JP2015080604A - Subject information acquisition device and optical characteristic measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire a highly-accurate optical coefficient by considering sensitivity of a phase to an optical coefficient of each modulation frequency.SOLUTION: A subject information acquisition device to be used includes: light detection means that detects multiple intensity-modulated light rays which mutually differ in intensity-modulated frequency showing a change in intensity of light transmitted through a subject, and then generates a light detection signal; acoustic wave detection means that generates a photoacoustic signal derived from the subject; and processing means that acquires a detected amplitude attenuation rate and a detected phase from the light detection signal, with respect to each intensity-modulated frequency, generates an estimated amplitude attenuation rate and an estimated phase, with respect to the intensity-modulated light, on the basis of both a prescribed estimated absorption coefficient and a prescribed estimated scattering coefficient concerning the subject, generates a weighted phase residual error which is weighted according to a phase residual error showing a residual error between the detected phase and the estimated phase, generates an amplitude attenuation rate residual error showing a residual error between the detected amplitude attenuation rate and the estimated amplitude attenuation rate, and then generates an absorption coefficient and a scattering coefficient, with respect to the subject, from a value obtained from the weighted phase residual error and the amplitude attenuation rate residual error.

Description

  The present invention relates to an object information acquisition apparatus and an optical characteristic measurement apparatus.

  In the technical field of biodiagnosis, attempts have been made to perform diagnosis using near-infrared light that absorbs light relatively little by the living body. It is possible to acquire the ratio and concentration of the components constituting the living tissue from the spectral information of the living tissue obtained by the near infrared light diagnosis. In addition, since near-infrared light diagnosis uses light, unlike X-ray imaging using X-rays, diagnosis can be performed without exposure. Since it is known that spectral information, component ratio, and concentration differ between normal tissue and tumor tissue, noninvasive tumor diagnosis by near-infrared light diagnosis is expected.

  The spectral information includes a rate (indicated by an absorption coefficient μa) at which a living tissue absorbs light energy. Based on the spectral absorption coefficient, it is possible to obtain the concentrations of oxyhemoglobin and deoxyhemoglobin, which are constituents of biological tissue. And the oxygen saturation of a biological tissue is acquirable from those concentration ratios. Since tumor tissue consumes a lot of oxygen when it grows, it is considered that the degree of oxygen saturation is lower than that of normal tissue. By detecting this, the tumor site may be diagnosed.

A living tissue has a property of absorbing light as well as a property of scattering light (a rate at which the tissue scatters light, indicated by a scattering coefficient μs ′). The light irradiated on the living body loses its straightness at several millimeters, and is then scattered and propagated over a wide area in the living body, so that the light energy is dispersed. That is, light attenuation also occurs due to scattering.
Thus, the attenuation of the intensity of light propagating through the living body includes both attenuation due to absorption and attenuation due to scattering. Therefore, in near-infrared light diagnosis, it is important to separate and acquire an absorption coefficient and a scattering coefficient (hereinafter, the absorption coefficient and the scattering coefficient are collectively referred to as an optical coefficient) from the detected light.

As a method for performing such measurement, there are a time-resolved measurement method using short pulse light and a phase modulation measurement method using intensity-modulated light.
In the time-resolved measurement method, a subject is irradiated with short pulse light, and a time waveform of light that has been scattered or absorbed in the subject is detected. Then, the absorption coefficient and the scattering coefficient when the detected time waveform coincides with the separately calculated time waveform are set as the optical coefficient of the subject.
In the phase modulation measurement method, the living body is irradiated with intensity-modulated light that is intensity-modulated with a sine wave or the like, and the amplitude attenuation rate and phase of the intensity-modulated light that has been scattered or absorbed in the living body are detected. Then, the absorption coefficient and the scattering coefficient when the detected value coincides with the separately calculated value are set as the optical coefficient of the subject.

  In either method, a transport equation or a diffusion equation is generally used for calculation at a certain optical coefficient. In contrast to the time-resolved measurement method, which generally requires a light source with a pulse width on the order of picoseconds and a photodetector with high time resolution, the phase modulation measurement method can measure with intensity-modulated light on the order of megahertz. And low cost.

Patent Document 1 discloses a measuring apparatus using a phase modulation measuring method.
Non-Patent Document 1 shows the possibility of improving the measurement accuracy of the absorption coefficient and the scattering coefficient by using a plurality of intensity modulation frequencies (fundamental frequencies and harmonics).

JP 7-159239 A JP 2010-88627 A

Jun Hui Ho, Hooi Ling Chin, Jing Dong, Kijoon Lee, “Multi-Harmonic homodyne approach for optical property measurement of trubid medium in tranmission geometry”, Optics Communications 285 (2012) 2007-2011

  In the phase modulation measurement method, the sensitivity of the phase with respect to the optical coefficient varies depending on the intensity modulation frequency. In the apparatuses described in Patent Document 1 and Non-Patent Document 1, the modulation frequency having a low phase sensitivity with respect to the optical coefficient is also used for the calculation, so that the accuracy of the optical coefficient is lowered.

  The present invention has been made in view of the above problems, and an object thereof is to acquire a highly accurate optical coefficient by considering the sensitivity of the phase with respect to the optical coefficient for each modulation frequency.

The present invention employs the following configuration. That is,
A light detection means for detecting each of a plurality of intensity-modulated lights, which are different from each other in intensity modulation frequency representing a change in light intensity, irradiated on the subject and generating a light detection signal after propagating through the subject;
Acoustic wave detection means for detecting a photoacoustic wave generated by irradiating the subject with pulsed light and generating a photoacoustic signal;
A processing means,
From the light detection signal, for each intensity modulation frequency, obtain a detection amplitude attenuation rate and a detection phase,
For each intensity modulation frequency, based on a predetermined estimated absorption coefficient and a predetermined estimated scattering coefficient for the subject, an estimated amplitude attenuation rate and an estimated phase of the intensity modulated light are generated,
A phase residual indicating a residual between the detected phase and the estimated phase is generated for each intensity modulation frequency, and a weighted phase residual is generated by applying a weight corresponding to the intensity modulation frequency to the phase residual. ,
For each intensity modulation frequency, an amplitude attenuation rate residual indicating a residual between the detected amplitude attenuation rate and the estimated amplitude attenuation rate is generated,
By comparing a value obtained from the weighted phase residual and the amplitude attenuation rate residual with a predetermined threshold value, an absorption coefficient and a scattering coefficient of the subject are generated,
Processing means for generating characteristic information of the subject based on the photoacoustic signal, the absorption coefficient, and the scattering coefficient;
A subject information acquisition apparatus characterized by comprising:

