WO2013076986A1 - Dispositif et procédé de traitement de signal photo-acoustique - Google Patents

Dispositif et procédé de traitement de signal photo-acoustique Download PDF

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Publication number
WO2013076986A1
WO2013076986A1 PCT/JP2012/007494 JP2012007494W WO2013076986A1 WO 2013076986 A1 WO2013076986 A1 WO 2013076986A1 JP 2012007494 W JP2012007494 W JP 2012007494W WO 2013076986 A1 WO2013076986 A1 WO 2013076986A1
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light
signal
waveform
photoacoustic
photoacoustic signal
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PCT/JP2012/007494
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English (en)
Japanese (ja)
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覚 入澤
辻田　和宏
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富士フイルム株式会社
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0093—Detecting, measuring or recording by applying one single type of energy and measuring its conversion into another type of energy
    • A61B5/0095—Detecting, measuring or recording by applying one single type of energy and measuring its conversion into another type of energy by applying light and detecting acoustic waves, i.e. photoacoustic measurements
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/7239—Details of waveform analysis using differentiation including higher order derivatives
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/7253—Details of waveform analysis characterised by using transforms
    • A61B5/7257—Details of waveform analysis characterised by using transforms using Fourier transforms
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/48—Other medical applications
    • A61B5/4887—Locating particular structures in or on the body
    • A61B5/489—Blood vessels

Definitions

  • the present invention relates to a photoacoustic signal processing apparatus and method, and more particularly to a photoacoustic signal processing apparatus and method for processing a photoacoustic signal generated in a subject by pulse light irradiated to the subject.
  • Ultrasonography is known as a type of imaging that can noninvasively inspect the internal condition of a living body.
  • an ultrasonic probe capable of transmitting and receiving ultrasonic waves is used.
  • the ultrasonic waves travel inside the living body and are reflected at the tissue interface.
  • the internal appearance can be imaged by calculating the distance based on the time it takes for the ultrasound probe to receive the reflected sound and the reflected ultrasound to return to the ultrasound probe.
  • photoacoustic imaging which image-forms the inside of a biological body using a photoacoustic effect is known.
  • pulsed laser light is applied to the inside of a living body.
  • living tissue absorbs the energy of pulse laser light, and adiabatic expansion due to the energy generates an ultrasonic wave (photoacoustic signal).
  • photoacoustic signal is detected by an ultrasonic probe or the like, and a photoacoustic image is constructed based on the detection signal, whereby visualization in the living body based on the photoacoustic signal is possible.
  • the ordinary reconstruction method for example, Fourier domain method (FTA method) or delay-and-add method (Delay & Sum method) substantially images the pressure distribution, and the generated photoacoustic image is a light absorber. It is not a distribution image.
  • FFA method Fourier domain method
  • Delay & Sum method delay-and-add method
  • a single blood vessel may be displayed in duplicate. This phenomenon can be explained as follows. That is, when a pressure waveform generated by a minute element (minute absorber) is a micro waveform, a pressure waveform generated from a blood vessel as a macro structure can be grasped as an overlap of micro waveforms.
  • the thermal impulse response h (x, y) of the sample is first calculated, and then the photoacoustic image p (x, y) is constructed.
  • the thermal impulse response is defined as a transfer function until an infinitesimal single point temperature change is converted to a minute displacement of the sample surface. Thereafter, the thermal impulse response h (x, y) and the photoacoustic image p (x, y) are respectively subjected to Fourier transform to obtain Fourier transform images H ( ⁇ , ⁇ ) and P ( ⁇ , ⁇ ).
  • the derivative of an optical pulse ⁇ (t) having a finite time width is Fourier-transformed into ⁇ (k), and the derivative thereof is i ⁇ It is stated to be considered as (k).
  • the subject is irradiated with a microwave whose light pulse width is extended so that the excitation light pulse waveform falls within the detection zone of PZT (lead zirconate titanate), which is an ultrasonic detection element, The photoacoustic signal is detected by the PZT probe to reconstruct the absorption distribution.
  • PZT lead zirconate titanate
  • Non-Patent Document 2 as a pressure waveform from a minute element in an object, a micro waveform obtained by combining an optical pulse differential function and a device impulse response function as a pressure waveform from a minute element in an object and an absorption distribution are shown. It has been described to relate to the observed pressure waveform.
  • Absorption image reconstruction measures p d0 including optical differentiation and system response in an indivisible state, and after deconvoluting p d0 from the pressure waveform of each element, the filtered back projection method (filtered backprojection method) Using.
  • excitation is performed with pulsed laser light with a short light pulse width
  • the detection band of ultrasonic waves is broadened compared to a normal ultrasonic diagnostic device
  • a photoacoustic signal is detected with a hydrophone and an oscilloscope to obtain absorption distribution. Reconfigure.
  • the above deviation ⁇ 12.5 ns
  • the above deviation may be considered as an error, but when the light pulse width is 10 ns, the above deviation can not be called an error. It will transfer to the pressure distribution of the propagation process of the pressure wave rather than the pressure distribution at the moment of contact.
  • the "pressure distribution in the pressure wave propagation process” does not match the "absorption distribution”.
  • the inventor has found that it is advantageous to deconvolute the differential waveform of the light pulse waveform from the observed waveform or the pressure waveform after reconstruction.
  • An absorption distribution can be obtained by deconvolving the light pulse differential waveform from the observed waveform.
  • the time waveform of the pulsed laser light irradiated to the subject is not always constant. For example, when irradiating pulsed laser light with a plurality of wavelengths, a difference may occur between the temporal waveform of pulsed laser light of a certain wavelength and the temporal waveform of pulsed laser light of another wavelength.
  • sampling means for sampling a photoacoustic signal generated in a subject from pulsed light after emitting pulsed light to the subject, time waveform of light intensity of pulsed light or the like
  • An optical waveform differential signal which is a differential waveform of a time waveform of light intensity of pulsed light emitted to a subject using a function that represents a differential waveform obtained by differentiating and using the pulse time width of pulsed light as an independent variable
  • An optical waveform differential signal generating means for generating the light waveform differential signal deconvoluting means for generating a signal obtained by deconvolving the optical waveform differential signal generated by the optical waveform differential signal generating means from the sampled photoacoustic signal;
  • a photoacoustic signal processing apparatus characterized by comprising.
  • the light waveform differential signal generation means indicates the correspondence between the light emission condition associated with the pulse light and the pulse time width of the pulse light emitted to the object under the light emission condition.
  • An optical pulse width estimation unit that estimates the pulse time width of pulsed light emitted to a subject based on the optical pulse width information and the light emission condition of pulsed light emitted to the subject with reference to the optical pulse width information
  • a function application unit that applies the estimated pulse duration to the function.
  • the light pulse width information may include a table in which the light emission condition and the pulse time width are associated with each other.
  • the light pulse width estimation unit When there is no light emission condition in the table matching the light emission condition of the pulsed light emitted to the object, the light pulse width estimation unit outputs the pulse emitted to the object by interpolation based on the pulse time width existing in the table The pulse time width of light may be estimated.
  • the pulsed light may be pulsed laser light.
  • the light emission conditions are: wavelength of pulse laser light, delay time from trigger of laser light emission to laser light emission frequency of pulse laser light, excitation energy of laser crystal in laser light source, condition regarding temporal change in laser light source, laser in laser light source It can include at least one of the crystal temperatures.
  • the function may be a fitting curve of a time waveform of pulse light measured in advance, a Gaussian function, a Lorentz function, a pseudo-folk function, or a combination of these functions.
  • the photoacoustic signal processing apparatus further comprises optical pulse width measurement means for measuring the pulse time width of the pulsed light emitted to the subject, and the optical waveform differential signal generation means is an optical pulse width measurement means.
  • the measured pulse duration may be applied to the function.
  • part of the pulsed light emitted to the subject is included in the optical path from when the light emitting end of the light source of the pulsed light emitted to the subject emits the pulsed light to the subject.
  • a branching unit may be provided to branch, and the light pulse width measuring unit may measure the pulse time width of the pulsed light emitted to the subject based on the light intensity of the pulsed light branched from the optical path. Good.
