light generation conditions. The light source may be controlled.

In addition, the excitation light generation condition may be adjusted based on the position of the distal end portion of the insert in the photoacoustic image.

Further, the excitation light generation condition may be adjusted based on the image depth of the photoacoustic image.

Further, the excitation light generation condition may be adjusted based on the focal depth of the photoacoustic image.

Further, the correction process may be performed on the photoacoustic image based on the excitation light generation condition.

According to the photoacoustic image generating apparatus and the image acquiring method of the present invention, the reception frequency characteristics of the acoustic wave detecting means with respect to the light source in the photoacoustic imaging using the insert provided with the photoacoustic wave generating unit near the tip. Since the control for adjusting the excitation light generation condition based on the pulse width of the excitation light generated in the light source and the plurality of pulses is performed based on the above, the reception efficiency of the photoacoustic wave in the acoustic wave detection means As a result, the visible depth in the photoacoustic image can be improved.

A block diagram showing a schematic configuration of a photoacoustic image generation apparatus according to a first embodiment of the present invention Cross-sectional view showing the configuration of the tip portion of the puncture needle Graph showing the waveform of excitation light Graph showing the photoacoustic wave waveform Graph showing spectrum of photoacoustic wave Graph showing the photoacoustic wave waveform Graph showing the waveform of excitation light Graph showing spectrum of photoacoustic wave Graph showing the waveform of excitation light Graph showing spectrum of photoacoustic wave Graph showing the waveform of excitation light Graph showing spectrum of photoacoustic wave Graph showing spectrum of photoacoustic wave Graph showing spectrum of photoacoustic wave

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing an overall configuration of a photoacoustic image generation apparatus 10 according to a first embodiment of the present invention. In FIG. 1, the shape of the ultrasonic probe (hereinafter simply referred to as a probe) 11 is schematically shown.

As shown in FIG. 1, the photoacoustic image generating apparatus 10 according to the present embodiment includes a probe 11 (corresponding to an acoustic wave detecting unit according to the present invention), an ultrasonic unit 12, a laser unit 13, and a puncture needle 15 (the present invention). Equivalent to the insert of The puncture needle 15 and the laser unit 13 are connected by an optical fiber 15 b. The puncture needle 15 is detachable from the laser unit 13 and is configured to be disposable. In the present embodiment, an ultrasonic wave is used as the acoustic wave, but the invention is not limited to the ultrasonic wave, and if an appropriate frequency is selected in accordance with an object to be detected, measurement conditions, etc. Acoustic waves may be used.

The laser unit 13 is provided with a solid-state laser light source using, for example, YAG (yttrium aluminum garnet) and alexandrite. The laser light emitted from the solid state laser light source of the laser unit 13 is guided by the optical fiber 15 b and is incident on the puncture needle 15. The laser unit 13 of the present embodiment emits pulsed laser light in the near infrared wavelength range. The near infrared wavelength range means and a wavelength range of 700 nm (nanometers) to 850 nm (nanometers). In the present embodiment, the solid-state laser light source is used, but another laser light source such as a gas laser light source may be used, or a light source other than the laser light source may be used.

The laser unit 13 can also be configured using a LD (Laser Diode) or an LED (Light Emitting Diode). Since the present invention improves the reception efficiency of photoacoustic waves, the light source can be a low power LD or LED instead of a high power individual laser. In addition, in order to generate excitation light of an arbitrary waveform as described later, LD or LED is generally preferable to a solid laser.

The puncture needle 15 is an embodiment of the insert of the present invention, and is a needle to be punctured by a subject. FIG. 2 is a cross-sectional view including a central axis extending in the longitudinal direction of the puncture needle 15. The puncture needle 15 has an opening at the tip formed at an acute angle, and guides the laser light emitted from the hollow needle body 15a and the laser unit 13 to the vicinity of the opening of the puncture needle 15 It includes an optical fiber 15b (corresponding to the light guide member of the present invention) and a photoacoustic wave generation unit 15c that absorbs the laser light emitted from the optical fiber 15b to generate a photoacoustic wave.