The present invention also employs the following configuration. That is,
An irradiation means for irradiating a subject with a plurality of intensity-modulated lights having different intensity-modulation frequencies representing changes in light intensity;
A light detection means for generating a light detection signal by detecting each of the plurality of intensity-modulated lights propagated through the subject;
A processing means,
From the light detection signal, for each intensity modulation frequency, obtain a detection amplitude attenuation rate and a detection phase,
For each intensity modulation frequency, based on a predetermined estimated absorption coefficient and a predetermined estimated scattering coefficient for the subject, an estimated amplitude attenuation rate and an estimated phase of the intensity modulated light are generated,
A phase residual indicating a residual between the detected phase and the estimated phase is generated for each intensity modulation frequency, and a weighted phase residual is generated by applying a weight corresponding to the intensity modulation frequency to the phase residual. ,
For each intensity modulation frequency, an amplitude attenuation rate residual indicating a residual between the detected amplitude attenuation rate and the estimated amplitude attenuation rate is generated,
Processing means for generating an absorption coefficient and a scattering coefficient of the object by comparing a value obtained from the weighted phase residual and the amplitude attenuation rate residual with a predetermined threshold;
It is an optical characteristic measuring apparatus characterized by having.

  According to the present invention, it is possible to acquire a highly accurate optical coefficient by considering the sensitivity of the phase with respect to the optical coefficient for each modulation frequency.

The figure which shows the flow of the algorithm of the inverse problem calculation which calculates | requires the optical coefficient of a subject. The figure which shows the sensitivity of the phase with respect to the optical coefficient change for every modulation frequency. The figure which shows the relationship between an optical coefficient and residual R. FIG. The figure which shows the optical characteristic measuring apparatus which concerns on 1st embodiment. The figure which shows the detail of the modulation signal generation part 102. FIG. The figure which shows the detail of the light source part 103. FIG. It shows an example of a weighting w _{(f i).} The flowchart of the optical characteristic measuring method which concerns on 1st embodiment. The figure which shows the optical characteristic measuring apparatus which concerns on 2nd embodiment. The figure which shows the detail of the modulation signal generation part 201. FIG. The figure which shows the method of generating the light which has a some modulation frequency. The figure which shows the detail of the detection part 202. FIG. The figure which shows the detail of the detection part 202. FIG. The figure which shows the detail of the detection part 202. FIG. The figure which shows the detail of the detection part 202. FIG. The flowchart of the optical characteristic measuring method which concerns on 2nd embodiment. The figure which shows the optical characteristic measuring apparatus which concerns on 3rd embodiment. The flowchart of the optical characteristic measuring method which concerns on 3rd embodiment. The flowchart of the optical characteristic measuring method which concerns on 3rd embodiment. The figure which shows the timing of the optical characteristic method which concerns on 3rd embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described below should be changed as appropriate according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the following description.

The optical characteristic measuring apparatus of the present invention is an apparatus that measures an optical coefficient using intensity-modulated light as described above. The present invention can also be applied to an object information acquiring apparatus using measured optical characteristics. That is, the object is irradiated with light (electromagnetic wave), the acoustic wave generated in the object is received according to the photoacoustic effect, and the characteristic information inside the object is obtained using the intensity of the acoustic wave and the measured optical characteristic. It is a photoacoustic imaging apparatus to acquire.
In the present invention, the acoustic wave includes an elastic wave (dense wave) called a sound wave, an ultrasonic wave, a photoacoustic wave, or an optical ultrasonic wave.

The characteristic information acquired by the photoacoustic imaging device reflects the initial sound pressure of the acoustic wave generated by light irradiation, the light energy absorption density and absorption coefficient derived from the initial sound pressure, the concentration of the substance constituting the tissue, etc. Sample information. Since the substance constituting the tissue reflects the function, it can be said that the photoacoustic characteristic distribution represents the function distribution information of the subject. The concentration of the substance is, for example, oxygenated hemoglobin concentration or reduced hemoglobin concentration, and oxygen saturation obtained from them. The generated characteristic information may be stored or used as numerical data, distribution information of each position in the subject, or image data for displaying an image.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In principle, the same components are denoted by the same reference numerals, and description thereof may be omitted. The present invention can also be understood as an operation method and a control method of an optical property measurement apparatus or an object information acquisition apparatus. The present invention can also be understood as a program for causing an information processing apparatus or the like to execute an operation method or a control method.

<First embodiment>
When calculating the optical coefficient using the amplitude attenuation rate and phase of a plurality of intensity modulation frequencies, the optical characteristic measuring apparatus of the present invention weights the residual of the measured phase value and the calculated estimated value for each modulation frequency. To calculate the optical coefficient of the subject. Here, the residual mainly refers to the difference between the measured value and the calculated value (estimated value).

  In the first embodiment, an optical characteristic measuring apparatus that performs measurement a plurality of times by changing the intensity modulation frequency is shown. Hereinafter, the intensity modulation frequency may be simply referred to as the modulation frequency. However, even in this case, it should be noted that the modulation frequency is a term indicating a frequency depending on a temporal change in intensity, and does not indicate a frequency of light (electromagnetic wave). The intensity modulation frequency represents a change in light intensity propagated through the subject.

  When an object such as a living body is irradiated with light from a light source whose intensity is modulated with a sine wave (or cosine wave), the intensity of the light changes at the same frequency as the modulation frequency of the light source. Propagates in the subject. Light undergoes scattering and absorption in the course of propagation, causing attenuation in the wave amplitude and delay in the wave phase. The amplitude attenuation rate and phase of a wave detected at a certain point on the subject vary depending on the optical coefficient and the modulation frequency.

The N modulation frequency _{f i (i = 0,1, ···} , N-1) to. The amplitude attenuation rate and phase measured for each modulation frequency are respectively A _m (f _i ) and Φ _m (f _i ), and the amplitude attenuation rate and phase estimated by calculation are respectively A _c (f _i ) and Φ _c (f _i). ). At this time, the residual R between measurement and calculation is defined by equation (1).

The calculation of A _c (f _i ) and Φ _c (f _i ) is repeated while changing μa and μs ′, and μa and μs ′ when the residual R becomes sufficiently small are used as the optical coefficients of the object (inversely) Problem calculation). At this time, since the expression (1) is normalized by the measured value, the contribution to the calculation of the amplitude attenuation rate and the phase becomes equal. As a result, it is possible to prevent a situation where a plurality of optical coefficient solutions exist because one of them does not contribute to the calculation.
By using a plurality of frequencies in this manner, it is possible to return to a modulation frequency-dependent curve, so that the influence of errors for each modulation frequency can be reduced. For this reason, the accuracy of the optical coefficient can be improved as compared with the case where the calculation is performed at a single modulation frequency.

