JP2013106822A - Photoacoustic image generating apparatus and photoacoustic image generating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire an image of a deep part in a subject in photoacoustic imaging.SOLUTION: This photoacoustic image generating apparatus includes: a light irradiation means 13 that irradiates the subject with a plurality of pulse lights with a mutually different pulse width; a probe 11 that has a plurality of acoustic wave detecting means 65, 66 and 67 having a mutually different detection band and composed to detect photoacoustic waves generated in the subject caused by the irradiation of pulse lights while separating them for each frequency band; and a photoacoustic image generation means 12 that generates a photoacoustic image based on a photoacoustic signal of each frequency band of photoacoustic waves detected by the plurality of acoustic wave detecting means 65, 66, and 67.

Description

  The present invention relates to a photoacoustic image generation apparatus and a photoacoustic image generation method for generating a photoacoustic image based on a photoacoustic wave generated due to light irradiation.

  Conventionally, as a method for acquiring a tomographic image inside a subject, an ultrasonic image is generated by detecting ultrasonic waves reflected in the subject by irradiating the subject with ultrasonic waves. Ultrasonic imaging for obtaining a morphological tomographic image is known. On the other hand, in the examination of a subject, development of an apparatus that displays not only a morphological tomographic image but also a functional tomographic image has been advanced in recent years. One of such devices is a device using a photoacoustic analysis method (Patent Document 1). This photoacoustic analysis method irradiates a subject with pulsed light having a predetermined wavelength (for example, wavelength band of visible light, near-infrared light, or mid-infrared light), and a specific substance in the subject is irradiated with the pulsed light. The photoacoustic wave, which is an elastic wave generated as a result of absorption of the energy, is detected, and the concentration of the specific substance is quantitatively measured. The specific substance in the subject is, for example, glucose or hemoglobin contained in blood. Such a technique for detecting a photoacoustic wave and generating a photoacoustic image based on the detection signal is called photoacoustic imaging (PAI) or photoacoustic tomography (PAT).

JP 2005-21380 A

  However, photoacoustic imaging has the following problems caused by using pulsed light.

  The frequency spectrum distribution of the photoacoustic wave depends on the pulse width of the irradiated pulsed light. Accordingly, in order to obtain a high-resolution photoacoustic image, pulse light having a short pulse width is generally used. However, since the photoacoustic wave generated due to irradiation with pulsed light having a short pulse width contains many high-frequency components, it is difficult to obtain information on the deep part of the subject. This is because the high-frequency component of the photoacoustic wave is easily attenuated in the subject.

  The present invention has been made in view of the above problems, and provides a photoacoustic image generation apparatus and a photoacoustic image generation method capable of acquiring an image of a deep portion in a subject in photoacoustic imaging. It is the purpose.

In order to solve the above problems, a photoacoustic image generation apparatus according to the present invention includes:
A light irradiation means for irradiating the subject with a plurality of pulse lights having different pulse widths;
A plurality of acoustic wave detection means having different detection bands, and a plurality of acoustic waves configured to detect and detect photoacoustic waves generated in a subject due to irradiation of pulsed light for each frequency band A probe having wave detection means;
And a photoacoustic image generation unit configured to generate a photoacoustic image based on a photoacoustic signal for each frequency band of the photoacoustic wave detected by the plurality of acoustic wave detection units.

  “Generating a photoacoustic image” means that a partial photoacoustic image (for example, an image of a deep part and an image of a surface vicinity part) is separately obtained based on each photoacoustic signal for each frequency band of the photoacoustic wave. This includes constructing and constructing one photoacoustic image as a whole by appropriately joining partial photoacoustic images together.

And in the photoacoustic image generation device according to the present invention,
The plurality of pulse lights are short pulse light having a pulse width of 1 to 10 nsec and long pulse light having a pulse width of 15 to 100 nsec,
The plurality of acoustic wave detection means are a high frequency detection means having a detection band on the high frequency side and a low frequency detection means having a detection band on a lower frequency side than the detection band of the high frequency detection means. It is preferable that the photoacoustic wave generated due to the irradiation of the light is detected and the photoacoustic wave generated due to the irradiation of the long pulse light is detected by the low frequency detection means.

In this case, the photoacoustic image generation apparatus according to the present invention further includes synchronization control means,
The light irradiation means is configured to switch the pulse width for each irradiation of the pulsed light,
The probe is configured to be driven while switching between the high frequency detection means and the low frequency detection means,
The synchronization control means preferably outputs a trigger signal to the light irradiation means and / or the probe so that the switching of the pulse width and the switching of the acoustic wave detection means are synchronized.

Alternatively, in the photoacoustic image generation apparatus according to the present invention, the light irradiation means is configured to irradiate a plurality of pulse lights simultaneously,
The plurality of acoustic wave detection means are configured such that the respective detection bands do not overlap each other,
The probe is preferably configured to drive the high frequency detection means and the low frequency detection means simultaneously.

  In the photoacoustic image generating apparatus according to the present invention, the high-frequency detection means includes a wide-band detection element and a high-pass filter that removes a signal in a frequency band equal to or lower than the detection band of the low-frequency detection means. Can do.

  Alternatively, in the photoacoustic image generation apparatus according to the present invention, the high-frequency detection means includes a wide-band detection element and a band-pass filter that transmits only a signal in a part of a frequency band higher than the detection band of the low-frequency detection means. It can consist of.

Moreover, in the photoacoustic image generating apparatus according to the present invention, the low frequency detection means is a low frequency detection element composed of lead zirconate titanate,
The broadband detection element can be composed of polyvinylidene fluoride.

  Moreover, in the photoacoustic image generating apparatus which concerns on this invention, each wavelength of several pulsed light can mutually differ.

  In the photoacoustic image generation device according to the present invention, the photoacoustic image generation means deconstructs a photodifferential waveform, which is a differential waveform of the time waveform of the light intensity of the irradiated pulsed light, from the photoacoustic signal based on the pulsed light. It is preferable to have a photodifferential waveform deconvolution means for convolution, and to generate a photoacoustic image based on the signal deconvolved by the photodifferential waveform deconvolution means.

In this case, the optical differential waveform deconvolution means is
First Fourier transform means for Fourier transforming the photoacoustic signal;
Second Fourier transform means for Fourier transforming a signal obtained by sampling the optical differential waveform at a predetermined sampling rate;
An inverse filter calculation means for obtaining an inverse filter of the inverse of the optical differential waveform subjected to Fourier transform;
Filter applying means for applying an inverse filter to the Fourier-transformed photoacoustic signal;
Inverse Fourier transform means for performing inverse Fourier transform on the photoacoustic signal to which the inverse filter is applied may be provided.

The photoacoustic signal is sampled at the first sampling rate,
The optical differential waveform is sampled at a second sampling rate higher than the first sampling rate,
The photodifferential waveform deconvolution means further comprises a resample means for resampling the photoacoustic signal sampled at the first sampling rate at the second sampling rate,
It is preferable that the first Fourier transform unit is a unit that performs Fourier transform on the photoacoustic signal resampled by the resample unit.

Alternatively, the photoacoustic signal is sampled at the first sampling rate,
The optical differential waveform is sampled at a second sampling rate higher than the first sampling rate,
The first Fourier transform means performs Fourier transform with the first number of data points,
The second Fourier transform means performs Fourier transform with a second number of data points greater than the first number of data points,
The photodifferential waveform deconvolution means performs zero padding on the Fourier-acoustic photoacoustic signal to add zero to the center by the difference between the first data point and the second data point. Further comprising
The filter application means preferably applies an inverse filter to the photoacoustic signal that has been zero-padded by the zero-padding means.

Alternatively, the photoacoustic signal is sampled at the first sampling rate,
The optical differential waveform is sampled at a second sampling rate higher than the first sampling rate,
The first Fourier transform means performs Fourier transform with the first number of data points,
The second Fourier transform means performs Fourier transform with a second number of data points greater than the first number of data points,
The optical differential waveform deconvolution means further includes high-frequency component sample point removal means for removing the high-frequency component sample points from the Fourier-transformed optical differential waveform by the difference between the first data point and the second data point. ,
It is preferable that the inverse filter calculation means obtains the inverse of the waveform obtained by removing the high frequency component sample points from the Fourier-transformed optical differential waveform as an inverse filter.

  Further, in the photoacoustic image generation apparatus according to the present invention, the photodifferential waveform deconvolution means removes the influence of the reception angle dependence characteristic of the detector that detects the photoacoustic signal from the deconvolved photoacoustic signal. As described above, it is preferable to further include correction means for correcting the deconvolved photoacoustic signal.

Further, in the photoacoustic image generating apparatus according to the present invention, the probe detects reflected ultrasonic waves with respect to ultrasonic waves transmitted to the subject,
The photoacoustic image generation apparatus may further include an ultrasonic image generation unit that generates an ultrasonic image based on an ultrasonic signal of a reflected ultrasonic wave detected by the probe.

A photoacoustic image generation method according to the present invention includes:
Irradiate the subject with multiple pulse lights with different pulse widths,
By detecting a plurality of acoustic wave detection means having different detection bands, the photoacoustic waves generated in the subject due to the irradiation of the pulsed light are separated and detected for each frequency band,
A photoacoustic image is generated based on a photoacoustic signal for each frequency band of the detected photoacoustic wave.

And in the photoacoustic image generation method according to the present invention,
The plurality of pulse lights are short pulse light having a pulse width of 1 to 10 nsec and long pulse light having a pulse width of 15 to 100 nsec,
The plurality of acoustic wave detection means are a high frequency detection means having a detection band on a relatively high frequency side and a low frequency detection means having a detection band on a lower frequency side than the detection band of the high frequency detection means,
It is preferable that the photoacoustic wave generated due to the irradiation of the short pulse light is detected by the high frequency detection means, and the photoacoustic wave generated due to the irradiation of the long pulse light is detected by the low frequency detection means.

  In particular, the photoacoustic image generation apparatus and the photoacoustic image generation method according to the present invention irradiate a subject with a plurality of pulse lights having different pulse widths, and use a plurality of acoustic wave detection units having different detection bands to generate pulsed light. The photoacoustic wave generated in the subject due to the irradiation of the light is separated and detected for each frequency band, and a photoacoustic image is generated based on the photoacoustic signal for each frequency band of the detected photoacoustic wave It is characterized by. Therefore, the photoacoustic image near the surface of the subject can be acquired with high resolution using pulsed light with a short pulse width, and the photoacoustic image at the deep part of the subject can be acquired with pulsed light with a long pulse width. can do. As a result, in the photoacoustic imaging, it is possible to acquire an image of a deep portion in the subject.