The optical fiber 15b and the photoacoustic wave generation unit 15c are disposed in the hollow portion 15d of the puncture needle main body 15a. The optical fiber 15b is connected to the laser unit 13 via, for example, an optical connector provided at the proximal end of the laser unit 13 side. For example, several μJ (micro joules) of laser light is emitted from the light emitting end of the optical fiber 15 b.

The photoacoustic wave generation unit 15c is provided at the light emitting end of the optical fiber 15b, and is provided near the tip of the puncture needle 15 and on the inner wall of the puncture needle main body 15a. The photoacoustic wave generation unit 15c absorbs the laser light emitted from the optical fiber 15b to generate a photoacoustic wave. The photoacoustic wave generation unit 15 c is formed of, for example, an epoxy resin mixed with a black pigment, a polyurethane resin, a fluorine resin, a silicone rubber, or the like. In addition, in FIG. 2, although the direction of the photoacoustic wave generation part 15c is drawn larger than the optical fiber 15b, it is not limited to this, The photoacoustic wave generation part 15c is comparable as the diameter of the optical fiber 15b. The size of the Moreover, the pigment mixed to the photoacoustic wave generation part 15c is not limited to a black pigment, An organic or inorganic pigment | dye which absorbs the wavelength of a laser beam, such as near-infrared absorption pigment | dye, may be sufficient.

The photoacoustic wave generation unit 15 c is not limited to the above-described one, and a metal film or an oxide film having light absorbability with respect to the wavelength of laser light may be used as the photoacoustic wave generation unit. For example, as the photoacoustic wave generation unit 15c, a film of iron oxide having high light absorbability with respect to the wavelength of the laser light, or an oxide film such as chromium oxide and manganese oxide can be used. Alternatively, a metal film such as Ti (titanium) or Pt (platinum) having a light absorbability lower than that of an oxide but having high biocompatibility may be used as the photoacoustic wave generation unit 15c. Further, the position at which the photoacoustic wave generation unit 15c is provided is not limited to the inner wall of the puncture needle main body 15a. For example, a metal film or oxide film, which is the photoacoustic wave generation unit 15c, is formed on the light emitting end of the optical fiber 15b to a film thickness of, for example, about 100 nm (nanometers) by evaporation or the like. The light emitting end may be covered. In this case, at least a portion of the laser light emitted from the light emitting end of the optical fiber 15b is absorbed by the metal film or oxide film covering the light emitting end, and the photoacoustic wave is transmitted from the metal film or oxide film. It occurs.

Returning to FIG. 1, the probe 11 detects the photoacoustic wave emitted from the photoacoustic wave generation unit 15 c after the puncture needle 15 is punctured in the subject. The probe 11 includes an acoustic wave detection unit 20 that detects a photoacoustic wave.

The acoustic wave detection unit 20 includes a piezoelectric element array in which a plurality of piezoelectric elements for detecting photoacoustic waves are arranged in one dimension, and a multiplexer. The piezoelectric element is an ultrasonic transducer, for example, a piezoelectric element or a piezoelectric element composed of a polymer film such as polyvinylidene fluoride (PVDF). Further, although not shown, the acoustic wave detection unit 20 includes an acoustic lens, an acoustic matching layer, a backing material, a control circuit of a piezoelectric element array, and the like.

The ultrasound unit 12 includes a reception circuit 21, a reception memory 22, a data separation unit 23, a photoacoustic image generation unit 24, an ultrasound image generation unit 25, an image output unit 26, a transmission control circuit 27, and a control unit 28. The control unit 28 generates excitation light generation conditions based on the pulse width of the laser light generated in the laser unit 13 and the number of pulses with respect to the laser unit 13 as the light source based on the reception frequency characteristic of the probe 11 Have functions such as control to adjust the The ultrasound unit 12 typically includes a processor, a memory, a bus, and the like. In the ultrasound unit 12, programs related to photoacoustic image generation processing, ultrasound image generation processing, control processing of the laser unit 13, and the like are incorporated in a memory. When the program is operated by the control unit 28 configured by a processor, the functions of the data separation unit 23, the photoacoustic image generation unit 24, the ultrasound image generation unit 25, and the image output unit 26 are realized. That is, these units are configured by a memory and a processor in which a program is incorporated.