  FIG. 2 is a diagram showing the relationship between frequency and phase when the optical coefficient is changed. 2A shows a plurality of graphs in which μs ′ is changed, and FIG. 2B shows a plurality of graphs in which μa is changed. It can be seen that the lower the modulation frequency, the greater the change in the optical coefficient when the phase changes. That is, when there is the same amount of phase noise, the lower the modulation frequency, the larger the error in the optical coefficient.

式（２）のＲ_Ａ＿ｉは振幅減衰率残差、Ｒ_Φ＿ｉは位相残差である。ｗ（ｆ_ｉ）は変調周波数ｆ_ｉにより変化させる加重である。 In the present invention, the optical coefficient error due to phase noise is reduced by applying a smaller weight to the phase residual as the modulation frequency is lower. The residual R used in the present invention is expressed by equation (2).

In Formula (2), R A — _i is an amplitude attenuation rate residual, and R _{Φ — i} is a phase residual. w (f _i ) is a weight that is changed by the modulation frequency f _i .

3A and 3B are diagrams showing the relationship between the optical coefficient and the residual R. FIG. The two horizontal axes are μa and μs ′, and the vertical axis is the residual R. The assumed conditions are as follows.
Number of modulation frequencies: N = 6
Each frequency (unit: [MHz]): f ₀ = 20, f ₁ = 40, f ₂ = 60, f ₃ = 80, f ₄ = 100, f ₅ = 120
Absorption coefficient: μa = 0.005 [/ mm]
Scattering coefficient: μs ′ = 1 [/ mm]
Under this condition, the amplitude attenuation rate and the phase are substituted into A _m (f _i ) and Φ _m (f _i ) of Equation (2), and the residual R is obtained. At this time, the noise of Φ _m (f ₀ ) × 0.05 is added to all of Φ _m (f _i ) (i = 0 to 5) as phase noise of measurement.

FIG. 3A shows a residual according to Equation (1) in which no weight is applied to the phase term. FIG. 3B corresponds to the present embodiment, and is a residual obtained by Equation (2) in which a linear weight is applied to the modulation frequency fi. This is the optical coefficient from which the point with the smallest residual is obtained. The specific weights are as follows.
w (f ₀ ) = 0, w (f ₁ ) = 0.2, w (f ₂ ) = 0.4, w (f ₃ ) = 0.6, w (f ₄ ) = 0.8, w ( f ₅ ) = 1

  In the case of FIG. 3A, μa = 0.444 [/ mm] and μs ′ = 1.065 [/ mm]. In FIG. 3B, μa = 0.0006 and μs ′ = 1.04. Therefore, FIG. 3B is closer to the actual values of the subject μa = 0.005 [/ mm] and μs ′ = 1 [/ mm]. Thus, by applying a weight to the phase term, the optical coefficient can be obtained with higher accuracy even when there is noise in the phase.

(Device configuration)
The apparatus configuration of the optical characteristic measuring apparatus according to the present embodiment will be described with reference to FIG.
The apparatus includes a modulation signal generation unit 102 and a light source unit 103 which are light source units, a photodetector 106 which is a light detection unit, and a detection unit 107 which measures amplitude phase. The apparatus further includes an optical coefficient calculation unit 108 that is a unit that calculates an optical coefficient, and a phase residual calculation unit 110 that is a unit that applies a weight to the phase residual.

The modulation signal generation unit 102 generates a plurality of modulation signals having different frequencies for generating intensity-modulated light. Details of the modulation signal generator 102 are shown in FIG. A plurality of oscillators (OSC) that oscillate at _N different frequencies (f _{0 to} f _N−1 ) are selected, and a frequency to be output by a switch (SW) is selected. FIG. 5 is an example, and the frequency may be changed using an oscillator having a variable frequency. The modulation signal is output to the light source unit 103 and the detection unit 107, and is used for generation and detection of intensity-modulated light, respectively.

  The light source unit 103 modulates the intensity of the light source with the modulation signal waveform of the modulation signal generation unit 102. FIG. 6A shows a case where the intensity of light is modulated by directly modulating the drive current of the laser diode with a modulation signal. The laser driver supplies a direct current to the laser diode via the laser head. The laser head converts the modulation signal from the modulation signal generator 102 into a current and superimposes it on the direct current.

  FIG. 6B shows a case where light is intensity-modulated by an acousto-optic modulator (AOM) which is a light intensity modulation element. A drive signal is output from a drive signal generator (DRV) in the AOM driver. The drive signal from the AOM driver is supplied to a transducer in the AOM to generate a dense wave in the acousto-optic crystal. Since the dense wave generates a refractive index distribution, the incident light is diffracted. At this time, by modulating the amplitude of the drive signal, the diffraction efficiency changes and the intensity of the diffracted light is modulated. In FIG. 6B, the amplitude of the drive signal of the AOM driver is modulated with the modulation signal from the modulation signal generator 102.

Since AOM generally uses a Bragg diffraction region, an AOM optical system that allows light from a light source to enter the AOM at a Bragg angle (θ _b ) is provided. The AOM optical system also has a function of making the beam diameter suitable for AOM. In FIG. 6B, the first-order diffracted light from the AOM is output (first-order diffraction angle θ ₁ ). However, 0th order light may be used. Output light from the AOM is coupled to the irradiation light guide unit 104 by a lens.

  The irradiation light guide unit 104 guides the light from the light source unit 103 and irradiates the subject 101. The detection light guide unit 105 guides the light propagated through the subject 101 to the photodetector 106. As the irradiation light guide unit 104 and the detection light guide unit 105, optical elements such as optical fibers, lenses, and prisms can be used.

  The photodetector 106 converts the light from the detection light guide unit 105 into a detection signal (also referred to as a light detection signal) such as an electrical signal, and outputs the detection signal to the detection unit 107. The light detection signal is a signal in which the intensity of light in time series is recorded. The photodetector 106 can be a photomultiplier tube (PMT), an avalanche photodiode (APD), a photodiode (PD), or the like.

The detection unit 107 measures the amplitude attenuation rate and phase of each modulation frequency from the light detection signal. In the present embodiment, as an example of measurement, homodyne detection is performed using the synchronization signal output from the modulation signal generation unit 102. Detection is performed using the modulation signal output from the modulation signal generator 102, and the amplitude attenuation rate and phase are measured for each measurement of each modulation frequency. The measured amplitude attenuation rate and phase correspond to the detected amplitude attenuation rate and the detection phase of the present invention.
At this time, the amplitude (reference amplitude) and phase (reference phase) of light irradiated on the subject 101 are acquired in advance. Then, the amplitude attenuation rate can be acquired by dividing the measurement amplitude by the reference amplitude, and the phase can be acquired by subtracting the reference phase from the measurement phase.