It is a block diagram which shows the structure of 1st Embodiment of the photoacoustic image generating apparatus of this invention. It is a block diagram which shows the structure of the laser unit in the photoacoustic image generating apparatus of 1st Embodiment. It is a block diagram which shows the structure of the ultrasonic probe in the photoacoustic image generating apparatus of 1st Embodiment. It is a wave form diagram which shows the pulse width dependence of the signal waveform of a photoacoustic wave (PA). It is a spectrum distribution figure which shows the pulse width dependence of the frequency spectrum distribution of a photoacoustic wave (PA) signal. It is a block diagram which shows the structure of the optical differential waveform reverse convolution means in the photoacoustic image generating apparatus of 1st Embodiment. It is a wave form diagram which shows the photoacoustic signal after a reconstruction. It is a wave form diagram which shows the photoacoustic signal FFT after FFT. It is a wave form diagram which shows an optical pulse differential waveform (h). It is a wave form diagram which shows optical pulse differential waveform FFT (fft_h) after FFT. It is a wave form diagram which shows an optical pulse differential waveform FFT filter. It is a wave form diagram which shows the FFT waveform after a deconvolution. It is a wave form diagram which shows the photoacoustic signal reversely converted. It is a figure which shows the photoacoustic image produced | generated based on the photoacoustic signal after a reconstruction. It is a figure which shows the photoacoustic image produced | generated based on the photoacoustic signal after a deconvolution. It is a flowchart which shows the operation | movement procedure of photoacoustic image generation. It is a block diagram which shows the structure of 2nd Embodiment of the photoacoustic image generation apparatus of this invention. It is a block diagram which shows the structure of the laser unit in the photoacoustic image generating apparatus of 2nd Embodiment. It is a figure which shows the structural example of the wavelength selection means in the photoacoustic image generating apparatus of 2nd Embodiment. It is a graph which shows the relationship between the wavelength and the transmittance | permeability in a transmissive area | region. It is a block diagram which shows the example of a specific structure of a part of laser unit. It is a timing chart which shows the timing of flash lamp light emission, and the timing of a pulse laser beam. It is a timing chart which shows pulse laser beam emission. It is a block diagram which shows the structure of 3rd Embodiment of the photoacoustic image generating apparatus of this invention. It is a block diagram which shows the structure of the laser unit in the photoacoustic image generating apparatus of 3rd Embodiment. It is a block diagram which shows the structure of the optical differential waveform reverse convolution means in the photoacoustic image generating apparatus of 4th Embodiment. It is a wave form diagram which shows the optical pulse differential waveform sampled with the sampling rate of 400 MHz. It is a wave form diagram which shows the optical pulse differential waveform sampled with the sampling rate of 40 MHz. It is a block diagram which shows the structure of the optical differential waveform reverse convolution means in the photoacoustic image generating apparatus of 5th Embodiment. It is a graph which shows a photoacoustic signal (frequency domain). It is a graph which shows the photoacoustic signal after zero padding. It is a block diagram which shows the structure of the optical differential waveform reverse convolution means in the photoacoustic image generating apparatus of 6th Embodiment. It is a graph which shows an optical pulse differential waveform (frequency domain). It is a graph which shows the optical pulse differential waveform from which the high frequency component sample point was removed. It is a block diagram which shows the structure of 7th Embodiment of the photoacoustic image generation apparatus of this invention.

  Hereinafter, although an embodiment of the present invention is described using a drawing, the present invention is not limited to this. In addition, for easy visual recognition, the scale of each component in the drawings is appropriately changed from the actual one.

“First Embodiment of Photoacoustic Image Generation Device”
First, a first embodiment of the photoacoustic image generation apparatus of the present invention will be described in detail. FIG. 1 is a block diagram showing the configuration of the first embodiment of the photoacoustic image generation apparatus of the present invention. FIG. 2 is a block diagram illustrating a configuration of a laser unit in the photoacoustic image generation apparatus according to the first embodiment. FIG. 3 is a block diagram illustrating a configuration of the ultrasonic probe in the photoacoustic image generation apparatus according to the first embodiment.

  Specifically, the photoacoustic image generation apparatus 10 according to the present embodiment includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser unit 13, and an image display unit 14.

<Laser unit>
The laser unit 13 emits pulsed laser light (pulsed light from a laser) to be irradiated on the subject. In the present embodiment, the laser unit 13 switches and emits a plurality of pulsed laser beams having the same wavelength but different pulse widths. The “pulse width” is a half width of a peak in the wavelength distribution of light intensity. As shown in FIG. 2, the laser unit 13 includes, for example, a laser rod 51, a flash lamp 52, mirrors 53 and 54 constituting a resonator, a Q switch (Qsw) 55, and light emission control for controlling the output of pulsed laser light. The control unit 59 includes the unit 61.

  The laser rod 51 is a laser medium. As the laser rod 51, for example, alexandrite crystal, Cr: LiSAF (Cr-doped LiSrAlF6) crystal, Cr: LiCAF (Cr-doped LiCaAlF6) crystal, or Ti-doped Sapphire crystal can be used. The flash lamp 52 is an excitation light source and irradiates the laser rod 51 with excitation light.

  The mirrors 53 and 54 are opposed to each other with the laser rod 51 interposed therebetween, and the mirrors 53 and 54 constitute an optical resonator. Here, it is assumed that the mirror 54 is an output side mirror.

  When the light emission control unit 61 receives the light trigger signal from the trigger control circuit 29 of the ultrasonic unit 12, the light emission control unit 61 controls the flash lamp 52 to be activated. When the flash lamp 52 is lit, the laser rod 51 is excited. The light output from the excited laser rod 51 is enhanced while resonating between the mirrors 53 and 54. After that, when receiving the Qsw trigger signal from the trigger control circuit 29 of the ultrasonic unit 12, the light emission control unit 61 controls to open Qsw. Then, for example, pulsed laser light is emitted from the mirror 54 side. The pulse width of the pulse laser beam is controlled by, for example, Qsw.

  The pulse width of the pulse laser beam is preferably 1 to 100 nsec. Furthermore, in order to make it easy to separate and detect the photoacoustic wave for each frequency band, a plurality of pulse laser beams include a short pulse laser beam having a pulse width of 1 to 10 nsec and a long pulse laser beam having a pulse width of 15 to 100 nsec. It is preferable to include. For example, a pulse laser beam having a pulse width of 4.2 nsec is used as the short pulse laser beam, and a pulse laser beam having a pulse width of 45 nsec is used as the long pulse laser beam.

  The wavelength of the pulse laser beam is appropriately determined depending on the light absorption characteristics of the substance in the subject to be measured. Although hemoglobin in a living body has different optical absorption characteristics depending on its state (oxygenated hemoglobin, reduced hemoglobin, methemoglobin, carbon dioxide hemoglobin, etc.), it generally absorbs light of 600 nm to 1000 nm. Therefore, for example, when the measurement target is hemoglobin in a living body (that is, when a blood vessel is imaged), it is generally preferable to set the thickness to about 600 to 1000 nm. Furthermore, from the viewpoint of reaching the deep part of the subject, the wavelength of the pulsed laser light is preferably 700 to 1000 nm.

  The laser unit 13 may be a light emitting element such as a semiconductor laser (LD), a solid-state laser, or a gas laser that generates a specific wavelength component or monochromatic light including the component.

<Probe (Ultrasonic probe)>
The probe 11 emits a photoacoustic wave (photoacoustic signal) generated when the light absorber in the subject absorbs the pulsed laser light after the subject is irradiated with the pulsed laser light emitted from the laser unit 13. To detect. The probe 11 is a plurality of acoustic wave detection means having different detection bands, and is configured to separate and detect photoacoustic waves generated in the subject due to irradiation of pulsed light for each frequency band. A plurality of acoustic wave detecting means. “Detection band” means a frequency band that includes a peak frequency having the highest sensitivity in the frequency distribution and whose sensitivity is 50% or more of the maximum sensitivity, and corresponds to a half-width of a peak in the so-called frequency distribution. It corresponds to. Further, “the detection bands are different from each other” means that the bandwidths of the detection bands are different from each other, and includes a case where some of the detection bands overlap. When one acoustic wave detection means is composed of a plurality of elements (for example, a detection element and a signal processing circuit connected in series with the detection element), the detection band takes into account all the elements and the sensitivity is high. The frequency band is 50% or more of the maximum sensitivity.

  For example, as shown in FIG. 3 in this embodiment, the probe 11 includes a wideband detection element 66 having sensitivity in a wide frequency band (for example, about 1 to 40 MHz), and a low-frequency component from a photoacoustic signal detected by the wideband detection element. A high-pass filter 67 that removes (for example, a component of 20 MHz or less), a low-frequency detection element 65 having a detection band in a relatively narrow range (for example, 5 to 12 MHz) on the relatively low frequency side, and a switching control unit 68 are included. Both the low-frequency detection element 65 and the broadband detection element 66 are ultrasonic transducers (detection elements) having an electroacoustic conversion function, but the detection bands of the respective ultrasonic waves are different.

  In the present embodiment, the wide band detection element 66 and the high pass filter 67 function as the high frequency detection means of the present invention having a detection band on the high frequency side. A typical example of the broadband detection element 66 is a piezoelectric element made of an organic material, and polyvinylidene fluoride (PVDF) is particularly preferable as the organic material. In the present embodiment, the low frequency detection element 65 corresponds to the low frequency detection means of the present invention. As the low-frequency detection element 65, for example, a piezoelectric element made of an inorganic material is representative, and as the inorganic material, lead zirconate titanate (PZT) is preferable.

  The switching control unit 68 switches the broadband detection element 66 and the low frequency detection element 65 as the detection elements to be used. Specifically, the switching control unit 68 receives the switching trigger signal from the trigger control circuit 29 serving as the synchronization control means, and synchronizes with the emission of the pulsed laser light, so that the broadband detection element 66 and the low frequency detection element 65 are synchronized. Switch. For example, in this embodiment, since a plurality of pulse laser beams having different pulse widths are switched and emitted alternately, the switching control unit 68 detects two detections in synchronization with each emission of one pulse laser beam. The element is switched.

  FIG. 4 is a waveform diagram showing the pulse width dependency of the signal waveform of the photoacoustic wave (PA). FIG. 5 is a spectrum distribution diagram showing the pulse width dependence of the frequency spectrum distribution of the photoacoustic wave (PA) signal. 4 and 5, it can be seen that as the pulse width becomes shorter, the waveform of the photoacoustic signal becomes steep, and the frequency spectrum of the photoacoustic signal extends to the high frequency side and changes to a wide band. Therefore, for example, when a PZT piezoelectric element having a center frequency in the detection band of 10 MHz is used as the low-frequency detection element 65 and a PVDF piezoelectric element having a wide detection band is used as the wideband detection element 66, the pulse width is 45 nsec. The photoacoustic signal generated due to the long pulse laser beam such as can be detected with high sensitivity by the PZT piezoelectric element, and the photoacoustic signal generated due to the short pulse laser beam having a pulse width of 4.2 nsec. The signal can be efficiently detected in a wide frequency band by the PVDF piezoelectric element. The photoacoustic signal generated due to the long pulse laser beam is mainly used as a signal when generating a photoacoustic image of the deep part of the subject, and the photoacoustic signal generated due to the short pulse laser beam is It is mainly used as a signal when generating a photoacoustic image of the vicinity of the surface of the subject.

  Thereby, the photoacoustic signal generated due to each of a plurality of pulse laser beams having different pulse widths can be detected separately for each frequency. As described above, it is possible to efficiently detect the photoacoustic signal by making use of the characteristics (intensity of detection sensitivity, width of detection band, etc.) of each of the plurality of acoustic wave detection means.

  In the present embodiment, a plurality of pulse laser beams having different pulse widths are switched and emitted alternately, so that depending on the time interval between the emission, photoacoustic generated due to a certain pulse laser beam When detecting a signal, a photoacoustic signal generated due to another pulse laser beam may not be noise. Therefore, in such a case, the high-pass filter 67 is not always necessary. Further, instead of the high pass filter, it is also possible to use a band pass filter that transmits only signals in a part of the frequency band on the higher frequency side than the detection band of the low frequency detecting means. Further, instead of the combination of the wide band detection element 66 and the high pass filter 67, a high frequency detection element having a detection band on the high frequency side that does not overlap with the detection band of the low frequency detection element 65 (for example, detection on the high frequency side of 40 MHz or higher) It is also possible to use a PZT piezoelectric element having a band.