The hardware configuration of the ultrasound unit 12 is not particularly limited, and a plurality of integrated circuits (ICs), processors, application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), memories, etc. It can be realized by appropriately combining

The receiving circuit 21 receives the detection signal output from the probe 11, and stores the received detection signal in the receiving memory 22. The receiving circuit 21 typically includes a low noise amplifier, a variable gain amplifier, a low pass filter, and an analog to digital converter. The detection signal of the probe 11 is amplified by a low noise amplifier, then gain adjusted according to the depth by a variable gain amplifier, high frequency components are cut by a low pass filter, and then converted to digital signals by an AD converter It is stored in the memory 22. The receiving circuit 21 is configured of, for example, one IC.

The probe 11 outputs a detection signal of the photoacoustic wave and a detection signal of the reflected ultrasonic wave, and the reception memory 22 stores detection signals (sampling data) of the photoacoustic wave and the reflected ultrasonic wave subjected to AD conversion. . The data separation unit 23 reads the detection signal of the photoacoustic wave from the reception memory 22 and transmits the detection signal to the photoacoustic image generation unit 24. Further, the detection signal of the reflected ultrasound is read from the reception memory 22 and transmitted to the ultrasound image generation unit 25.

The photoacoustic image generation unit 24 generates a photoacoustic image based on the detection signal of the photoacoustic wave detected by the probe 11. The photoacoustic image generation process includes, for example, image reconstruction such as phase matching addition, detection, logarithmic conversion, and the like. The ultrasound image generation unit 25 generates an ultrasound image (reflection acoustic wave image) based on the detection signal of the reflection ultrasound detected by the probe 11. The ultrasonic image generation process also includes image reconstruction such as phase matching addition, detection, logarithmic conversion, and the like. The image output unit 26 outputs the photoacoustic image and the ultrasound image to an image display unit 30 such as a display device.

The control unit 28 controls each unit in the ultrasonic unit 12. When acquiring the photoacoustic image, the control unit 28 transmits a trigger signal to the laser unit 13 based on the excitation light generation condition, and causes the laser unit 13 to emit a laser beam. Further, according to the emission of the laser light, the sampling trigger signal is transmitted to the receiving circuit 21 to control the sampling start timing of the photoacoustic wave and the like.

In the image display unit 30, the photoacoustic wave image and the ultrasound image may be displayed separately, or may be displayed in combination. By combining and displaying, it becomes possible to confirm where in the living body the tip of the puncture needle 15 is located, thereby enabling accurate and safe puncture.

Here, the method of acquiring the photoacoustic image in the photoacoustic image generation apparatus 10 according to the present embodiment will be described in detail. At the time of photoacoustic image acquisition, the control unit 28 causes the laser unit 13 (light source) to generate laser light (excitation light) to be generated in the laser unit 13 based on the reception frequency characteristics of the probe 11 (acoustic wave detection means). Control is performed to adjust the excitation light generation condition based on the pulse width of and the number of pulses. In addition, although a center frequency is considered as a frequency characteristic here, it is good also as other frequency characteristics, such as peak frequency.

The control unit 28 performs control to adjust the excitation light generation condition based on the reception frequency characteristic of the probe 11 (acoustic wave detection means), that is, the center frequency in the sensitivity of the probe 11.

For example, consider the case where the center frequency in the sensitivity of the probe 11 is 6.5 MHz (megahertz). In this case, it is desirable that the center frequency of the photoacoustic wave generated in the subject be around 6.5 MHz (megahertz). FIG. 3 is a graph showing the waveform of the excitation light, FIG. 4 is a graph showing the waveform of the photoacoustic wave, FIG. 5 is a graph showing the spectrum of the photoacoustic wave, and as shown in FIGS. Since it can be considered that generation occurs at the intensity edge in the waveform of the laser light (excitation light), when the pulse number of the laser light is 1, the pulse width t _LP of the laser light is 1 / (2 × 6.5 M) When set to 77 ns (nanoseconds), it is possible to generate a photoacoustic wave having a center frequency of 6.5 MHz (megahertz).

