WO2013128921A1

WO2013128921A1 - Image-generation device and method

Info

Publication number: WO2013128921A1
Application number: PCT/JP2013/001181
Authority: WO
Inventors: 辻田　和宏
Original assignee: 富士フイルム株式会社
Priority date: 2012-02-28
Filing date: 2013-02-27
Publication date: 2013-09-06
Also published as: JP2013208422A; JP5873816B2

Abstract

[Problem] To apply a sound-speed distribution generated on the basis of a detection signal of an acoustic wave differing from a generation subject, and generate an image, using a device for detecting both a photoacoustic wave and a reflected acoustic wave. [Solution] A probe (11) detects a reflected acoustic signal in a transmitted acoustic wave, and a photoacoustic signal produced inside the body of a subject by photoirradiating the subject. A sound-speed-distribution generation means (27) generates a sound-speed distribution of the interior of the body of the subject on the basis of the reflected acoustic signal. A photoacoustic-image generation means (25) generates a photoacoustic image on the basis of the photoacoustic signal and the sound-speed distribution.

Description

Image generating apparatus and method

The present invention relates to an image generation apparatus and method, and more particularly to an image generation apparatus and method for generating an image based on an acoustic wave detected from within a subject.

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

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

Usually, in the generation of an ultrasonic image and a photoacoustic image, image reconstruction is performed on the assumption that the sound velocity of the acoustic wave traveling in the subject is constant. However, there are individual differences in the sound speed, and the sound speed is not always uniform within the subject. If a difference occurs between the sound speed used at the time of image reconstruction and the actual sound speed in the subject, there arises a problem that the resolution of the generated image is deteriorated. To deal with this problem, Patent Document 1 describes that a sound velocity distribution in a subject is measured based on an acoustic wave detection signal, and an image is generated using the measured sound velocity distribution.

JP 2011-120765 A

Patent Document 1 describes that the distribution of sound speed is obtained based on an acoustic wave (photoacoustic wave) generated by irradiating a subject with intensity-modulated light from a light source. However, the photoacoustic signal is usually generated from a limited location in the subject, and when a large number of light absorbers are not distributed over the entire image, the sound velocity distribution cannot be obtained with high accuracy. On the other hand, when the sound speed distribution is obtained based on the reflected ultrasonic wave with respect to the transmitted ultrasonic wave, generally, the ultrasonic image has more points (signal generation sources) that have higher luminance than the photoacoustic image. It is considered that the distribution can be obtained with high accuracy. However, in that case, since many points must be processed, there is a problem that processing takes time. Conventionally, in the generation of a photoacoustic image, a sound velocity distribution is generated based on a photoacoustic wave, and in the generation of an ultrasonic image, a sound velocity distribution is generated based on a reflected ultrasonic wave, and it is considered to combine them with each other. There wasn't.

In view of the above, the present invention performs image generation by applying a sound velocity distribution generated based on a detection signal of an acoustic wave different from the generation target in an apparatus that detects both a photoacoustic wave and a reflected acoustic wave. It is an object of the present invention to provide an image generation apparatus and method that can perform the above-described process.

In order to achieve the above object, the present invention provides a light source, an acoustic wave transmitting means for transmitting an acoustic wave to a subject, a reflected acoustic wave for the acoustic wave transmitted from the acoustic wave transmitting means, and light from the light source. An acoustic wave detecting means for detecting a photoacoustic wave generated in the subject after being emitted to the subject, a reflected acoustic signal that is a detection signal of the reflected acoustic wave detected by the acoustic wave detecting means, and a photoacoustic A sound velocity distribution generating means for generating a sound velocity distribution of an acoustic wave traveling in the subject based on one of the photoacoustic signals, which is a wave detection signal, and the other of the reflected acoustic signal and the photoacoustic signal and the sound velocity. There is provided an image generation apparatus comprising: a first image generation unit configured to generate a first image based on a distribution.

In the present invention, the first image generation unit delay-adds the other one of the reflected acoustic signal and the photoacoustic signal detected by the plurality of acoustic wave detector elements of the acoustic wave detecting unit with a delay time based on the sound velocity distribution. By doing so, it is possible to adopt a configuration for generating the first image.

The sound velocity distribution generating means may generate a sound velocity distribution based on the reflected acoustic signal, and the first image generating means may generate a photoacoustic image based on the photoacoustic signal as the first image.

The light source emits light of a plurality of wavelengths different from each other, and the first image generation unit detects a plurality of wavelengths of the plurality of wavelengths detected by the acoustic wave detection unit for the light of the plurality of wavelengths emitted to the subject. Two-wavelength data calculation means for extracting the relative magnitude of the relative signal intensity between the corresponding photoacoustic signals, and intensity information indicating the signal intensity is generated based on the photoacoustic signals corresponding to each of the plurality of wavelengths. An intensity information extracting means, and determining the gradation value of each pixel of the photoacoustic image based on the intensity information, and determining the display color of each pixel based on the relative relationship of the signal intensity Also good.

Instead of the above, the sound velocity distribution generating means generates sound velocity distribution based on the photoacoustic signal, and the first image generating means uses the reflected acoustic wave image based on the reflected acoustic signal as the first image. It may be generated.

A second image generation means for generating a second image based on one of the reflected acoustic signal and the photoacoustic signal and the sound velocity distribution may be further provided.

In the present invention, the second image generating means delay-adds one of the reflected acoustic signal and the photoacoustic signal detected by the plurality of acoustic wave detector elements of the acoustic wave detecting means with a delay time based on the sound velocity distribution. By doing so, a configuration for generating the second image can be adopted.

An image composition means for synthesizing the first image and the second image may be further provided.

The sound velocity distribution generation means delay-adds so that the luminance of the pixel after delay addition becomes maximum when one of the reflected acoustic signal and the photoacoustic signal corresponding to the pixel of interest is equal to or greater than a predetermined value. It is also possible to adjust the delay time for each element in the range of the acoustic wave detector element of the acoustic wave detecting means to generate the sound velocity distribution based on the adjusted delay time.

The present invention also includes a step of detecting a photoacoustic wave from the subject after light is emitted toward the subject, a step of transmitting the acoustic wave to the subject, and a reflected acoustic wave with respect to the transmitted acoustic wave. Detecting the sound velocity distribution of the acoustic wave traveling in the subject based on one of the photoacoustic wave and the reflected acoustic wave, and the sound velocity of the other of the photoacoustic wave and the reflected acoustic wave. And a step of generating a first image based on the distribution.

