JP2013128760A - Photoacoustic image generation device and photoacoustic image generation method - Google Patents

Abstract

In photoacoustic imaging, a photoacoustic image representing an absorption distribution of a light absorber can be generated from a photoacoustic signal.
A probe 11 having a light emitting portion 13 and an ultrasonic transducer 60, a position information acquisition means 15 for acquiring spatial information defining the position and orientation of the probe 11 in real space, and a probe 11 detect the position. And photoacoustic image generation means 12 for generating tomographic data and / or volume data for the photoacoustic signal using the photoacoustic signal of the photoacoustic wave and the spatial information acquired by the position information acquisition means 15. The photoacoustic image generation means 12 includes a photodifferential waveform deconvolution means 25 that deconvolutes a photodifferential waveform, which is a differential waveform of the time waveform of the light intensity of the measurement light, from the photoacoustic signal, and includes tomographic data and / or It is assumed that the deconvolved photoacoustic signal is used when generating the volume data.
[Selection] Figure 1

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. 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).

  Further, as in Patent Document 1, for example, the acoustic wave receiver is moved relative to the subject to receive the acoustic wave, and the information inside the subject is two-dimensional or three-dimensional based on the received signal. It is known to acquire as an image.

JP 2011-125571 A

  However, conventional reconstruction methods (for example, the Fourier domain method (FTA method), delay addition method (Delay & Sum method), etc.) substantially only image the pressure distribution, and light generated by such a method is used. The acoustic image does not represent the absorption distribution of the light absorber. In the photoacoustic image obtained by imaging the pressure distribution, one blood vessel may be displayed twice, and it may be difficult to confirm the position of the blood vessel for image determination. In addition, when calculating images acquired in a plurality of different directions and a plurality of different wavelengths, there is a problem that the position is easily shifted and an appropriate result cannot be obtained.

  The present invention has been made in view of the above problems, and in photoacoustic imaging, a photoacoustic image generation apparatus and a photoacoustic image that can generate a photoacoustic image representing an absorption distribution of a light absorber from a photoacoustic signal. The object is to provide an image generation method.

In order to solve the above problems, a photoacoustic image generation apparatus according to the present invention includes:
A light emitting section for emitting measurement light toward the subject, and a probe having an acoustic detection element for detecting a photoacoustic wave generated in the subject due to the emission of the measurement light;
Position information acquisition means for acquiring spatial information defining the position and / or orientation of the probe in real space;
Photoacoustic image generation means for generating tomographic data and / or volume data for the photoacoustic signal using the photoacoustic signal of the photoacoustic wave detected by the probe and the spatial information acquired by the position information acquisition means; With
The photoacoustic image generating means has photodifferential waveform deconvolution means for deconvoluting a photodifferential waveform, which is a differential waveform of the time waveform of the light intensity of the measuring light, from the photoacoustic signal, and tomographic data and / or volume data is obtained. In the generation, the photoacoustic signal deconvoluted by the optical differential waveform deconvolution means is used.

  In the photoacoustic image generation apparatus according to the present invention, it is preferable that the optical differential waveform deconvolution unit further includes an optical differential waveform acquisition unit that acquires the optical differential waveform of the measurement light.

Moreover, in the photoacoustic image generating apparatus according to the present invention, the photodifferential 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;
It is preferable to have a Fourier inverse transform means for performing Fourier inverse transform on the photoacoustic signal to which the inverse filter is applied.

In this case, 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, in the above case, 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, in the above case, 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 device according to the present invention, the photodifferential waveform deconvolution means generates the photodifferential waveform from the photoacoustic signal corresponding to the light of each wavelength when the measurement light includes light of a plurality of wavelengths. To generate a deconvolved signal,
It is preferable that the photoacoustic image generation means further includes a two-wavelength data calculation means for calculating the signals after deconvolution corresponding to the light of each wavelength.

  Further, in the photoacoustic image generation apparatus according to the present invention, the photoacoustic image generation means removes the influence of the reception angle dependency characteristic of the detector that detects the photoacoustic signal from the deconvolved photoacoustic signal. It is preferable to further include correction means for correcting the deconvolved photoacoustic signal.

The photoacoustic image generation apparatus according to the present invention further includes an observation method selection unit that selects an observation method of volume data,
The photoacoustic image generation means preferably generates a photoacoustic image based on the volume data and according to the observation method selected by the observation method selection means.

  In the photoacoustic image generating apparatus according to the present invention, it is preferable that the position information acquisition unit includes a magnetic sensor unit and acquires spatial information using the magnetic sensor unit.

Further, in the photoacoustic image generating apparatus according to the present invention, the probe detects a reflected acoustic wave with respect to the acoustic wave transmitted to the subject,
It is preferable that the photoacoustic image generation apparatus further includes a reflected acoustic wave image generation unit that generates a reflected acoustic wave image based on the reflected acoustic wave signal of the reflected acoustic wave detected by the probe.

A photoacoustic image generation method according to the present invention includes:
Using a photoacoustic image generation apparatus provided with a probe having a light emitting part and an acoustic detection element,
Detect photoacoustic waves generated in the subject due to the emission of measurement light,
Obtaining spatial information defining the position and / or orientation of the probe in real space;
Deconvolute the photodifferential waveform, which is the differential waveform of the time waveform of the light intensity of the measurement light, from the photoacoustic signal of the photoacoustic wave,
The deconvolved photoacoustic signal and the spatial information are used to generate tomographic data and / or volume data for the photoacoustic signal.

  In the photoacoustic image generation method according to the present invention, the deconvolution includes a Fourier transform of a photoacoustic signal, a Fourier transform of a signal obtained by sampling the optical differential waveform at a predetermined sampling rate, and a Fourier transformed optical differential waveform. Preferably, the inverse filter is obtained as an inverse filter, the inverse filter is applied to the Fourier-transformed photoacoustic signal, and the photoacoustic signal to which the inverse filter is applied is inversely Fourier-transformed.

  In this case, when the photoacoustic signal is sampled at the first sampling rate and the optical differential waveform is sampled at the second sampling rate higher than the first sampling rate, the first The photoacoustic signal sampled at the sampling rate can be resampled at the second sampling rate, and the resampled photoacoustic signal can be Fourier transformed.