  • the light waveform differential signal deconvoluting means performs first Fourier transform means for Fourier transforming the sampled photoacoustic signal, and the light waveform differential signal is sampled at a predetermined sampling rate.
  • Second Fourier transform means for Fourier transforming a signal Inverse filter operation means for obtaining inverse of Fourier transformed light waveform differential signal as inverse filter, and filter application means for applying inverse filter to Fourier transformed photoacoustic signal
  • filter application means for applying inverse filter to Fourier transformed photoacoustic signal
  • an inverse Fourier transform means for inverse Fourier transform of the photoacoustic signal to which the inverse filter has been applied.
  • the photoacoustic signal is sampled at a first sampling rate
  • the light waveform differential signal corresponds to a signal sampled at a second sampling rate higher than the first sampling rate, and at the first sampling rate
  • the apparatus further comprises resampling means for resampling the sampled photoacoustic signal at a second sampling rate
  • the first Fourier transform means adopts a configuration for Fourier transforming the photoacoustic signal resampled by the resampling means. it can.
  • the photoacoustic signal is sampled at a first sampling rate
  • the light waveform differential signal corresponds to a signal sampled at a second sampling rate higher than the first sampling rate
  • the 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 audio signal further comprises zero padding means for zero padding in which zero is added at the center by the difference between the first data score and the second data score, and the filter applying means is zeroed by the zero padding means.
  • An inverse filter may be applied to the signal subjected to the padding.
  • the photoacoustic signal is sampled at a first sampling rate
  • the light waveform differential signal corresponds to a signal sampled at a second sampling rate higher than the first sampling rate
  • a first Fourier transform means Performs the Fourier transform with the first number of data points
  • the second Fourier transform means performs the Fourier transformation with the second number of data points larger than the first number of data points
  • the Fourier-transformed optical waveform differential signal The apparatus further comprises high-frequency component sample point removing means for removing high-frequency component sample points by the difference between the first data score and the second data score
  • the inverse filter computing means comprises the Fourier-transformed optical waveform differential signal
  • the inverse of the signal from which the high frequency component sample points have been removed may be obtained as an inverse filter.
  • the sampling interval of the photoacoustic signal may be longer than the pulse time width of the light emitted to the subject.
  • the photoacoustic signal processing apparatus further includes photoacoustic signal reconstruction means for reconstructing a photoacoustic signal based on the photoacoustic signal detected by the plurality of detection elements and sampled by the sampling means,
  • a configuration may be adopted in which the signal deconvolution unit deconvolutes the light waveform differential signal from the photoacoustic signal reconstructed by the photoacoustic signal reconstruction unit.
  • the light waveform differential signal deconvoluting means may deconvolute the photowave signal from the light waveform differential signal by the device response function.
  • the light emitted to the object contains light of a plurality of wavelengths
  • the sampling means samples the photoacoustic signal corresponding to the light of each wavelength
  • the light waveform differential signal deconvoluting means corresponds to the light of each wavelength
  • a signal obtained by deconvolving the light waveform differential signal from the photoacoustic signal may be generated.
  • the signal obtained by deconvolving the light waveform differential signal from the photoacoustic signal corresponding to the light of each wavelength is calculated It can be set as the structure further provided with the 2 wavelength data calculating means to process.
  • composition further provided with the photoacoustic image generation means which generates a photoacoustic image based on the signal which deconvoluted the light waveform differential signal from the photoacoustic signal.
  • Reflection acoustic wave image generation means for generating a reflection acoustic wave image based on the sampled reflection acoustic wave, the sampling means further sampling the reflection acoustic wave with respect to the acoustic wave transmitted to the subject;
  • a configuration further including image combining means for combining the photoacoustic image and the reflected acoustic wave image may be employed.
  • the image combining means may perform image combining by superimposing the photoacoustic image and the reflected acoustic wave image.
  • the present invention further includes the steps of detecting a photoacoustic signal generated in the subject due to the pulsed light after emitting the pulsed light to the subject, and differentiating a temporal waveform of light intensity of the pulsed light or the step Generating an optical waveform differential signal that is a differential waveform of a light intensity temporal waveform of the pulsed light emitted to the object using a function representing the differential waveform and using the pulse time width of the pulsed light as an independent variable; And D. deconvolving the generated light waveform differential signal from the detected photoacoustic signal.
  • a time waveform of light intensity of pulse light or a differentiated waveform obtained by differentiating the time waveform is represented, and a function using pulse time width of pulse light as an independent variable is used.
  • a light waveform differential signal is generated which is a differential waveform of the time waveform of the light intensity of the pulsed light irradiated to the object.
  • the block diagram which shows the basic algorithm of light pulse differential waveform deconvolution The wave form diagram which shows the photoacoustic signal after reconstruction.
  • micro-absorbent particle which is a light absorber
  • this micro-absorbent particle absorbs pulse laser light to generate a pressure wave (photoacoustic pressure wave).
  • the pressure waveform p micro (R, t) when a photoacoustic pressure wave generated from a micro-absorbing particle at position r is observed at position R, where t is time, is [Phys. Rev. Lett. 86 (2001) ] 3550.], it becomes the following spherical waves.
  • 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
  • v s is the sound velocity of the object is there.
  • Positions r and R are vectors indicating positions in space.
  • the pressure generated from the micro-absorbing particles is a spherical wave proportional to the light pulse differential waveform as shown in the above equation.
  • the pressure waveform obtained from the subject to be actually imaged is considered to be a waveform obtained by superimposing the above-mentioned micro absorption waveform because it has a more macroscopic absorber size (the principle of superposition).
  • a (r ⁇ R) be the absorption distribution of particles that emit macro photoacoustic waves
  • p macro (R, t) be an observed waveform of pressure from the macro absorber.
  • the observation position R the photoacoustic wave from the absorbing particle located at the radius v s t from the observation position R is observed at each time, so the observation waveform p macro (R, t) has the following pressure It is shown by a waveform equation.
  • the observed waveform shows a convolution type of light pulse differentiation. Therefore, in the present invention, in the deconvolution processing, deconvolution is performed in consideration of the light pulse differential term.
  • the pressure distribution after reconstruction is t ⁇ 0. That is, on the basis of the recognition that it is the pressure distribution of the pressure wave propagation process, it was considered to convert it into the absorption distribution.
  • p rec (R, t) in which the photoacoustic waves generated and propagating from the micro absorber present in the detection axis (r ⁇ R) are superimposed can be expressed as follows.
  • a pressure can be expressed as in the above equation.
  • the above equation (2) can be expressed as follows, where the detection axis (r ⁇ R) is the z axis and the distance
  • the light pulse differential can be deconvoluted by Fourier transforming both sides of the equation (4) and dividing the Fourier coefficient of the pressure distribution by the Fourier coefficient of the time differential of the light pulse on the frequency axis. After deconvolution, it is possible to obtain A (x, y, v s t) and to image the absorption distribution by performing inverse Fourier transform on the obtained equation.
  • the detection element reception angle dependency D (x, y, z) and the natural vibration of the probe band may be superimposed on A (x, y, v s t) obtained here.
  • the influence can be eliminated if intensity imaging is performed by Hilbert transform or orthogonal detection processing.
  • FIG. 1 shows the basic algorithm of optical pulse differential waveform deconvolution.
  • the reconstructed photoacoustic signal is input, and the reconstructed photoacoustic signal is Fourier-transformed by FFT (Fast Fourier Transform) (step S101).
  • the photoacoustic signal after reconstruction is shown in FIG. 2A
  • the photoacoustic signal FFT after FFT is shown in FIG. 2B.
  • FIG. 2B shows the absolute value of the photoacoustic signal FFT, it is processed as it is in a complex number in actual processing.
  • the light pulse differential waveform h is subjected to Fourier transform by FFT (step S102).
  • the light pulse differential waveform (h) is shown in FIG. 2C
  • the light pulse differential waveform FFT (fft_h) after the FFT is shown in FIG. 2D.
  • the signal (waveform) in the time domain shown in FIG. 2C is converted into the signal in the frequency domain shown in FIG. 2D.