In the image generation apparatus and method of the present invention, when an image is generated based on one of a photoacoustic signal and a reflected acoustic signal, a sound speed distribution generated based on the other signal is used. For example, when generating a photoacoustic image based on a photoacoustic signal, a sound speed distribution generated based on the reflected acoustic signal is used. In addition, when the reflected acoustic wave image is generated based on the reflected acoustic signal, the sound velocity distribution generated based on the photoacoustic signal is used. As described above, in the present invention, image generation can be performed by applying a sound speed distribution generated based on a detection signal of an acoustic wave different from the generation target.

1 is a block diagram showing an image generation apparatus according to a first embodiment of the present invention. The figure which shows the example of a data acquisition sequence. The figure which shows the reflected acoustic signal detected with the aperture element corresponding to each line of US mode. The figure which shows the ultrasonic image after a reconstruction. The figure which shows the photoacoustic signal detected with the aperture element corresponding to each area of PA mode. The figure which shows the photoacoustic signal after a reconstruction. The figure which shows the ultrasonic transducer | vibrator of a probe, and the light absorber in a subject. The figure shown in the time distribution of the reflected acoustic signal detected with the aperture element. The figure which shows the data for 1 line reconfigure | reconstructed. The figure which shows the time distribution of the reflected acoustic signal when the sound speed in a subject is not constant. The flowchart which shows the operation | movement procedure at the time of calculating | requiring sound speed distribution. The flowchart which shows the operation | movement procedure of a photoacoustic image processing apparatus. The block diagram which shows the structural example of the photoacoustic image generation means in the case of irradiating the subject with the light of a some wavelength.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an image generation apparatus according to a first embodiment of the present invention. The image generation apparatus (photoacoustic image generation apparatus) 10 includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, and a light source (laser unit) 13. The photoacoustic image generation apparatus 10 can generate both an ultrasonic image and a photoacoustic image.

The laser unit 13 is a light source and generates light (laser light) to be irradiated onto the subject. What is necessary is just to set the wavelength of a laser beam suitably according to an observation target object. For example, the laser unit 13 emits light having a wavelength with a large absorption of hemoglobin, specifically, light having a wavelength of 750 nm or 800 nm. Laser light emitted from the laser unit 13 is guided to the probe 11 using light guide means such as an optical fiber, and is irradiated from the probe 11 to the subject. Alternatively, light irradiation may be performed from a place other than the probe 11.

The probe 11 includes an acoustic wave transmitting unit that outputs (transmits) an acoustic wave (ultrasonic wave) to the subject, and an acoustic wave detecting unit that detects an acoustic wave (ultrasonic wave) from within the subject. The acoustic wave detecting element of the acoustic wave detecting means may also serve as the acoustic wave transmitting element of the acoustic wave transmitting means. For example, one ultrasonic transducer (element) may be used for both transmission and detection of ultrasonic waves. The probe 11 has, for example, a plurality of ultrasonic transducers arranged in a one-dimensional manner, outputs ultrasonic waves from the plurality of ultrasonic transducers, and reflects reflected acoustic waves (hereinafter referred to as “acoustic waves”) to the output ultrasonic waves. Are also detected by a plurality of ultrasonic transducers. In addition, the probe 11 detects a photoacoustic wave (hereinafter also referred to as a photoacoustic signal) generated by the measurement object in the subject absorbing light from the laser unit 13 by using a plurality of ultrasonic transducers. Note that it is not necessary for one probe 11 to have both the ultrasonic transmission means and the ultrasonic detection means. The ultrasonic transmission means and the ultrasonic detection means are separated to transmit ultrasonic waves and ultrasonic waves. Reception may be performed at a different location.

The ultrasonic unit 12 includes a reception circuit 21, an AD conversion unit 22, a reception memory 23, a data separation unit 24, a photoacoustic image generation unit 25, an ultrasonic image generation unit 26, a sound velocity distribution generation unit 27, an image synthesis unit 29, a trigger. A control circuit 30, a transmission control circuit 31, and a control means 32 are included. The control means 32 controls each part in the ultrasonic unit 12. The receiving circuit 21 receives an acoustic wave detection signal (a photoacoustic signal or a reflected acoustic signal) detected by the probe 11. The AD converter 22 samples the photoacoustic signal and the reflected acoustic signal received by the receiving circuit 21 and converts them into a digital signal. The AD conversion means 22 samples the acoustic wave detection signal at a predetermined sampling period, for example, in synchronization with the AD clock signal.

The trigger control circuit 30 outputs a light trigger signal that instructs the laser unit 13 to emit light. The laser unit 13 includes a flash lamp 41 that excites a laser medium (not shown) such as YAG or titanium-sapphire, and a Q switch 42 that controls laser oscillation. When the trigger control circuit 30 outputs a flash lamp trigger signal, the laser unit 13 turns on the flash lamp 41 and excites the laser medium. For example, when the flash lamp 41 sufficiently excites the laser medium, the trigger control circuit 30 outputs a Q switch trigger signal. The Q switch 42 is turned on when a Q switch trigger signal is received, and emits laser light from the laser unit 13. The time required from when the flash lamp 41 is turned on until the laser medium is sufficiently excited can be estimated from the characteristics of the laser medium.

In addition, instead of controlling the Q switch from the trigger control circuit 30, the Q switch 42 may be turned on after the laser medium is sufficiently excited in the laser unit 13. In that case, a signal indicating that the Q switch 42 is turned on may be notified to the ultrasonic unit 12 side. Here, the light trigger signal is a concept including at least one of a flash lamp trigger signal and a Q switch trigger signal. When outputting the Q switch trigger signal from the trigger control circuit 30, the Q switch trigger signal corresponds to the optical trigger signal. When the laser unit 13 generates the timing of the Q switch trigger, the flash lamp trigger signal is used as the optical trigger signal. It may correspond. By outputting the optical trigger signal, the subject is irradiated with laser light and the photoacoustic signal is detected.

Further, the trigger control circuit 30 outputs an ultrasonic transmission trigger signal that instructs ultrasonic transmission to the transmission control circuit 31. When receiving the ultrasonic transmission trigger signal, the transmission control circuit 31 transmits ultrasonic waves from the probe 11. By outputting the ultrasonic transmission trigger signal, transmission of ultrasonic waves to the subject and detection of reflected acoustic signals are performed.