  Alternatively, when the photoacoustic signal is sampled at the first sampling rate and the photodifferential waveform is sampled at the second sampling rate higher than the first sampling rate, the Fourier of the photoacoustic signal is obtained. A photoacoustic signal that has been converted by the first data points, Fourier-transformed a signal obtained by sampling the photodifferential waveform at a predetermined sampling rate, by a second data point that is larger than the first data points, and Fourier-transformed On the other hand, zero padding is performed to add 0 to the center by the difference between the first data point and the second data point, and the inverse filter is applied to the photoacoustic signal subjected to zero padding. be able to.

  Alternatively, when the photoacoustic signal is sampled at the first sampling rate and the photodifferential waveform is sampled at the second sampling rate higher than the first sampling rate, the Fourier of the photoacoustic signal is obtained. An optical differential waveform obtained by performing a Fourier transform on a signal obtained by performing conversion at a first data point and sampling an optical differential waveform at a predetermined sampling rate with a second data point greater than the first data point. Is obtained by removing the high frequency component sample points by the difference between the first data point and the second data point, and obtaining the inverse of the optical differential waveform after removing the high frequency component sample points as the inverse filter. it can.

  Further, in the photoacoustic image generation method according to the present invention, when the measurement light includes light of a plurality of wavelengths, a signal obtained by deconvolution of the optical differential waveform from the photoacoustic signal corresponding to the light of each wavelength is generated, It is preferable to perform arithmetic processing on signals after deconvolution corresponding to light of each wavelength.

  In particular, the photoacoustic image generation apparatus and the photoacoustic image generation method according to the present invention deconvolutes a photodifferential waveform, which is a differential waveform of a time waveform of the light intensity of measurement light, from the photoacoustic signal of the photoacoustic wave, and deconvolutes The tomographic data and / or volume data for the photoacoustic signal is generated using the photoacoustic signal and the spatial information. Therefore, the conventional photoacoustic signal representing the pressure distribution in the propagation process of the pressure wave can be converted into a photoacoustic signal representing the absorption distribution of the light absorber. As a result, in photoacoustic imaging, a photoacoustic image representing the absorption distribution of the light absorber can be generated from the photoacoustic signal.

It is a block diagram which shows the structure of 1st Embodiment of the photoacoustic image generating apparatus of this invention. It is the schematic which shows the example of the scanning aspect of a probe. It is the schematic which shows the example of the display aspect of a photoacoustic image. 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 the optical differential waveform reverse convolution means in the photoacoustic image generating apparatus of 2nd 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 3rd 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 4th 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 5th Embodiment of the photoacoustic image generating apparatus of this invention. It is a block diagram which shows the structure of 6th Embodiment of the photoacoustic image generating 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 order to facilitate 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.

  Specifically, the photoacoustic image generation apparatus 10 of the present embodiment includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser unit 13, an image display unit 14, a position information acquisition unit 15, and an input unit 16. Is provided.

<Laser unit>
The laser unit 13 emits laser light to be irradiated on the subject as measurement light. Laser light emitted from the laser unit 13 is guided to the probe 11 using light guide means such as an optical fiber, and is irradiated from the probe 11 to the subject. This laser unit 13 corresponds to a light emitting part in the present invention. For example, in the present embodiment, the laser unit 13 is a Q-switched laser including a flash lamp 31 that is an excitation light source and a Q switch 32 that controls laser oscillation. When the trigger control circuit 29 outputs an optical trigger signal, the laser unit 13 turns on the flash lamp 31 and excites the Q switch laser.

  The laser unit 13 preferably outputs pulsed light having a pulse width of 1 to 100 nsec as laser light. The wavelength of the laser light is appropriately determined according to the light absorption characteristics of the substance in the subject to be measured. In general, hemoglobin in a living body absorbs light of 360 to 1000 nm, although the optical absorption characteristics differ depending on the state (oxygenated hemoglobin, deoxygenated hemoglobin, methemoglobin, etc.). Therefore, when measuring hemoglobin in a living body, it is preferable to set the thickness to about 600 to 1000 nm with relatively little absorption of other biological substances. Further, from the viewpoint of reaching the deep part of the subject in the living body, the wavelength of the 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 detects a photoacoustic wave (photoacoustic signal) generated when the light absorber in the subject absorbs the laser light after the subject is irradiated with the laser light emitted from the laser unit 13. . The probe 11 has, for example, a plurality of ultrasonic transducers (vibrator array) arranged one-dimensionally or two-dimensionally. The probe 11 is a hand-held probe, and is configured to be manually scanned by an operator. This ultrasonic transducer corresponds to the acoustic detection element in the present invention.

  FIG. 2 is a schematic diagram illustrating an example of a scanning mode of the probe. FIGS. 2A and 2B show scanning modes in the array direction (direction in which the ultrasonic transducers are arranged) of the transducer array 60 arranged in one dimension. FIG. 2a shows a state in which the transducer array 60 is scanned such that an axis 61 perpendicular to the array direction and directed into the subject rotates in the array direction A around a region 62 to be imaged. . FIG. 2b shows a state in which the transducer array 60 is scanned in the array direction B within a plane defined by the array direction and the elevation direction (direction perpendicular to both the array direction and the axis 61). . On the other hand, FIGS. 2c to 2e show scanning modes in the elevation direction of the transducer array 60 arranged one-dimensionally. FIG. 2 c shows a state in which the transducer array 60 is scanned in the elevation direction C within a plane defined by the array direction and the elevation direction. FIG. 2d shows a state in which the transducer array 60 is scanned in the direction D with the axis 61 passing through the center of the transducer array 60 as the rotation axis. 2e shows a state in which the transducer array 60 is scanned such that an axis 61 that is perpendicular to the array direction and goes into the subject rotates in the elevation direction E around the region 62 to be imaged. Show. The above scanning mode is merely a basic mode of scanning, and actual scanning is performed by appropriately combining the above scanning modes. Further, the scanning is not limited to manual scanning, and may be performed by a mechanical mechanism.