  • black circles in FIG. 2C represent sampling points in the light pulse differential waveform.
  • FIG. 2D shows the absolute value of the light pulse differential waveform FFT, it is processed as it is in a complex number in actual processing.
  • the reciprocal of the light pulse differential waveform FFT (fft_h) after FFT obtained in step S102 is determined as a light pulse differential waveform FFT filter (inverse filter) (step S103).
  • the light pulse differential waveform FFT filter can be obtained by conj (fft_h) / abs (fft_h) 2 .
  • conj (fft_h) represents a conjugate complex number of fft_h
  • abs (fft_h) represents an absolute value of fft_h.
  • FIG. 2E shows an optical pulse differential waveform FFT filter.
  • FIG. 2F shows the FFT waveform after deconvolution.
  • the FFT waveform obtained by deconvolving the light pulse differential waveform in step S104 is subjected to inverse Fourier transform by inverse FFT, and the signal in the frequency domain is returned to the signal in the time domain (step S105).
  • FIG. 2G shows the inverse converted photoacoustic signal.
  • the photoacoustic signal after this deconvolution is an absorption distribution obtained by deconvoluting the light pulse differential waveform from the reconstructed photoacoustic signal (FIG. 2A) in which the light pulse differential waveform (FIG. 2C) is convoluted to the light absorption distribution It corresponds to
  • FIG. 3A shows a photoacoustic image generated based on the reconstructed photoacoustic signal (FIG. 2A)
  • FIG. 3B shows a photoacoustic image generated based on the deconvoluted photoacoustic signal (FIG. 2G) Show.
  • the photoacoustic image generated on the basis of the photoacoustic signal after reconstruction shown in FIG. 3A is substantially an image of the pressure distribution, and an image determination such as displaying one blood vessel in a double manner is performed. Above, it is difficult to confirm the position of the blood vessel.
  • the distribution of the absorber can be imaged by deconvoluting the light pulse differential waveform, and the blood vessel It is easy to check the position.
  • FIG. 4 shows a photoacoustic image generating apparatus including the photoacoustic signal processing apparatus according to the first embodiment of the present invention.
  • the photoacoustic image generation apparatus (photoacoustic image diagnostic apparatus) 10 includes an ultrasound probe (probe) 11, an ultrasound unit 12, and a light source unit (laser unit) 13.
  • the laser unit 13 generates a laser beam to be irradiated to the subject.
  • the wavelength of the laser light may be appropriately set according to the object to be observed.
  • the laser beam emitted from the laser unit 13 is guided to the probe 11 using a light guiding means such as an optical fiber, for example, and is irradiated onto the subject from the probe 11.
  • the probe 11 detects an ultrasonic wave (photoacoustic signal) generated by the light absorber in the subject absorbing the laser light after the subject is irradiated with the light emitted from the laser unit 13.
  • the probe 11 has, for example, a plurality of ultrasonic transducers arranged in a one-dimensional manner.
  • the ultrasound unit 12 corresponds to a photoacoustic signal processor.
  • the ultrasound unit 12 includes a receiving circuit 21, an AD conversion unit 22, a reception memory 23, a photoacoustic image reconstruction unit 24, an optical waveform differential signal generation unit 25, an optical waveform differential signal inverse convolution unit 26, and a detection / logarithmic conversion unit 27, a photoacoustic image constructing unit 28, a trigger control circuit 29, and a control unit 30.
  • the receiving circuit 21 receives the photoacoustic signal detected by the probe 11.
  • the AD conversion means 22 is a sampling means, samples the photoacoustic signal received by the receiving circuit 21 and converts it into a digital signal.
  • the AD conversion means 22 samples the photoacoustic signal at a predetermined sampling cycle based on, for example, an AD clock signal of a predetermined frequency input from the outside.
  • the reception memory 23 stores the photoacoustic signal sampled by the AD conversion unit 22.
  • the photoacoustic image reconstruction means 24 reads the photoacoustic signal from the reception memory 23, and generates data of each line of the photoacoustic image based on the photoacoustic signal 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 according to the position of the ultrasonic transducer, and generates data for one line (delay Addition).
  • 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 means 24 may perform reconstruction using a Hough transform method or a Fourier transform method.
  • the light waveform differential signal generation means 25 has a function representing a time waveform of the light intensity of the pulsed light.
  • the light waveform differential signal generation means 25 uses the function to generate a light waveform differential signal which is a differential waveform of the light waveform of the light intensity of the pulsed light (typically, pulsed laser light) irradiated to the object.
  • the function representing the time waveform of the light intensity of the pulsed laser light uses the pulse time width of the pulsed laser light as an independent variable.
  • the light waveform differential signal generation means 25 obtains the time waveform of the light intensity of the pulse laser beam by applying the pulse time width of the pulse laser beam irradiated to the object to a function, and differentiates the waveform. It is determined as an optical waveform differential signal.
  • the light waveform differential signal generation means 25 may have a function representing a light differential waveform obtained by differentiating the time waveform of the light intensity of the pulse laser light instead of the function representing the time waveform of the light intensity of the pulse laser light. . In that case, the light waveform differential signal generation means 25 may obtain the light waveform differential signal by applying the pulse time width of the pulsed laser light irradiated to the object to a function.
  • the light waveform differential signal generation unit 25 inputs the generated light waveform differential signal to the light waveform differential signal deconvoluting unit 26.
  • the light waveform differential signal deconvoluting means 26 may deconvolute the photoacoustic signal before reconstruction.
  • the detection / logarithmic conversion means 27 finds the envelope of the data of each line after deconvolution, and logarithmically transforms the found envelope.
  • a detection means for obtaining the envelope it is possible to use a conventionally used method such as Hilbert transform or quadrature detection. Thereby, the influence of the band due to the natural vibration of the ultrasonic transducer can be removed.
  • the photoacoustic image construction means 28 generates a photoacoustic image based on the data of each line subjected to logarithmic conversion.
  • the photoacoustic image construction means 28 converts, for example, the position in the time axis direction of the photoacoustic signal (peak portion) into the position in the depth direction in the photoacoustic layer image to generate a photoacoustic image.
  • the control means 30 controls each part in the ultrasonic unit 12.
  • the trigger control circuit 29 sends a flash lamp trigger signal to the laser unit 13 at the time of photoacoustic image generation. Also, after the flash lamp trigger signal is output, a Q switch trigger signal is sent.
  • the laser unit 13 includes a flash lamp 31 and a Q switch 32.
  • the laser unit 13 receives a flash lamp trigger signal, turns on the flash lamp 31, and starts laser excitation.
  • the Q switch trigger signal is input, the laser unit 13 turns on the Q switch and emits pulsed laser light.
  • the trigger control circuit 29 sends a sampling trigger signal to the AD conversion means 22 in synchronization with the laser light irradiation to the subject, and controls the sampling start timing of the photoacoustic signal in the AD conversion means 22.
  • a correction means is provided at the subsequent stage of the light waveform differential signal deconvoluting means 26, and the correction means influences the reception angle dependence characteristic of the ultrasonic transducer in the probe 11 from the signal in which the light waveform differential signal is deconvoluted. May be removed.
  • the correction means may remove the influence of the incident light distribution of the light on the object from the signal in which the light waveform differential signal is deconvoluted in addition to or instead of the reception angle dependent characteristic.
  • FIG. 5 shows the light waveform differential signal generation means 25.
  • the light waveform differential signal generation unit 25 includes a light pulse width estimation unit 251, a function application unit 252, and a light pulse width information storage unit 253.
  • the light pulse width information storage unit 253 corresponds the light emission condition (laser light emission condition) associated with the pulse laser light to the pulse time width (light pulse width) of the pulse laser light irradiated to the object under the light emission condition.
  • the light pulse width information indicating the relationship is stored.
  • the laser emission conditions include, for example, the wavelength of the pulsed laser light, the delay time from the trigger of the laser emission in the laser light source to the laser emission, the emission frequency of the pulsed laser light, the excitation energy of the laser crystal in the laser light source, and the time change in the laser light source , At least one of the laser crystal temperatures in the laser light source.