Furthermore, the trigger control circuit 30 outputs a sampling trigger signal for instructing the AD conversion means 22 to start sampling. The trigger control circuit 30 outputs a sampling trigger signal at a predetermined timing after outputting the optical trigger signal or the ultrasonic transmission trigger signal. For example, when detecting a photoacoustic signal, the trigger control circuit 30 preferably outputs a sampling trigger signal after the output of the optical trigger signal, preferably at a timing when the subject is actually irradiated with the laser light. For example, the trigger control circuit 30 outputs a sampling trigger signal in synchronization with the output of the Q switch trigger signal. The trigger control circuit 30 outputs a sampling trigger signal in synchronization with the ultrasonic transmission trigger signal when detecting a reflected acoustic signal. When receiving the sampling trigger signal, the AD conversion unit 22 starts sampling the photoacoustic signal or the reflected acoustic signal detected by the probe 11.

The AD conversion means 22 stores the sampled photoacoustic signal and reflected acoustic signal in the reception memory 23. As the reception memory 23, for example, a semiconductor memory device can be used. Alternatively, other storage devices such as a magnetic storage device may be used for the reception memory 23. The reception memory 23 stores photoacoustic signal sampling data (photoacoustic data) and reflected acoustic signal sampling data (reflected ultrasound data). The data separation unit 24 separates the photoacoustic signal and the reflected acoustic signal stored in the reception memory 23. The data separation unit 24 passes the separated photoacoustic signal to the photoacoustic image generation unit 25. The separated reflected acoustic signal is passed to the ultrasonic image generation means 26 and the sound speed distribution generation means 27.

The sound velocity distribution generating means 27 receives the reflected acoustic signal from the data separating means 24, and generates the sound velocity distribution of the acoustic wave traveling in the subject based on the received reflected acoustic signal. The method of generating the sound speed distribution is not particularly limited. For generating the sound velocity distribution, any method for estimating the sound velocity distribution based on the acoustic wave can be used.

The photoacoustic image generation means 25 is a first image means, and generates a photoacoustic image (first image) based on the photoacoustic signal. The photoacoustic image generation unit 25 includes a photoacoustic image reconstruction unit 251, a detection / logarithm conversion unit 252, and a photoacoustic image construction unit 253. The ultrasonic image generation unit 26 is a second image unit, and generates an ultrasonic image (second image) based on the reflected acoustic signal. The ultrasonic image generation means (reflected acoustic wave image generation means) 26 includes an ultrasonic image reconstruction means 261, a detection / logarithm conversion means 262, and an ultrasonic image construction means 263.

The photoacoustic image reconstruction unit 251 receives the photoacoustic signal from the data separation unit 24 and reconstructs the photoacoustic signal. The photoacoustic image reconstruction unit 251 generates data of each line of the photoacoustic image that is a tomographic image based on the photoacoustic signal. Here, the reconstructed photoacoustic signal can be regarded as a photoacoustic image. The photoacoustic image reconstruction means 251 reconstructs a photoacoustic signal by a delay addition method (synonymous with Delay と and Sum, phase matching addition, and phasing addition). The photoacoustic image reconstruction unit 251 adds, for example, photoacoustic signals for 64 elements with a delay time corresponding to the position of each element (each ultrasonic transducer) to generate data for one line. At this time, the photoacoustic image reconstruction means 251 delays and adds the photoacoustic signal detected by each element while correcting the delay time of each element using the sound speed distribution generated by the sound speed distribution generation means 27.

The detection / logarithm conversion means 252 generates an envelope of the data of each line output from the photoacoustic image reconstruction means 251 and logarithmically converts the envelope to widen the dynamic range. The photoacoustic image construction unit 253 generates a photoacoustic image based on the data of each line subjected to logarithmic transformation. The photoacoustic image construction unit 253 generates a photoacoustic image by converting, for example, the position in the time axis direction of the photoacoustic signal (peak portion) into the position in the depth direction in the tomographic image.

The ultrasonic image reconstruction unit 261 receives the reflected acoustic signal from the data separation unit 24 and reconstructs the reflected acoustic signal. The ultrasonic image reconstruction unit 261 generates data of each line of an ultrasonic image (reflected acoustic image) that is a tomographic image based on the received reflected acoustic signal. Here, the reconstructed reflected acoustic signal can be regarded as an ultrasonic image. The ultrasonic image reconstruction means 261 adds, for example, reflected acoustic signals for 64 elements with a delay time corresponding to the position of each element, and generates data for one line. At this time, the ultrasonic image reconstructing unit 261 delays and adds the reflected acoustic signal detected by each element while correcting the delay time of each element using the sound speed distribution generated by the sound speed distribution generating unit 27.

The detection / logarithm conversion means 262 generates an envelope of the data of each line output by the ultrasonic image reconstruction means 261, and logarithmically transforms the envelope to widen the dynamic range. The ultrasonic image construction unit 263 generates an ultrasonic image based on the data of each line subjected to logarithmic transformation. The generation of the ultrasonic image in the ultrasonic image generation unit 26 may be the same as the generation of the photoacoustic image in the photoacoustic image generation unit 25 except that the signal is a reflected acoustic signal.

The image synthesis unit 29 synthesizes the photoacoustic image generated by the photoacoustic image generation unit 25 and the ultrasonic image generated by the ultrasonic image generation unit 26. The image composition unit 29 performs image composition by superimposing a photoacoustic image on an ultrasonic image, for example. The image display unit 14 displays the image synthesized by the image synthesis unit 29 on a display monitor or the like. The image display means 14 may switch and display the photoacoustic image and the ultrasonic image without performing image synthesis. Alternatively, the photoacoustic image and the ultrasonic image may be displayed side by side.

The acquisition sequence of the photoacoustic signal and the reflected acoustic signal will be described. FIG. 2 shows an example of a data acquisition sequence. In the figure, mode “US” represents acquisition of reflected acoustic signals, and mode “PA” represents acquisition of photoacoustic signals. Here, the probe 11 has 128 ultrasonic transducers arranged one-dimensionally as an acoustic wave detector element and an acoustic wave transmission element.

In acquiring the photoacoustic signal, the photoacoustic signal is taken in 64 elements after irradiating the subject with light from the laser unit 13. That is, data for a total of 128 elements is acquired in two steps. For example, a photoacoustic signal detected by an ultrasonic transducer having an element number of 1 to 64 elements after the first laser emission is obtained, and an ultrasonic transducer having an element number of 65 to 128 elements is acquired after the second laser emission. The detected photoacoustic signal is acquired. On the other hand, in the acquisition of the reflected acoustic signal, after transmitting ultrasonic waves from the 64-element ultrasonic transducer, the reflected acoustic signal is acquired by the 64-element ultrasonic transducer. It should be noted that ultrasonic waves are transmitted and received with fewer elements than 64 elements at the ends of the ultrasonic transducers arranged one-dimensionally. In the acquisition of the reflected acoustic signal, the reflected acoustic signal is acquired by the line by line while shifting the range (opening position) of the ultrasonic transducer that transmits and receives the ultrasonic wave one element at a time.