<Position information acquisition means>
The position information acquisition means 15 sequentially acquires spatial information (hereinafter simply referred to as position information) that defines the position and orientation of the probe 11 in the real space while detecting the photoacoustic signal while the probe 11 is scanned. To do. This position information is used when generating volume data based on the photoacoustic signal. The start or end of acquisition of position information is controlled by a position trigger signal from the trigger control circuit 29. The acquired position information is transmitted to the reception memory 23 after being associated with the photoacoustic signal detected at the position. The position information acquisition unit 15 includes a magnetic sensor unit having a magnetic field generator and a plurality of magnetic sensors, for example, and the magnetic sensor is incorporated into the probe 11. In the space on the pulsed magnetic field formed by the magnetic field generation unit, the magnetic sensor unit includes relative position coordinates (x, y, z) of the magnetic sensor with respect to the magnetic field generation unit, and attitude information (angles (α, β, γ) information) can be obtained. The position information acquisition unit 15 may be configured to acquire position information using an acceleration sensor or an infrared sensor in addition to the magnetic sensor unit.

<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. A construction unit 28, a trigger control circuit 29, a control unit 30, an image composition unit 38, and an observation method selection unit 39 are included.

  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. The reception memory 23 also stores the position information of the probe 11 acquired by the position information acquisition unit 15. In this embodiment, the reception memory 23 outputs the photoacoustic signal detected by the probe 11 to the photoacoustic image reconstruction unit 24.

  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 unit 28 generates a photoacoustic image (tomographic data) for one frame 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 observation method selection means 39 is for selecting a display mode of the photoacoustic image. Examples of the volume data display mode for the photoacoustic signal include a mode as a three-dimensional image, a mode as a cross-sectional image based on tomographic data, and a mode as a graph on a predetermined axis. The display mode is selected according to the initial setting or the input from the input means 16 by the operator.

  The image synthesizing unit 38 generates volume data using the photoacoustic signal and the position information obtained by deconvolution of the optical pulse differential waveform obtained at each position. The volume data is generated by assigning the signal value of each photoacoustic signal to a calculation space (virtual space) according to the positional information associated therewith. When assigning signal values, if the locations to be assigned overlap, for example, the average value of the signal values or the maximum value among them is adopted as the signal value of the overlapping location. Further, if there is no signal value to be assigned, it is preferable to interpolate using the peripheral signal values as necessary. Interpolation is performed, for example, by assigning weighted average values of four adjacent points in order from the closest point to the interpolation location. As a result, more natural volume data can be generated. Further, the image composition unit 38 performs necessary processing (for example, scale correction and coloring according to the voxel value) on the generated volume data.

  In addition, the image composition unit 38 generates a photoacoustic image according to the observation method selected by the observation method selection unit 39. FIG. 3 is a schematic diagram illustrating an example of a display mode of a photoacoustic image. FIG. 3A is a three-dimensional image 63a showing the value of the volume data when viewed from a predetermined viewpoint in the virtual space. When a method for observing a three-dimensional absorption distribution is selected by the observation method selection means 39, a three-dimensional image 63a as shown in FIG. 3a is displayed. The viewpoint in the virtual space that defines the three-dimensional image 63a is set in the observation method selection means 39, for example, as an initial setting or by an input from the input means 16 by the operator, and this information is also transmitted to the image composition means 38. The FIG. 3B is a cross-sectional image 63b showing the value of volume data in a cross section by a predetermined two-dimensional plane. When a method for observing a two-dimensional absorption distribution is selected by the observation method selection means 39, a cross-sectional image 63b as shown in FIG. 3b is displayed. The two-dimensional plane that defines the cross-sectional image 63b is set in the observation method selection unit 39, for example, as an initial setting or by input from the input unit 16 by the operator, and this information is also transmitted to the image synthesis unit 38. FIG. 3c is a graph 63c showing the value of the volume data along a predetermined one-dimensional axis. When a method of observing a one-dimensional absorption distribution is selected by the observation method selection means 39, a graph 63c as shown in FIG. 3c is displayed. The one-dimensional axis that defines the graph 63c is set in the observation method selection unit 39, for example, as an initial setting or by an input from the input unit 16 by an operator, and this information is also transmitted to the image synthesis unit 38.

  The photoacoustic image generated according to the selected observation method becomes the final image (display image) to be displayed on the image display means 14.

  In the above-described photoacoustic image generation method, it is naturally possible for the operator to rotate or move the image as necessary after the photoacoustic image is once generated. That is, when a three-dimensional image as shown in FIG. 3a is displayed, the photoacoustic image is recalculated by the operator sequentially specifying or moving the viewpoint direction using the input means 16. As a result, the three-dimensional image is rotated. It is also possible for the operator to change the observation method as appropriate using the input means 16.

  The image display means 14 displays the display image generated by the image composition means 38.

  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, a Q switch trigger signal is sent. Upon receiving the optical trigger signal, the laser unit 13 turns on the flash lamp 31 and starts laser excitation. When a Q switch trigger signal is input, the laser unit 13 turns on the Q switch 32 and emits 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.

  FIG. 4 shows a detailed configuration of the optical differential waveform deconvolution means 25. The optical differential waveform deconvolution means 25 includes optical differential waveform acquisition means 40, Fourier transform means 41 and 42, inverse filter calculation means 43, filter application means 44, and Fourier inverse transform means 45. The optical differential waveform acquisition means 40 acquires an optical pulse differential waveform. The optical differential waveform acquisition means 40 reads the optical pulse differential waveform from, for example, a memory. Instead of this, a time waveform of the light intensity of the light applied to the subject may be read from the memory, and it may be time differentiated. Further, the optical pulse differential waveform may be obtained by measuring the time waveform of the light intensity of the light irradiated to the subject and differentiating the measurement result with respect to time. Further, the function represents a time waveform of the light intensity of the pulsed light irradiated to the subject or a differential waveform thereof, and a function having the pulse width of the pulsed light as an independent variable, and the pulse light irradiated to the subject. An optical pulse differential waveform may be obtained using the measurement result of the pulse width. 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, the basic algorithm of deconvolution in the present invention will be outlined.

