JP5171564B2 - Acousto-optic tomography measuring apparatus and measuring method - Google Patents

Description

  The present invention relates to a technique for measuring light absorption characteristics and scattering characteristics inside an absorption scatterer such as a living body using light and ultrasonic waves.

  In recent years, as one of techniques for imaging the inside of a living body, there is a technique of optical CT using near infrared light. By using light, the inside of a living body can be measured more easily and without fear of exposure. In addition, it is possible to perform functional imaging such as metabolism of hemoglobin inside the living body from the spectral information, and it is very useful to measure in vivo non-invasively using light. On the other hand, the light is strongly scattered, and the light that has entered the inside of the living body repeatedly scatters one after another. As a result, it becomes difficult to obtain local spectral characteristics inside the living body.

  As a method for acquiring local spectral characteristics inside a living body, there is a method using a light modulation effect (acousto-optic effect) by ultrasonic waves. This measuring method is known as AOT (Acousto-Optical Tomography). In patent document 1, near-infrared light is irradiated to a living body, and at the same time, an ultrasonic wave is focused inside the living body. In the ultrasonic focusing region, local optical information is acquired by detecting light modulated by interaction with ultrasonic waves. Such AOT technology enables imaging with higher resolution than the above-described optical CT.

In AOT, by comparing the speckle contrast when an ultrasonic wave is applied with the speckle contrast when no ultrasonic wave is applied, the intensity of the interaction between the ultrasonic wave and light is quantified as a modulation depth. . This Modulation
Since Depth depends on the absorption coefficient / scattering coefficient inside the living body, the absorption / scattering information inside the living body is known. Furthermore, it is possible to acquire the distribution of absorption / scattering information inside the living body by moving the ultrasound convergence area.

Non-Patent Document 1 describes a change in the correlation of speckle patterns with time change in the interaction between ultrasonic waves and light.
US Pat. No. 6,738,653 "Transmission- and side-detection configuration in ultrasound-modulated optical tomography of thick biologics", Liong V. Wang, APPLIED OPTICS, 2003, Vol 42, No. 19

  In the living body, the speckle state changes with time due to temporal flow caused by biomolecules and blood flow. For this reason, when speckle is observed using an area sensor or the like, the speckle contrast decreases as the capture time by the area sensor increases, and the S / N in AOT measurement decreases. On the other hand, although the speckle contrast is increased by shortening the capturing time by the area sensor, the S / N is decreased because the integration time at the area sensor is not sufficient. In AOT measurement, it is desirable to perform speckle observation using an acquisition time that maximizes S / N.

  Non-Patent Document 1 merely measures changes in the correlation of speckle patterns with time changes in the interaction between ultrasonic waves and light, and does not mention the setting of the time at which the S / N is maximized. In principle, it is possible to estimate the measurement time at which the S / N is maximum using only the area sensor, but the S / N of the signal from the area sensor is poor and the measurement must be performed with time resolution. In other words, it is conceivable that a large amount of error is included.

  Therefore, an object of the present invention is to provide a technique capable of easily calculating a measurement time (capture time) at which the S / N is maximum in acousto-optic tomography measurement.

In order to solve the above-described problems, an acousto-optic tomography measurement device according to the present invention includes:
A coherent light source for irradiating the measurement target with coherent light, and
An area sensor for detecting speckles of light emitted from the measurement object;
Ultrasonic irradiation means for irradiating the measurement object with ultrasonic waves;
An acousto-optic tomography measuring apparatus for performing acousto-optic tomography measurement,
Exit light detection means for detecting the exit light from the measurement object;
The temporal change C _off (t) of the speckle contrast and the noise amount σ _noise (t) of the area sensor are calculated from the detection result by the emitted light detection means, and the temporal change of the calculated speckle contrast is calculated. Based on C _off (t) and the noise amount σ _noise (t) of the area sensor, the area so that the S / N of the speckle detection signal by the area sensor at the time of the acousto-optic tomography measurement is maximized. Measurement time determining means for determining a measurement time ts of the speckle by the sensor;
It is characterized by having.

In addition, the acousto-optic tomography measurement method according to the present invention includes:
A coherent light source for irradiating the measurement target with coherent light, and
Ultrasonic irradiation means for irradiating the measurement object with ultrasonic waves;
An area sensor for detecting speckles of light emitted from the measurement object;
Exit light detection means for detecting the exit light from the measurement object;
An acousto-optic tomography measuring method performed by an acousto-optic tomography measuring device having:
An emission light detection step of measuring the emission light from the measurement object;
Calculating a temporal change C _off (t) of speckle contrast from the detection result of the emission light detection step;
Calculating a noise amount σ _noise (t) of the area sensor;
Based on the calculated temporal change C _off (t) of the speckle contrast and the noise amount σ _noise (t) of the area sensor, the detection signal of the speckle detection signal by the area sensor at the time of acousto-optic tomography measurement A measurement time determining step of determining the speckle measurement time ts by the area sensor so that S / N is maximized;
And an acousto-optic tomography measurement step of performing acousto-optic tomography measurement with a measurement time by the area sensor as ts.