On the other hand, as shown in FIGS. 3 to 5, the laser light pulse number is set to 2 or more, and the laser light pulse width t _LP = 1 / (2 × 6.5 M) = 77 ns (nanosecond) Setting the pulse repetition period t _LR = 1 / 6.5 M = 154 ns (nanoseconds), the center frequency is around 6.5 MHz (megahertz), and the peak spectral intensity is larger than in the case of one pulse; A narrower photoacoustic wave can be generated than in the case of one pulse in width.

Generally, the reception frequency band of the probe 11 is a band having a width of 70% to 100% with respect to the center frequency, so the frequency of acoustic waves that can be received by the probe with a center frequency of 6.5 MHz (megahertz) is 3.2. It is considered to be about 9.8 MHz (megahertz). When the number of pulses of laser light is 1, as shown in FIG. 5, many photoacoustic waves other than the frequency that can be received by the probe 11 are generated, and the reception efficiency of the photoacoustic wave at the probe 11 is low. On the other hand, when the number of pulses of laser light is 2, most of the generated photoacoustic waves become frequencies that can be received by the probe 11, and the photoacoustic wave reception efficiency in the probe 11 is high.

Furthermore, when the puncture needle 15 is used, as shown in FIG. 4, the intensity of the photoacoustic wave generated at the second pulse can be made larger than that of the photoacoustic wave generated at the first pulse of the laser light. This is considered to be due to the following two effects.

The first is the temperature dependency of the photoacoustic wave generation unit 15c. The intensity of the generated photoacoustic wave is proportional to the thermal expansion coefficient of the photoacoustic wave generation unit 15c. The glass transition temperature of the black epoxy resin used for the photoacoustic wave generation unit 15c in the present embodiment is about 55 degrees, and the thermal expansion coefficient is 30 × 10 ⁻⁶ / ° C., 100 × below and above the glass transition temperature, respectively. It is greatly changed to 10 ^-6 / ° C. It is generally said that the thermal expansion coefficient does not change suddenly at the glass transition temperature, but changes stepwise at the near temperature (Epoxy technology company application guide). Therefore, the thermal expansion coefficient gradually increases in the vicinity of 55 degrees, and the intensity of the generated photoacoustic wave also gradually increases in the vicinity of 55 degrees. When the first pulse of the excitation light reaches the photoacoustic wave generation unit 15c, the light is absorbed and a photoacoustic wave is generated. At this time, the temperature of the photoacoustic wave generation unit 15c rises due to the absorption of light energy. Next, the second pulse reaches the photoacoustic wave generation unit 15c, but the temperature of the photoacoustic wave generation unit 15c is higher than that of the first pulse, so the thermal expansion coefficient becomes high, and as shown in FIG. The intensity of the photoacoustic wave also increases.

The second is the superposition of photoacoustic waves. The photoacoustic wave is generated in all directions in the photoacoustic wave generation unit 15c. The photoacoustic wave reaching the probe 11 is a superposition of one coming from the photoacoustic wave generation part 15 c directly in the probe direction and one coming from the photoacoustic wave generation part 15 c not directly but after being reflected by the needle tube toward the probe 11. For example, when the center frequency of the generated photoacoustic wave is 9 MHz (megahertz), the center wavelength of the photoacoustic wave in the photoacoustic wave generation unit 15c which is an epoxy resin (sound velocity 2500 to 3000 m / s (meters / second)) is 0 It is considered to be about .3 mm (millimeter). Since the outer diameter of the optical fiber is about 0.15 mm (millimeter), the distance from the center of the optical fiber to the needle tube is also about 0.15 mm (millimeter), and the photoacoustic wave directed from the photoacoustic wave generator 15c directly to the probe The path difference between the light beam reflected by the needle tube and the photoacoustic wave traveling in the probe direction is about 0.3 mm (millimeters). At this time, since the path difference corresponds to one wavelength, it is generated by the photoacoustic wave that is generated by the first pulse of the laser light and reflected by the needle tube and then travels in the probe direction and the second pulse of the laser light. The photoacoustic waves coming toward the probe direction strengthen each other by superposition. In order to reinforce each other, the path difference does not necessarily have to be an integral multiple of the wavelength, and can be reinforced even in the vicinity thereof.