A lock-in amplifier can be used as the detection unit 107. The lock-in amplifier may be a method of detecting by an electric circuit, or a method of detecting by a software or the like after converting the light detection signal and the synchronization signal into digital values. In this embodiment, the synchronization signal is obtained from the modulation signal generator 102. However, detection may be performed by providing an oscillator inside the detection unit 107.
Further, not only homodyne detection but also heterodyne detection may be performed. Furthermore, in addition to the lock-in amplifier, a desired modulation frequency component may be measured using a spectrum analyzer.

  The optical coefficient calculator 108 calculates the optical coefficient of the subject 101 from the measured amplitude attenuation rate and phase. The optical coefficient calculation unit 108 includes an amplitude phase calculation unit 109, an optical coefficient update unit 110, a phase residual calculation unit 111, and an amplitude attenuation rate residual calculation unit 112.

  The detector 107 and the optical coefficient calculator 108 may be configured as an integrated processing unit or may be configured separately. When configured as a processing means, an information processing apparatus that operates according to a predetermined program can be used. Each component in the optical coefficient calculation unit 108 may be collected as in the present embodiment, or may be provided separately. For example, there are a method for realizing each component by a circuit and a method for realizing it by an information processing apparatus.

The amplitude phase calculation unit 109 calculates an amplitude attenuation rate (estimated amplitude attenuation rate) and a phase (estimated phase) at a certain optical coefficient (estimated optical coefficient). The calculation is performed for each modulation frequency, and A _c (f _i ) and Φ _c (f _i ) in equation (2) are calculated. For the calculation, an analytical solution of a diffusion equation, a numerical solution using a diffusion equation, a transport equation, a Monte Carlo method, or the like can be used. At this time, it is desirable to improve the accuracy of the calculation by taking into account the measurement system model such as the shape of the subject 101, the light irradiation position, and the detection position. The estimated amplitude attenuation rate and the estimated phase are output to the amplitude attenuation rate residual calculation unit 112 and the phase residual calculation unit 111, respectively.

The amplitude attenuation rate residual calculation unit 112 calculates the amplitude attenuation rate residual _{RA_i} of Expression (2) using the estimated amplitude attenuation rate from the amplitude phase calculation unit and the measured amplitude attenuation rate from the detection unit 107. .
The phase residual calculation unit 111 calculates the phase residual _{RΦ_i} of Expression (2) using the estimated phase from the amplitude phase calculation unit and the measured phase from the detection unit 107. At this time, w (f _i ) in Expression (2) is weighted according to the modulation frequency. w (f _i ) is a weight that becomes smaller as the modulation frequency is lower.

FIG. 7 is an example of the weight w (f _i ). For example, a weight that increases linearly with respect to the modulation frequency described above (reference A in FIG. 7), a weight that increases exponentially with respect to the modulation frequency (reference B in FIG. 7), and a stepwise weight with respect to the modulation frequency. (C in FIG. 7) can be used. By such weighting, an error in calculating the optical coefficient due to phase noise can be reduced.
The amplitude attenuation rate residual and the phase residual are added and output to the optical coefficient updating unit 110 as the residual R in Equation (2).

  The optical coefficient update unit 110 outputs an estimated optical coefficient used for calculation by the amplitude phase calculation unit 109. Estimating optics so that the residual R becomes smaller using various search methods such as gradient methods such as Newton's method and conjugate gradient method, non-gradient methods such as simplex method, and global search methods such as genetic algorithm. Update the coefficient.

  FIG. 1 shows a flow of an inverse problem calculation algorithm for calculating an optical coefficient of a subject from an input amplitude attenuation rate (input amplitude attenuation rate) and phase (input phase), which is executed by the optical coefficient calculation unit 108.

(A101: Input of amplitude attenuation rate and phase)
In A101, an amplitude attenuation rate A _m (f _i ) and a phase Φ _m (f _i ) of a plurality of different modulation frequencies are input. FIG. 1 shows a case where there are N modulation frequencies (N = 0 to N−1).
(A102: Calculation of estimated amplitude attenuation rate and estimated phase)
In A102, the estimated amplitude attenuation rate and the estimated phase of each modulation frequency are calculated using the estimated absorption coefficient μa_c and the estimated scattering coefficient μs′_c (estimated optical coefficient). A general optical coefficient of a living body (for example, μa to 0.01 / mm, μs ′ to 1 / mm) may be used as the initial value of the estimated optical coefficient.

(A103: Calculation of phase residual for each modulation frequency)
In A103, for each modulation frequency, the residual between the input phase Φ _m (f _i ) and the estimated phase Φ _c (f _i ) obtained in A102 is calculated.
(A104: Calculation of residual of amplitude attenuation rate for each modulation frequency)
In A104, for each modulation frequency, the residual between the input amplitude attenuation rate Am (f _i ) and the estimated amplitude attenuation rate Ac (f _i ) obtained in A102 is calculated.

(A105: Weighting of residual between input phase and estimated phase)
In A105, a weight corresponding to the modulation frequency is applied to the residual between the input phase and the estimated phase of each modulation frequency obtained in A103. This corresponds to the weighted phase residual of the present invention.
(A106: Calculation of residual)
In A106, the residual R is calculated by adding the phase residual _RΦ and the amplitude attenuation rate residual _RA .

(A107: Update of estimated optical coefficient)
When the residual R obtained in A106 is not less than ε (that is, the comparison result is not less than a predetermined threshold), the estimated optical coefficient is updated. The amount by which the estimated optical coefficient is updated can be calculated from the residual R. The predetermined threshold value ε used for this comparison is appropriately determined based on required calculation accuracy and conventional knowledge.
Step A102 to step A107 are repeated until the residual R becomes smaller than ε. The repetition is interrupted when the residual R becomes smaller than ε, and the estimated absorption coefficient μa_c and the estimated scattering coefficient μs′_c at that time are set as the absorption coefficient μa and the scattering coefficient μs ′ of the subject 101.

  The above algorithm can be executed as a program such as a computer. In this embodiment, the amplitude attenuation rate and the phase are measured. However, by inputting separately acquired amplitude attenuation rate and phase data to a computer and executing the above algorithm, the optical coefficient of the subject can be calculated as in the case of using the measured amplitude attenuation rate and phase.

The optical coefficient calculation unit 108 is for calculating the amplitude attenuation rate and phase by the amplitude phase calculation unit 109, calculating the residual by the amplitude attenuation rate residual calculation unit 112 and the phase residual calculation unit 111, and calculating by the optical coefficient update unit 110. The optical coefficient is updated repeatedly. The calculation optical coefficient when the residual R becomes sufficiently small is output to the display unit 113 as the optical coefficient of the subject 101.
The display unit 113 displays the calculated optical coefficient of the subject 113 to the measurer.