In the sequence example of FIG. 2, the acquisition of the reflected acoustic signal and the acquisition of the photoacoustic signal are performed alternately. More specifically, the apparatus starts operating in the US mode, shifting the opening position from line 1 to line 31 one element at a time (since line 1 to line 31 is an end, in fact one element at a time ) Transmit and receive ultrasonic waves and obtain reflected acoustic signals. Next, the mode is changed to the PA mode, and the subject is irradiated with the laser beam from the laser unit 13, and the photoacoustic signal is detected by 64 elements corresponding to the first area. Next, in the US mode, ultrasonic waves are transmitted and received while shifting the opening position from the line 32 to the line 95 one element at a time, and a reflected acoustic signal is acquired. Thereafter, the PA mode is entered and the subject is irradiated with the laser light from the laser unit 13, and a photoacoustic signal is acquired with 64 elements corresponding to the second area. Subsequently, in the US mode, transmitting and receiving ultrasonic waves while shifting the opening position from line 96 to line 128 one element at a time (since line 95 to line 128 is an end, the opening element is actually narrowed one element at a time) To obtain a reflected acoustic signal.

FIG. 3 shows the reflected acoustic signal detected by the aperture element corresponding to each line in the US mode of FIG. 2, and FIG. 4 shows the ultrasonic image after reconstruction. In FIG. 3, the vertical axis indicates the elapsed time from ultrasonic transmission. Data of each line from line 1 to line 128 is generated by delay-adding (phase matching addition) the reflected acoustic signals of 64 elements in each line (however, the opening elements are fewer than 64 elements at the end). 1 can be generated.

FIG. 5 shows a photoacoustic signal detected by an aperture element corresponding to each area of the PA mode in FIG. 2, and FIG. 6 shows a reconstructed photoacoustic signal (photoacoustic image). In FIG. 5, the vertical axis indicates the elapsed time from the irradiation of the laser beam on the subject. The photoacoustic image shown in FIG. 6 can be generated by reconstructing the photoacoustic signals for a total of 128 elements in the two areas.

In the above description, it has been described that the ultrasonic wave is a line by line and the photoacoustic signal is divided into two areas to detect the photoacoustic signal, but the ultrasonic wave is also transmitted and received in each of the two areas. The reflected acoustic signal may be detected. For example, the object is irradiated with light and a photoacoustic signal is detected by the ultrasonic transducer of element number 1-64 corresponding to area 1, and then the ultrasonic transducer of element number 1-64 is not focused. An ultrasonic wave may be transmitted to the subject to detect a reflected acoustic signal. Similarly, for area 2, after the light irradiation, a photoacoustic signal is detected by the ultrasonic transducer of element number 65-128 corresponding to area 2, and then the ultrasonic transducer of element number 65-128 is applied to the subject. Then, the reflected acoustic signal may be detected by transmitting an ultrasonic wave. Either the photoacoustic signal or the reflected acoustic signal may be detected first.

In the above description, the photoacoustic signal is detected by being divided into two areas, but the area division may not be performed. For example, photoacoustic signals may be detected by all 128 elements after irradiating the subject with light. In this case, only one light irradiation is required. Similarly, for reflected acoustic signals, for example, ultrasonic waves may be transmitted from all 128 elements without focus, and reflected acoustic signals may be detected by 128 elements.

When the photoacoustic signal and the reflected acoustic signal are detected in the same area, after the detection of one signal is started, the other signal is detected while sampling by the AD conversion means 22 is continued, and both signals are continuously detected. You may make it acquire to. For example, when the photoacoustic signal is detected first, the trigger control circuit 30 outputs the optical trigger signal (flash lamp trigger signal or Q switch trigger signal), and then transmits the ultrasonic wave at a timing to end the detection of the photoacoustic signal. Outputs a trigger signal. At this time, the AD conversion means 22 continues sampling without interrupting sampling. In other words, the trigger control circuit 30 outputs an ultrasonic transmission trigger signal in a state where the AD conversion means 22 continues sampling. When the probe 11 performs ultrasonic transmission in response to the ultrasonic transmission trigger signal, the acoustic wave detected by the probe 11 changes from a photoacoustic wave to a reflected acoustic wave. Since the AD conversion means 22 continues sampling, the photoacoustic signal and the reflected acoustic signal can be sampled continuously. In this case, the time from the start of detection of the photoacoustic wave to the end of detection of the reflected acoustic wave can be shortened as compared to the case of sampling separately, and when both images are superimposed and displayed, A positional shift between images can be suppressed.

Here, when the AD conversion means 22 samples the photoacoustic signal and the reflected acoustic signal at the same sampling rate, a resample means for resampling the reflected acoustic signal to ½ may be provided. The ½ resampling unit compresses the reflected acoustic signal to ½ in the time axis direction, for example. The reason for resampling is that if the photoacoustic signal and the reflected acoustic signal are generated at the same position in the depth direction in the subject, in the case of the reflected acoustic signal, the ultrasonic wave transmitted from the probe 11 reaches that position. This is because the time required to proceed is necessary, and the time from ultrasonic transmission to reflected acoustic signal detection is twice the time from light irradiation to photoacoustic signal detection. That is, the photoacoustic signal is detected in one-way time, whereas the reflected acoustic signal takes time for a round trip. Instead of performing resampling, the sampling rate of the AD conversion means 22 at the time of detecting the reflected acoustic signal may be controlled to half the sampling rate at the time of detecting the photoacoustic signal.

Next, the generation of sound speed distribution will be described. FIG. 7 shows the ultrasonic transducer of the probe and the light absorber in the subject. In the figure, the horizontal axis direction represents the arrangement direction of the ultrasonic transducers arranged one-dimensionally, and the vertical axis represents the depth direction of the subject. A region indicated by diagonal lines represents an aperture element when a reflected acoustic signal is detected. A reflector 45 exists immediately below the aperture element. Consider, for example, that ultrasonic waves are transmitted from the 64 elements forming the aperture elements in the depth direction of the subject and the reflected acoustic waves from the reflector 45 are detected.