  • the light pulse width estimation unit 251 refers to the light pulse width information storage unit 253, and based on the light pulse width information and the light emission condition of the pulse laser light irradiated to the object, the pulse laser light irradiated to the object Estimate the light pulse width of
  • the function application unit 252 applies the estimated light pulse width to a time waveform of the light intensity of the pulse laser light or a function representing its differential waveform to generate a light waveform differential signal.
  • the light pulse width information storage unit 253 stores the wavelength of the pulse laser light and the light pulse width in association with each other.
  • the light pulse width estimation unit 251 obtains, for example, information on the wavelength of the pulsed laser light emitted to the object from the control unit 30 (FIG. 4).
  • Optical pulse width estimator 251, for example, the wavelength of the pulsed laser light irradiated to the subject is when the lambda 1, to estimate the optical pulse width T p1. In this case, even when the light pulse width of the pulse laser light emitted from the laser unit 13 (FIG. 4) changes according to the wavelength, the light pulse width of the pulse laser light of each wavelength can be correctly estimated.
  • the light pulse width information storage unit 253 may store the delay time from the trigger of the laser light emission to the laser unit 13 to the actual laser light emission in association with the light pulse width.
  • the light pulse width information storage unit 253 stores, for example, light pulse width information in the form of a table in which delay times are associated with light pulse widths for the respective delay times.
  • the light pulse width estimation unit 251 obtains the delay time from the trigger of the laser emission to the actual laser emission when the object is irradiated with the pulse laser beam.
  • the delay time from the trigger of the laser light emission to the actual laser light emission is, for example, the pulse laser light to the ultrasonic detection element of the probe 11 from the timing when the Q switch trigger signal is output to the laser unit 13 (FIG.
  • the light pulse width estimation unit 251 refers to the light pulse width information storage unit 253 and estimates the light pulse width corresponding to the obtained delay time as the pulse width of the pulsed laser light irradiated to the subject. In this case, even when the light pulse width of the pulse laser light changes due to the difference in delay time, the light pulse width of the pulse laser light irradiated to the object can be correctly estimated.
  • the light pulse width information storage unit 253 may store the light emission frequency of the pulse laser light in association with the light pulse width.
  • the light pulse width information storage unit 253 stores, for example, light pulse width information in the form of a table in which the light emission frequency is associated with the light pulse width in the case of each light emission frequency delay time.
  • the emission frequency of the pulse laser beam represents the frequency of laser emission when the laser unit 13 repeatedly and periodically emits the pulse laser beam.
  • the light pulse width estimation unit 251 acquires the emission frequency of the pulse laser light from, for example, the control unit 30.
  • the light pulse width estimation unit 251 refers to the light pulse width information storage unit 253 and estimates the light pulse width corresponding to the acquired light emission frequency as the pulse width of the pulsed laser light irradiated to the subject.
  • the light pulse width of the pulsed laser light changes between when the frequency of the laser unit 13 emits pulsed laser light is high and when the frequency is low.
  • the light pulse width information in which the light emission frequency of the pulse laser light is associated with the light pulse width even when the light pulse width of the pulse laser light changes due to the light emission frequency of the pulse laser light, The light pulse width of the pulsed laser light irradiated to the sample can be correctly estimated.
  • the light pulse width information storage unit 253 may store information related to the excitation energy of the laser crystal in the laser unit 13 in association with the light pulse width.
  • the light pulse width information storage unit 253 stores, for example, light pulse width information in a table format in which information associated with the excitation energy of the laser crystal is associated with the light pulse width in the case of each excitation energy.
  • Information applied to the flash lamp 31 of the laser unit 13 can be considered as the information related to the excitation energy.
  • the light pulse width estimation unit 251 acquires information on a voltage applied to the flash lamp 31 from the laser unit 13 as information related to excitation energy, for example, when the object is irradiated with pulsed laser light. .
  • the light pulse width estimation unit 251 refers to the light pulse width information storage unit 253, and estimates the light pulse width corresponding to the acquired applied voltage (excitation energy) as the pulse width of the pulse laser light irradiated to the subject. . It is considered that the excitation energy of the laser crystal in the laser unit 13 fluctuates according to the applied voltage of the flash lamp, and that when the excitation energy changes, the light pulse width of the pulsed laser light fluctuates. By using the light pulse width information in which the excitation energy of the laser crystal is associated with the light pulse width, the object is irradiated even when the light pulse width of the pulse laser light changes due to the change of the excitation energy. It is possible to correctly estimate the light pulse width of the pulsed laser light that has been
  • the light pulse width information storage unit 253 may store information associated with the condition regarding the temporal change in the laser unit 13 in association with the light pulse width. As information related to the condition related to the temporal change, for example, the cumulative number of times of light emission of the flash lamp 31 in the laser unit 13, the cumulative light emission time, and the like can be considered.
  • the light pulse width information storage unit 253 stores, for example, light pulse width information in a table format in which the cumulative number of times of light emission / light emission time of the flash lamp and the light pulse width in the case of each cumulative number of light emission times / light emission time .
  • the light pulse width estimation unit 251 obtains the accumulated number of times of light emission or the light emission time of the flash lamp 31 from, for example, the laser unit 13 when the object is irradiated with the pulsed laser light.
  • the light pulse width estimation unit 251 refers to the light pulse width information storage unit 253, and estimates the light pulse width corresponding to the obtained accumulated number of times of light emission / light emission time as the pulse width of the pulse laser light irradiated to the object. .
  • the performance of the flash lamp 31 is considered to decrease as the light emission time / number of times of light increase, and it is considered that the excitation energy of the laser crystal is also reduced accordingly. Then, it is considered that the light pulse width of the pulse laser light changes as the excitation energy of the laser crystal decreases.
  • the light pulse width information in which the condition regarding the temporal change in the laser unit 13 is associated with the light pulse width even when the light pulse width of the pulse laser light changes due to the temporal change, The light pulse width of the irradiated pulsed laser light can be estimated correctly.
  • the light pulse width information storage unit 253 may store information associated with the laser crystal temperature in the laser unit 13 in association with the light pulse width. As information related to the laser crystal temperature, for example, the temperature of cooling water of the solid-state laser crystal in the laser unit 13 can be considered.
  • the light pulse width information storage unit 253 stores, for example, light pulse width information in the form of a table in which the cooling water temperature of the solid laser crystal and the light pulse width in the case of each cooling water temperature are associated.
  • the laser unit 13 monitors the temperature of the cooling water of the solid laser crystal.
  • the light pulse width estimation unit 251 obtains the cooling water temperature of the solid-state laser crystal from, for example, the laser unit 13 when the object is irradiated with the pulsed laser light.
  • the light pulse width estimation unit 251 refers to the light pulse width information storage unit 253, and estimates the light pulse width corresponding to the obtained cooling water temperature as the pulse width of the pulsed laser light irradiated to the subject. In this case, even when the light pulse width of the pulse laser light emitted from the laser unit 13 changes according to the laser crystal temperature, the light pulse width of the pulse laser light of each wavelength can be correctly estimated.
  • the light pulse width may be estimated from the combination of the two of the wavelength of the pulsed laser light and the light emission frequency.
  • the light pulse width information storage unit 253 may store, for example, a two-dimensional table in which the wavelength and the light emission frequency are associated with the light pulse width.
  • the pulse time width existing in the table Based on the pulse time width of the pulsed laser light irradiated to the object may be estimated by interpolation. For example, when the pulse time width for the wavelength equal to the wavelength of the pulsed laser light irradiated to the object is not stored in the light pulse width information storage unit 253, the pulse time width for the wavelength before and after existing in the table Based on this, the pulse time width for the wavelength of the pulsed laser light irradiated to the subject may be interpolated and estimated. Specifically, when the wavelength between the two wavelengths lambda 1 and lambda pulse laser light irradiated to the subject, the light pulses a value between the optical pulse width Tp 1 and Tp 2 It can be estimated as the width.
  • the light waveform differential signal deconvoluting means 26 is shown in FIG.
  • the light waveform differential signal deconvoluting means 26 has Fourier transforming means 41 and 42, an inverse filter computing means 43, a filter applying means 44, and a Fourier inverse transforming means 45.