<Ultrasonic unit>
The ultrasonic unit 12 corresponds to a photoacoustic image generation unit. The ultrasonic unit 12 includes a reception circuit 21, an AD conversion unit 22, a reception memory 23, a photoacoustic image reconstruction unit 24, a photodifferential waveform deconvolution unit 25, a correction unit 26, a detection / logarithmic conversion unit 27, and a photoacoustic image. It has a construction means 28, a trigger control circuit 29, a control means 30, and an image composition means 38.

  The receiving circuit 21 receives the photoacoustic signal detected by the probe 11. The AD conversion means 22 is a sampling means, which samples the photoacoustic signal received by the receiving circuit 21 and converts it into a digital signal. The AD conversion means 22 samples a photoacoustic signal with a predetermined sampling period based on, for example, an AD clock signal with a predetermined frequency input from the outside. The reception memory 23 stores the photoacoustic signal sampled by the AD conversion means 22. In the present embodiment, the reception memory 23 transmits the low-frequency side photoacoustic signal detected by the low-frequency detection element 65 and the high-frequency side photoacoustic signal detected by the broadband detection element 66 in two paths. The output is divided into each photoacoustic image reconstruction means 24. The signal processing performed in each of the two paths is the same. Therefore, a single signal processing system path may be used to alternately output the low frequency side photoacoustic signal and the high frequency side photoacoustic signal.

  The photoacoustic image reconstruction unit 24 reads out the photoacoustic signal from the reception memory 23 and generates data of each line of the photoacoustic image based on the photoacoustic signals detected by the plurality of ultrasonic transducers of the probe 11. . The photoacoustic image reconstruction means 24 adds, for example, data from 64 ultrasonic transducers of the probe 11 with a delay time corresponding to the position of the ultrasonic transducer, and generates data for one line (delay). Addition method). The photoacoustic image reconstruction means 24 may perform reconstruction by the BP method (Back Projection) instead of the delay addition method. Alternatively, the photoacoustic image reconstruction unit 24 may perform reconstruction using the Hough transform method or the Fourier transform method.

  The optical differential waveform deconvolution means 25 is an optical pulse differential waveform (optical differential waveform for pulsed laser light) that is a differential waveform of the time waveform of the light intensity of light irradiated on the subject from the reconstructed photoacoustic signal. To generate a deconvoluted signal. By deconvolution of the optical pulse differential waveform, the pressure distribution reconstructed at t = 0, that is, the absorption distribution can be obtained from the pressure distribution reconstructed at t ≠ 0. The optical differential waveform deconvolution means 25 may perform deconvolution on the photoacoustic signal before reconstruction. A detailed description of the deconvolution will be given later.

  The correction unit 26 corrects the signal with the optical pulse differential waveform deconvoluted, and removes the influence of the reception angle dependent characteristic of the ultrasonic transducer in the probe 11 from the signal with the optical pulse differential waveform deconvoluted. Further, the correction unit 26 removes the influence of the incident light distribution of the light on the subject from the signal obtained by deconvolution of the optical pulse differential waveform in addition to or instead of the reception angle dependency characteristic. The photoacoustic image may be generated without the correction means 26 and without performing these corrections.

  The detection / logarithm conversion means 27 obtains the envelope of the corrected data of each line, and logarithmically transforms the obtained envelope. Conventional detection methods such as Hilbert transform and quadrature detection can be used as detection means for obtaining the envelope. Thereby, the influence of the zone | band by the natural vibration of an ultrasonic transducer | vibrator can be removed. The photoacoustic image construction means 28 generates a photoacoustic image based on the data of each line subjected to logarithmic transformation. The photoacoustic image construction unit 28 generates a photoacoustic image by converting, for example, a position in the time axis direction of the photoacoustic signal (peak portion) into a position in the depth direction of the photoacoustic image.

  The image synthesis unit 38 generates a composite image of two photoacoustic images constructed by the two photoacoustic image construction units 28, for example. In the present embodiment, for example, a low-frequency photoacoustic signal is used for an image region showing a deep part of the subject, while a high-frequency photoacoustic signal is used for an image region showing a surface vicinity of the subject. As a result, a deeper image and a high resolution image can be obtained on the surface. Further, the image synthesizing unit 38 performs a necessary process (for example, scale correction) on the synthesized image and generates a final image (display image) to be displayed on the image display unit 14.

  The control means 30 controls each part in the ultrasonic unit 12. The trigger control circuit 29 sends a light trigger signal to the laser unit 13 when generating the photoacoustic image. Further, after outputting the optical trigger signal, the Qsw trigger signal is sent. Upon receiving the optical trigger signal, the laser unit 13 turns on the flash lamp 52 and starts laser excitation. When the Qsw trigger signal is input, the laser unit 13 turns on Qsw and emits pulsed laser light. The trigger control circuit 29 sends a sampling trigger signal to the AD conversion means 22 in synchronization with laser light irradiation on the subject, and controls the sampling start timing of the photoacoustic signal in the AD conversion means 22. In addition, the trigger control circuit 29 transmits a switching trigger signal to the switching control unit 68 together with the Qsw trigger signal so that the switching of the pulse width and the switching of the acoustic wave detection means are synchronized.

  FIG. 6 shows a detailed configuration of the optical differential waveform deconvolution means 25. The optical differential waveform deconvolution means 25 includes Fourier transform means 41 and 42, an inverse filter calculation means 43, a filter application means 44, and a Fourier inverse transform means 45. The Fourier transform means (first Fourier transform means) 41 converts the reconstructed photoacoustic signal from a time domain signal to a frequency domain signal by discrete Fourier transform. The Fourier transform means (second Fourier transform means) 42 converts a signal obtained by sampling the optical pulse differential waveform at a predetermined sampling rate from a time domain signal to a frequency domain signal by discrete Fourier transform. FFT (Fast Fourier Transform) can be used as the Fourier transform algorithm.

  Here, a basic algorithm for deconvolution of the optical pulse differential waveform will be described.

  First, the reconstructed photoacoustic signal is input, and the reconstructed photoacoustic signal is Fourier-transformed by FFT in the Fourier transform means 41. FIG. 7A shows the photoacoustic signal after reconstruction, and FIG. 7B shows the photoacoustic signal FFT after FFT. By performing the Fourier transform, the time domain signal shown in FIG. 7A is converted into a frequency domain signal as shown in FIG. 7B. In FIG. 7B, the absolute value of the photoacoustic signal FFT is shown, but in an actual process, it is processed as a complex number.

  The optical pulse differential waveform h is Fourier-transformed by FFT in the Fourier transform means 42. FIG. 7C shows an optical pulse differential waveform (h), and FIG. 7D shows an optical pulse differential waveform FFT (fft_h) after FFT. By performing Fourier transform, the time-domain signal (waveform) shown in FIG. 7C is converted into the frequency-domain signal shown in FIG. 7D. Note that black circles in FIG. 7C represent sampling points in the optical pulse differential waveform. In FIG. 7D, the absolute value of the optical pulse differential waveform FFT is shown, but in an actual process, it is processed as a complex number.

Then, the inverse filter calculation means 43 obtains the inverse of the post-FFT optical pulse differential waveform FFT (fft_h) obtained above as an optical pulse differential waveform FFT filter (inverse filter). Specifically, the optical pulse differential waveform FFT filter can be obtained by conj (fft_h) / abs (fft_h) ² . Here, conj (fft_h) represents the conjugate complex number of fft_h, and abs (fft_h) represents the absolute value of fft_h. FIG. 7E shows an optical pulse differential waveform FFT filter. By obtaining the reciprocal of the optical pulse differential waveform FFT shown in FIG. 7D, an optical pulse differential waveform FFT filter as shown in FIG. 7E can be obtained.

  The optical pulse differential FFT filter obtained as described above and the reconstructed photoacoustic signal FFT are multiplied for each element by the filter applying means 44, and the optical pulse differential waveform is deconvolved from the photoacoustic signal FFT. FIG. 7F shows the FFT waveform after deconvolution. By multiplying the photoacoustic signal FFT shown in FIG. 7B by the optical pulse differential waveform FFT filter shown in FIG. 7E, the FFT waveform shown in FIG. 7F is obtained.

  Then, the FFT waveform obtained by deconvolution of the optical pulse differential waveform is subjected to Fourier inverse transform by inverse FFT in the Fourier inverse transform means 45 to return the frequency domain signal to the time domain signal. FIG. 7G shows the inversely converted photoacoustic signal. By performing inverse FFT on the FFT waveform (frequency domain signal) shown in FIG. 7F, the deconvolution photoacoustic signal (time domain signal) shown in FIG. 7G is obtained. This deconvolved photoacoustic signal is an absorption distribution obtained by deconvolution of the optical pulse differential waveform from the reconstructed photoacoustic signal (FIG. 7A) in which the optical pulse differential waveform (FIG. 7C) is convolved with the optical absorption distribution. It corresponds to.

  8A shows a photoacoustic image generated based on the reconstructed photoacoustic signal (FIG. 7A), and FIG. 8B shows a photoacoustic image generated based on the deconvolved photoacoustic signal (FIG. 7G). Show. The photoacoustic image generated based on the reconstructed photoacoustic signal shown in FIG. 8A is substantially an image of the pressure distribution, and image determination such that one blood vessel is displayed in duplicate. The blood vessel position is difficult to confirm. On the other hand, the photoacoustic image generated based on the deconvolved photoacoustic signal shown in FIG. 8B can visualize the distribution of the absorber by deconvolution of the optical pulse differential waveform, It is easy to confirm the position.

  In the present embodiment, it is assumed that the sampling rate of the photoacoustic signal is equal to the sampling rate of the optical pulse differential waveform. For example, the photoacoustic signal is sampled in synchronization with a sampling clock of Fs = 40 MHz, and the photodifferential pulse is also sampled at a sampling rate of Fs_h = 40 MHz. The Fourier transform means 41 performs a Fourier transform on the photoacoustic signal sampled at 40 MHz by, for example, a 1024-point Fourier transform. Further, the Fourier transform means 42 performs Fourier transform on the optical pulse differential waveform sampled at 40 MHz by 1024 points of Fourier transform.

  FIG. 9 shows an operation procedure in the photoacoustic image generation method according to this embodiment.

  The trigger control circuit 29 outputs an optical trigger signal to the laser unit 13. The laser unit 13 turns on the flash lamp 52 in response to the light trigger signal. The trigger control circuit 29 outputs a Qsw trigger signal at a predetermined timing. When a Qsw trigger signal is input, the laser unit 13 turns on Qsw55 and emits a pulsed laser beam. The emitted pulsed laser light is guided to the probe 11, for example, and irradiated from the probe 11 to the subject (step S1).

  The probe 11 detects the photoacoustic signal generated in the subject by the laser beam irradiation after the laser beam irradiation (step S2). The receiving circuit 21 of the ultrasonic unit 12 receives the photoacoustic signal detected by the probe 11. The trigger control circuit 29 sends a sampling trigger signal to the AD conversion means 22 in accordance with the timing of light irradiation on the subject. The AD conversion means 22 receives the sampling trigger signal, starts sampling of the photoacoustic signal, and stores the sampling data of the photoacoustic signal in the reception memory 23.