  Conventionally, several techniques for generating an absorption distribution image instead of a pressure distribution image have been known so far. For example, Japanese Patent Laid-Open No. 3-156362 (hereinafter referred to as Patent Document 2) obtains an inverse filter that repairs resolution degradation of a photoacoustic image from a thermal impulse response of a sample, and applies the inverse filter to the obtained photoacoustic image. By doing so, it is described that an ideal photoacoustic image, that is, thermal impedance information (= a set of point heat sources that are infinitely small) that is excited and detected by a point light source on the sample surface is obtained. Has been.

  In Patent Document 2, more specifically, first, a thermal impulse response h (x, y) of a sample is calculated, and then a photoacoustic image p (x, y) is constructed. The thermal impulse response is defined as a transfer function until a temperature change at an infinitely small point is converted into a minute displacement on the sample surface. Thereafter, the thermal impulse response h (x, y) and the photoacoustic image p (x, y) are Fourier transformed to obtain Fourier transformed images H (μ, υ) and P (μ, υ). Using 1 / H (μ, υ) as an inverse filter, Q (μ, υ) is calculated by Q (μ, υ) = P (μ, υ) · (1 / H (μ, υ)). An ideal photoacoustic image q (x, y) is obtained by inversely transforming Q (μ, υ) thus calculated.

  In addition to the above-mentioned patent documents, Yuan Xu, et al., IEEE Transactions on Medical Imaging, Volume 21 (2002), p.823-828 (hereinafter, Non-Patent Document 1) has a logically limited number. It is described that, when an optical pulse η (t) having a time width is Fourier-transformed η (k), the derivative is considered as iη (k). Experimentally, the subject is irradiated with microwaves having a long pulse width so that the excitation light pulse waveform is within the detection band of PZT (lead zirconate titanate), which is an ultrasonic detection element, and normal PZT. The probe detects the photoacoustic signal and reconstructs the absorption distribution.

Yi Wang, et al., Physics in Medicine and Biology, Volume 49 (2004), p.3117-3124 (hereinafter, Non-Patent Document 2) describes a micro waveform as a pressure waveform from a microelement in a subject. It is described that the micro waveform combining the optical pulse differential function and the device impulse response function and the absorption distribution are associated with the observed pressure waveform. Absorption image reconstruction measures p _d0 including optical differentiation and system response in an indivisible state, deconvolutes p _d0 from the pressure waveform of each element, and then performs a filtered back projection method (Filtered Backprojection method) To do. Experimentally, excitation is performed with a pulse laser beam with a short pulse width, the detection band of ultrasonic waves is expanded from that of normal ultrasonic diagnostic equipment, photoacoustic signals are detected with a hydrophone + oscilloscope, and the absorption distribution is reconstructed. To do.

  However, Non-Patent Document 1 does not treat η (k) obtained by Fourier transforming an optical pulse as a position-dependent function η (r, k. Therefore, it can be reconfigured to t = 0 (based on the detected waveform). Although it is possible to calculate the pressure distribution generated at the moment when light is incident retroactively (t = 0), an accurate absorption distribution can be obtained, but it is reconfigured so that t ≠ 0. In the case (when the pressure distribution at the moment when the light is incident (t = 0) cannot be reconstructed and the pressure distribution after a while has elapsed from time t = 0), the optical pulse width The component cannot be removed, resulting in a pressure distribution.

In Non-Patent Documents 1 and 2, either the excitation laser or the ultrasonic detector is removed from the practical range, and the laser emission time and the ultrasonic detection time are reconfigured. For this reason, although the problem does not appear clearly in Non-Patent Documents 1 and 2, when a practical device configuration is considered, it is difficult to reconfigure t = 0 with the methods of Non-Patent Documents 1 and 2. . That is, for example, as a practical device configuration,
-Ultrasonic detection device using a narrowband probe using PZT or the like with a sampling frequency of 100 MHz or less-When using an excitation laser with an optical pulse width of the order of 1-100 ns that produces a strong photoacoustic signal, laser pulse emission Since the phenomenon is shorter than the ultrasonic detection time, it cannot be accurately reconstructed to a state corresponding to t = 0 (a time zone in which the absorption distribution and the pressure distribution are proportional).

  Here, since “pressure distribution at time t = 0” represents “absorption distribution”, the absorption distribution can be obtained if the pressure distribution at time t = 0 is obtained. However, the sampling interval of a general ultrasonic detection apparatus is about 25 ns, and even if the calculation is made with the intention of the time t = 0 at the moment when the light hits, the deviation actually takes place with a time width of about t = ± 12.5 ns. Arise. For example, when the optical pulse width is as long as 100 ns, the above deviation (± 12.5 ns) can be considered as an error, but when the optical pulse width is 10 ns, the above deviation cannot be called an error, Instead of the pressure distribution at the moment of hitting, the pressure wave is transferred to a pressure wave propagation process. The “pressure distribution of the propagation process of the pressure wave” does not coincide with the “absorption distribution”.

  Furthermore, it is difficult to define a pressure distribution at t = 0 in a sample such as an experimental living body. Assuming that the speed of sound in the living body is 1530 m / s, for example, and the difference between the detection time and the laser irradiation time is the propagation time, the propagation distance is obtained from the propagation time. If the sound speed in the living body is constant at 1530 m / s, the propagation distance obtained from the propagation time coincides with the actual propagation distance. However, in practice, the speed of sound is not uniform in the living body, and there is a difference between the calculated propagation distance and the actual propagation distance. Therefore, when the propagation distance is estimated from the detection signal, the ambiguity of the propagation distance due to the sound speed difference remains. If the ambiguity of the propagation distance in the living body is regarded as the ambiguity of the propagation time, the time t = 0 is also ambiguous, and the pressure distribution at t = 0 is also ambiguous, making it difficult to define. The distribution of t = 0 is an absorption distribution, whereas the distribution of t> 0 is a pressure distribution during propagation, and if these are mixed, it cannot be said to be an absorption distribution.