(Optical characteristics measurement method)
Next, the optical characteristic measuring method according to the present embodiment will be described with reference to the flowchart of FIG.

(S101: Step of irradiating intensity modulated light)
In this step, by switching the switch of the modulation signal generator 102 to the oscillator of the modulation frequency f _i, and outputs a modulated signal of the modulation frequency f _i to the light source unit 103. Light source unit 103 outputs the light intensity-modulated at a modulation frequency f _i with the modulated signal is applied to the subject 101 using the irradiation light guide 104.
(S102: Step of detecting light propagated through the subject)
In this step, the light that has been irradiated on the subject 101 and propagated in S101 is detected by the photodetector 106. A light detection signal is acquired by detecting the light intensity in time series.

(S103: Step of obtaining amplitude attenuation rate and phase)
In this step, from the light detection signal acquired in S103, to acquire the amplitude attenuation factor and phase of the light modulation frequency f _i at the detection section 107.
S101 to S103 are repeated for the number N of modulation frequencies to be measured, and the amplitude attenuation rate and phase of each modulation frequency f _i (i = 0 to N−1) are acquired. When N measurements are completed (D101 = Yes), the process proceeds to S104.

(S104: Step of calculating optical coefficient of subject)
In this step, the optical coefficient of the subject 101 is acquired by the optical coefficient calculation unit 108 using the N amplitude attenuation rates and phases acquired in S103. The acquired optical coefficient is displayed to the measurer through the display unit 113.

  As described above, according to the optical characteristic measuring apparatus according to the present embodiment, the optical coefficient can be obtained with high accuracy by using the weight according to the modulation frequency. Furthermore, subject information can be calculated more accurately by performing photoacoustic tomography calculation using such optical coefficients.

<Second Embodiment>
In the second embodiment, an optical characteristic measuring apparatus that performs measurement once using light including a plurality of modulation frequencies is shown.

(Device configuration)
The apparatus configuration of the optical characteristic measuring apparatus according to this embodiment will be described with reference to FIG. 9, the same elements as those in the first embodiment are denoted by the same reference numerals as those in FIG. 4, and description thereof is omitted.

  The apparatus includes a modulation signal generation unit 201 and a light source unit 103 which are light source units, a photodetector 106 which is a light detection unit, and a detection unit 202 which is a unit for measuring an amplitude phase. The apparatus further includes an optical coefficient calculation unit 108 that is a unit that calculates an optical coefficient, and a phase residual calculation unit 110 that is a unit that applies a weight to the phase residual.

The modulation signal generator 201 generates one modulation signal for generating intensity modulated light. Details of the modulation signal generator 201 are shown in FIG.
FIG. 10A illustrates a configuration in the case where one modulated signal obtained by adding outputs from a plurality of oscillators is output to the light source unit 103. In this case, a signal for each oscillator is output to the detection unit 202 so that the detection unit 202 performs detection for each modulation frequency.
FIG. 10B shows a configuration when a single modulation frequency (f ₀ ) is output to the light source unit 103 and the detection unit 202. In this case, to generate harmonics of _{f 0} in the light source unit 103.

  The light source unit 103 generates light having a plurality of modulation frequencies using the modulation signal from the modulation signal generation unit 102 as in the first embodiment. When the modulation signal generator 201 has the configuration of FIG. 10A, that is, when a modulation signal in which a plurality of modulation frequencies are mixed is supplied, FIG. 6A (laser diode drive current modulation) or FIG. 6B (external modulation by AOM) can be used. In this case, the output light includes the modulation frequency of each oscillator shown in FIG.

On the other hand, when the modulation signal generator 201 has the configuration of FIG. 10B, the configuration of FIG. 6A can be used. A method for generating light having a plurality of modulation frequencies in this case will be described below with reference to FIG. FIG. 11A illustrates a light source portion 103 having the same configuration as that in FIG. FIG. 11B shows the drive current of the laser diode in this embodiment.

In the configuration of FIG. 11, the direct current drive current supplied from the laser driver to the laser head is set near the laser oscillation threshold of the laser diode (reference numeral (1) in FIG. 11B). When the modulation signal having the frequency f0 from the modulation signal generator 102 is superimposed on this (reference numeral (2) in FIG. 11B), the laser diode emits light with sufficient intensity only when the modulation signal exceeds the laser oscillation threshold. To do. Because DC drive current is near the laser oscillation threshold, the light emission waveform of the laser diode is only approximately half amplitude of the frequency f _0. Since such a waveform includes harmonics of the modulation frequency f ₀ , light including a plurality of modulation frequencies can be generated.

The detector 202 measures the amplitude attenuation rate and phase of a plurality of modulation frequencies included in the light detection signal.
First, the configuration of the detection unit 202 when the configuration of the modulation signal generation unit 201 is as shown in FIG. In the configuration of FIG. 12A, the amplitude attenuation rate and the phase are measured by the detection processing unit in the detection unit 202 using the light detection signal from the light detector 106 and the synchronization signal selected by the switch. The light irradiation to the subject is continued until the measurement is completed for all the modulation frequencies.

In the configuration of FIG. 12B, a buffer for storing the light detection signal is provided. Since the detection process is performed on the buffer signal, it is only necessary to irradiate the subject with light for the minimum time necessary for the detection process for one modulation frequency. For this reason, measurement time can be shortened rather than the structure of FIG. 12A.
Here, the amount of light that can be irradiated to the living body is limited by MPE (Maximum Perspective Exposure), and the shorter the irradiation time, the larger the allowable amount of light. When the subject is a living body, the light irradiation time can be shortened by using the configuration of FIG. 12B, so that the light intensity can be increased. As a result, the SN ratio of measurement can be improved.

  In the configuration of FIG. 12C, detection processing units are provided for the number of modulation frequencies. Thereby, the amplitude attenuation rate and phase of each modulation frequency can be acquired simultaneously.

Next, the configuration of the detection unit 202 when the configuration of the modulation signal generation unit 201 is FIG. 10B will be described with reference to FIG. 12D. The detection unit 202 includes a local oscillator corresponding to the frequency f ₀ of the modulation signal generation unit 201 and its harmonics (f ₀ , f ₁ ,..., F _N-1 ). Since the intensity-modulated light distorted with the frequency f ₀ shown in FIG. 10B is irradiated, the frequency of the harmonic can be determined in advance. Further, when f ₀ of modulation signal generating section 201 is variable, it is preferable to change the frequency of the local oscillator by giving information on frequency f ₀ as shown by the dashed arrow in FIG. 12D. In this case, a local oscillator having a variable frequency is used.
Also in FIG. 12D, buffers can be provided as shown in FIG. 12B, or detection processing units can be provided as many as the number of local oscillators as shown in FIG. 12C.