FIG. 8 shows the time distribution of the reflected acoustic signal detected by the aperture element. In the figure, the vertical axis represents the elapsed time from ultrasonic transmission. As shown in the figure, the detection time of the reflected acoustic signal from the reflector 45 (FIG. 7) detected by each element in the opening is the position of the reflector 45 in the opening and each ultrasonic transducer. It changes according to the positional relationship. FIG. 9 shows the reconstructed data for one line. By delay-adding the reflected acoustic signals for 64 elements shown in FIG. 8, data for one line of the ultrasonic image in which the reflected acoustic signal converges to one point is obtained. By performing a series of processes on each line, an ultrasonic image of one frame can be generated.

FIG. 10 shows the time distribution of the reflected acoustic signal when the speed of sound in the subject is not constant. When reconstructing the reflected acoustic signal shown in FIG. 8, if the sound speed in the subject matches the assumed sound speed and the sound speed does not change depending on the position in the subject, the reflected acoustic signal is The delay time given to each element when performing delay addition is uniquely determined from the positional relationship between the reflector and each element. However, when the sound speed is not uniform, the time distribution of the detected reflected acoustic signal deviates from the case where the sound speed indicated by the solid line is uniform, as indicated by the broken line in FIG. In that case, even if the delay is added with an ideal delay curve assuming a uniform assumed sound speed, the reflected acoustic signal cannot be converged to one point. Therefore, a virtual sound speed value is calculated so that the detected reflected acoustic signal is reconstructed into one point. By calculating the virtual sound speed value for each pixel, the sound speed distribution in the subject can be determined.

FIG. 11 shows an example of the operation procedure when obtaining the sound velocity distribution. Here, the reflected acoustic signal is described as an image in which the time axis is replaced with a position in the depth direction. The sound velocity distribution generation means 27 determines whether or not the signal intensity of the reflected acoustic signal at a position in a certain time axis direction (a certain pixel) of a certain element is equal to or higher than a predetermined value (step A1). When the signal intensity is equal to or higher than a predetermined value, the sound velocity distribution generation unit 27 calculates a phase for the pixel (target pixel) (step A2). In step A2, for example, the sound velocity distribution generation unit 27 assumes a sound velocity distribution in the subject, and based on the assumption, performs a delay addition for each of the aperture elements that substantially include the element corresponding to the target pixel. Set the delay time when performing.

The sound velocity distribution generation means 27 evaluates the luminance value (signal intensity of the reconstructed signal) of the pixel when the reflected acoustic signal in the aperture element is delayed and added based on the phase calculated in step A2 (step A3). ). The sound velocity distribution generation means 27 determines whether or not the luminance value evaluated in step A3 is the maximum value (step A4). If it is not the maximum value, the process returns to step A2, and the phase is recalculated assuming a different sound velocity distribution. The sound velocity distribution generation means 27 repeatedly executes step A2 and step A3 until it determines that the luminance value has become maximum in step A4, and obtains the phase that gives the maximum luminance value.

When determining that the luminance value is maximum in step A4, the sound velocity distribution generation means 27 stores the phase data (phase distribution) in the pixel of interest in a storage means such as a memory (step A5). The sound velocity distribution generation means 27 stores, for example, information on the delay time given to each aperture element when the luminance value is maximized in the storage means as phase data in the pixel of interest. Instead of the delay time information, sound speed data in a direction from the target pixel toward each element may be stored as phase data. Further, function parameters obtained by approximating a delay time given to each element or sound speed data in a direction toward each element by a predetermined function (for example, a function of a quadratic function or more) may be stored in the storage means as phase data. Good.

The sound velocity distribution generation means 27 determines whether or not all pixels have been processed (step A6). If unprocessed pixels remain, the process returns to step A1, and it is determined whether or not the luminance value of the next pixel is equal to or greater than a predetermined value. Here, a pixel whose luminance value is determined to be smaller than a predetermined value cannot evaluate a change in luminance value with respect to a phase change. Therefore, when it is determined in step A1 that the luminance value is smaller than the predetermined value, step A1 is repeated until a pixel having a luminance value equal to or higher than the predetermined value is selected without performing phase calculation.

When determining that there is no unprocessed pixel in Step A6, the sound speed distribution generating means 27 generates a sound speed distribution based on the phase data stored in Step A5 (Step A7). A known method can be used to generate (estimate) the sound velocity distribution based on the phase data.

The sound speed distribution generation means 27 outputs phase data based on the sound speed distribution to the photoacoustic image reconstruction means 251 and the ultrasonic image reconstruction means 261 as a sound speed correction table. The photoacoustic image reconstruction means 251 delays and adds the photoacoustic signal with a delay time based on the sound speed correction table. Further, the ultrasonic image reconstruction unit 261 reconstructs the reflected acoustic signal with a delay time based on the sound speed correction table. Instead of outputting the sound speed correction table from the sound speed distribution generation means 27, sound speed distribution data is output to the photoacoustic image reconstruction means 251 and the ultrasonic image reconstruction means 261, and the delay based on the sound speed distribution data in these means. You may make it perform delay addition by time.

The method for obtaining the sound velocity distribution is not limited to the above. For example, the local sound velocity value may be calculated by a method similar to the method described in Patent Document 1, and the distribution thereof may be obtained. That is, using Huygens' principle, the optimum sound speed value at the lattice point set in the region shallower than the region of interest in the subject and the region of interest is determined, and the ultrasonic wave is determined based on the optimum sound speed value in the region of interest. Calculates the received wave received from the region of interest when transmitted to the region of interest, assumes the assumed sound speed in the region of interest, and receives from each lattice point obtained from the optimum sound speed value at each lattice point based on the assumed sound speed A synthesized reception wave may be obtained by synthesizing waves, and a local sound velocity value may be obtained by determining a local sound velocity value in the region of interest based on the reception wave and the synthesized reception wave, and the distribution thereof may be obtained.

Next, the operation procedure will be explained. FIG. 12 shows an operation procedure of the photoacoustic image generation apparatus. The trigger control circuit 30 outputs an ultrasonic transmission trigger signal to the transmission control circuit 31. When receiving the ultrasonic transmission trigger signal, the transmission control circuit 31 transmits ultrasonic waves from the probe 11 (step B1). After transmitting the ultrasonic wave, the probe 11 detects a reflected acoustic signal for the transmitted ultrasonic wave (step B2). The reflected acoustic signal detected by the probe 11 is input to the AD conversion means 22 via the receiving circuit 21. The AD conversion means 22 samples the reflected acoustic signal, converts it into digital data, and stores it in the reception memory 23.