  Therefore, the present inventor tried to obtain the absorption distribution from the detection signal even in a practical apparatus.

Consider a micro-absorbing particle that is a light absorber, and consider that this micro-absorbing particle absorbs pulsed laser light to generate a pressure wave (photoacoustic pressure wave). The pressure waveform p _micro (R, t) when the photoacoustic pressure wave generated from the microabsorbent particle at the position r is observed at the position R, where time is t, is [Phys. Rev. Lett. 86 (2001 ) 3550.], the following spherical wave is obtained.

Here, I (t) is a time waveform of the light intensity of the excitation light, the coefficient k is a conversion coefficient when the particle absorbs light and outputs an acoustic wave, and v _s is the sound velocity of the subject. is there. Positions r and R are vectors indicating positions in space. The pressure generated from the microabsorbent particles is a spherical wave proportional to the optical pulse differential waveform, as shown in the above formula.

Since the pressure waveform actually obtained from the object to be imaged has a macroscopic absorber size, it is considered to be a waveform obtained by superimposing the above micro absorption waveforms (superposition principle). Here, the absorption distribution of particles emitting macrophotoacoustic waves is A (r-R), and the observation waveform of pressure from the macro absorber is p _macro (R, t). At the observation position R, since the photoacoustic wave from the absorbing particles located at the radius v _s t from the observation position R is observed at each time, the observation waveform p _macro (R, t) has the following pressure It is shown by the waveform formula.

  As can be seen from the above equation (1), the observed waveform shows a convolution type of optical pulse differentiation.

In Non-Patent Document 2, an equation obtained by further convolving a device impulse response with the above equation is basically considered, and after absorption of p _d0 including an optical differentiation and a system response in an inseparable state from the observed waveform p _macro , absorption is performed. It has been proposed to reconstruct the distribution A (r−R) by the filtered back projection method. Non-Patent Document 2 places importance on considering the device impulse response rather than the influence of optical pulse differentiation, and therefore emphasizes even the frequency band where the S / N ratio (Signal to Noise Ratio) is not sufficient for the device. Image noise after processing increases. Therefore, in Non-Patent Document 2, it is necessary to perform processing including a high-frequency filter.

  If an ultrasonic probe with a wide band is used as in Non-Patent Document 2, the above method may be used. However, when a practical narrow-band probe is used, the frequency of the ultrasonic signal detected with respect to the impulse response of the apparatus is low, so the signal detected with a normal ultrasonic probe (low frequency) The band of the waveform to be convolved is widened and cannot be properly deconvolved, resulting in image corruption. Therefore, since it is important to consider the optical pulse differential term in obtaining the absorption distribution, in the present invention, in the deconvolution process, the deconvolution is performed considering only the optical pulse differential term.

Furthermore, in the present invention, after applying reconstruction (FTA method, DnS method, BP method, etc.) for obtaining a pressure distribution that is also used in conventional ultrasound systems, the pressure distribution of the image after reconstruction is t ≠ 0. In other words, after recognizing the pressure distribution in the propagation process of the pressure wave, we considered converting it into an absorption distribution. The basic concept of the pressure distribution reconstruction is that the pressure distribution p _rec (R, t) after the reconstruction at the detection position R = (x, y, 0) is the R detection axis (r -R) is obtained by adding the spherical waves generated from the absorber present at the position | r-R | on the position including the signals of the surrounding piezoelectric elements and calculating the pressure intensity at that position. Therefore, p _rec (R, t) generated by superimposing propagating photoacoustic waves generated from a micro absorber existing on the detection axis (r-R) can be expressed as follows.

As described above, the absorption distribution can be considered in a one-dimensional manner, whereby the pressure notation as described above can be performed. The above equation (2) can be expressed as follows, where the detection axis (r−R) is the z-axis and the distance | r−R | from the detection element is z.

Further, from the equation (3), x and y which are not related to integration are omitted, and the z-axis is represented by time, the above equation can be expressed as the following equation.

  In this way, one-axis (time axis or z′-axis) convolution notation in the detection element located at (x, y, 0) becomes possible.

The optical pulse derivative can be deconvoluted by Fourier-transforming both sides of the above formula (4) and dividing the Fourier coefficient of the pressure distribution by the Fourier coefficient of the time derivative of the optical pulse on the frequency axis.

After deconvolution, the resulting equation, by inverse Fourier transform to obtain the A (x, y, v s t), can be imaged absorption distribution. Here, the A (x, y, v s t) determined, the detection element receives the angle-dependent D (x, y, z) and, the natural vibration of the probe band is likely to have been superimposed. For example, by obtaining the device function D (x, y, z) in advance and multiplying the reciprocal by A (x, y, v _s t), the influence of the detection element reception angle dependency can be removed. . Further, regarding the natural vibration of the band, if the intensity is imaged by Hilbert transform or orthogonal detection processing, the influence can be removed. Further, the light spatial distribution L (x, y, z) incident on the specimen is separately obtained by observation or simulation, and the pixel value μ (x, y, z) proportional to the absorption coefficient is determined by μ (x, y, z). _{= A (x, y, v} s t) / L (x, y, z) may be obtained by. In this case, an absorption coefficient distribution image, which is a physical quantity more closely related to the living tissue, can be obtained.

  Based on the above, the procedure 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. 5A shows the photoacoustic signal after reconstruction, and FIG. 5B shows the photoacoustic signal FFT after FFT. By performing Fourier transform, the time domain signal shown in FIG. 5A is converted into a frequency domain signal as shown in FIG. 5B. In FIG. 5B, the absolute value of the photoacoustic signal FFT is shown, but in actual processing, 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. 5C shows an optical pulse differential waveform (h), and FIG. 5D shows an optical pulse differential waveform FFT (fft_h) after FFT. By performing Fourier transform, the time domain signal (waveform) shown in FIG. 5C is converted into the frequency domain signal shown in FIG. 5D. Note that black circles in FIG. 5C represent sampling points in the optical pulse differential waveform. Further, FIG. 5D shows the absolute value of the optical pulse differential waveform FFT, 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. 5E shows an optical pulse differential waveform FFT filter. By obtaining the reciprocal of the optical pulse differential waveform FFT shown in FIG. 5D, an optical pulse differential waveform FFT filter as shown in FIG. 5E 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. 5F shows the FFT waveform after deconvolution. The FFT waveform shown in FIG. 5F is obtained by multiplying the photoacoustic signal FFT shown in FIG. 5B by the optical pulse differential waveform FFT filter shown in FIG. 5E.