  According to the present invention, it is possible to obtain with high accuracy the measurement time for maximizing S / N in acousto-optic tomography measurement, and it is possible to obtain the spectral characteristics of absorption scatterers such as living bodies with high accuracy.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. However, the functions, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention only to those unless otherwise specified. The functions and shapes of the components and components once described in the following description are the same as those in the first description unless otherwise described.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a diagram illustrating a configuration of an acousto-optic tomography measurement apparatus (AOT measurement apparatus) according to the present embodiment. In the measurement system according to the present embodiment, acousto-optic tomography measurement (AOT measurement) is performed on a biological tissue or the like as a measurement target, and measurement information is imaged and displayed. In the present embodiment, a measurement time (capture time) at which the S / N of the detection signal at the time of AOT measurement is maximized is obtained, and AOT measurement is performed at the measurement time.

<Constitution>
First, a configuration for performing AOT measurement will be described.

  A measurement object 1 such as a biological tissue is stored in a measurement container 2. Between the measurement object 1 and the measurement container 2 is a medium (matching material 3) having a known and uniform characteristic in which the refractive index and scattering coefficient of light and the acoustic characteristics of the ultrasonic wave can be regarded as almost the same as those of the measurement object 1. be satisfied.

  The signal generator 11 is driven by the control unit 10 and emits coherent light from the coherent light source 12. The irradiated coherent light is guided to the optical fiber 13. The optical fiber 13 is connected to the side surface of the measurement container 2, and the measurement object 1 is irradiated with coherent light through the measurement container 2. The irradiated coherent light is repeatedly absorbed and scattered inside the measurement object 1 and propagates as diffused light in various directions. The light propagated through the measurement object 1 is emitted from the emission opening 21.

  Note that the light irradiation position may be changed by moving the optical fiber 13. Alternatively, the incident position of light may be sequentially switched by connecting two or more optical fibers to a coherent light source and selecting an optical fiber to be guided using a switch.

  The signal generator 11 is driven by the control unit 10 and irradiates the measurement object 1 with ultrasonic waves from the ultrasonic generator 5. The ultrasonic generator 5 corresponds to the ultrasonic irradiation means of the present invention. The signal generator 11 irradiates ultrasonic waves so as to converge at the ultrasonic convergence position 4. At the ultrasonic convergence position 4, the density change of the medium due to the sound pressure occurs. When coherent light passes through the ultrasonic convergence position 4, the phase of the light is modulated according to a certain efficiency due to this density change. That is, an interaction between light and ultrasonic waves (acousto-optic effect) occurs.

  The light modulated by the interaction with the ultrasonic wave is detected by the area sensor 23. The area sensor 23 uses, for example, a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like. The area sensor 23 is driven by the controller for the driving time ts to detect light. As will be described later, the driving time ts is separately obtained as a time that maximizes the S / N of the signal.

The light detected by the area sensor 23 is converted into an electric signal, and is separated into modulated light and non-modulated light by the signal extraction unit 31. Among these, the absorption coefficient and scattering coefficient inside the measurement object 1 are calculated from the modulated light component. The calculated absorption coefficient and scattering coefficient are stored in the memory 33. Further, the information inside the measurement object 1 is obtained by sequentially moving the ultrasonic convergence position 4. All of the information is stored in the memory 33. The stored values are mapped by the image generation unit 34, and the monitor 35 displays the three-dimensional absorption coefficient, scattering coefficient, and component ratio distribution.

  Next, a configuration for obtaining the drive time ts that maximizes the S / N will be described.

  The detector 25 detects the diffused light emitted from the emission opening 21 through the opening 24. The detector 25 corresponds to the emitted light detection means of the present invention. As the detector 25, for example, a highly sensitive detector such as PMT (Photo Multiplier) or APD (Avalanche Photo Diode) is used.

  A beam splitter 24 is disposed between the exit aperture 21 and the aperture 24, and part of the emitted light is guided to the area sensor 23 described above. At this time, the optical distance from the ejection opening 21 to the area sensor 23 and the optical distance from the ejection opening 21 to the detector 25 are the same. Furthermore, the area of the opening 24 and the pixel area of the area sensor 23 are set to be the same. By doing so, the noise of the area sensor 23 can be estimated by the detector 25. Further, the opening size As of the injection opening 21 and the optical distance z are set to satisfy the following expression.