Next, FIG. 6 shows a graph showing the waveform of the photoacoustic wave in the case where the pulse width t _{LP of} laser light is 90 ns (nanoseconds) and the pulse repetition cycle of laser light is t _LR = 3 μs (microseconds). . As shown in FIG. 6, it can be seen that the amplitude of the second pulse is larger than that of the first pulse. From this, in the puncture needle 15 capable of making the intensity of the photoacoustic wave generated in the second pulse greater than that of the photoacoustic wave generated in the first pulse of the laser light, an effect that can be suitably used is at least It can be seen that the pulse repetition period occurs in the range of 3 μs (microseconds) or less.

In the puncture needle 15, t _LP = t _LR / 2, Fc = 1 / between the pulse width t _LP of the laser light, the repetition cycle t _LR of the pulse of the laser light, and the center frequency Fc of the probe 11. Most preferably, there is a relationship of t _LR . Using this relationship, when t _LR <3 μs (microseconds), this corresponds to Fc> 0.33 MHz (megahertz), and at least the probe 11 with a center frequency of 0.33 MHz (megahertz) or more has the present effect. It can be seen that can be used. In general, the center frequency of the ultrasound probe 11 is 1 MHz (megahertz) or more, so it is possible to use this effect.

In the above description, although the relationship of t _LP = t _LR / 2 is described between the pulse width t _LP of the laser beam and the repetition period t _LR of the pulse of the laser beam, it is not limited thereto. Since the center frequency Fc of the photoacoustic wave generated when the laser beam is irradiated to the subject is determined depending on both the pulse width t _LP of the laser beam and the repetition period t _LR of the pulse of the laser beam, Although it is desirable to calculate individually, since the contribution of the repetition period t _LR is generally larger, the first approximation may be Fc ≒ 1 / t _LR .

In addition, when t _LP ≠ t _LR / 2, the generated photoacoustic wave contains more frequency components, so that the generated photoacoustic wave is generally larger than that of t _LP = t _LR / 2. Bandwidth is broadened. The bandwidth of the photoacoustic wave generated can also be adjusted by utilizing this effect.

Since the generation efficiency of the photoacoustic wave in the puncture needle 15 can be enhanced and the reception efficiency of the photoacoustic wave in the probe 11 can be enhanced by performing the control described above, the visible depth of the puncture needle 15 in the photoacoustic image Can be significantly improved.

The number of pulses of the laser beam is not limited to two, and may be three or more.

In addition, for example, when the number of pulses of laser light increases, the tip position of the puncture needle 15 in the photoacoustic image is displaced in the deep direction, and the excitation light generation condition changes, so that the puncture needle in the photoacoustic image The position of the tip of 15 changes. Therefore, it is desirable that the photoacoustic image generation unit 24 correct the tip position of the puncture needle 15 in the photoacoustic image according to the excitation light generation condition.

In addition, the center frequency of the photoacoustic wave generated in the object and the center frequency in the sensitivity of the probe 11 do not necessarily have to coincide with each other. For example, the center frequency of the photoacoustic wave may be set at an arbitrary position in the frequency band in the sensitivity of the probe 11 from the requirement of image quality and the like.

Next, a photoacoustic image generation apparatus 10 according to a second embodiment of the present invention will be described. The photoacoustic image generation apparatus 10 according to the present embodiment is different from the photoacoustic image generation apparatus 10 according to the first embodiment only in the control method of the laser unit 13 (light source) in the control unit 28. Since the configuration is the same, the description of the same part is omitted.

In the present embodiment, the control unit 28 is based on the reception frequency characteristics of the probe 11 (acoustic wave detection means) and the depth of the tip position of the puncture needle 15 with respect to the laser unit 13 (light source) at the time of photoacoustic image acquisition. The pulse width of the laser light (excitation light) generated in the laser unit 13 so that the frequency characteristic of the photoacoustic wave immediately before the probe 11 approaches the reception frequency characteristic of the probe 11 (acoustic wave detection means), and Control is performed to adjust the excitation light generation condition based on the number of pulses and the pulse repetition period. In addition, although a center frequency is considered as a frequency characteristic here, it is good also as other frequency characteristics, such as peak frequency.