  The photoacoustic image reconstruction means 24 reads the photoacoustic signal sampling data from the reception memory 23, and reconstructs the photoacoustic signal based on the read photoacoustic signal sampling data (step S3). The optical differential waveform deconvolution means 25 deconvolutes the optical pulse differential waveform obtained by differentiating the time waveform of the light intensity of the pulsed laser light applied to the subject from the reconstructed photoacoustic signal (step S4). By this deconvolution, a photoacoustic signal indicating an absorption distribution is obtained.

  The correction unit 26 corrects the signal obtained by deconvoluting the optical pulse differential waveform with the detection element reception angle dependency and the light incident distribution on the subject. The detection / logarithm conversion means 27 obtains the envelope of the photoacoustic signal corrected by the correction means 26 and logarithmically converts the obtained envelope. The photoacoustic image construction means 28 generates a photoacoustic image based on the data of each line subjected to logarithmic transformation (step S5). This photoacoustic signal is an absorption distribution image obtained by imaging the absorption distribution. After the signal processing from step 3 to step 5 described above is performed on the low-frequency side photoacoustic signal and the high-frequency side photoacoustic signal, these photoacoustic images are synthesized by the image synthesis unit 38. The image display means 14 displays the synthesized photoacoustic image that is an absorption distribution image on the display screen (step S6).

  In the present embodiment, the photoacoustic image (photoacoustic image) is first reconstructed by the photoacoustic image reconstruction means 24 as the pressure distribution at the light emission time (t = 0) by the normal reconstruction method. Next, since the light emission time is actually a finite length, the time when t = 0 at the time of reconstruction is regarded as a finite time, and the optical differential waveform deconvolution means 25 performs reconstruction after the reconstruction. The photopulse differential waveform is deconvolved from the photoacoustic image. By deconvolution of the optical pulse differential waveform, an absorption distribution can be obtained and an absorption distribution image can be generated. By adopting such a method, the absorption distribution can be imaged even when a practical light pulse width and a practical ultrasonic system or an actual living body is observed. This has the advantage that the current system detector bandwidth and AD sampling can be used. Further, in this embodiment, since the pressure distribution is once obtained by reconstructing the photoacoustic image, the compatibility with the existing ultrasonic algorithm and apparatus is high.

  As described above, the photoacoustic image generation apparatus and the photoacoustic image generation method according to the present invention particularly irradiate a subject with a plurality of pulse lights having different pulse widths, and detect a plurality of acoustic waves having different detection bands. By means of means, photoacoustic waves generated in the subject due to irradiation of pulsed light are separated and detected for each frequency band, and photoacoustic is based on the photoacoustic signal for each frequency band of the detected photoacoustic wave. An image is generated. Therefore, the photoacoustic image near the surface of the subject can be acquired with high resolution using pulsed light with a short pulse width, and the photoacoustic image at the deep part of the subject can be acquired with pulsed light with a long pulse width. can do. As a result, in the photoacoustic imaging, it is possible to acquire an image of a deep portion in the subject.

“Second Embodiment of Photoacoustic Image Generation Device”
Next, a second embodiment of the photoacoustic image generation apparatus of the present invention will be described in detail. FIG. 10 is a block diagram showing the configuration of the second embodiment of the photoacoustic image generation apparatus of the present invention. FIG. 11 is a block diagram illustrating a configuration of a laser unit in the photoacoustic image generation apparatus according to the second embodiment. This embodiment is different from the first embodiment in that the laser unit 13 switches a plurality of pulsed laser beams having different pulse widths and wavelengths and emits them alternately. Therefore, a detailed description of the same components as those in the first embodiment will be omitted unless particularly necessary.

  The photoacoustic image generation apparatus 10 of this embodiment includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser unit 13, and an image display unit 14.

<Laser unit>
The laser unit 13 switches a plurality of pulsed laser beams having different pulse widths and wavelengths and emits them alternately. Thereby, it becomes possible to separate and detect photoacoustic signals from a plurality of tissues having different absorption characteristics for each frequency band. “The wavelengths are different from each other” means that the peak wavelengths having the highest light intensity in the wavelength distribution are different from each other. The wavelength of the pulse laser beam is appropriately determined depending on the light absorption characteristics of the substance in the subject to be measured. For example, using a pulse laser beam having a pulse width of 4.2 nsec and a wavelength of 800 nm and a pulse laser beam having a pulse width of 45 nsec and a wavelength of 750 nm, and based on the intensity ratio of the acquired photoacoustic signal of each wavelength It is possible to separate and image the artery and vein inside the living body.

  The laser unit 13 as described above can be configured as follows, for example. As shown in FIG. 11, the laser unit 13 includes a laser rod 51, a flash lamp 52, mirrors 53 and 54, a condenser lens 55, a wavelength selection unit 56, a drive unit 57, a drive state detection unit 58, and a control unit 59. Have

  A condensing lens 55 and a wavelength selection unit 56 are disposed in the optical resonator composed of the mirrors 53 and 54. The wavelength selection unit 56 controls the wavelength of light resonating in the optical resonator to any one of a plurality of wavelengths to be emitted. The condenser lens 55 is disposed between the laser rod 51 and the wavelength selection unit 56, converges the light incident from the laser rod 51 side, and emits the light to the wavelength selection unit 56 side. That is, the condensing lens 55 reduces the beam diameter of the light traveling toward the wavelength selection unit 56 in the optical resonator.

  The wavelength selection unit 56 includes, for example, a plurality of transmission regions and non-transmission regions that are alternately arranged along the circumferential direction. The plurality of transmission regions selectively transmit light having predetermined wavelengths corresponding to the plurality of wavelengths. The wavelength selection means 56 has, for example, two transmission regions and two non-transmission regions. For example, a first band pass filter (BPF) that transmits light having a wavelength of 750 nm (center wavelength) is provided in one of the transmission regions, and a wavelength of 800 nm (center wavelength) is provided in the other. A second band-pass filter that transmits the light is provided.

  The wavelength selection means 56 having the above configuration selectively inserts any one of a plurality of band pass filters on the optical path of the optical resonator as it rotates. For example, the wavelength selection unit 56 sequentially inserts a non-transmission region → a first bandpass filter → a non-transmission region → a second bandpass filter on the optical path of the optical resonator. By inserting the first bandpass filter on the optical path of the optical resonator, the oscillation wavelength of the optical oscillator can be set to 750 nm, and by inserting the second bandpass filter on the optical path of the optical resonator. The oscillation wavelength of the optical oscillator can be 800 nm.

  The wavelength selection means 56 is configured to change the insertion loss in the optical resonator from a large loss (first loss) to a small loss (second loss) in accordance with the rotational drive. When the first or second bandpass filter is inserted on the optical path of the optical resonator, the insertion loss of the optical resonator is small (high Q), and when an opaque region is inserted on the optical path, The insertion loss of the resonator is large (low Q). The wavelength selection unit 56 also serves as Qsw, and the wavelength selection unit 56 rapidly changes the insertion loss in the optical resonator from a large loss (low Q) to a small loss (high Q) with rotation driving. Thus, a pulsed laser beam can be obtained.

  The driving unit 57 drives the wavelength selecting unit 56 so that the optical resonator oscillates in a Qsw pulse. That is, the drive unit 57 drives the wavelength selection unit 56 so that the wavelength selection unit 56 rapidly changes the insertion loss in the optical resonator from a large loss (low Q) to a small loss (high Q). For example, when the wavelength selection unit 56 is configured by a filter rotating body in which transmission regions (bandpass filters) and non-transmission regions are alternately arranged along the circumferential direction, the driving unit 57 is on the optical path of the optical resonator. The filter rotator is continuously rotated so that the opaque regions and the transparent regions are alternately inserted into the filter. The switching time when the insertion loss in the optical resonator is switched from high loss to low loss due to the driving of the wavelength selection unit 56 is preferably shorter than the Qsw pulse generation delay time. By switching the region inserted on the optical path of the optical resonator from the non-transmissive region to the transmissive region (first or second bandpass filter), the transmissive region (bandpass filter) inserted on the optical path is transmitted. The optical resonator can be subjected to Qsw pulse oscillation at a wavelength corresponding to the wavelength of the light to be generated.

  The drive state detection unit 58 detects the drive state of the wavelength selection unit 56. The drive state detection means 58 detects the rotational displacement of the wavelength selection means 56 that is a filter rotator, for example. The drive state detection means 58 outputs BPF state information indicating the rotational displacement of the filter rotator to the control unit 59 as a BPF state signal.

  The control unit 59 includes a rotation control unit 60 and a light emission control unit 61. The rotation control unit 60 controls the driving unit 58 so that the wavelength selection unit 56 rotates at a predetermined rotation speed. The rotational speed of the wavelength selection unit 56 is based on, for example, the number of wavelengths of pulsed laser light to be emitted from the laser unit 13 (number of bandpass filters in the filter rotating body) and the number of pulsed laser light per unit time. Can be determined. The rotation control unit 59 controls the drive unit 57 so that the amount of change per predetermined time of the rotation position detected by the drive state detection unit 58 is constant. For example, the rotation control unit 59 controls the driving unit 57 so that the amount of change in the BPF state information during a predetermined time becomes a change amount according to a predetermined band-pass filter switching speed (rotational speed of the filter rotating body). Control.

  The light emission control unit 61 controls the flash lamp 52. The light emission control unit 61 outputs a flash lamp (FL) control signal to the flash lamp 52 and irradiates the laser rod 51 with excitation light from the flash lamp 52. The light emission control unit 61 outputs the FL control signal to the flash lamp 52 at a time that is a predetermined time before the time when the wavelength selection unit 56 switches the insertion loss of the optical resonator from the large loss to the small loss. Irradiate. In other words, the light emission control unit 61 detects that the rotational position detected by the drive state detection unit 58 is a predetermined amount before the rotational position where the wavelength selection unit 56 switches the insertion loss of the optical resonator from the large loss to the small loss. When the position is reached, an FL control signal is sent to the flash lamp 52 to irradiate the excitation light.

  For example, the light emission control unit 61 determines that the information represented by the BPF state signal indicates that the laser beam from the driving position of the wavelength selection unit 56 in which a bandpass filter corresponding to the wavelength of the pulsed laser beam to be emitted is inserted on the optical path of the optical resonator When information indicating the position obtained by subtracting the amount of displacement of the wavelength selection means 56 during the time required for excitation of the rod 51 is output, an FL control signal is output, and the laser lamp 51 is irradiated with excitation light from the flash lamp 52. After the output of the FL control signal, the light emission control unit 61 detects that the rotation position detected by the drive state detection unit 58 is a rotation position where the wavelength selection unit 56 switches the insertion loss of the optical resonator from a large loss to a small loss. A Qsw synchronization signal indicating the timing when Qsw is turned on is generated and output to the ultrasound unit 12.

  Returning to FIG. 10, the control means 30 controls each part in the ultrasonic unit 12. The trigger control circuit 29 outputs a BPF control signal for controlling the rotation speed of the wavelength selection unit 56 to the laser unit 13. The trigger control circuit 29 outputs an FL standby signal for controlling the light emission of the flash lamp 52 to the laser unit 13. For example, the trigger control circuit 29 receives the current rotational displacement position of the filter rotating body from the rotation control unit 60 of the laser unit 13 and outputs an FL standby signal at a timing based on the received rotational displacement position.