  • the Fourier transform means (first Fourier transform means) 41 transforms the reconstructed photoacoustic signal from a time domain signal into a frequency domain signal by discrete Fourier transform.
  • the Fourier transform means (second Fourier transform means) 42 converts the light waveform differential signal from the time domain signal to the frequency domain signal by discrete Fourier transform.
  • An FFT can be used as an algorithm of the Fourier transform.
  • the sampling rate of the photoacoustic signal and the sampling rate of the light waveform differential signal are equal.
  • the Fourier transform means 41 Fourier-transforms the photoacoustic signal sampled at 40 MHz, for example, by 1024-point Fourier transform.
  • the Fourier transform means 42 Fourier-transforms the light waveform differential signal corresponding to the signal sampled at 40 MHz by 1024-point Fourier transform.
  • the inverse filter computing means 43 finds the inverse of the Fourier transformed light waveform differential signal as an inverse filter. For example, when the signal obtained by subjecting the light waveform differential signal h to Fourier transform is fft_h, the inverse filter computing means 43 obtains conj (fft_h) / abs (fft_h) 2 as an inverse filter.
  • the filter application unit 44 applies the inverse filter obtained by the inverse filter operation unit 43 to the photoacoustic signal Fourier-transformed by the Fourier transform unit 41.
  • the filter application means 44 multiplies, for example, the Fourier coefficient of the photoacoustic signal and the Fourier coefficient of the inverse filter, element by element.
  • the Fourier inverse transform means 45 transforms the photoacoustic signal to which the inverse filter is applied from the signal of the frequency domain into the signal of the time domain by the inverse Fourier transform.
  • the inverse Fourier transform provides an absorption distribution signal in the time domain.
  • FIG. 7 shows an operation procedure.
  • the trigger control circuit 29 outputs a flash lamp trigger signal to the laser unit 13.
  • the laser unit 13 lights the flash lamp 31 in response to the flash lamp trigger signal.
  • the trigger control circuit 29 outputs a Q switch trigger signal at a predetermined timing.
  • the Q switch trigger signal is input, the laser unit 13 turns on the Q switch 32 and emits pulsed laser light.
  • the emitted pulse laser light is, for example, guided to the probe 11 and irradiated onto the subject from the probe 11 (step S1).
  • the probe 11 detects the photoacoustic signal generated in the subject by the irradiation of the pulse laser light after the irradiation of the pulse laser light (step S2).
  • the receiving circuit 21 of the ultrasound unit 12 receives the photoacoustic signal detected by the probe 11.
  • the trigger control circuit 29 sends a sampling trigger signal to the AD conversion means 22 in accordance with the timing of light irradiation on the subject.
  • the AD conversion means 22 receives the sampling trigger signal, starts sampling of the photoacoustic signal, and stores sampling data of the photoacoustic signal in the reception memory 23.
  • the photoacoustic image reconstruction means 24 reads out the sampling data of the photoacoustic signal from the reception memory 23, and reconstructs the photoacoustic signal based on the sampling data of the read out photoacoustic signal (step S3).
  • the light waveform differential signal generation means 25 estimates the light pulse width based on, for example, a laser emission condition, and applies the estimated light pulse width to a time waveform of light intensity of pulse laser light or a function representing the differential waveform thereof. Then, an optical waveform differential signal is generated (step S4).
  • the light waveform differential signal deconvoluting means 26 deconvolutes the light waveform differential signal generated in step S4 from the photoacoustic signal reconstructed in step S3 (step S5). By this deconvolution, the photoacoustic signal which shows absorption distribution is obtained.
  • the detection / logarithmic conversion means 27 calculates the envelope of the photoacoustic signal subjected to the deconvolution, and logarithmically converts the obtained envelope.
  • the photoacoustic image construction means 28 generates a photoacoustic image based on the data of each line subjected to the logarithmic conversion (step S6).
  • the photoacoustic signal is an absorption distribution image obtained by imaging the absorption distribution.
  • the image display means 14 displays the photoacoustic image which is an absorption distribution image on a display screen (step S7).
  • the light waveform differential signal deconvoluting means 26 And deconvolute the light waveform differential signal from the reconstructed photoacoustic image.
  • an absorption distribution can be obtained and an absorption distribution image can be generated.
  • the light waveform differential signal generation means 25 is implemented with a function representing a time waveform of the light intensity of the light pulse or its differential waveform and having the light pulse width as an independent variable.
  • a light waveform differential signal is generated by differentiating the time waveform of the light intensity of the pulsed laser light irradiated to the sample.
  • By generating the light waveform differential signal using a function it is possible to generate a light waveform differential signal close to the differential waveform of the time waveform of the pulsed laser light actually irradiated to the object.
  • the light waveform differential signal generated in such a manner for deconvolution it is possible to obtain an absorption distribution more accurately than in the case of deconvolving a fixed light waveform differential signal.
  • the light pulse width is estimated using the light pulse width information in which the laser emission condition is associated with the light pulse width.
  • the light pulse width information for example, the laser light, the laser light emission frequency, the actual laser light emission from the light emission trigger It is possible to correctly estimate the light pulse width of the pulsed laser light, which changes due to the change of the laser emission condition such as the delay time up to.
  • the light waveform differential signal used for the deconvolution is the pulse laser light actually irradiated to the object. It can be approximated to the differential waveform of the time waveform.
  • the sampling rate of the photoacoustic signal coincides with the sampling rate of the light waveform differential signal, and both signals are subjected to Fourier transform with the same number of data points.
  • the light pulse waveform differential signal is used as a signal of high speed sampling. That is, the light waveform differential signal is a signal corresponding to a signal sampled at a sampling rate higher than the sampling rate of the photoacoustic signal.
  • the sampling interval (the reciprocal of the sampling rate) of the photoacoustic signal is set to be longer than the pulse time width of the light irradiated to the object.
  • the low-sampling-rate photoacoustic signal is resampled (up-sampled) at the same sampling rate as the sampling rate of the light waveform differential signal, and then the Fourier transform is performed.
  • the other points may be the same as in the first embodiment.
  • FIG. 8 shows the light waveform differential signal deconvoluting means 26a in the present embodiment.
  • the light waveform differential signal deconvoluting means 26a in the present embodiment has resampling means 46 and 47 in addition to the configuration of the light waveform differential signal deconvolving means 26 in the first embodiment shown in FIG.
  • the resampling means 46 is an upsampling means, and upsamples sampling data of the photoacoustic signal sampled at a low sampling rate at the same sampling rate as the sampling rate of the light waveform differential signal.
  • the resampling means 46 performs upsampling, for example, by applying a low pass filter that adds zeros between sample points of the photoacoustic signal sampled at a low sampling rate and cuts it at the Nyquist frequency before upsampling.
  • the sampling rate (first sampling rate) of the photoacoustic signal in the AD conversion means 22 (FIG. 4) is 40 MHz
  • the sampling rate (second sampling rate) of the light waveform differential signal is 400 MHz
  • the resampling means 46 upsamples the 40 MHz photoacoustic signal to a 400 MHz signal.
  • the Fourier transform means 41 Fourier transforms the photoacoustic signal upsampled by the resampling means 46.
  • the Fourier transform means 41 for performing a Fourier transform on the photoacoustic signal and the Fourier transform means for performing a Fourier transform on the light waveform differential signal perform the Fourier transform with the same number of data points.
  • the Fourier transform means 41 converts the photoacoustic signal into a signal in the frequency domain of 8192 points
  • the Fourier transform means 42 converts the light waveform differential signal into a signal in the frequency domain of 8192 points.
  • the filter application means 44 applies an inverse filter to the Fourier-transformed signal of the upsampled photoacoustic signal.
  • the Fourier inverse transform means 45 transforms the signal to which the inverse filter is applied, from the signal in the frequency domain to the signal in the time domain (absorption distribution).
  • the absorption distribution signal returned to the time domain signal is, for example, a signal in a state of being upsampled to 400 MHz.
  • the resampling means 47 downsamples the absorption signal so that the absorption distribution signal becomes a signal sampled at the original sampling rate of the photoacoustic signal.