For example, consider the case where the center frequency of the sensitivity of the probe 11 is 6.5 MHz (megahertz) and the depth of the main observation target is 4 cm (centimeter). FIG. 7 is a graph showing the waveform of excitation light, and FIG. 8 is a graph showing the spectrum of photoacoustic waves. As shown in FIG. 7, in the first embodiment, the excitation light generation condition (laser light L (excitation light) such that the center frequency of the photoacoustic wave generated in the subject M is 6.5 MHz (megahertz) The pulse width t _{LP of} 77 ns (nanoseconds), the pulse repetition period t _LR of laser light L 154 ns (nanoseconds) was set, but the generated photoacoustic wave is attenuated in the subject M (In particular, as the high frequency component is attenuated more,) the center frequency of the photoacoustic wave immediately before the probe 11 changes from 6.5 MHz (megahertz) to a lower center frequency, as shown in FIG.

Therefore, in the present embodiment, the excitation light generation condition is set so that the center frequency of the photoacoustic wave immediately before the probe 11 approaches the center frequency in the sensitivity of the probe 11 in consideration of the attenuation in the subject M. . FIG. 9 is a graph showing the waveform of excitation light, and FIG. 10 is a graph showing the spectrum of photoacoustic waves. As shown in FIG. 9, for example, assuming that the number of pulses of the laser light L is 2, the pulse width t _{LP of} the laser light L 62.5 ns (nanoseconds), and the pulse repetition period t _LR of the laser light L 125 ns (nano In the case of second), as shown in FIG. 10, the center frequency of the photoacoustic wave immediately before the probe 11 can be set to 6.5 MHz (megahertz). Thereby, the receiving efficiency of the photoacoustic wave in the probe 11 can be raised rather than the said 1st Embodiment.

A plurality of patterns of excitation light generation conditions such that the center frequency of the photoacoustic wave immediately before the probe 11 and the center frequency in the sensitivity of the probe 11 are close to each other as a table in the ultrasonic unit 12 for each type of probe 11 in advance. (For example, when the tip position of the puncture needle 15 is located at a shallow location, for being located at an intermediate location, for being located at a deep location, etc.) and stored so that the user can select them Is desirable.

At this time, it is desirable that the detection conditions of the photoacoustic wave be optimized in accordance with each mode. Further, the excitation light generation condition may be automatically switched in accordance with the photoacoustic image or the image depth (maximum depth in the image) or the focal depth of an ultrasound image to be synthesized with the photoacoustic image.

In addition, for example, when the number of pulses of laser light increases, the object position in the photoacoustic image changes, such as the object position in the photoacoustic image shifts in a deep direction, and the excitation light generation condition changes. I will. Therefore, it is desirable for the photoacoustic image generation unit 24 to correct the object position in the photoacoustic image according to the excitation light generation condition.

In addition, the center frequency of the photoacoustic wave immediately before the probe 11 and the center frequency in the sensitivity of the probe 11 do not necessarily have to coincide with each other. For example, the center frequency of the photoacoustic wave may be set at an arbitrary position in the frequency band in the sensitivity of the probe 11 from the requirement of image quality and the like.

Next, a photoacoustic image generation apparatus 10 according to a third embodiment of the present invention will be described. The photoacoustic image generation apparatus 10 according to the present embodiment is different from the photoacoustic image generation apparatus 10 according to the first embodiment only in the control method of the laser unit 13 (light source) in the control unit 28. Since the configuration is the same, the description of the same part is omitted.

In the present embodiment, the control unit 28 is based on the reception frequency characteristics of the probe 11 (acoustic wave detection means) and the depth of the tip position of the puncture needle 15 with respect to the laser unit 13 (light source) at the time of photoacoustic image acquisition. Excitation based on the pulse width of the laser light (excitation light) generated in the laser unit 13, the number of pulses, and the repetition period of the pulse so as to obtain appropriate reception characteristics such as resolution priority or sensitivity priority. Regarding the light generation condition, control is performed to select an optimum setting from among a plurality of settings in which the center frequency of the photoacoustic wave generated in the subject M is different. In addition, although a center frequency is considered as a frequency characteristic here, it is good also as other frequency characteristics, such as peak frequency.