  The trigger control circuit 29 receives from the laser unit 13 a Qsw synchronization signal indicating the timing at which Qsw is turned on, that is, the laser emission timing. When receiving the Qsw synchronization signal, the trigger control circuit 29 outputs a sampling trigger signal to the AD conversion means 22. The AD conversion unit 22 starts sampling of the photoacoustic signal based on the sampling trigger signal.

  FIG. 12 shows a configuration example of the wavelength selection unit 56. The wavelength selection unit 56 is configured as a filter rotating body 70 including a plurality of transmission regions (bandpass filters) having different transmission wavelengths as shown in FIG. 12, for example. The filter rotating body 70 includes a first transmission region 71 that selectively transmits light having a wavelength of 750 nm, a second transmission region 72 that selectively transmits light having a wavelength of 800 nm, and a non-transmission region 73 that does not transmit light. , 74. The non-transparent area is not required to have the ability to completely block light. The light may be slightly transmitted to such an extent that unnecessary laser oscillation does not occur.

  The first transmissive region 71 and the second transmissive region 72 are formed, for example, in fan shapes with central angles θ1 and θ2, respectively. The magnitudes of the central angles θ1 and θ2 are appropriately set according to the length of the pulse width of the pulse laser beam having each wavelength. The light condensed by the condensing lens 55 is irradiated to the peripheral portion of the filter rotating body 70 as shown in FIG. When the filter rotating body 70 is rotated clockwise, the first transmission region 71, the non-transmission region 73, the second transmission region 72, and the non-transmission region 74 can be inserted in this order on the optical path of the optical resonator. As described above, the first transmission region 71 and the second transmission region 72 change the wavelength of light transmitted through each region, that is, by changing the transmission wavelength of the bandpass filter provided in each transmission region, It is possible to obtain pulsed laser beams having different wavelengths.

  FIG. 13 shows the relationship between wavelength and transmittance in the transmission region. It is assumed that the transmittance of the first transmission region (first bandpass filter) 71 with respect to light having a center wavelength of 750 nm is 90% or more. Its bandwidth is approximately 10 nm. In the second transmission region (second bandpass filter) 72, the transmittance with respect to light having a central wavelength of 800 nm is 90% or more. Its bandwidth is approximately 10 nm.

  Here, it is assumed that the rotation frequency of the filter rotating body 70 is 100 Hz (rotational speed 6000 rpm). In this case, since the laser beam passes through two transmission regions per rotation, the number of pulsed laser beams emitted from the laser unit 13 is 200 per second (200 Hz operation). For example, a filter rotating body having a radius of 2 inches (50.4 mm) is considered as the filter rotating body 70. The beam diameter is 100 μm. The angular velocity is ω = 2πf = 628.3 [rad / sec], and the linear velocity is v = rω = 628.8 [rad / sec] × 50.4 [mm] = 31.7 [m / s]. The time for crossing the beam (switching time) is 3.15 μsec.

  As a characteristic of Qsw, the switching time (for example, the switching time from the non-transmissive region to the first or second transmissive region) is approximately several microseconds or less (smaller than the generation delay time of the Qsw pulse). This is a condition for obtaining a pulse. The central angle θ of the transmission region is selected on the condition that the beam is not disturbed during the time of traversing the beam + Qsw delay time. In the above numerical example, the transmissive region may be continued for 3.15 μsec + several μsec = approximately 10 μsec. Therefore, 31.7 [m / s] × 10 μsec = 317 μm is the width of the width, and 0.35 ° in angle. Considering the production, the central angle θ should be 1 ° to several degrees.

  FIG. 14 shows a part of the laser unit 13. The wavelength selection unit 56 is configured as a filter rotating body 70 including two band-pass filters (two transmission regions having different wavelengths of transmitted light) as shown in FIG. 12, for example. The beam diameter on the filter rotator 70 should be small. Therefore, in the present embodiment, the beam is converged using the condenser lens 55. The beam diameter on the filter rotating body 70 is desirably 100 μm or less. The lower limit is determined by the diffraction limit and is several μm. The filter rotator 70 may be tilted by, for example, about 0.5 ° to 1 ° with respect to the optical axis so as to rotate in a plane inclined at a predetermined angle with respect to the optical axis of the optical resonator. preferable. In this way, by arranging it slightly oblique to the optical axis of the optical resonator, it is possible to prevent unnecessary reflection components from causing parasitic oscillation.

  The drive unit 57 is, for example, a servo motor, and rotates the wavelength selection unit 56 (filter rotating body 70) along the rotation axis. The rotation frequency of the filter rotating body 70 is preferably higher. Mechanically, it can be up to about 1 kHz. The drive state detection means 58 is composed of, for example, a rotary encoder. The rotary encoder detects the rotational displacement of the filter rotator with a slit-type rotating plate attached to the output shaft of the servo motor and a transmission type photo interrupter, and the rotation of the filter rotator 70 is converted into an electrical signal (BPF state signal). Convert. This BPF state signal is used as a master clock and sent to the light emission control unit 61 as a synchronization signal. The light emission control unit 61 determines the flash lamp light emission timing in accordance with the rotation of the filter rotating body 70 rotating with high accuracy.

  FIG. 15 shows the timing of flash lamp light emission and the timing of pulsed laser light. The time t2 is assumed to be a time corresponding to a rotational position at which the rotating filter rotating body 70 (wavelength selection means 56) switches from the non-transmissive region to the transmissive region. Time t1 is the time obtained by subtracting the time required for excitation of the laser rod 51 from time t2. The light emission control unit 61 causes the flash lamp 52 to emit light when the rotation position of the filter rotator 70 reaches a position corresponding to time t1 ((a) of FIG. 15). When the flash lamp 52 emits light, the laser rod 51 is excited.

  After the flash lamp emission, at time t2, the filter rotator 70 is switched from the non-transmissive area to the transmissive area (the first transmissive area 71 or the second transmissive area 72) at approximately the same time that the flash lamp is extinguished. (FIG. 15B). The time required for switching from the non-transmissive region to the transmissive region (switching time) is preferably as short as possible, and is several μsec or less, more desirably 0.5 μsec or less. When a transmission region that transmits light of 750 nm is inserted on the optical path of the optical resonator, light having a wavelength of 750 nm oscillates at time t3 and pulse laser light having a wavelength of 750 nm is obtained ((c in FIG. 15). )). On the other hand, when the transmissive region inserted on the optical path of the optical resonator is a transmissive region that transmits light having a wavelength of 800 nm, light having a wavelength of 800 nm oscillates in a Qsw pulse, and pulse laser light having a wavelength of 800 nm is obtained. After the transmission region portion of the filter rotator 70 continues for about 10 μsec, the filter rotator 70 switches to the non-transmission region again at time t4.

  FIG. 16 shows pulsed laser beam emission. As shown in FIG. 16, when the filter rotating body 70 in which the first transmission region 71 and the second transmission region 72 are provided between the non-transmission regions 73 and 74 as shown in FIG. It is possible to switch between a pulse laser having a wide pulse width of 750 nm and a pulse laser beam having a narrow pulse width of 800 nm for each pulse. If the rotation frequency of the filter rotator is 100 Hz, 200 pulsed laser beams can be obtained per second while alternately switching the pulse width and wavelength.

  An operation procedure of the photoacoustic image generation apparatus 10 will be described. The trigger control circuit 29 outputs to the laser unit 13 a BPF control signal for rotating the wavelength selection means 56 in the laser unit 13 at a predetermined rotation speed prior to the irradiation of the pulse laser beam on the subject.

  When the trigger control circuit 29 is ready to receive the photoacoustic signal, the trigger control circuit 29 outputs an FL standby signal to the laser unit 13 at a predetermined timing so as to emit a pulse laser beam having the first wavelength (for example, 750 nm). After receiving the FL standby signal, the light emission control unit 61 of the laser unit 13 sends the FL control signal to the flash lamp 52 to turn on the flash lamp 52. Based on the BPF state signal, the light emission control unit 61, for example, a timing calculated backward from the timing at which the rotational displacement position of the wavelength selection unit 56 is switched from the non-transmissive region 74 to the first transmissive region 71 that transmits light having a wavelength of 750 nm. Then, the FL control signal is output. When the flash lamp 52 is turned on, excitation of the laser rod 51 is started.

  After the flash lamp is turned on, the wavelength selection means 56 continues to rotate, and when the portion inserted on the optical path of the optical resonator is switched from the non-transmissive region 74 to the first transmissive region 71, the insertion loss in the optical resonator is increased. Changes rapidly from a large loss (low Q) to a small loss (high Q), and Qsw pulse oscillation occurs. At this time, since the first transmission region 71 selectively transmits light having a wavelength of 750 nm, the laser unit 13 emits pulsed laser light having a wavelength of 750 nm. The light emission control unit 61 outputs to the ultrasound unit 12 a Qsw synchronization signal indicating the timing when Qsw is turned on, in other words, the timing when the pulse laser beam is emitted.

  A pulse laser beam having a wavelength of 750 nm emitted from the laser unit 13 is guided to, for example, the probe 11 and irradiated from the probe 11 to the subject. Then, the low-frequency detection element 65 of the probe 11 detects a photoacoustic signal generated due to a pulse laser beam having a long pulse width and a wavelength of 750 nm. The photoacoustic signal detected by the probe 11 is received by the receiving circuit 21.

  Then, an FL standby signal is output from the trigger control circuit 29 to the laser unit 13 in order to emit the next pulsed laser light having a wavelength of 800 nm. The light emission control unit 61 sends an FL control signal to the flash lamp 52 to turn on the flash lamp 52. After the flash lamp is turned on, the portion inserted on the optical path of the optical resonator is switched from the non-transmissive region 73 to the second transmissive region 72 corresponding to the wavelength of 800 nm, and Qsw pulse oscillation occurs. Thereby, pulsed laser light with a wavelength of 800 nm is emitted. The light emission control unit 61 outputs a Qsw synchronization signal to the ultrasonic unit 12.

  The pulsed laser light having a wavelength of 800 nm emitted from the laser unit 13 is guided to, for example, the probe 11 and irradiated from the probe 11 to the subject. The broadband detection element 66 of the probe 11 detects a photoacoustic signal generated due to a pulse laser beam having a short pulse width and a wavelength of 800 nm.

  The image synthesis unit 38 generates a composite image of two photoacoustic images constructed by the two photoacoustic image construction units 28, for example. In the present embodiment, the region representing the artery and the region representing the vein are color-coded based on the acquired intensity ratio of the photoacoustic signal of each wavelength. Thereby, the arteries and veins can be identified. Further, the image synthesizing unit 38 performs a necessary process (for example, scale correction) on the synthesized image and generates a final image (display image) to be displayed on the image display unit 14.

“Third Embodiment of Photoacoustic Image Generating Device”
Next, a third embodiment of the photoacoustic image generation apparatus of the present invention will be described in detail. FIG. 17 is a block diagram showing the configuration of the third embodiment of the photoacoustic image generation apparatus of the present invention. FIG. 18 is a block diagram illustrating a configuration of a laser unit in the photoacoustic image generation apparatus according to the third embodiment. This embodiment is different from the first embodiment in that the laser unit 13 is composed of a plurality of light sources that emit pulsed laser beams having different pulse widths and wavelengths. Therefore, a detailed description of the same components as those in the first embodiment will be omitted unless particularly necessary.