In the detection unit 202, the amplitude (reference amplitude) and phase (reference phase) of each modulation frequency of the light irradiated on the subject 101 are acquired in advance. The amplitude can be acquired by dividing the measurement amplitude by the reference amplitude and subtracting the reference phase from the measurement phase. In the present embodiment, these processes are included in the processes performed by the detection processing unit in the detection unit 202.
As in the first embodiment, the phase residual calculator 111 reduces the optical coefficient calculation error due to phase noise by applying the weight of FIG. 7 to the phase residual R _{Φ_i} according to the modulation frequency. Can do.

(Optical characteristics measurement method)
Next, the optical property measuring method according to the present embodiment will be described with reference to the flowchart of the optical property measuring method shown in FIG.

(S201: Step of irradiating intensity modulated light)
In this step, the subject is irradiated with light having a plurality of modulation frequencies from the light source unit 103 through the irradiation light guide unit 104.
(S202: Step of detecting light propagated through subject)
In this step, the light that has been irradiated on the subject 101 and propagated in S201 is detected by the photodetector 106 in S201. The light intensity is detected in time series to obtain a light detection signal.

(S203: Step of obtaining amplitude attenuation rate and phase)
In this step, from the light detection signal acquired in S202, to acquire the amplitude attenuation factor and phase of the light modulation frequency f _i at the detection section 202. If detection is performed by changing the synchronization signal used for detection and the amplitude attenuation rate and phase are acquired by the number N of modulation frequencies (D201 = Yes), the process proceeds to S204. In addition, when the structure of the detection part 202 is FIG. 12C which has several detection process parts, it is not necessary to change a synchronous signal.
(S204: Step of calculating optical coefficient of subject)
This step is the same as S104.

<Third embodiment>
In the third embodiment, an apparatus for imaging an inside of a subject using light, particularly an apparatus in which the present invention is applied to a photoacoustic imaging apparatus is shown.

A photoacoustic imaging device irradiates a subject with pulsed light generated from a light source, and absorbs elastic waves (photoacoustic waves) generated from a living tissue or the like that absorbs energy of light propagated and diffused in the subject at a plurality of locations. To detect. By analyzing these signals, image data indicating the sound pressure distribution (initial sound pressure distribution) at the moment when an elastic wave is generated inside the subject can be obtained.
The initial sound pressure distribution is related to the light energy absorption rate distribution in the subject, that is, the absorption coefficient distribution. Furthermore, measurement is performed at a plurality of wavelengths, and a functional information image such as an oxygen saturation distribution is obtained from the absorption coefficient distribution at each wavelength. Since oxygen saturation corresponds to the neovascularization characteristic of tumors, functional information images may be used for cancer diagnosis.

  In order to acquire the absorption coefficient distribution by the photoacoustic imaging apparatus, as described in Patent Document 2, it is necessary to correct the initial sound pressure distribution with the light amount distribution in the subject. If the spatial average absorption coefficient μa and scattering coefficient μs ′ (average optical coefficient) of the subject are known, the light quantity distribution can be calculated by a diffusion equation, a Monte Carlo method, or the like.

  Therefore, in the present embodiment, the average optical coefficient of the subject is acquired using the intensity-modulated light, the initial sound pressure distribution is corrected with the light amount distribution calculated using the average optical coefficient, and the absorption coefficient distribution is acquired. When the average optical coefficient is acquired using a plurality of modulation frequencies, the average optical coefficient can be acquired with high accuracy by applying a weight corresponding to the modulation frequency to the phase residual. As a result, the accuracy of correction when obtaining the absorption coefficient distribution is improved.

(Device configuration)
The apparatus configuration of the optical characteristic measuring apparatus according to the present embodiment will be described with reference to FIG. In FIG. 14, the same elements as those in the first embodiment are denoted by the same reference numerals as those in FIG. 4, and description thereof is omitted. The optical property measurement apparatus of the present embodiment is also a subject information acquisition apparatus using photoacoustic tomography technology.

The apparatus includes a modulation signal generation unit 307 and a light source unit 103 that are light source units, a photodetector 106 that is a light detection unit, a detection unit 107 that measures amplitude phase, and an optical coefficient calculation unit that calculates optical coefficients. Part 108. The apparatus further includes a phase residual calculation unit 110 that is means for applying a weight to the phase residual, a pulse light source unit 301 that is a pulse light source unit, a probe 302 that is an acoustic wave detection unit, and a unit that calculates an initial sound pressure. An image reconstruction unit 303 is included. The apparatus further includes a light amount calculation unit 304 that is a unit that calculates a light amount, and a correction unit 305 that is a unit that performs correction.

  The pulse light source unit 301 generates pulsed light that irradiates the subject 101 and excites a photoacoustic wave in the subject 101. As the pulse light source, an incoherent light source such as a flash lamp or a coherent light source such as a laser can be used. Since the intensity of the photoacoustic signal is proportional to the amount of light, the output of the pulse light source 301 is preferably high. For example, a high-power pulsed laser light source such as a titanium sapphire laser or an alexandrite laser is suitable. In order to allow a sufficient amount of light to excite the photoacoustic wave to reach a wide range in the subject 101, an optical system for expanding the beam diameter may be provided to expand the irradiation area.

  The probe 302 receives a photoacoustic wave generated in the subject 101, generates a reception signal, and outputs the reception signal to the reconstruction unit 303. As the probe 302, a transducer using a piezoelectric phenomenon, a transducer using optical resonance, a transducer using a change in capacitance, or the like can be used. If a probe in which a plurality of transducers (elements) are arranged one-dimensionally or two-dimensionally is used, effects such as wide-ranging measurement, time reduction, and SN ratio improvement can be obtained. In order to measure a wider area, a mechanism for scanning the probe 302 with respect to the subject 101 may be provided.

  The image reconstruction unit 303 acquires the initial sound pressure distribution in the subject 101 by performing image reconstruction processing using the received signal from the probe 302. As the image reconstruction processing, for example, a time domain back projection method, a time reversal reconstruction method, a Fourier domain reconstruction method, a model-based reconstruction method, or the like can be used. The initial sound pressure distribution is output to the correction unit 305.

  The light amount calculation unit 304 calculates the light amount distribution in the subject 101 using the average optical coefficient calculated by the optical coefficient calculation unit 108. The light quantity can be calculated by solving equations describing the energy behavior of light (diffusion equation or transport equation) using the finite element method or the difference method, or by considering the behavior of light energy as the statistical behavior of photons. The Monte Carlo method to be performed can be used. The light amount distribution is output to the correction unit 305.