  • the resampling means 47 downsamples, for example, the 400 MHz absorption signal to a 40 MHz absorption signal. Downsampling is performed, for example, by decimating sample points after applying a low pass filter that cuts at the Nyquist frequency after downsampling.
  • FIG. 9A shows an optical waveform differential signal corresponding to a sampling rate of 400 MHz
  • FIG. 9B shows an optical waveform differential signal corresponding to a sampling rate of 40 MHz.
  • a sampling rate of 400 MHz as shown in FIG. 9A, it is possible to accurately reproduce a waveform obtained by differentiating the time waveform of the light intensity of the pulse laser light.
  • the sampling rate of the light waveform differential signal is matched to the sampling rate of the photoacoustic signal and it is a signal equivalent to 40 MHz, as shown in FIG. 9B, the light differential waveform can not be reproduced accurately.
  • the filter application means 44 When applying the inverse filter to the signal obtained by Fourier-transforming the photoacoustic signal by the filter application means 44, it is necessary that both data points be uniform.
  • the sampling rate of the light waveform differential signal is set in accordance with the sampling rate of the photoacoustic signal, as shown in FIG. 9B, the sampling frequency is too low for waveform change, and the light differential waveform can not be accurately reproduced.
  • the light pulse differential term may not be accurately deconvoluted, and the absorption distribution may not be obtained correctly.
  • the light waveform differential signal is a signal equivalent to 400 MHz to accurately reproduce the light differential waveform, and the sampling rate of the photoacoustic signal is 400 MHz, the light pulse differential term can be accurately deconvoluted and absorbed.
  • the distribution can be determined correctly.
  • a high speed AD converter is required for the AD conversion means 22 and the total memory of sampling data is increased, so that the memory capacity required for the reception memory 23 (FIG. 4) is increased.
  • the time required for the reconstruction also increases.
  • the resampling unit 46 resamples the sampling data of the photoacoustic signal later.
  • the photoacoustic signal after detection is upsampled by signal processing, it is possible to accurately deconvolute the light pulse differential term while performing slow sampling from photoacoustic detection to reconstruction.
  • a high speed AD converter is not necessary for the AD conversion unit 22, and the memory capacity required for the reception memory 23 does not increase.
  • the time required to reconstruct the photoacoustic signal does not increase, and the processing time can be shortened as compared to the case of sampling at a high sampling rate when detecting the photoacoustic signal.
  • the sampling rate of the light waveform differential signal is set higher than the sampling rate of the photoacoustic signal.
  • the photoacoustic signals sampled at a low sampling rate are upsampled, and both signals are Fourier transformed with the same data points.
  • the Fourier transform of the light waveform differential signal is performed with data points that are larger than the data points of the Fourier transform of the photoacoustic signal, and the center of the Fourier transformed photoacoustic signal is the difference of the data points. A zero point is added to (high frequency component region). The other points may be the same as in the first embodiment.
  • FIG. 10 shows the light waveform differential signal deconvoluting means 26b in the present embodiment.
  • the light waveform differential signal deconvoluting means 26b in the present embodiment has a zero padding means 48 and a zero point removing means 49 in addition to the configuration of the light waveform differential signal deconvolving means 26 in the first embodiment shown in FIG. Have.
  • the sampling rate (first sampling rate) of the photoacoustic signal is 40 MHz
  • the sampling rate (second sampling rate) of the light waveform differential signal is 320 MHz.
  • the Fourier transform means 41 converts, for example, a 40 MHz photoacoustic signal into a signal of a frequency domain of 1024 points (first data points), and the Fourier transform means 42 converts an optical waveform differential signal of 320 MHz to 8192 points (second Convert to a signal in the frequency domain).
  • 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 to the first sampling rate.
  • the zero padding means 48 receives the photoacoustic signal converted from the Fourier transform means 41 into a signal in the frequency domain.
  • the zero padding means 48 adds a zero point (point of signal value zero) at the center of the Fourier-transformed photoacoustic signal by the difference between data points of the photoacoustic signal after the Fourier transform and the light waveform differential signal. Do.
  • the zero padding means 48 divides the photoacoustic signal (frequency domain) of 1024 data points, for example, into two at the center frequency of the frequency band, and makes zero by the difference of the data scores between the two divided frequency domains.
  • a point is added to generate a photoacoustic signal having 8192 data points, which is the same as the data points of the light waveform differential signal (frequency domain). The addition of zeros corresponds to upsampling in the frequency domain.
  • the filter application means 44 applies an inverse filter to the signal that has been zero padded by the zero padding means 48.
  • the zero point removal means 49 removes the frequency band to which "0" is added by the zero padding means 48 from the signal to which the inverse filter is applied. For example, when the photoacoustic signal (frequency domain) of 1024 data points is converted to a signal of 8192 data points by the zero padding means 48, the zero point removing means 49 outputs the signal after the filter application (8192 points of data). ) Is returned to the signal of 1024 data points. Removal of the zero corresponds to downsampling in the frequency domain.
  • the inverse Fourier transform means 45 converts the signal returned to 1024 data points from the signal in the frequency domain to the signal in the time domain.
  • FIG. 11A shows a photoacoustic signal subjected to Fourier transform
  • FIG. 11B shows a photoacoustic signal after zero padding.
  • the sampling rate of the photoacoustic signal in the AD conversion means 22 is 40 MHz
  • the signal obtained by Fourier transforming the photoacoustic signal is a signal in the frequency band from 0 MHz to 40 MHz as shown in FIG. 11A. It becomes.
  • This signal is divided into two regions A and B at the border of 20 MHz which is the Nyquist frequency (1/2 of the sampling frequency).
  • the signal in region B becomes a signal corresponding to the frequency region of 300 MHz to 320 MHz.
  • the photoacoustic signal sampled at a low sampling rate is converted into a signal in the frequency domain, and the zero point in the domain of the high frequency component of the converted signal in the frequency domain is added.
  • the difference between the present embodiment and the second embodiment is that in the second embodiment, the photoacoustic signal is upsampled, whereas in the present embodiment, the photoacoustic signal is upsampled in the frequency domain.
  • resampling up-sampling
  • slow sampling is performed from photoacoustic detection to reconstruction.
  • the light pulse differential term can be deconvoluted accurately.
  • the sampling rate of the light waveform differential signal is set higher than the sampling rate of the photoacoustic signal.
  • the Fourier transform of the light waveform differential signal is performed with data points larger than the data points of the Fourier transform of the photoacoustic signal, and the high frequency component sample points are removed from the Fourier transformed light waveform differential signal.
  • the other points may be the same as in the first embodiment.
  • FIG. 12 shows the light waveform differential signal deconvoluting means 26c in the present embodiment.
  • the optical waveform differential signal deconvoluting means 26c in the present embodiment has a high frequency component sample point removing means 50 in addition to the configuration of the optical waveform differential signal deconvolving means 26 in the first embodiment shown in FIG.
  • the sampling rate (first sampling rate) of the photoacoustic signal is 40 MHz
  • the sampling rate (second sampling rate) of the light waveform differential signal is 320 MHz.
  • the Fourier transform means 41 converts, for example, a photoacoustic signal of 40 MHz into a signal of a frequency domain of 1024 points (first data points), and the Fourier transform means 42 converts an optical waveform differential signal of 320 MHz into 8192 points (second Converted into a signal in the frequency domain of 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 to the first sampling rate.
  • the high frequency component sample point removal means 50 receives the light waveform differential signal converted from the Fourier transform means 42 into a signal in the frequency domain.
  • the high frequency component sample point removing means 50 removes high frequency component sample points from the Fourier-transformed light waveform differential signal by the difference between the data points of the photoacoustic signal after the Fourier transform and the light waveform differential signal.
  • the high frequency component sample point removing means 50 for example, deletes the central data point corresponding to the high frequency component from the light waveform differential signal (frequency domain) of 8192 data points, and the same data as the data score of the photoacoustic signal (frequency domain) An optical waveform differential signal of 1024 points is generated.
  • the removal of high frequency component sample points corresponds to the downsampling of the light waveform differential signal in the frequency domain.