  The photoacoustic image generation apparatus 10 of this embodiment includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser unit 13, and an image display unit 14.

<Laser unit>
The laser unit 13 simultaneously emits a plurality of pulsed laser beams having different pulse widths and wavelengths. Thereby, it becomes possible to separate and detect photoacoustic signals from a plurality of tissues having different absorption characteristics for each frequency band. The wavelength of the pulse laser beam is appropriately determined depending on the light absorption characteristics of the substance in the subject to be measured. For example, using a pulse laser beam having a pulse width of 4.2 nsec and a wavelength of 800 nm and a pulse laser beam having a pulse width of 45 nsec and a wavelength of 750 nm, and based on the intensity ratio of the acquired photoacoustic signal of each wavelength It is possible to separate and image the artery and vein inside the living body.

  The laser unit 13 as described above can be configured as follows, for example. As shown in FIG. 18, the laser unit 13 includes a light source 13a that emits a pulse laser beam having a pulse width of 4.2 nsec and a wavelength of 800 nm, and a light source 13b that emits a pulse laser beam having a pulse width of 45 nsec and a wavelength of 750 nm. Consists of The configurations of the light sources 13a and 13b are the same as those in the first embodiment. The light sources 13a and 13b receive the light trigger signal from the trigger control circuit 29, and turn on the flash lamps 52a and 52b. When the Qsw trigger signal is input after the flash lamps 52a and 52b are turned on, the light sources 13a and 13b turn on Qsw 55a and 55b, respectively, and emit pulsed laser beams.

<Probe (Ultrasonic probe)>
The probe 11 simultaneously detects two photoacoustic signals generated due to the respective pulsed laser beams after the subject is irradiated with the two pulsed laser beams emitted from the laser unit 13. Such a probe 11 removes a low-frequency component (for example, a component of 20 MHz or less) from a photoacoustic signal detected by, for example, a broadband detection element having sensitivity in a wide frequency band (for example, about 1 to 40 MHz) and the broadband detection element. And a low-frequency detection element having a detection band in a narrow range (for example, 5 to 12 MHz) on the relatively low frequency side. That is, the probe 11 in this embodiment has a configuration in which the switching control unit 68 is removed from the probe as shown in FIG. With such a configuration, a photoacoustic signal generated due to a long pulse laser beam having a pulse width of 45 nsec can be detected with high sensitivity by the low-frequency detection element, and a pulse width of 4.2 nsec is detected. A photoacoustic signal generated due to such a short pulse laser beam can be efficiently detected in a wide frequency band by the broadband detection element. In the present embodiment, it is necessary to remove a low-frequency component from the photoacoustic signal detected by the wideband detection element. Therefore, when using the wideband detection element, a high-pass filter is essential. However, as in the first embodiment, when a high-frequency detection element having a detection band on the high frequency side that does not overlap with the detection band of the low-frequency detection element is used, a high-pass filter is not necessary.

  Pulse laser beams with wavelengths of 800 nm and 750 nm respectively emitted from the light sources 13a and 13b are guided to the probe 11, for example, and are irradiated from the probe 11 to the subject. Then, the photoacoustic signal generated due to the pulse laser beam having a short pulse width of 800 nm is detected by the broadband detection element of the probe 11, and the low frequency detection element is caused by the pulse laser beam having a long pulse width of wavelength 800nm. The photoacoustic signal generated is detected. As described above, in this embodiment, the photoacoustic wave generated due to each of the irradiations of the plurality of pulsed laser beams can be detected at the same time, so that the image construction speed can be improved.

  The image synthesis unit 38 generates a composite image of two photoacoustic images constructed by the two photoacoustic image construction units 28, for example. In the present embodiment, the region representing the artery and the region representing the vein are color-coded based on the acquired intensity ratio of the photoacoustic signal of each wavelength. Thereby, the arteries and veins can be identified. Further, the image synthesizing unit 38 performs a necessary process (for example, scale correction) on the synthesized image and generates a final image (display image) to be displayed on the image display unit 14.

“Fourth Embodiment of Photoacoustic Image Generating Device”
Next, a fourth embodiment of the photoacoustic image generation apparatus of the present invention will be described in detail. In the first embodiment, the sampling rate of the photoacoustic signal coincides with the sampling rate of the optical pulse differential waveform, and both signals are Fourier-transformed with the same number of data points. In this embodiment, the photoacoustic signal is sampled at low speed, while the optical pulse differential waveform is sampled at high speed. That is, the sampling rate of the optical pulse differential waveform is set higher than the sampling rate of the photoacoustic signal. For example, the sampling interval of the photoacoustic signal (the reciprocal of the sampling rate) is set longer than the pulse time width of the light irradiated to the subject. In the Fourier transform, the photoacoustic signal sampled at the low sampling rate is resampled (upsampled) at the same sampling rate as the sampling rate of the optical pulse differential waveform, and then the Fourier transform is performed. Therefore, the configuration itself of the photoacoustic image generation apparatus is the same as that of the first embodiment except for the optical differential waveform deconvolution means. In description of this embodiment, the code | symbol shown by FIG. 1 is used about elements other than an optical differential waveform deconvolution means. A detailed description of the same components as those in the first embodiment will be omitted unless particularly required.

  The photoacoustic image generation apparatus 10 of this embodiment includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser unit 13, and an image display unit 14.

  FIG. 19 shows the optical differential waveform deconvolution means 25a in this embodiment. The optical differential waveform deconvolution means 25a in the present embodiment has resample means 46 and 47 in addition to the configuration of the optical differential waveform deconvolution means 25 in the first embodiment shown in FIG. The resample means 46 is an upsample means and resamples the sampling data of the photoacoustic signal sampled at a low sampling rate at the same sampling rate as the sampling rate of the optical pulse differential waveform (upsample). The resampling means 46 performs upsampling, for example, by adding zero between sample points of the photoacoustic signal sampled at a low sampling rate and applying a low-pass filter that cuts at the Nyquist frequency before upsampling.

  For example, it is assumed that the photoacoustic signal sampling rate (first sampling rate) in the AD conversion means 22 is 40 MHz and the optical pulse differential waveform sampling rate (second sampling rate) is 400 MHz. In this case, the resampling means 46 upsamples the 40 MHz photoacoustic signal to a 400 MHz signal. The Fourier transform unit 41 performs a Fourier transform on the photoacoustic signal upsampled by the resample unit 46. The Fourier transform means 41 for Fourier transforming the photoacoustic signal and the Fourier transform means 42 for Fourier transforming the optical pulse differential waveform perform Fourier transform with the same number of data points. For example, the Fourier transform unit 41 converts the photoacoustic signal into a signal in the frequency region of 8192 points, and the Fourier transform unit 42 converts the optical pulse differential waveform into a signal in the frequency region of 8192 points.

  The filter application unit 44 applies an inverse filter to a signal obtained by Fourier transforming the upsampled photoacoustic signal. The Fourier inverse transform means 45 transforms the signal to which the inverse filter is applied from a frequency domain signal into a time domain signal (absorption distribution). The absorption distribution signal returned to the time domain signal is a signal in a state of being upsampled to, for example, 400 MHz. The resampling means 47 downsamples the absorption signal to the original sampling rate of the photoacoustic signal. The resampling unit 47 downsamples, for example, a 400 MHz absorption signal into a 40 MHz absorption signal. Downsampling is performed, for example, by thinning sample points after applying a low-pass filter that cuts at the Nyquist frequency after downsampling.

  FIG. 20A shows an optical pulse differential waveform sampled at a sampling rate of 400 MHz, and FIG. 20B shows an optical pulse differential waveform sampled at a sampling rate of 40 MHz. At a sampling rate of 400 MHz, the optical pulse differential waveform can be accurately reproduced as shown in FIG. 20A. On the other hand, if the sampling rate of the optical pulse differential waveform is matched with the sampling rate of the photoacoustic signal and sampling is performed at 40 MHz, the optical pulse differential waveform cannot be accurately reproduced as shown in FIG. 20B.

  When the inverse filter is applied to the signal obtained by Fourier transforming the photoacoustic signal by the filter applying means 44, it is necessary to have both data points. When the sampling rate of the optical pulse differential waveform is set in accordance with the sampling rate of the photoacoustic signal, as shown in FIG. 20B, the sampling frequency is too low for the waveform change, and the optical pulse differential waveform cannot be accurately reproduced. When an inverse filter obtained from such an optical pulse differential waveform is applied, the optical pulse differential term may not be accurately deconvolved, and the absorption distribution may not be obtained correctly.

  On the other hand, if the sampling rate of the optical pulse differential waveform is set to 400 MHz, for example, and the photoacoustic signal sampling rate is set to 400 MHz in order to accurately reproduce the optical pulse differential waveform, the optical pulse differential term is accurately Volume can be obtained, and absorption distribution can be obtained correctly. However, in that case, a high-speed AD converter is required for the AD conversion means 22, and the total number of sampling data increases, so that the memory capacity required for the reception memory 23 increases. Furthermore, since the data handled by the photoacoustic image reconstruction means 24 increases, the time required for reconstruction also increases.

  In the present embodiment, the resampler 46 resamples the sampling data of the photoacoustic signal afterwards. In this embodiment, since the photoacoustic signal after detection is upsampled by signal processing, the optical pulse differential term can be accurately deconvolved while performing low-speed sampling from photoacoustic detection to reconstruction. . In the present embodiment, a high-speed AD converter is not necessary for the AD conversion means 22 and the memory capacity required for the reception memory 23 does not increase. Further, the time required for reconstructing the photoacoustic signal does not increase, and the processing time can be shortened as compared with the case of sampling at a high sampling rate when detecting the photoacoustic signal.

“Fifth Embodiment of Photoacoustic Image Generating Device”
Next, a fifth embodiment of the photoacoustic image generation apparatus of the present invention will be described in detail. In the present embodiment, similarly to the fourth embodiment, the sampling rate of the optical pulse differential waveform is set higher than the sampling rate of the photoacoustic signal. In the fourth embodiment, a photoacoustic signal sampled at a low sampling rate is upsampled, and both signals are Fourier transformed with the same number of data points. In the present embodiment, the Fourier transform of the optical pulse differential waveform is performed with more data points than the Fourier transform data points of the photoacoustic signal, and the Fourier transform photoacoustic signal is centered by the difference in the data points. A zero point is added to (high frequency component region). Therefore, the configuration itself of the photoacoustic image generation apparatus is the same as that of the first embodiment except for the optical differential waveform deconvolution means. In description of this embodiment, the code | symbol shown by FIG. 1 is used about elements other than an optical differential waveform deconvolution means. A detailed description of the same components as those in the first embodiment will be omitted unless particularly required.

  The photoacoustic image generation apparatus 10 of this embodiment includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser unit 13, and an image display unit 14.

  FIG. 21 shows the optical differential waveform deconvolution means 25b in this embodiment. The optical differential waveform deconvolution means 25b in this embodiment includes a zero padding means 48 and a zero point removal means 49 in addition to the configuration of the optical differential waveform deconvolution means 25 in the first embodiment shown in FIG. Have. For example, it is assumed that the sampling rate of the photoacoustic signal (first sampling rate) is 40 MHz, and the sampling rate of the optical pulse differential waveform (second sampling rate) is 320 MHz. For example, the Fourier transform means 41 converts a photoacoustic signal of 40 MHz into a signal in the frequency domain of 1024 points (first data point), and the Fourier transform means 42 converts the optical pulse differential waveform of 320 MHz to 8192 points (second Converted to a frequency domain signal. The second data score is equal to or greater than the data score obtained by multiplying the first data score by the ratio of the second sampling rate and the first sampling rate.