  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. 5G shows the inversely converted photoacoustic signal. By performing inverse FFT on the FFT waveform (frequency domain signal) shown in FIG. 5F, the deconvolution photoacoustic signal (time domain signal) shown in FIG. 5G is obtained. This deconvolved photoacoustic signal is an absorption distribution obtained by deconvoluting the optical pulse differential waveform from the reconstructed photoacoustic signal (FIG. 5A) in which the optical pulse differential waveform (FIG. 5C) is convolved with the optical absorption distribution. It corresponds to.

  6A shows a photoacoustic image generated based on the reconstructed photoacoustic signal (FIG. 5A), and FIG. 6B shows a photoacoustic image generated based on the deconvolved photoacoustic signal (FIG. 5G). Show. The photoacoustic image generated based on the reconstructed photoacoustic signal shown in FIG. 6A is substantially an image of the pressure distribution, and image determination such that one blood vessel is displayed twice. 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. 6B can visualize the distribution of the absorber by deconvoluting 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. 7 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 31 in response to the light trigger signal. The trigger control circuit 29 outputs a Q switch trigger signal at a predetermined timing. When the Q switch trigger signal is input, the laser unit 13 turns on the Q switch 32 and emits a pulse 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 1).

  The probe 11 detects the photoacoustic signal generated in the subject by the laser light irradiation after the laser light irradiation, and acquires the position information of the probe 11 at this time (Step 2). The receiving circuit 21 of the ultrasonic unit 12 receives the photoacoustic signal detected by the probe 11. Then, when the probe 11 is scanned (Step 3) and the entire region to be imaged as a photoacoustic image is scanned, the detection of the photoacoustic signal and the acquisition of the position information are finished (Step 4). 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 (Step 5). At this time, the position information is also stored in the reception memory 23 together.

  The photoacoustic image reconstruction unit 24 reads out the photoacoustic signal sampling data from the reception memory 23, and reconstructs the photoacoustic signal based on the read out photoacoustic signal sampling data (Step 6). 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 7). 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 in a certain cross section based on the data of each line subjected to logarithmic transformation. This photoacoustic image is an absorption distribution image obtained by converting the absorption distribution into data.

  The image composition means 38 generates volume data using these photoacoustic images and position information (Step 8). Further, the display mode of the volume data is determined by the observation method selection means 39 (Step 9). The image display means 14 displays the photoacoustic image showing the absorption distribution by a predetermined display mode on the display screen (Step 10).

  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.

  In comparison with Non-Patent Document 2, in Non-Patent Document 2, the present invention is different from the invention of Non-Patent Document 2 in that the optical differential function and the device impulse response function are deconvoluted in an inseparable state. That is, when a normal ultrasonic probe of a narrow band, for example, an 8 MHz ultrasonic probe is used, a 4 to 12 MHz signal can be detected by the ultrasonic probe, but detection sensitivity is low at 4 MHz or 12 MHz at the end of the band. Therefore, the S / N at 4 MHz or 12 MHz is lower than the S / N at 8 MHz. Non-Patent Document 2 places importance on considering (correcting) the device impulse response. As a result, an image in which a 4 MHz or 12 MHz signal having a low detection sensitivity is emphasized and a frequency component having a poor S / N is emphasized. Will be generated. On the other hand, in the present invention, only the optical pulse differential waveform is deconvoluted. Accordingly, the component corresponding to the device impulse response can be removed from the photoacoustic signal after deconvolution while processing the photoacoustic signal without lowering the S / N with the optical pulse differential waveform, so that the S / N is not lowered. A photoacoustic image can be generated.

  As described above, the photoacoustic image generation apparatus and the photoacoustic image generation method according to the present invention, in particular, convert the photodifferential waveform, which is a differential waveform of the time waveform of the light intensity of the measurement light, from the photoacoustic signal of the photoacoustic wave. Volume data about the photoacoustic signal is generated by using the photoacoustic signal that has been convolved and deconvoluted and the spatial information. Therefore, the conventional photoacoustic signal representing the pressure distribution in the propagation process of the pressure wave can be converted into a photoacoustic signal representing the absorption distribution of the light absorber. As a result, in photoacoustic imaging, a photoacoustic image representing the absorption distribution of the light absorber can be generated from the photoacoustic signal.

“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. 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, an image display unit 14, a position information acquisition unit 15, and an input unit 16.

  FIG. 8 shows the optical differential waveform deconvolution means 25a in the present 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. 9A shows an optical pulse differential waveform sampled at a sampling rate of 400 MHz, and FIG. 9B 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. 9A. On the other hand, if the sampling rate of the optical pulse differential waveform is adjusted to 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. 9B.

  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. 9B, 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.

“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. In the present embodiment, as in the second embodiment, the sampling rate of the optical pulse differential waveform is set higher than the sampling rate of the photoacoustic signal. In the second 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, an image display unit 14, a position information acquisition unit 15, and an input unit 16.

  FIG. 10 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. 11A shows a photoacoustic signal subjected to Fourier transform, and FIG. 11B 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. 11A. This signal is divided into two regions A and B with a center frequency of 20 MHz as a boundary. As shown in FIG. 11B, 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.

“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. 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 second and third 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, an image display unit 14, a position information acquisition unit 15, and an input unit 16.

  FIG. 12 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. 13A shows an optical pulse differential waveform obtained by Fourier transform, and FIG. 13B shows an optical pulse differential waveform from which high-frequency component sample points have been 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. 13A. 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. 13B, 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 fourth 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. 11B and the inverse of the optical pulse differential waveform shown in FIG. 13A. . 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. 13A) 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 third embodiment. That is, also in this embodiment, the same effect as the third embodiment can be obtained.