Subsequently, the trigger control circuit 30 outputs a flash lamp trigger signal to the laser unit 13. In the laser unit 13, the flash lamp 41 is turned on in response to the flash lamp trigger signal, and excitation of the laser medium is started. The trigger control circuit 30 sends a Q switch trigger signal to the laser unit 13 and turns on the Q switch 42 to emit pulsed laser light from the laser unit 13 (step B3). The trigger control circuit 30 outputs the Q switch trigger signal at a timing that is in a predetermined time relationship with the timing at which the flash lamp trigger signal is output, for example. For example, the trigger control circuit 30 outputs a Q switch trigger signal 150 seconds after the flash lamp emission.

The laser beam emitted from the laser unit 13 is irradiated to the subject. In the subject, a photoacoustic signal is generated by the irradiated pulsed laser beam. The probe 11 detects a photoacoustic signal generated in the subject (step B4). The photoacoustic signal detected by the probe is input to the AD conversion means 22 via the receiving circuit 21. The AD conversion means 22 samples the photoacoustic signal, converts it into digital data, and stores it in the reception memory 23. Note that either the reflected acoustic signal or the photoacoustic signal may be detected first. Further, for example, the reflected acoustic signal and the photoacoustic signal may be detected alternately according to the sequence shown in FIG.

The data separation unit 24 reads the photoacoustic signal from the reception memory 23 and gives the read photoacoustic signal to the photoacoustic image generation unit 25. Further, the reflected acoustic signal is read from the reception memory 23, and the read reflected acoustic signal is given to the ultrasonic image generating unit 26 and the sound speed distribution generating unit 27. The sound speed distribution generation means 27 generates a sound speed distribution based on the reflected acoustic signal received from the data separation means 24 (step B5).

The photoacoustic image generation means 25 generates a photoacoustic image based on the photoacoustic signal received from the data separation means 24 (step B6). At that time, the photoacoustic image generation means 25 delays and adds the photoacoustic signals of the respective elements with a delay time based on the sound speed distribution generated in step B5. By performing reconstruction in consideration of the difference in sound speed according to the position inside the subject, even if the sound speed distribution is not uniform, the photoacoustic signal emitted from one photoacoustic wave source is displayed on the photoacoustic image. It can be converged to one point.

The ultrasonic image generation unit 26 generates an ultrasonic image based on the reflected acoustic signal received from the data separation unit 24 (step B7). At that time, the ultrasonic image generating means 26 delay-adds the reflected acoustic signals of the respective elements with a delay time based on the sound speed distribution generated in step B5. By performing reconstruction in consideration of the difference in sound speed depending on the position inside the subject, even if the sound speed distribution is not uniform, the reflected acoustic signal from one reflected acoustic wave source is displayed on the ultrasound image. It can be converged to one point. The image synthesizing unit 29 synthesizes the ultrasonic image and the photoacoustic image (step B8), and displays the synthesized image on the display screen of the image display unit 14.

In the present embodiment, a sound speed distribution is generated based on the reflected acoustic signal among the photoacoustic signal and the reflected acoustic signal, and the sound speed distribution generated based on the reflected acoustic signal is used for generating a photoacoustic image. Comparing the photoacoustic image and the ultrasonic image, in general, the ultrasonic image includes more points with higher luminance (higher signal strength). In addition, the ultrasonic image has a higher luminance point throughout the image. For this reason, for example, when the sound speed distribution is generated according to the procedure shown in FIG. 11, phase data is obtained at more points, and the sound speed distribution is more accurately compared with the case where the sound speed distribution is obtained based on the photoacoustic signal. Can be sought. By generating a photoacoustic image using such a sound velocity distribution, the image quality of the photoacoustic image can be improved.

Next, a second embodiment of the present invention will be described. The configuration of the image generation apparatus in this embodiment is the same as that shown in FIG. In the present embodiment, a photoacoustic signal is used instead of a reflected acoustic signal for generating the sound velocity distribution. Other points may be the same as in the first embodiment. In the present embodiment, the ultrasonic image corresponds to the first image, and the photoacoustic image corresponds to the second image. Further, the ultrasonic image generating means corresponds to the first image generating means, and the photoacoustic image generating means corresponds to the second image generating means.

In the present embodiment, the sound velocity distribution generation unit 27 receives a photoacoustic signal (photoacoustic data) from the data separation unit 24. The sound speed distribution generating unit 27 generates a sound speed distribution based on the photoacoustic signal. The generation of the sound velocity distribution may be the same as that in the first embodiment except that the signal to be used is changed from the reflected acoustic signal to the photoacoustic signal. The sound speed distribution generation means 27 generates a sound speed distribution according to the procedure shown in FIG. 11, for example.

The sound speed distribution generation means 27 outputs, for example, a sound speed correction table based on the generated sound speed distribution to the photoacoustic image generation means 25 and the ultrasonic image generation means 26. The photoacoustic image reconstruction means 251 of the photoacoustic image generation means 25 delays and adds the photoacoustic signals detected by the respective elements with a delay time based on the sound velocity distribution generated based on the photoacoustic signals. The ultrasonic image reconstruction means 261 of the ultrasonic image generation means 26 is a delay time based on the sound velocity distribution generated based on the photoacoustic signal, and delay-adds the reflected acoustic signal detected by each element with the delay time. To do.

In the present embodiment, a sound speed distribution is generated based on the photoacoustic signal among the photoacoustic signal and the reflected acoustic signal, and the sound speed distribution generated based on the photoacoustic signal is used for generating an ultrasonic image. Comparing the photoacoustic image and the ultrasonic image, the photoacoustic image generally has few points with high luminance (high signal intensity). Therefore, the number of times that the phase adjustment (steps A2 to A4 in the flowchart of FIG. 11) is performed when the sound speed distribution is generated is smaller than when the sound speed distribution is generated based on the reflected acoustic signal. Therefore, the sound speed distribution can be obtained at a higher speed than when the sound speed distribution is generated using the reflected acoustic signal. When performing image display at high speed, it is advantageous to generate a sound speed distribution based on the photoacoustic signal as in the second embodiment.

When generating the photoacoustic image, the laser unit 13 may be configured to emit light having a plurality of wavelengths, and the laser unit 13 may irradiate the subject with laser beams having a plurality of different wavelengths. In this case, the photoacoustic image generation means 25 may generate a photoacoustic image that can distinguish, for example, an artery and a vein, using the wavelength dependence of the light absorption characteristics of the light absorber in the subject.