Specifically, the photoacoustic wave generated in the subject is attenuated in the subject (in particular, it attenuates more as the high frequency component) reaches the probe 11. Therefore, when the tip position of the puncture needle 15 is at a deep position, the excitation light generation condition is adjusted so that a low-frequency photoacoustic wave with a small attenuation rate per unit length is generated, and a shallow position. Since the influence of attenuation is small, the excitation light generation conditions are adjusted so that a high-resolution photoacoustic wave with high resolution is generated, and a more desirable photoacoustic image is obtained at each depth.

For example, consider the case where the number of pulses is 3, and the center frequencies of the photoacoustic waves generated in the subject M are 6.5 MHz (megahertz) and 8 MHz (megahertz), respectively. FIG. 11 is a graph showing the waveform of excitation light, and FIG. 12 is a graph showing the spectrum of photoacoustic waves. As shown in FIG. 11, under the excitation light generation condition that the center frequency of the photoacoustic wave generated in the subject M is 6.5 MHz (megahertz), the pulse width t _LP of the laser light L (excitation light) is Excitation light generation with 77 ns (nanoseconds), pulse repetition period t _LR = 154 ns (nanoseconds) of laser light L, and a center frequency of the photoacoustic wave generated in the subject M being 8 MHz (megahertz) The conditions are a pulse width t _{LP of} 62.5 ns (nanoseconds) of the laser light L (excitation light), and a repetition cycle t _{LR of} 125 ns (nanoseconds) of the pulses of the laser light L. Further, the spectrum of the photoacoustic wave generated under these conditions is as shown in FIG.

As shown in FIG. 13 which is a graph showing the spectrum of the photoacoustic wave, when the depth of the tip position of the puncture needle 15 is shallow (for example, 1 cm (centimeter)), the influence of attenuation in the subject is small. The difference in intensity between the two photoacoustic waves is small. In such a case, the high frequency waveform may be selected with emphasis on resolution. The main component of the high frequency photoacoustic wave is in the receivable frequency band (about 3.2 to 9.8 MHz (megahertz)) of the probe having a center frequency of 6.5 MHz (megahertz).

As shown in FIG. 14 which is a graph showing the spectrum of the photoacoustic wave, when the tip position of the puncture needle 15 is deep (for example, 8 cm (centimeter)), the attenuation in the subject is large. The difference in intensity between the two photoacoustic waves is large. In such a case, the low frequency waveform may be selected with emphasis on sensitivity. The main component of the low frequency photoacoustic wave is in the receivable frequency band (about 3.2 to 9.8 MHz (megahertz)) of the probe having a center frequency of 6.5 MHz (megahertz).

As described above, by adjusting the excitation light generation condition based on the depth of the distal end position of the puncture needle 15, it is possible to acquire a suitable photoacoustic image for each depth of the distal end position of the puncture needle 15.

The number of pulses of the laser beam is not limited to three, and may be two or more.

In addition, the center frequency of the photoacoustic wave immediately before the probe 11 and the center frequency in the sensitivity of the probe 11 do not necessarily have to coincide with each other. For example, the center frequency of the photoacoustic wave may be set at an arbitrary position in the frequency band in the sensitivity of the probe 11 from the requirement of the image quality and the like.

Moreover, in the said embodiment, although the puncture needle 15 was used as one embodiment of an insert, as an insert, it is not limited to this. The insert may be a radiofrequency ablation needle containing an electrode used for radiofrequency ablation, or a catheter inserted into a blood vessel. The catheter may be inserted into a blood vessel. It may be a guide wire of Alternatively, it may be an optical fiber for laser treatment.

Moreover, the insert of the present invention is not limited to a needle such as an injection needle, and may be a biopsy needle used for a biopsy. That is, the biopsy needle may be a biopsy needle which can be punctured into a subject to be examined in a living body to collect a tissue at a biopsy site in the subject. In that case, the photoacoustic wave may be generated in a collection unit (suction port) for suctioning and collecting the tissue at the biopsy site. The needle may also be used as a guiding needle for deep puncture, such as subcutaneous and intra-abdominal organs.