  The zero padding means 48 inputs the photoacoustic signal converted from the Fourier transform means 41 into a frequency domain signal. Zero padding means 48 adds a zero point (point of zero signal value) to the center by the difference between the number of data points of the photoacoustic signal after Fourier transform and the optical pulse differential waveform to the photoacoustic signal subjected to Fourier transform. To do. The zero padding means 48 divides, for example, a photoacoustic signal having 1024 data points expressed in the frequency domain into two at the Nyquist frequency (1/2 of the sampling frequency), and data between the divided two frequency domains. A zero point is added by the difference in the number of points, and a photoacoustic signal having the same number of data points 8192 as the number of data points of the optical pulse differential waveform expressed in the frequency domain is generated. The addition of the zero point corresponds to upsampling in the frequency domain.

  The filter applying unit 44 applies an inverse filter to the signal that has been subjected to zero padding by the zero padding unit 48. The zero point removing unit 49 removes the frequency band to which “0” is added by the zero padding unit 48 from the signal to which the inverse filter is applied. For example, when the photoacoustic signal (frequency domain) having 1024 data points is converted into a signal having 8192 data points by the zero padding unit 48, the zero point removing unit 49 uses the signal after applying the filter (data points 8192 points). ) To a signal having 1024 data points. Zero point removal corresponds to downsampling in the frequency domain. The inverse Fourier transform means 45 converts the signal returned to the number of data points of 1024 from a frequency domain signal to a time domain signal.

  FIG. 22A shows a photoacoustic signal subjected to Fourier transform, and FIG. 22B shows a photoacoustic signal after zero padding. For example, when the sampling rate of the photoacoustic signal in the AD conversion means 22 is 40 MHz, a signal obtained by Fourier transforming the photoacoustic signal becomes a signal in a frequency band from 0 MHz to 40 MHz as shown in FIG. 22A. This signal is divided into two regions A and B with a center frequency of 20 MHz as a boundary. As shown in FIG. 22B, the zero padding means 48 inserts 8192-1024 = 7168 zero points between two regions. As a result of adding the zero point, the signal in the region B becomes a signal corresponding to the frequency region from 300 MHz to 320 MHz.

  In the present embodiment, a photoacoustic signal sampled at a low sampling rate is converted into a frequency domain signal, and a zero point in the high frequency component area of the converted frequency domain signal is added. The difference between the present embodiment and the second embodiment is that the photoacoustic signal is upsampled in the second embodiment, whereas the photoacoustic signal is upsampled in the frequency domain in the present embodiment. is there. Even when resampling (up-sampling) is performed so as to fill the band difference between both signals in the frequency domain instead of the time domain, low-speed sampling is performed from photoacoustic detection to reconstruction as in the second embodiment. However, the optical pulse differential term can be accurately deconvolved.

“Sixth Embodiment of Photoacoustic Image Generation Device”
Next, a sixth embodiment of the photoacoustic image generation apparatus of the present invention will be described in detail. Also in this embodiment, the sampling rate of the optical pulse differential waveform is set higher than the sampling rate of the photoacoustic signal, as in the fourth and fifth embodiments. In the present embodiment, the optical pulse differential waveform is performed with more data points than the Fourier transform data points of the photoacoustic signal, the high frequency component sample points are removed from the Fourier transformed optical differential waveform, and the inverse is used as an inverse filter. Ask. Therefore, the configuration itself of the photoacoustic image generation apparatus is the same as that of the first embodiment except for the optical differential waveform deconvolution means. In description of this embodiment, the code | symbol shown by FIG. 1 is used about elements other than an optical differential waveform deconvolution means. A detailed description of the same components as those in the first embodiment will be omitted unless particularly required.

  The photoacoustic image generation apparatus 10 of this embodiment includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser unit 13, and an image display unit 14.

  FIG. 23 shows the optical differential waveform deconvolution means 25c in this embodiment. The optical differential waveform deconvolution means 25c in this embodiment has a high frequency component sample point removal means 50 in addition to the configuration of the optical differential waveform deconvolution means 25 in the first embodiment shown in FIG. For example, it is assumed that the sampling rate of the photoacoustic signal (first sampling rate) is 40 MHz, and the sampling rate of the optical pulse differential waveform (second sampling rate) is 320 MHz. For example, the Fourier transform means 41 converts a photoacoustic signal of 40 MHz into a signal in the frequency domain of 1024 points (first data point), and the Fourier transform means 42 converts the optical pulse differential waveform of 320 MHz to 8192 points (second Converted to a frequency domain signal. The second data score is equal to or greater than the data score obtained by multiplying the first data score by the ratio of the second sampling rate and the first sampling rate.

  The high frequency component sample point removing means 50 receives the optical pulse differential waveform converted from the Fourier transform means 42 into a frequency domain signal. The high frequency component sample point removing means 50 removes the high frequency component sample points from the Fourier transformed optical pulse differential waveform by the difference between the number of data points of the photoacoustic signal after Fourier transformation and the optical pulse differential waveform. The high frequency component sample point removing means 50 deletes the central data point corresponding to the high frequency component from, for example, the optical pulse differential waveform having 8192 data points represented in the frequency domain, and the photoacoustic signal data represented in the frequency domain. An optical pulse differential waveform having the same number of data points as 1024 points is generated. The removal of the high frequency component sample points corresponds to downsampling of the optical pulse differential waveform in the frequency domain.

  FIG. 24A shows an optical pulse differential waveform obtained by Fourier transform, and FIG. 24B shows an optical pulse differential waveform from which high-frequency component sample points are removed. For example, when the sampling rate of the optical pulse differential waveform is 320 MHz, a signal obtained by Fourier transforming the optical pulse differential waveform (8192 data points) is a signal in a frequency band from 0 MHz to 320 MHz as shown in FIG. 24A. Become. This signal is divided into the region from the first data point to the 512th region (region A), the region from the 513th data point to the 7680th data point (region B), and the 8192nd from the 7681st data point. The area is divided into three areas up to the data point (area C), and the data points in area B are removed. As shown in FIG. 24B, by connecting region A and region C, an optical pulse differential waveform having 1024 data points corresponding to the frequency band from 0 MHz to 40 MHz can be obtained.

  The inverse filter calculation means 43 obtains the inverse of the optical pulse differential waveform expressed in the frequency domain and from which the high frequency component sample points are removed as an inverse filter. The inverse filter calculation unit 43 obtains, as an inverse filter, the inverse of the optical pulse differential waveform in which the data points are reduced from 8192 points to 1024 points, for example. The filter application unit 44 multiplies, for each element, a photoacoustic signal having 1024 data points represented in the frequency domain and an inverse filter, for example. The Fourier inverse transform means 45 transforms the signal to which the inverse filter is applied from a frequency domain signal to a time domain signal.

  Here, in the sixth embodiment, the filter application unit 44 multiplies the photoacoustic signal in which the zero point is added to the high-frequency component region shown in FIG. 22B and the inverse of the optical pulse differential waveform shown in FIG. 24A. . Since the value of the high-frequency component region of the photoacoustic signal is “0”, the high-frequency component of the optical pulse differential waveform (region B in FIG. 24A) does not affect the photoacoustic signal after application of the inverse filter. Therefore, as in this embodiment, the high frequency component sampling points are removed from the frequency domain signal of the optical pulse differential waveform, the inverse filter is obtained from the optical pulse differential waveform from which the high frequency component has been removed, and the obtained inverse filter is obtained in the frequency domain. Even when applied to the represented photoacoustic signal, the obtained result is the same as that of the fifth embodiment. That is, also in this embodiment, the same effect as the fifth embodiment can be obtained.

“Seventh Embodiment of Photoacoustic Image Generation Device”
Next, a seventh embodiment of the photoacoustic image generation apparatus of the present invention will be described in detail. FIG. 25 is a block diagram showing a configuration of the seventh embodiment of the photoacoustic image generation apparatus. This embodiment is different from the first embodiment in that an ultrasonic image is generated in addition to the photoacoustic image. Therefore, a detailed description of the same components as those in the first embodiment will be omitted unless particularly necessary.

  The photoacoustic image generation apparatus 10 of this embodiment includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser unit 13, and an image display unit 14.

<Ultrasonic unit>
In addition to the configuration of the photoacoustic image generation apparatus shown in FIG. 1, the ultrasound unit of the present embodiment includes a transmission control circuit 33, a data separation unit 34, an ultrasound image reconstruction unit 35, a detection / logarithm conversion unit 36, and Ultrasonic image construction means 37 is provided.

  In the present embodiment, in addition to detecting a photoacoustic signal, the probe 11 performs output (transmission) of ultrasonic waves to the subject and detection (reception) of reflected ultrasonic waves from the subject with respect to the transmitted ultrasonic waves. As the ultrasonic transducer for transmitting and receiving ultrasonic waves, the ultrasonic transducer included in the acoustic wave detecting means of the present invention may be used, or a new probe 11 provided in the probe 11 for transmitting and receiving ultrasonic waves. A simple ultrasonic transducer may be used. In addition, transmission and reception of ultrasonic waves may be separated. For example, ultrasonic waves may be transmitted from a position different from the probe 11, and reflected ultrasonic waves with respect to the transmitted ultrasonic waves may be received by the probe 11.

  When generating an ultrasonic image, the trigger control circuit 29 sends an ultrasonic transmission trigger signal to the transmission control circuit 33 to instruct ultrasonic transmission. When receiving the trigger signal, the transmission control circuit 33 transmits an ultrasonic wave from the probe 11. The probe 11 detects the reflected ultrasonic wave from the subject after transmitting the ultrasonic wave.

  The reflected ultrasonic wave detected by the probe 11 is input to the AD conversion means 22 via the receiving circuit 21. The trigger control circuit 29 sends a sampling trigger signal to the AD conversion means 22 in synchronization with the timing of ultrasonic transmission to start sampling of reflected ultrasonic waves. Here, the reflected ultrasonic waves reciprocate between the probe 11 and the ultrasonic reflection position, whereas the photoacoustic signal is one way from the generation position to the probe 11. Since the detection of the reflected ultrasonic wave takes twice as long as the detection of the photoacoustic signal generated at the same depth position, the sampling clock of the AD conversion means 22 is half the time when the photoacoustic signal is sampled, for example, It may be 20 MHz. The AD conversion means 22 stores the reflected ultrasound sampling data in the reception memory 23. Either detection (sampling) of the photoacoustic signal or detection (sampling) of the reflected ultrasonic wave may be performed first.

  The data separation unit 34 separates the photoacoustic signal sampling data and the reflected ultrasound sampling data stored in the reception memory 23. The data separation unit 34 inputs the sampling data of the separated photoacoustic signal to the photoacoustic image reconstruction unit 24. The signal processing path may be changed according to the pulse width of the pulsed laser beam, and the generation of the photoacoustic image (absorption distribution image) including the deconvolution of the optical pulse differential waveform is the same as in the first embodiment. is there. The data separation unit 34 inputs the separated reflected ultrasound sampling data to the ultrasound image reconstruction unit 35.