For example, the subject is irradiated with light having a wavelength of about 750 nm and light having a wavelength of about 800 nm. A molecular absorption coefficient at a wavelength of 750 nm of oxygenated hemoglobin (oxy-Hb combined with oxygen) contained in a large amount of human arteries is lower than a molecular absorption coefficient at a wavelength of 800 nm. On the other hand, the molecular absorption coefficient at a wavelength of 750 nm of deoxygenated hemoglobin (hemoglobin deoxy-Hb not bound to oxygen) contained in a large amount in the vein is higher than the molecular absorption coefficient at a wavelength of 800 nm. Using this property, by examining whether the photoacoustic signal obtained at a wavelength of 750 nm is relatively large or small with respect to the photoacoustic signal obtained at a wavelength of 800 nm, the photoacoustic signal from the artery and the vein From the photoacoustic signal.

FIG. 13 shows a configuration example of the photoacoustic image generation means when the subject is irradiated with light of two wavelengths. The photoacoustic image generation unit 25 a includes a two-wavelength data calculation unit 254 and an intensity information extraction unit 255 in addition to the photoacoustic image reconstruction unit 251, the detection / logarithm conversion unit 252, and the photoacoustic image construction unit 253. The photoacoustic image reconstruction unit 251 has a photoacoustic signal (first photoacoustic signal) when the subject is irradiated with light having a first wavelength (for example, 750 nm) and a second wavelength (for example, 800 nm). The photoacoustic signal (second photoacoustic signal) when the light is irradiated is reconstructed. The photoacoustic image reconstruction unit 251 passes the reconstructed first and second photoacoustic signals to the two-wavelength data calculation unit 254 and the intensity information extraction unit 255.

The two-wavelength data calculation means 254 generates data indicating the relative magnitude of the relative signal intensity between the photoacoustic signals corresponding to each of a plurality of wavelengths of light irradiated on the subject. The two-wavelength data calculation unit 254 generates, for example, a ratio between the first photoacoustic signal and the second photoacoustic signal as data indicating the relative relationship between the signal intensities. For example, when the signal intensity of the first photoacoustic signal is X and the signal intensity of the second photoacoustic signal is Y, Y / X is data indicating the relative magnitude of the signal intensity. Instead of using the ratio (Y / X) of the two photoacoustic signals as data indicating the relative magnitude of the relative signal intensity, tan ⁻¹ (Y / X) indicates the relative magnitude of the signal intensity. It may be used as data.

The intensity information extraction unit 255 generates intensity information indicating the signal intensity based on the photoacoustic signal corresponding to each wavelength. The intensity information extraction unit 255 generates, for example, (X ² + Y ² ) ^1/2 as the intensity information. The detection / logarithm conversion means 252 generates an envelope of data indicating the intensity information extracted by the intensity information extraction means 255, and then logarithmically converts the envelope to widen the dynamic range.

The photoacoustic image construction means 253 is based on the relative magnitude relationship information of the two-wavelength data generated by the two-wavelength data calculation means 254 and the intensity information generated by the intensity information extraction means 255. Is generated. For example, the photoacoustic image construction unit 253 determines the luminance (gradation value) of each pixel in the distribution image of the light absorber based on the input intensity information. The photoacoustic image construction unit 253 determines the color (display color) of each pixel in the light absorber distribution image based on, for example, phase information. The photoacoustic image construction unit 253 determines the color of each pixel based on the input data indicating the magnitude relationship using, for example, a color map in which the range of data indicating the relative magnitude relationship is associated with a predetermined color. To do.

When the photoacoustic image construction unit 253 uses, for example, tan ⁻¹ (Y / X) as data indicating the relative magnitude relationship between the photoacoustic signals, the photoacoustic image construction unit 253 is blue (for example, 0 ° is blue and becomes colorless as 45 ° approaches). A photoacoustic image is generated using a color map that gradually changes so that the color gradually changes so that the color gradually changes so that 90 ° is red and 45 ° approaches 45 °. . A portion where the first photoacoustic signal is larger than the second photoacoustic signal corresponds to a vein, and a portion where the second photoacoustic signal is larger than the first photoacoustic signal corresponds to an artery. By using the color map, the portion corresponding to the artery can be represented in red and the portion corresponding to the vein can be represented in blue on the photoacoustic image.

In the case of irradiating light of a plurality of wavelengths and obtaining the sound speed distribution based on the photoacoustic signal, if the sound speed distribution is generated based on the photoacoustic signal when one of the plurality of wavelengths is irradiated Good. For example, the wavelength having the highest signal intensity of the photoacoustic signal is selected from a plurality of wavelengths, and the sound speed distribution is generated based on the photoacoustic signal corresponding to the wavelength. For example, when light having a wavelength of 750 nm and light having a wavelength of 800 nm are irradiated, a sound speed distribution may be generated based on a photoacoustic signal detected when the light having a wavelength of 750 nm is irradiated.

In the above description, an example in which light of two wavelengths is irradiated has been described. However, the number of wavelengths of pulsed laser light irradiated to the subject when generating a photoacoustic image is not limited to two. The subject may be irradiated with three or more pulsed laser beams, and a photoacoustic image may be generated based on a photoacoustic signal corresponding to each wavelength.

The acoustic wave detection signal used when generating the sound velocity distribution is not limited to a reflected acoustic signal detected for one acoustic wave transmission or a photoacoustic signal generated by one light irradiation. For example, the sound speed distribution may be generated by performing ultrasonic transmission a plurality of times and averaging the reflected acoustic signals for a plurality of times. Moreover, light irradiation may be performed a plurality of times, and the sound speed distribution may be generated by averaging the photoacoustic signals for a plurality of times. Similarly, the generation of the ultrasonic image and the photoacoustic image may be performed based on the reflected acoustic signal and the photoacoustic signal which are averaged.

In each of the above embodiments, the image generation apparatus has been described as generating both a photoacoustic image and an ultrasonic image. However, in the first embodiment, generation of an ultrasonic image is omitted, and in the second embodiment, light is generated. Generation of an acoustic image can be omitted. In this case, for example, in the first embodiment, the reflected acoustic signal is used to generate a sound velocity distribution used when generating a photoacoustic image. When generating a photoacoustic image, the image quality of the photoacoustic image can be improved by using a highly accurate sound velocity distribution based on the reflected acoustic signal. On the other hand, in the second embodiment, the photoacoustic signal is used to generate a sound velocity distribution used when generating an ultrasonic image. When generating an ultrasonic image, the time required for generating an ultrasonic image can be shortened by using a sound velocity distribution that can be generated in a shorter time based on the photoacoustic signal.