ここで、ｒは位置ベクトル、Ｐ_０（ｒ）は初期音圧分布、Γはグリュナイゼン係数、μａ（ｒ）は吸収係数分布、Φ（ｒ）は光量分布である。位置ｒごとに初期音圧をグリュナイゼン係数と光量で割ることで、吸収係数を取得できる。グリュナイゼン係数は被検体の体積膨張係数と音速の２乗の積を定圧比熱で割ったものであり、生体では略一定の既知の値を取るといわれている。 The correction unit 305 corrects the initial sound pressure distribution calculated by the image reconstruction unit 303 with the light amount distribution calculated by the light amount calculation unit 304, and calculates the absorption coefficient distribution in the subject 101. The following equation (3) is used for the correction (see Patent Document 2).

Here, r is a position vector, P ₀ (r) is an initial sound pressure distribution, Γ is a Gruneisen coefficient, μa (r) is an absorption coefficient distribution, and Φ (r) is a light quantity distribution. The absorption coefficient can be acquired by dividing the initial sound pressure by the Gruneisen coefficient and the amount of light for each position r. The Gruneisen coefficient is obtained by dividing the product of the volume expansion coefficient of the subject and the square of the speed of sound by the constant pressure specific heat, and is said to take a substantially constant known value in the living body.

The display unit 306 displays the absorption coefficient distribution in the subject 101 calculated by the correction unit 305 to the measurer. Functional information such as oxygen saturation distribution may be calculated and displayed from absorption coefficient distributions of a plurality of wavelengths. Also in this embodiment, the display of the subject information as an image is not essential, and may be displayed as a numerical value or stored as analysis data.

  As the modulation signal generation unit 307, the modulation signal generation unit 102 of the first embodiment or the modulation signal generation unit 201 of the second embodiment can be used. The modulation signal generation unit 307 outputs a modulation signal for generating intensity modulated light to the light source unit 103.

  With respect to the light source unit 103, the same configuration as in the first and second embodiments can be used. However, it is desirable that the wavelength of light generated by the light source unit 103 is as close to the wavelength of the pulse light source unit 301 as possible. By doing so, the light quantity distribution in the subject 101 by the pulse light source unit 301 can be calculated more accurately. Alternatively, a configuration in which a single light source serves as both the pulse light source unit 301 and the light source unit 103 can be employed.

  The detection unit 308 adopts the configuration of the detection unit 107 of the first embodiment if the modulation signal generation unit 307 is the configuration of the modulation signal generation unit 102 of the first embodiment. On the other hand, if the modulation signal generation unit 307 has the configuration of the modulation signal generation unit 201 of the second embodiment, the configuration of the detection unit 202 of the second embodiment is adopted. The detector 308 outputs the amplitude attenuation rates and phases of the plurality of modulation frequencies to the optical coefficient calculator 108.

  The optical coefficient calculator 108 calculates the average optical coefficient of the subject 101 and outputs it to the light quantity distribution calculator 304. In the calculation of the average optical coefficient, as in the first and second embodiments, the phase residual calculation unit 111 performs weighting according to the modulation frequency, thereby reducing the error of the average optical coefficient due to phase noise and improving the accuracy.

  With the above configuration, the initial sound pressure distribution can be corrected with the light amount distribution obtained by using the average optical coefficient with higher accuracy. As a result, the accuracy of the acquired absorption coefficient distribution is improved.

(Optical characteristics measurement method)
Next, the optical characteristic measuring method according to the present embodiment will be described with reference to the flowcharts of FIGS. 15A and 15B.

  FIG. 15A is a flowchart when the configurations of the modulation signal generation unit 307 and the detection unit 308 are the configurations of the modulation signal generation unit 102 and the detection unit 107 of the first embodiment, respectively.

(S301: Step of irradiating pulsed light)
In this step, the subject 101 is irradiated with pulsed light generated by the pulse light source unit 301.
(S302: Step of detecting photoacoustic wave)
In this step, the photoacoustic wave generated by the pulsed light irradiation in S301 is detected by the probe 302, and a received signal is acquired.
Until the received signal becomes sufficient SN (D301 = Yes), S301 and S302 are repeated to integrate the received signals.
(S303: Step of obtaining initial sound pressure distribution)
In this step, the image reconstruction unit 303 acquires the initial sound pressure distribution in the subject 101 using the reception signal acquired in S302.

(S304 to S307: step of obtaining the average optical coefficient of the subject)
Steps S304 to S307 are the same as steps S101 to S104 in the first embodiment shown in FIG. Through these steps, the average optical coefficient of the subject is acquired.
The measurement of the amplitude attenuation rate and the phase performed in S304 to S306 is executed at a time when S301 and S302 are not performed (D302 = Yes). This is because pulse light for photoacoustic wave measurement and intensity-modulated light for amplitude attenuation rate and phase measurement do not affect each other's measurement.

(S308: Step of obtaining light quantity distribution)
In this step, the light amount distribution calculation unit 304 acquires the light amount distribution in the subject 101 when the subject is irradiated with pulsed light using the average optical coefficient of the subject 101 acquired in S307.
(S309: Step of obtaining absorption coefficient distribution)
In this step, the correction unit 304 corrects the initial sound pressure distribution acquired in S303 with the light amount distribution acquired in S308, and acquires the absorption coefficient distribution in the subject 101. The acquired absorption coefficient distribution is sent to the display unit 306, and the function information distribution in the subject 101 is displayed to the measurer.

  FIGS. 16A and 16B are diagrams showing the timing of the photoacoustic wave measurement in S301 and S302 and the amplitude attenuation rate / phase measurement in S304 to S306.

  In general, a pulsed light for photoacoustic wave measurement requires a high output, so a Q-switched laser is used. A Q-switched laser requires a long irradiation cycle in order to irradiate light with sufficient intensity. The repetition interval between S301 and S302 is substantially defined by this irradiation cycle. In a Q-switched laser having a pulse width of several tens of nanoseconds and a pulse energy of several tens to several hundreds mJ, which is generally used for photoacoustic wave measurement, the period is several tens to several hundreds milliseconds.

On the other hand, in the intensity-modulated light / phase measurement, the average optical coefficient of the subject 101 is μa to 0.01 / mm, μs ′ to 1 / mm, which are general values of the living body, and the light irradiation point and the detection point are When it is assumed that the interval is generally ˜3, 4 cm, the detection can be executed in about 10 milliseconds. For this reason, amplitude attenuation rate / phase measurement can be performed between photoacoustic wave measurements. For example, a plurality of modulation frequencies can be measured sequentially as shown in FIG.
Also, as shown in FIG. 16B, when the number of times of acousto-acoustic wave measurement is large and there is a lot of time during which the amplitude attenuation rate / phase measurement can be performed, the detection time is increased by increasing the time of amplitude attenuation rate / phase measurement once. The SN may be improved.