“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. FIG. 14 is a block diagram showing a configuration of the fifth 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. In the present embodiment, an ultrasonic wave is used as an acoustic wave, and an ultrasonic image is generated as a reflected acoustic wave image. However, an acoustic wave with an audible frequency may be used instead of the ultrasonic wave by selecting an appropriate frequency according to the subject to be examined, measurement conditions, and the like. Moreover, the form which produces | generates an ultrasonic image can also be combined with either of the 2nd to 4th embodiment.

  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 include an ultrasonic image generation unit (reflection acoustic wave image generation unit) that generates an ultrasonic image based on the reflected ultrasonic wave. Configure.

  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.

“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. FIG. 15 is a block diagram showing a configuration of the sixth embodiment of the photoacoustic image generation apparatus. The present embodiment is different from the first embodiment in that a subject is irradiated with light having a plurality of wavelengths. In addition to the configuration of the photoacoustic image generation apparatus 10 according to the first embodiment illustrated in FIG. 1, the photoacoustic image generation apparatus 10 b according to the present embodiment has each wavelength component (light having each wavelength) of light including a plurality of wavelengths. Is provided with a two-wavelength data calculation means 52 for performing a calculation between photoacoustic signals (photoacoustic images). Therefore, a detailed description of the same components as those in the first embodiment will be omitted unless particularly necessary. In addition, combining this embodiment with any one of the second to fifth embodiments, irradiating the light in those embodiments, and calculating photoacoustic signals (photoacoustic images) for each wavelength component. Good.

  In the present embodiment, the laser unit 13 is configured to be able to switch and emit light having a plurality of wavelengths. For example, the laser unit 13 switches and emits a pulse laser beam having a wavelength of 750 nm and a pulse laser beam having a wavelength of 800 nm. The probe 11 detects the photoacoustic signal from the subject after the emission of the pulsed laser light of each wavelength, and the reception memory 23 stores the photoacoustic signal sampling data corresponding to the light of each wavelength. The photoacoustic signals corresponding to the stored light of each wavelength are reconstructed by the photoacoustic image reconstruction means.

  After the reconstruction by the photoacoustic image reconstruction unit 24, the photodifferential waveform deconvolution unit 25 is configured to transmit the light of each wavelength irradiated on the subject from the photoacoustic signal (photoacoustic image) corresponding to the light of each wavelength. Each of the differential waveforms (optical differential waveforms) of the light intensity time waveform is deconvoluted. The photoacoustic signal obtained by deconvolution of the optical differential waveform corresponding to the light of each wavelength is processed by the two-wavelength data calculation unit 52 after being corrected by the correction unit 26.

  Here, in many living tissues, the light absorption characteristics vary depending on the wavelength of light, and generally, the light absorption characteristics are also unique to each tissue. For example, the molecular absorption coefficient at a wavelength of 750 nm of oxygenated hemoglobin (hemoglobin combined with oxygen: oxy-Hb) contained in a large amount of human arteries is also low at a wavelength of 800 nm. Moreover, the molecular absorption coefficient at a wavelength of 750 nm of deoxygenated hemoglobin (hemoglobin deoxy-Hb not bound to oxygen) contained in a large amount in veins is higher than that at a wavelength of 800 nm. Using this property, by examining whether the photoacoustic signal corresponding to the light of wavelength 750 nm is relatively large or small with respect to the photoacoustic signal corresponding to the light of wavelength 800 nm, the photoacoustic signal from the artery A photoacoustic signal from a vein can be discriminated.

  The two-wavelength data calculation means 52 compares the relative magnitude relationship between photoacoustic signals corresponding to a plurality of wavelengths, for example. Specifically, the two-wavelength data calculation means 52 compares the photoacoustic signal detected when light with a wavelength of 750 nm is irradiated with the photoacoustic signal detected when light with a wavelength of 800 nm is irradiated. And how big is it. When displaying an image, if the photoacoustic signal detected when light having a wavelength of 750 nm is irradiated can be determined as a photoacoustic signal from a vein, the portion may be displayed in, for example, blue. In addition, if the photoacoustic signal detected when the light having a wavelength of 800 nm is irradiated is large, it can be determined that the photoacoustic signal is from the artery. As described in the first embodiment, the correction unit 26 may be omitted.

  In the present embodiment, the two-wavelength data calculation means 52 calculates the photoacoustic signals corresponding to the light of each wavelength after the deconvolution of the optical differential waveform. When irradiating a subject with light of a plurality of wavelengths, for example, after detecting a photoacoustic signal generated by irradiating light of the first wavelength, a photoacoustic signal generated by irradiating the second light is detected. Sometimes, a position shift may occur for each irradiation of light of each wavelength due to the influence of body movement. When comparing the photoacoustic signals corresponding to the light of each wavelength, it is preferable to compare the photoacoustic signals generated from the same place. When the optical differential waveform is not deconvolved, one blood vessel is displayed twice as shown in FIG. 6A, and it is difficult to confirm the position of the blood vessel for image determination, and it is difficult to correct the displacement. On the other hand, when the optical differential waveform is deconvoluted, the light absorption distribution can be imaged as shown in FIG. 6B, the position of the blood vessel can be easily confirmed, and the positional deviation can be easily corrected.

  In addition, when one blood vessel is displayed twice as shown in FIG. 6A, since there is no signal in the portion corresponding to the inside of the blood vessel (or the signal level is lower than the predetermined level), If there is a positional shift between images corresponding to light of each wavelength, the portion where the signal exists, that is, the overlapping portion of the blood vessel image is reduced. In this case, it becomes difficult to appropriately compare the relative magnitude relationship between the photoacoustic signals corresponding to the light of each wavelength. On the other hand, when the light absorption distribution is imaged as shown in FIG. 6B, many portions in the blood vessel image are portions where signals are present, and the position of the blood vessel image in each image is slightly shifted. However, many portions of the blood vessel images in each image overlap. Therefore, in this embodiment, even when comparing without aligning both images, the influence of the positional deviation can be reduced.