  The ultrasonic image reconstruction unit 35 generates data of each line of the ultrasonic image based on the reflected ultrasonic waves (its sampling data) detected by the plural ultrasonic transducers of the probe 11. For the generation of the data of each line, a delay addition method or the like can be used as in the generation of the data of each line in the photoacoustic image reconstruction means 24. The detection / logarithm conversion means 36 obtains the envelope of the data of each line output from the ultrasonic image reconstruction means 35 and logarithmically transforms the obtained envelope.

  The ultrasonic image construction unit 37 generates an ultrasonic image based on the data of each line subjected to logarithmic transformation. The ultrasonic image reconstruction unit 35, the detection / logarithm conversion unit 36, and the ultrasonic image construction unit 37 constitute an ultrasonic image generation unit that generates an ultrasonic image based on the reflected ultrasonic waves.

  The image synthesizing unit 38 synthesizes the photoacoustic image and the ultrasonic image. The image composition unit 38 performs image composition by superimposing a photoacoustic image and an ultrasonic image, for example. The synthesized image is displayed on the image display means 14. It is also possible to display the photoacoustic image and the ultrasonic image side by side on the image display means 14 without performing image synthesis, or to switch between the photoacoustic image and the ultrasonic image.

  In the present embodiment, the photoacoustic image generation apparatus generates an ultrasonic image in addition to the photoacoustic image. By referring to the ultrasonic image, a portion that cannot be imaged in the photoacoustic image can be observed. Similar to the first embodiment, the absorption distribution can be imaged by deconvolution of the optical pulse differential waveform. In addition, the generation of ultrasonic images and the generation of photoacoustic images can share most of the algorithms such as image reconstruction, detection and logarithmic conversion, and the FPGA circuit configuration and software can be simplified. Has the above advantages.

  In each of the above embodiments, the photoacoustic signal and the optical pulse differential waveform are converted into a frequency domain signal and returned to a time domain signal after deconvolution in the frequency domain. However, the present invention is not limited to this. It is also possible to perform deconvolution of the optical pulse differential waveform in the time domain. Further, the optical differential waveform deconvolution means 25 may perform a process of applying some filter to the photoacoustic signal at the time of deconvolution. For example, the optical differential waveform deconvolution means 25 may filter the noise amplification frequency band at the time of deconvolution.

  In each of the above embodiments, the photoacoustic image (absorption distribution image) is generated after deconvolution of the photodifferential waveform from the photoacoustic signal, but in addition to or instead of this, the photodifferential waveform is deconvolved. A photoacoustic image (pressure distribution image) may be generated without the volume. For example, the user can select whether or not to perform the deconvolution process by performing an operation on the switch or the display monitor, and when the user selects to perform the deconvolution process, the photodifferential waveform is deconvolved. When the photoacoustic image is generated above and the user selects not to perform the deconvolution process, the photoacoustic image may be generated without performing the deconvolution of the photodifferential waveform. For example, when deconvolution of the photodifferential waveform is performed, the photoacoustic signal is displayed in association with red and black colors. When there is no deconvolution, the photoacoustic signal is associated with blue and black colors. It may be displayed.

  Further, a photoacoustic image without deconvolution is generated, and the computer analyzes the photoacoustic image to determine whether or not the blood vessel portion is divided into two, and the blood vessel is divided into two. When it is determined that, the deconvolution processing of the optical differential waveform may be performed only on the blood vessel portion. At that time, the display color of the blood vessel part that has undergone the deconvolution process is different from the display color of the other unprocessed blood vessel part, and the blood vessel that has undergone the deconvolution process and the other unprocessed blood vessel It may be possible to easily discriminate.

10: Photoacoustic image generation device 11: Probe 12: Ultrasonic unit 13: Laser unit 14: Image display means 21: Reception circuit 22: AD conversion means 23: Reception memory 24: Photoacoustic image reconstruction means 25, 25a, 25b 25c: optical differential waveform deconvolution means 26: correction means 27: detection / logarithmic conversion means 28: photoacoustic image construction means 29: trigger control circuit 30: control means 33: transmission control circuit 34: data separation means 35: super Sound image reconstruction means 36: detection / logarithm conversion means 37: ultrasonic image construction means 38: image synthesis means 41, 42: Fourier transform means 43: inverse filter calculation means 44: filter application means 45: Fourier inverse transform means 46, 47: Resample means 48: Zero padding means 49: Zero point removing means 50: High frequency component sample point removing means 51: Laser lock 52: flash lamp 53, 54: mirror 55: condenser lens 56: wavelength selection means 57: drive means 58: drive state detection means 59: controller 60: rotation controller 61; light emission controller 70: filter rotator 71 72: Transmission region 73, 74: Non-transmission region

Claims (17)

A light irradiation means for irradiating the subject with a plurality of pulse lights having different pulse widths;
A plurality of acoustic wave detection means having different detection bands, wherein the plurality of acoustic wave detection means are configured to separate and detect photoacoustic waves generated in the subject due to irradiation of pulsed light for each frequency band. A probe having the acoustic wave detecting means of
A photoacoustic image generation device comprising: a photoacoustic image generation unit configured to generate a photoacoustic image based on a photoacoustic signal for each frequency band of the photoacoustic wave detected by the plurality of acoustic wave detection units. . The plurality of pulse lights are short pulse light having a pulse width of 1 to 10 nsec and long pulse light having a pulse width of 15 to 100 nsec,
The plurality of acoustic wave detection means are a high frequency detection means having a detection band on a high frequency side and a low frequency detection means having a detection band on a lower frequency side than the detection band of the high frequency detection means, and the high frequency detection means The photoacoustic wave generated due to the irradiation of the short pulse light is detected, and the photoacoustic wave generated due to the irradiation of the long pulse light is detected by the low frequency detecting means. The photoacoustic image generating apparatus according to claim 1, wherein: A synchronization control means;
The light irradiation means is configured to switch the pulse width for each irradiation of pulsed light,
The probe is configured to be driven while switching the high frequency detection means and the low frequency detection means,
The synchronization control means outputs a trigger signal to the light irradiation means and / or the probe so that switching of the pulse width and switching of the acoustic wave detection means are synchronized. Item 3. The photoacoustic image generation apparatus according to Item 2. The light irradiation means is configured to irradiate the plurality of pulse lights simultaneously,
The plurality of acoustic wave detection means are configured such that the detection bands do not overlap each other,
3. The photoacoustic image generation apparatus according to claim 2, wherein the probe is configured to drive the high-frequency detection unit and the low-frequency detection unit simultaneously.   5. The high-frequency detection unit includes a wide-band detection element and a high-pass filter that removes a signal in a frequency band equal to or lower than a detection band of the low-frequency detection unit. The photoacoustic image generating apparatus described in 1.   The high-frequency detection means includes a wide-band detection element and a band-pass filter that transmits only signals in a part of the frequency band on the high-frequency side with respect to the detection band of the low-frequency detection means. The photoacoustic image generating apparatus in any one of Claim 1 to 4. The low frequency detection means is a low frequency detection element composed of lead zirconate titanate,
The photoacoustic image generation apparatus according to claim 5 or 6, wherein the broadband detection element is made of polyvinylidene fluoride.   The photoacoustic image generating apparatus according to any one of claims 1 to 7, wherein wavelengths of the plurality of pulse lights are different from each other.   The photoacoustic image generating means has a photodifferential waveform deconvolution means for deconvoluting a photodifferential waveform, which is a differential waveform of the time waveform of the light intensity of the irradiated pulsed light, from the photoacoustic signal based on the pulsed light. 9. The photoacoustic image generation apparatus according to claim 1, wherein the photoacoustic image is generated based on a signal deconvolved by the photodifferential waveform deconvolution means. The optical differential waveform deconvolution means comprises:
First Fourier transform means for Fourier transforming the photoacoustic signal;
Second Fourier transform means for Fourier transforming a signal obtained by sampling the optical differential waveform at a predetermined sampling rate;
An inverse filter calculating means for obtaining an inverse filter of the inverse of the optical differential waveform that has undergone Fourier transform;
Filter applying means for applying the inverse filter to the photoacoustic signal that has undergone Fourier transform;
The photoacoustic image generating apparatus according to claim 9, further comprising a Fourier inverse transform unit that performs Fourier inverse transform on the photoacoustic signal to which the inverse filter is applied. The photoacoustic signal is sampled at a first sampling rate;
The optical differential waveform is sampled at a second sampling rate higher than the first sampling rate;
The optical differential waveform deconvolution means further comprises resample means for resampling the photoacoustic signal sampled at the first sampling rate at the second sampling rate,
11. The photoacoustic image generation apparatus according to claim 10, wherein the first Fourier transform means performs Fourier transform on the photoacoustic signal resampled by the resample means. The photoacoustic signal is sampled at a first sampling rate;
The optical differential waveform is sampled at a second sampling rate higher than the first sampling rate;
The first Fourier transform means performs Fourier transform with a first number of data points;
The second Fourier transform means performs Fourier transform with a second number of data points greater than the first number of data points;
The optical differential waveform deconvolution means performs zero padding for adding 0 to the center by the difference between the first data point and the second data point for the Fourier-transformed photoacoustic signal. Further comprising zero padding means to perform,
The photoacoustic image generation apparatus according to claim 10, wherein the filter applying unit applies the inverse filter to the photoacoustic signal that has been subjected to zero padding by the zero padding unit. The photoacoustic signal is sampled at a first sampling rate;
The optical differential waveform is sampled at a second sampling rate higher than the first sampling rate;
The first Fourier transform means performs Fourier transform with a first number of data points;
The second Fourier transform means performs Fourier transform with a second number of data points greater than the first number of data points;
The optical differential waveform deconvolution means removes a high frequency component sample point from the Fourier-transformed optical differential waveform by the difference between the first data point and the second data point. Further comprising means,
11. The photoacoustic image generation according to claim 10, wherein the inverse filter calculation means obtains an inverse of a waveform obtained by removing high-frequency component sampling points from the Fourier-differentiated optical differential waveform as the inverse filter. apparatus.   The photoacoustic image generation means corrects the deconvolved photoacoustic signal so as to remove the influence of the reception angle dependent characteristic of the detector that detects the photoacoustic signal from the deconvolved photoacoustic signal. The photoacoustic image generating apparatus according to claim 9, further comprising a correcting unit that performs the correction. The probe detects reflected ultrasonic waves with respect to ultrasonic waves transmitted to the subject;
The photoacoustic image generation according to claim 1, further comprising an ultrasonic image generation unit that generates an ultrasonic image based on an ultrasonic signal of the reflected ultrasonic wave detected by the probe. apparatus. Irradiate the subject with multiple pulse lights with different pulse widths,
By detecting a plurality of acoustic wave detection means having different detection bands, the photoacoustic waves generated in the subject due to irradiation of pulsed light are separated and detected for each frequency band,
A photoacoustic image generation method characterized by generating a photoacoustic image based on a photoacoustic signal for every frequency band of the photoacoustic wave detected. The plurality of pulse lights are short pulse light having a pulse width of 1 to 10 nsec and long pulse light having a pulse width of 15 to 100 nsec,
The plurality of acoustic wave detection means are a high frequency detection means having a detection band on a relatively high frequency side and a low frequency detection means having a detection band on a lower frequency side than the detection band of the high frequency detection means,
The photoacoustic wave generated due to the irradiation of the short pulse light is detected by the high frequency detection means, and the photoacoustic wave generated due to the irradiation of the long pulse light is detected by the low frequency detection means. The photoacoustic image generation method according to claim 16.