As mentioned above, although the present invention was explained based on the suitable embodiment, an insert and a photoacoustic measuring device of the present invention are not limited only to the above-mentioned embodiment, and various modification from composition of the above-mentioned embodiment Also, modifications are included in the scope of the present invention.

Claims

The photoacoustic wave generation unit disposed at the tip of the insert inserted into the subject is obtained by detecting the photoacoustic wave generated by receiving the excitation light emitted from the light source by the acoustic wave detection means. In a photoacoustic image generation apparatus including a photoacoustic image generation unit that generates a photoacoustic image based on a selected signal,
Control for adjusting the excitation light generation condition based on the pulse width of excitation light generated in the light source and the number of pulses based on the reception frequency characteristic of the acoustic wave detection unit for the light source A photoacoustic image generating apparatus provided with the following.
The control unit adjusts the excitation light generation condition to perform control to bring the frequency characteristic of the photoacoustic wave detected by the acoustic wave detection unit closer to the reception frequency characteristic of the acoustic wave detection unit. The photoacoustic image generation apparatus of description.
The control unit stores a plurality of excitation light generation conditions having different frequency characteristics of photoacoustic waves generated in the subject, and the excitation selected from among the plurality of the excitation light generation conditions stored. The photoacoustic image generating apparatus according to claim 1, wherein the light source is controlled based on a light generation condition.
The control unit stores a plurality of excitation light generation conditions for each type in which the reception frequency characteristics of the acoustic wave detection means are different, and the control unit is selected by the user from among the plurality of excitation light generation conditions stored. The photoacoustic image generation apparatus according to claim 3, wherein the light source is controlled based on excitation light generation conditions.
The photoacoustic image generation apparatus according to any one of claims 1 to 4, wherein the control unit adjusts the excitation light generation condition based on the position of the tip portion of the insert in the photoacoustic image.
The photoacoustic image generation apparatus according to any one of claims 1 to 5, wherein the control unit adjusts the excitation light generation condition based on an image depth of the photoacoustic image.
The photoacoustic image generation apparatus according to any one of claims 1 to 5, wherein the control unit adjusts the excitation light generation condition based on a focal depth of the photoacoustic image.
The photoacoustic image generation apparatus according to any one of claims 1 to 7, wherein the photoacoustic image generation unit performs a correction process on the photoacoustic image based on the excitation light generation condition.
The photoacoustic wave generation unit disposed at the tip of the insert inserted into the subject is obtained by detecting the photoacoustic wave generated by receiving the excitation light emitted from the light source by the acoustic wave detection means. It is an image acquisition method in a photoacoustic image generation apparatus provided with the photoacoustic image generation part which produces | generates a photoacoustic image based on the said signal, Comprising:
An image for performing control of adjusting the excitation light generation condition based on the pulse width of excitation light generated in the light source and the number of pulses based on the reception frequency characteristic of the acoustic wave detection unit with respect to the light source Acquisition method.
10. The image acquisition method according to claim 9, wherein the excitation light generation condition is adjusted to make the frequency characteristic of the photoacoustic wave detected by the acoustic wave detection unit approach the reception frequency characteristic of the acoustic wave detection unit. .
Based on the excitation light generation condition selected from among the plurality of excitation light generation conditions stored and stored a plurality of excitation light generation conditions having different frequency characteristics of the photoacoustic wave generated in the subject The image acquisition method according to claim 9, wherein the light source is controlled.
A plurality of the excitation light generation conditions are stored for each type in which the reception frequency characteristics of the acoustic wave detection means are different, and the excitation light generation condition selected by the user from among the stored plurality of excitation light generation conditions is stored. The image acquisition method according to claim 11, wherein the light source is controlled based on the image.
The image acquisition method according to any one of claims 9 to 12, wherein the excitation light generation condition is adjusted based on the position of the distal end portion of the insert in the photoacoustic image.
The image acquisition method according to any one of claims 9 to 13, wherein the excitation light generation condition is adjusted based on an image depth of the photoacoustic image.
The image acquisition method according to any one of claims 9 to 13, wherein the excitation light generation condition is adjusted based on a focal depth of the photoacoustic image.
The image acquisition method according to any one of claims 9 to 15, wherein the correction process is performed on the photoacoustic image based on the excitation light generation condition.