Although the present invention has been described based on the preferred embodiment, the image generation apparatus and method of the present invention are not limited to the above embodiment, and various modifications and changes can be made to the configuration of the above embodiment. Those subjected to are also included in the scope of the present invention.

Claims

A light source;
An acoustic wave transmitting means for transmitting an acoustic wave to the subject;
An acoustic wave detecting means for detecting a reflected acoustic wave with respect to the acoustic wave transmitted from the acoustic wave transmitting means, and a photoacoustic wave generated in the subject after the light from the light source is emitted to the subject;
An acoustic wave that travels in the subject based on one of a reflected acoustic signal that is a detection signal of the reflected acoustic wave detected by the acoustic wave detection means and a photoacoustic signal that is a detection signal of the photoacoustic wave. A sound speed distribution generating means for generating a sound speed distribution of
An image generation apparatus comprising: a first image generation unit configured to generate a first image based on the other of the reflected acoustic signal and the photoacoustic signal and the sound velocity distribution.
The first image generating means delay-adds the other one of the reflected acoustic signal and the photoacoustic signal detected by the plurality of acoustic wave detector elements of the acoustic wave detecting means with a delay time based on the sound velocity distribution. The image generation apparatus according to claim 1, wherein the first image is generated.
The sound speed distribution generating means generates a sound speed distribution based on a reflected acoustic signal, and the first image generating means generates a photoacoustic image based on the photoacoustic signal as a first image. The image generation apparatus according to claim 1, wherein the image generation apparatus is provided.
The light source emits light having a plurality of different wavelengths;
Relative signals between the photoacoustic signals corresponding to each of the plurality of wavelengths detected by the acoustic wave detecting unit with respect to the light of the plurality of wavelengths emitted by the first image generation unit. Two-wavelength data calculating means for extracting magnitude relations, and intensity information extracting means for generating intensity information indicating signal intensity based on photoacoustic signals corresponding to each of a plurality of wavelengths, 4. The image according to claim 3, wherein a gradation value of each pixel is determined based on the intensity information, and a display color of each pixel is determined based on the relative relationship between the relative signal intensities. Generator.
The sound speed distribution generating means generates a sound speed distribution based on a photoacoustic signal, and the first image generating means generates a reflected acoustic wave image based on the reflected acoustic signal as a first image. The image generation apparatus according to claim 1, wherein the image generation apparatus is an image generation apparatus.
6. The apparatus according to claim 1, further comprising second image generation means for generating a second image based on one of the reflected acoustic signal and the photoacoustic signal and the sound velocity distribution. The image generating apparatus described.
The second image generating means delay-adds one of a reflected acoustic signal and a photoacoustic signal detected by a plurality of acoustic wave detector elements of the acoustic wave detecting means with a delay time based on the sound velocity distribution. The image generation apparatus according to claim 6, wherein the second image is generated.
The image generating apparatus according to claim 6 or 7, further comprising an image synthesizing unit that synthesizes the first image and the second image.
When the sound velocity distribution generating means has one signal value of the reflected acoustic signal and the photoacoustic signal corresponding to the pixel of interest equal to or greater than a predetermined value, the luminance of the pixel after delay addition is maximized. 9. The acoustic velocity distribution is generated based on the adjusted delay time by adjusting the delay time for each element in the range of the acoustic wave detector element of the acoustic wave detecting means for performing delay addition. An image generating apparatus according to claim 1.
A step of detecting a photoacoustic wave from the subject after light is emitted toward the subject;
Transmitting an acoustic wave to the subject;
Detecting a reflected acoustic wave with respect to the transmitted acoustic wave;
Obtaining a sound velocity distribution of an acoustic wave traveling in the subject based on one of the photoacoustic wave and the reflected acoustic wave;
An image generation method comprising: generating a first image based on the other of the photoacoustic wave and the reflected acoustic wave and the sound velocity distribution.
In the step of generating the first image, among the reflected acoustic signal and the photoacoustic signal detected by a plurality of acoustic wave detector elements of the acoustic wave detector used for detecting the photoacoustic wave and the reflected acoustic wave. The image generation method according to claim 10, wherein the first image is generated by delay-adding the other with a delay time based on the sound velocity distribution.
In the step of generating the sound velocity distribution, a sound velocity distribution is generated based on the reflected acoustic signal, and in the step of generating the first image, a photoacoustic image based on the photoacoustic signal is generated as a first image. The image generation method according to claim 10 or 11, characterized in that:
Multiple different wavelengths of light are emitted toward the subject,
Generating the first image comprises:
Extracting relative magnitudes of relative signal intensities between photoacoustic signals corresponding to each of a plurality of wavelengths, detected with respect to light of a plurality of wavelengths emitted to a subject;
Generating intensity information indicating signal intensity based on photoacoustic signals corresponding to each of a plurality of wavelengths;
Determining a gradation value of each pixel of the photoacoustic image based on the intensity information, and determining a display color of each pixel based on the relative relationship between the relative signal intensities. The image generation method according to claim 12.
In the step of generating the sound velocity distribution, a sound velocity distribution is generated based on the photoacoustic signal, and in the step of generating the first image, a reflected acoustic wave image based on the reflected acoustic signal is generated as a first image. The image generation method according to claim 10, wherein the image generation method is performed.
15. The method according to claim 10, further comprising a second image generation step of generating a second image based on one of the reflected acoustic signal and the photoacoustic signal and the sound velocity distribution. Image generation method.
In the step of generating the second image, among the reflected acoustic signal and the photoacoustic signal detected by a plurality of acoustic wave detector elements of an acoustic wave detector used for detecting the photoacoustic wave and the reflected acoustic wave. The image generation method according to claim 15, wherein the second image is generated by delay-adding one of the two at a delay time based on the sound velocity distribution.
The image generation method according to claim 15 or 16, further comprising a step of synthesizing the first image and the second image.
In the step of generating the sound velocity distribution, when one of the reflected acoustic signal and the photoacoustic signal corresponding to the target pixel is equal to or greater than a predetermined value, the luminance of the pixel after delay addition is maximized. The acoustic velocity distribution is generated based on the adjusted delay time by adjusting the delay time for each element in the range of the acoustic wave detector elements to be delay-added. The image generation method as described.