  • FIG. 13A shows a Fourier-transformed light waveform differential signal
  • FIG. 13B shows a light waveform differential signal from which high frequency component sample points have been removed.
  • the sampling rate of the light waveform differential signal is 320 MHz
  • the signal obtained by subjecting the light waveform differential signal to Fourier transform (the number of data points 8192) is a signal in the frequency band from 0 MHz to 320 MHz as shown in FIG. 13A.
  • Become. This signal is divided into the first data point to the 512th area (area A), the 513th data point to the 7680th data point area (area B), and the 8192th data point from the 7681th data point.
  • the inverse filter computing means 43 finds the inverse of the light waveform differential signal (frequency domain) from which the high frequency component sample points have been removed as an inverse filter. For example, the inverse filter calculating unit 43 obtains, as an inverse filter, an inverse number of the light waveform differential signal in which the data points are reduced from 8192 points to 1024 points.
  • the filter application unit 44 multiplies, for each element, the photoacoustic signal (frequency domain) of 1024 data points, for example, and the inverse filter.
  • the inverse Fourier transform means 45 converts the signal to which the inverse filter is applied from the signal in the frequency domain to the signal in the time domain.
  • the filter application unit 44 outputs the photoacoustic signal (frequency domain) in which the zero point is added to the high frequency component domain shown in FIG. 11B and the light waveform differential signal (frequency domain shown in FIG. Multiplication with the reciprocal of Since the value of the high frequency component region of the photoacoustic signal is “0”, the high frequency component (region B of FIG. 13A) of the light waveform differential signal does not affect the photoacoustic signal after the inverse filter application. Therefore, as in the present embodiment, the high frequency component sample point is removed from the signal in the frequency domain of the light waveform differential signal, and the inverse filter is determined from the light waveform differential signal from which the high frequency component has been removed. Even when applied to (frequency domain), the obtained result is the same as the third embodiment. That is, also in this embodiment, the same effect as that of the third embodiment can be obtained.
  • FIG. 14 shows a photoacoustic image generation apparatus according to a fifth embodiment of the present invention.
  • the ultrasound unit 12a in the photoacoustic image generation apparatus 10a according to the present embodiment includes a transmission control circuit 33 and data separation.
  • Means 34, ultrasound image reconstruction means 35, detection / logarithmic conversion means 36, ultrasound image construction means 37, and image combining means 38 are provided.
  • the photoacoustic image generation apparatus 10a of the present embodiment is different from the photoacoustic image generation apparatus 10 of the first embodiment in that an ultrasonic image is generated in addition to the photoacoustic image.
  • an ultrasonic wave is used as an acoustic wave in the present embodiment
  • an acoustic wave of an audio frequency may be used by selecting an appropriate frequency in accordance with an object to be detected, a measurement condition, and the like.
  • the present embodiment may be combined with any of the second to fourth embodiments, and an ultrasound image may be generated in these embodiments.
  • the probe 11 in addition to the detection of the photoacoustic signal, the probe 11 outputs (transmits) an acoustic wave (ultrasound) to the object, and detects (receives) reflected ultrasound from the object to the transmitted ultrasonic wave (reception )I do.
  • the trigger control circuit 29 sends an ultrasonic wave transmission trigger signal to instruct the transmission control circuit 33 to transmit an ultrasonic wave when generating an ultrasonic image (reflection acoustic wave image).
  • the transmission control circuit 33 causes the probe 11 to transmit an ultrasonic wave.
  • the probe 11 detects the reflected ultrasound from the subject after transmitting the ultrasound. Transmission and reception of ultrasonic waves may be separated. For example, ultrasonic waves may be transmitted from a position different from that of the probe 11, and the reflected ultrasonic waves for the transmitted ultrasonic waves may be received by the probe 11.
  • the reflected ultrasonic waves detected by the probe 11 are input to the AD conversion means 22 through the reception circuit 21.
  • the trigger control circuit 29 sends a sampling trigger signal to the AD conversion means 22 in accordance with the timing of ultrasonic wave transmission to start sampling of reflected ultrasonic waves.
  • the photoacoustic signal is one way from the generation position to the probe 11. Since the detection of the reflected ultrasound 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 of that at the time of the photoacoustic signal sampling, for example It may be 20 MHz.
  • the AD conversion means 22 stores the sampling data of the reflected ultrasound 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 means 34 separates the sampling data of the photoacoustic signal stored in the reception memory 23 and the sampling data of the reflected ultrasound.
  • the data separation unit 34 inputs sampling data of the separated photoacoustic signal to the photoacoustic image reconstruction unit 24.
  • the generation of the light waveform differential signal and the generation of the photoacoustic image (absorption distribution image) including the deconvolution are the same as in the first embodiment.
  • the data separation means 34 inputs sampling data of the separated reflected ultrasonic waves to the ultrasonic image reconstruction means 35.
  • the ultrasonic image reconstruction means 35 generates data of each line of the ultrasonic image based on the reflected ultrasonic waves (the sampling data thereof) detected by the plurality of ultrasonic transducers of the probe 11. Similarly to the generation of the data of each line in the photoacoustic image reconstruction means 24, a delay addition method or the like can be used to generate data of each line.
  • the detection / logarithmic conversion means 36 finds the envelope of the data of each line output from the ultrasonic image reconstruction means 35, and logarithmically transforms the found envelope.
  • the ultrasound image construction means 37 generates an ultrasound image based on the data of each line subjected to logarithmic transformation.
  • the ultrasonic image reconstruction means 35, the detection / logarithmic conversion means 36, and the ultrasonic image construction means 37 are ultrasonic image generation means (reflection acoustic wave image generation means) for generating an ultrasonic image based on the reflected ultrasonic waves.
  • the image combining means 38 combines the photoacoustic image and the ultrasound image.
  • the image combining means 38 performs image combining by superimposing a photoacoustic image and an ultrasonic image, for example.
  • the combined image is displayed on the image display means 14. It is also possible to display the photoacoustic image and the ultrasound image side by side on the image display unit 14 or to switch between the photoacoustic image and the ultrasound image without performing image synthesis.
  • the photoacoustic image generation device generates an ultrasound image in addition to the photoacoustic image.
  • the ultrasound image it is possible to observe a portion that can not be imaged in the photoacoustic image.
  • the point that the absorption distribution can be imaged by generating an optical waveform differential signal representing the differential waveform of the pulse laser light irradiated to the object and deconvoluting the optical waveform differential signal from the observed waveform is the same as the first embodiment. It is.
  • most of the algorithms for image reconstruction and detection / logarithmic conversion can be shared by the generation of ultrasonic images and the generation of photoacoustic images, and it is possible to simplify FPGA circuit configuration and software. It has the above merit.
  • FIG. 15 shows a photoacoustic image generation apparatus according to the sixth embodiment of the present invention.
  • the present embodiment is different from the first embodiment in that light of a plurality of wavelengths is emitted to a subject.
  • the ultrasound unit 12 b in the photoacoustic image generation apparatus 10 b according to the present embodiment includes photoacoustics for light of multiple wavelengths.
  • a two-wavelength data calculation unit 40 is provided to calculate a signal (photoacoustic image). Note that this embodiment may be combined with any of the second to fifth embodiments, and light of a plurality of wavelengths may be irradiated in those embodiments to calculate photoacoustic signals (photoacoustic images) for a plurality of wavelengths.
  • the laser unit 13 is configured to be able to switch and emit light of a plurality of wavelengths.
  • the laser unit 13 switches and emits, for example, pulsed laser light with a wavelength of 750 nm and pulsed laser light with a wavelength of 800 nm.
  • the probe 11 detects a photoacoustic signal from the subject after emission of pulsed laser light of each wavelength, and the reception memory 23 stores sampling data of the photoacoustic signal corresponding to each wavelength.
  • the photoacoustic signals corresponding to the stored wavelengths are respectively reconstructed by the photoacoustic image reconstruction means.
  • the light waveform differential signal deconvolution unit 26 generates each wavelength generated by the light waveform differential signal generation unit 25 from the photoacoustic signal (photoacoustic image) corresponding to each wavelength after the reconstruction by the photoacoustic image reconstruction unit 24. Deconvolute the light waveform differential signal corresponding to.