  FIG. 15B is a flowchart when the configurations of the modulation signal generation unit 307 and the detection unit 308 are the configurations of the modulation signal generation unit 201 and the detection unit 201 of the first embodiment, respectively. Steps S401 to S403, S408, and S409 are the same as steps S301 to S303, S308, and S309 in FIG. 15A, respectively. In addition, each process from S404 to S407 is the same as S201 to S204 in the second embodiment of FIG.

FIGS. 16C and 16D are diagrams showing the timing of the photoacoustic wave measurement in S401 and S402 and the amplitude attenuation rate / phase measurement in S404 and S405.
Figure 16 (C) and .SIGMA.f _i shown in FIG. 16 (D) is meant an intensity-modulated light comprising a plurality of modulation frequencies. Since the intensity-modulated light includes a plurality of modulation frequencies, the amplitude attenuation rate / phase measurement may be performed once after the first photoacoustic wave measurement as shown in FIG. Further, as shown in FIG. 16D, the SN of detection may be improved by increasing the time of amplitude attenuation rate / phase measurement.

  As described above, according to the subject information acquiring apparatus of the present embodiment, the light amount distribution can be measured using a highly accurate optical coefficient, and can be used for calculating the absorption coefficient distribution in photoacoustic tomography. As a result, the characteristic information in the subject can be acquired more accurately.

102: Modulation signal generation unit, 103: Light source unit, 106: Photo detector, 107: Detection unit, 10
8: optical coefficient calculation unit, 109: amplitude phase calculation unit, 111: phase residual calculation unit, 112: amplitude attenuation rate residual calculation unit

Claims (15)

A light detection means for detecting each of a plurality of intensity-modulated lights, which are different from each other in intensity modulation frequency representing a change in light intensity, irradiated on the subject and generating a light detection signal after propagating through the subject;
Acoustic wave detection means for detecting a photoacoustic wave generated by irradiating the subject with pulsed light and generating a photoacoustic signal;
A processing means,
From the light detection signal, for each intensity modulation frequency, obtain a detection amplitude attenuation rate and a detection phase,
For each intensity modulation frequency, based on a predetermined estimated absorption coefficient and a predetermined estimated scattering coefficient for the subject, an estimated amplitude attenuation rate and an estimated phase of the intensity modulated light are generated,
A phase residual indicating a residual between the detected phase and the estimated phase is generated for each intensity modulation frequency, and a weighted phase residual is generated by applying a weight corresponding to the intensity modulation frequency to the phase residual. ,
For each intensity modulation frequency, an amplitude attenuation rate residual indicating a residual between the detected amplitude attenuation rate and the estimated amplitude attenuation rate is generated,
By comparing a value obtained from the weighted phase residual and the amplitude attenuation rate residual with a predetermined threshold value, an absorption coefficient and a scattering coefficient of the subject are generated,
Processing means for generating characteristic information of the subject based on the photoacoustic signal, the absorption coefficient, and the scattering coefficient;
A subject information acquisition apparatus characterized by comprising: The object information acquiring apparatus according to claim 1, wherein the weight is a smaller value as the intensity modulation frequency is lower. The object information acquiring apparatus according to claim 1, wherein the weight increases linearly, exponentially, or stepwise with respect to the intensity modulation frequency. The object information acquiring apparatus according to claim 1, further comprising light source means for irradiating the intensity-modulated light. 5. The object information acquiring apparatus according to claim 4, wherein the light source means generates a plurality of intensity-modulated lights having different intensity modulation frequencies by generating a plurality of modulation signals having different frequencies. . 6. The object information acquiring apparatus according to claim 5, wherein the light source means modulates the intensity of light by modulating a drive current of a laser diode with the modulation signal. 6. The object information acquiring apparatus according to claim 5, wherein the light source means modulates light intensity by an acousto-optic modulator.   The object information acquiring apparatus according to claim 4, wherein the light source unit irradiates a plurality of the intensity-modulated lights by switching the intensity-modulation frequency. The object information acquiring apparatus according to claim 4, wherein the light source unit emits light including a plurality of the intensity modulation frequencies. 10. The object information acquiring apparatus according to claim 1, wherein the processing unit uses a general value of the object as the estimated absorption coefficient and the estimated scattering coefficient. 11. The processing means compares a residual R obtained by adding the weighted phase residual and the amplitude attenuation rate residual with the predetermined threshold, and when the residual R is equal to or larger than the predetermined threshold, The object information acquiring apparatus according to claim 10, wherein the estimated absorption coefficient and the estimated scattering coefficient are updated based on the residual R. The subject information acquiring apparatus according to claim 1, further comprising pulse light source means for irradiating the subject with the pulsed light. The processing means obtains a light quantity distribution in the subject using the absorption coefficient and the scattering coefficient, and generates an absorption coefficient distribution in the subject generated based on the photoacoustic signal and the light quantity distribution. The object information acquiring apparatus according to claim 12, wherein the characteristic information is used. The pulse light source means irradiates the subject with pulsed light of a plurality of frequencies, generates an oxygen saturation distribution in the subject from the absorption coefficient distribution obtained at the plurality of frequencies, and generates the characteristic information and The object information acquiring apparatus according to claim 13, wherein: An irradiation means for irradiating a subject with a plurality of intensity-modulated lights having different intensity-modulation frequencies representing changes in light intensity;
A light detection means for generating a light detection signal by detecting each of the plurality of intensity-modulated lights propagated through the subject;
A processing means,
From the light detection signal, for each intensity modulation frequency, obtain a detection amplitude attenuation rate and a detection phase,
For each intensity modulation frequency, based on a predetermined estimated absorption coefficient and a predetermined estimated scattering coefficient for the subject, an estimated amplitude attenuation rate and an estimated phase of the intensity modulated light are generated,
A phase residual indicating a residual between the detected phase and the estimated phase is generated for each intensity modulation frequency, and a weighted phase residual is generated by applying a weight corresponding to the intensity modulation frequency to the phase residual. ,
For each intensity modulation frequency, an amplitude attenuation rate residual indicating a residual between the detected amplitude attenuation rate and the estimated amplitude attenuation rate is generated,
Processing means for generating an absorption coefficient and a scattering coefficient of the object by comparing a value obtained from the weighted phase residual and the amplitude attenuation rate residual with a predetermined threshold;
An optical property measuring apparatus comprising:

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