"Design changes"
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 15: Position information acquisition means 16: Input means 21: Reception circuit 22: AD conversion means 23: Reception memory 24: Light Acoustic image reconstruction means 25, 25a, 25b, 25c: photodifferential waveform deconvolution means 26: correction means 27: detection / logarithmic conversion means 28: photoacoustic image construction means 29: trigger control circuit 30: control means 31: flash Lamp 32: Q switch 33: Transmission control circuit 34: Data separation means 35: Ultrasound image reconstruction means 36: Detection / logarithmic conversion means 37: Ultrasound image construction means 38: Image composition means 39: Observation method selection means 60: Vibrator array

Claims (17)

A light emitting section for emitting measurement light toward the subject, and a probe having an acoustic detection element for detecting a photoacoustic wave generated in the subject due to the emission of the measurement light;
Position information acquisition means for acquiring spatial information defining the position and / or direction of the probe in real space;
Light that generates tomographic data and / or volume data for the photoacoustic signal using the photoacoustic signal of the photoacoustic wave detected by the probe and the spatial information acquired by the position information acquisition means Acoustic image generating means,
The photoacoustic image generation means includes photodifferential waveform deconvolution means for deconvoluting a photodifferential waveform, which is a differential waveform of a time waveform of the light intensity of the measurement light, from the photoacoustic signal, and tomographic data and / or In generating volume data, the photoacoustic image generating apparatus uses the photoacoustic signal deconvolved by the optical differential waveform deconvolution means.   The photoacoustic image generating apparatus according to claim 1, wherein the optical differential waveform deconvolution means further includes optical differential waveform acquisition means for acquiring the optical differential waveform of the measurement light. 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 generation apparatus according to claim 1, 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,
4. The photoacoustic image generation apparatus according to claim 3, wherein the first Fourier transform unit performs Fourier transform on the photoacoustic signal resampled by the resample 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 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,
4. The photoacoustic image generation apparatus according to claim 3, 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,
4. The photoacoustic image generation according to claim 3, wherein the inverse filter calculation means obtains, as the inverse filter, an inverse of a waveform obtained by removing high-frequency component sampling points from the Fourier-transformed optical differential waveform. apparatus. The optical differential waveform deconvolution means generates a signal obtained by deconvolution of the optical differential waveform from a photoacoustic signal corresponding to the light of each wavelength when the measurement light includes light of a plurality of wavelengths.
7. The photoacoustic image according to claim 1, wherein the photoacoustic image generation unit further includes a two-wavelength data calculation unit that performs calculation processing on signals after deconvolution corresponding to light of each wavelength. Image generation device.   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 1, further comprising a correcting unit that performs the correction. An observation method selection means for selecting an observation method of the volume data;
9. The photoacoustic image generation unit generates a photoacoustic image according to an observation method selected by the observation method selection unit based on the volume data. Photoacoustic image generation apparatus.   The photoacoustic image generation apparatus according to claim 1, wherein the position information acquisition unit includes a magnetic sensor unit and acquires the spatial information using the magnetic sensor unit. The probe detects a reflected acoustic wave with respect to an acoustic wave transmitted to the subject;
11. The light according to claim 1, further comprising a reflected acoustic wave image generation unit configured to generate a reflected acoustic wave image based on a reflected acoustic wave signal of the reflected acoustic wave detected by the probe. Acoustic image generation device. Using a photoacoustic image generation apparatus provided with a probe having a light emitting part and an acoustic detection element,
Detect photoacoustic waves generated in the subject due to the emission of measurement light,
Obtaining spatial information defining the position and / or orientation of the probe in real space;
Deconvolute the photodifferential waveform that is the differential waveform of the time waveform of the light intensity of the measurement light from the photoacoustic signal of the photoacoustic wave,
A photoacoustic image generation method, wherein tomographic data and / or volume data for the photoacoustic signal is generated using the deconvolved photoacoustic signal and the spatial information.   The deconvolution is performed by Fourier-transforming the photoacoustic signal, Fourier-transforming a signal obtained by sampling the optical differential waveform at a predetermined sampling rate, and obtaining an inverse filter of the Fourier-transformed optical differential waveform as an inverse filter. The photoacoustic image generation method according to claim 12, wherein the photoacoustic image is generated by applying the inverse filter to the photoacoustic signal that has been applied and performing Fourier inverse transform on the photoacoustic signal to which the inverse filter has been applied. When the photoacoustic signal is sampled at a first sampling rate, and the photodifferential waveform is sampled at a second sampling rate higher than the first sampling rate,
The photoacoustic signal sampled at the first sampling rate is resampled at the second sampling rate, and the resampled photoacoustic signal is Fourier transformed. Photoacoustic image generation method. When the photoacoustic signal is sampled at a first sampling rate, and the photodifferential waveform is sampled at a second sampling rate higher than the first sampling rate,
Performing a Fourier transform of the photoacoustic signal with a first number of data points;
Fourier transform of a signal obtained by sampling the optical differential waveform at a predetermined sampling rate is performed with a second number of data points greater than the first number of data points,
Zero padding is performed for the Fourier-transformed photoacoustic signal to add 0 to the center by the difference between the first data point and the second data point,
The photoacoustic image generation method according to claim 13, wherein the inverse filter is applied to the photoacoustic signal subjected to zero padding. When the photoacoustic signal is sampled at a first sampling rate, and the photodifferential waveform is sampled at a second sampling rate higher than the first sampling rate,
Performing a Fourier transform of the photoacoustic signal with a first number of data points;
Fourier transform of a signal obtained by sampling the optical differential waveform at a predetermined sampling rate is performed with a second number of data points greater than the first number of data points,
The high frequency component sample points are removed from the Fourier transformed signal of the optical differential waveform by the difference between the first data points and the second data points,
14. The photoacoustic image generation method according to claim 13, wherein an inverse of the optical differential waveform after removing a high-frequency component sample point is obtained as the inverse filter. In the case where the measurement light includes light of a plurality of wavelengths,
17. A signal obtained by deconvolution of an optical differential waveform from a photoacoustic signal corresponding to light of each wavelength is generated, and signals after deconvolution corresponding to light of each wavelength are subjected to arithmetic processing. The photoacoustic image generation method in any one.