  • the photoacoustic signal in which the light waveform differential signal corresponding to each wavelength is deconvoluted is processed by the two-wavelength data calculating means 40.
  • the light absorption characteristics are also unique to each tissue.
  • the molecular absorption coefficient at a wavelength of 750 nm of oxygenated hemoglobin (hemoglobin combined with oxygen: oxy-Hb) abundant in human arteries is also low at a wavelength of 800 nm.
  • the molecular absorption coefficient at a wavelength of 750 nm of deoxygenated hemoglobin (hemoglobin deoxy-Hb not bound to oxygen) abundant in veins is higher than that at a wavelength of 800 nm.
  • the two-wavelength data computing means 40 compares, for example, relative magnitude relationships between photoacoustic signals corresponding to a plurality of wavelengths. Specifically, the two-wavelength data computing means 40 compares the photoacoustic signal detected when the light of wavelength 750 nm is irradiated with the photoacoustic signal detected when the light of wavelength 800 nm is irradiated. And find out which one is bigger.
  • the photoacoustic signal detected when the light with a wavelength of 750 nm is irradiated is large, it can be judged as a photoacoustic signal from a vein, so that part may be displayed in blue.
  • the photoacoustic signal detected when the light with a wavelength of 800 nm is irradiated is large, it can be judged as a photoacoustic signal from an artery, so that portion may be displayed in red.
  • the two-wavelength data computing means 40 computes photoacoustic signals corresponding to a plurality of wavelengths after deconvolution of the light waveform differential signal.
  • the photoacoustic signal is irradiated with the second light to the subject.
  • the light waveform differential signal When the light waveform differential signal is not deconvoluted, as shown in FIG. 3A, for example, one blood vessel is displayed in a double manner, and the position of the blood vessel is difficult to confirm in image determination.
  • the light absorption distribution can be imaged, the position of the blood vessel can be easily confirmed, and the positional deviation correction can be facilitated.
  • the photoacoustic signal and the light waveform differential signal are converted into signals in the frequency domain, and after being deconvoluted in the frequency domain, they are converted back into signals in the time domain, but the present invention is not limited thereto. It is also possible to perform deconvolution of the light waveform differential signal in the time domain.
  • the light waveform differential signal deconvoluting means 26 may perform some kind of filtering process on the photoacoustic signal at the time of deconvolution.
  • the light waveform differential signal deconvoluting means 26 may filter the noise amplification frequency band at the time of deconvolution.
  • the product of the light waveform differential signal and the device response function piezoelectric element or frequency filter of electrical system may be deconvoluted.
  • the photoacoustic image (absorption distribution image) is generated after the light waveform differential signal is deconvoluted from the photoacoustic signal, but in addition to or instead of this, the light waveform differential signal is generated.
  • a photoacoustic image pressure distribution image
  • the user can select the presence or absence of the deconvolution processing by performing an operation on the switch or the display monitor, and when the user selects the execution of the deconvolution processing, the optical waveform differential signal is deconvoluted.
  • a photoacoustic image may be generated, and the photoacoustic image may be generated without performing deconvolution of the light waveform differential signal when the user selects non-execution of the deconvolution processing. For example, when deconvolution of the light waveform differential signal is performed, the photoacoustic signal is displayed in association with red and black colors, and when no deconvolution is performed, the photoacoustic signal is associated with blue and black colors. May be displayed.
  • 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.
  • the light waveform differential signal may be deconvoluted only for the blood vessel portion.
  • the display color of the blood vessel portion subjected to the deconvolution processing is set to a color different from the display color of the other unprocessed blood vessel portions, and the blood vessel subjected to the deconvolution processing and the other unprocessed blood vessels It may be easily distinguishable.
  • the light pulse width of the pulsed laser light irradiated to the subject is estimated based on the laser emission condition, but the present invention is not limited to this.
  • the light waveform differential signal may be generated by measuring the light pulse width and applying the measured light pulse width to the function.
  • FIG. 16 shows a photoacoustic image generation apparatus according to a modification.
  • the ultrasound unit 12c in the photoacoustic image generation apparatus 10c of the modification further includes an optical pulse width measurement unit 39 in addition to the configuration of the ultrasound unit 12 shown in FIG.
  • the light pulse width measuring means 39 measures the pulse time width of the pulsed laser light emitted to the subject.
  • the light waveform differential signal generation means 25 applies the light pulse width measured by the light pulse width measurement means 39 to the function in place of the estimated light pulse width to generate a light waveform differential signal.
  • the light pulse waveform differential signal may be generated by the measured light pulse width and the function.
  • the light pulse width measurement unit 39 includes, for example, a photodetector that detects light, and an arithmetic unit that measures the length of time during which the photodetector detects light. For example, in an optical path (for example, an optical fiber) from the light emitting end of the laser unit 13 (FIG. 4) to when the pulsed laser light is irradiated to the subject, the pulsed laser light to be irradiated to the subject There is provided a branch portion which branches a part of.
  • the photodetector outputs an electric signal indicating that, for example, when part of the pulse laser light branched by the branching unit has a predetermined light intensity or more.
  • the arithmetic unit measures, as the light pulse width, the time during which the light intensity of the light detected by the photodetector is equal to or higher than the threshold value, based on the output signal of the photodetector.
  • a mirror having a high transmittance specifically, a mirror having a transmittance of 95% or more can be used for the above-described branch portion.
  • a mirror is disposed, for example, at an angle of 45 ° with respect to the main stream of the laser directed to the subject direction, and the reflection component of the mirror is branched in the direction of the photodetector of the light pulse width measuring means 39.
  • a transparent glass may be used at the branch portion, and the reflection component of the transparent glass may be branched in the direction of the photodetector of the light pulse width measurement unit 39.
  • a laser beam is guided using, for example, a bundle fiber in which a large number of optical fibers are bundled, some (for example, one) of a plurality of optical fibers , And may guide part of the pulsed laser light to the photodetector of the light pulse width measurement means 39.

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Abstract

L'invention vise à obtenir correctement une distribution d'absorption à partir d'un signal détecté dans un dispositif de traitement de signal photo-acoustique, y compris en présence de variations dans la forme d'onde d'impulsion de lumière. À cet effet, un signal photo-acoustique est généré dans un échantillon d'essai lorsque ce dernier est irradié avec de la lumière. Le signal photo-acoustique, qui est détecté à l'aide d'une sonde (11), est échantillonné dans un moyen de conversion analogique-numérique (22) par l'intermédiaire d'un circuit de réception (21). Un moyen de génération de signal de forme d'onde optique différentielle (25) utilise une fonction pour générer un signal de forme d'onde optique différentielle qui est une forme d'onde différentielle de la forme d'onde temporelle de l'intensité lumineuse du faisceau pulsé avec lequel l'échantillon d'essai a été irradié. La fonction mentionnée ci-dessus représente une forme d'onde temporelle de l'intensité optique du faisceau pulsé ou une forme d'onde différentielle obtenue par différenciation de la forme d'onde temporelle, et utilise la largeur temporelle d'impulsion du faisceau pulsé comme variable indépendante. Un moyen de déconvolution de signal de forme d'onde optique différentielle (26) déconvolutionne un signal de forme d'onde optique différentielle à partir du signal photo-acoustique. La distribution d'absorption est obtenue au moyen de cette déconvolution.
PCT/JP2012/007494 2011-11-22 2012-11-21 Dispositif et procédé de traitement de signal photo-acoustique WO2013076986A1 (fr)

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CN115177217A (zh) * 2022-09-09 2022-10-14 之江实验室 基于球形粒子光脉冲激发效应的光声信号仿真方法、装置
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JP2015029550A (ja) * 2013-07-31 2015-02-16 船井電機株式会社 光音響画像化装置
JP6682282B2 (ja) * 2016-01-29 2020-04-15 キヤノン株式会社 被検体情報取得装置および信号処理方法
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CN115177217A (zh) * 2022-09-09 2022-10-14 之江实验室 基于球形粒子光脉冲激发效应的光声信号仿真方法、装置

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