  Here, z is an optical distance from the ejection opening 21 to the detector 25 and the area sensor 23. Further, As is the area of the emission opening 21, p is the area of the opening 24 and the pixel area of the area sensor 23, and λ is the wavelength of coherent light.

  With this setting, the speckle size in the area sensor 23 becomes equal to the pixel area p, and the speckle contrast can be maximized for measurement. Further, as will be described later, the noise amount of the area sensor 23 can be easily calculated from the detection result of the detector 21.

The light detected by the detector 25 is converted into an electrical signal, and necessary information is extracted by the signal extraction unit 31. The arithmetic processing unit 32 obtains an autocorrelation function g ₂ (τ) based on the extracted information. The arithmetic processing unit 32 also estimates the noise amount of the area sensor 23 from the extracted information and accumulates it in the memory 33. Then, the arithmetic processing unit 32 maximizes the S / N of the detection signal at the time of AOT measurement from the autocorrelation function g ₂ (τ) of the intensity accumulated in the memory 33 and the noise amount of the area sensor 23. The drive time ts of the area sensor 23 is obtained. As described above, at the time of AOT measurement, the area sensor 23 is driven for the drive time ts to perform measurement.

  If the optical distance from the ejection opening 21 to the area sensor 23 and the optical distance from the ejection opening 21 to the detector 25 are the same, the area sensor 23 and the detector 25 may not be used at the same time. That is, the area sensor 23 may be replaced with the position of the detector 25 after the measurement by the detector 25 without using the beam splitter 22.

The signal extraction unit 31, the arithmetic processing unit 32, and the image generation unit 45 in the present embodiment can be realized as a signal processing unit 8 by a general-purpose computer executing a program. However, some or all of these functional units may be realized by dedicated hardware. Each functional unit may be realized by a plurality of processors. For example, the processing for determining the measurement time ts and the processing for performing acousto-optic measurement may be implemented by different processors. The signal processing unit 8 corresponds to the measurement time determining unit in the present invention.

<Processing content>
Next, the flow of processing when AOT measurement is performed by the measurement system according to the present embodiment will be described in more detail with reference to the flowchart of FIG. FIG. 2 is a flowchart for explaining the operation of the first embodiment.

  In step 101, the photon correlation method is measured using the aperture 24 and the detector 25. That is, the coherent light is irradiated from the coherent light source 11 to the measurement object 1, and the temporal fluctuation of the intensity of the scattered light is measured. At this stage, only the coherent light is irradiated without irradiating the ultrasonic wave.

Next, in step 102, the calculation processing unit 32 obtains the autocorrelation function g ₂ (τ) of the light intensity from the detection result of the emitted light (scattered light) by the detector 25. Alternatively, the arithmetic processing unit 32 may be connected to a correlator, and the autocorrelation function g ₂ (τ) may be obtained using the correlator.

Next, in step 103, the arithmetic processing unit 32 estimates the noise amount σ _noise of the area sensor 23 from the light intensity detected by the detector 25. Since the area of the opening 24 is the same as the pixel area of the area sensor, and the optical distance from the exit opening 21 to the area sensor 23 is the same as the optical distance from the exit opening 21 to the detector 25, detection is performed. The light intensity detected by the device 25 is equal to the light intensity detected by the area sensor 23. Therefore, it is possible to estimate the noise amount of the area sensor 23 from the light intensity measured by the detector 25. The amount of noise (standard deviation of light intensity) of the area sensor is shown below.

Here, sigma _r readout noise, Dt represents the dark current noise, D is the dark current, t is the area sensor acquisition time (measurement time). QI ₀ t represents shot noise, Q is quantum efficiency, I ₀ is light intensity per unit time, and the unit is W (watt). The light intensity detected by the detector 25 is applied to I ₀ t. Since σ _r , D, and Q are values unique to the area sensor 23 and are known, they are stored in the memory 33 and used. Thereby, the noise amount of the area sensor 23 according to the capture time t can be estimated using the equation (2).

Next, in step 104, the calculation processing unit 32 determines a measurement time ts in which the S / N of the detection signal of the area sensor 23 is maximum from the calculated g ₂ (τ) and σ _noise . First, the principle of the method for calculating the measurement time ts will be described.

  A value indicating the degree of speckle detected by the area sensor 23 is speckle contrast. The speckle contrast is given by:

  <I> is an average value of the light intensity acquired by the area sensor 23, and σ is a standard deviation of the light intensity acquired by the area sensor 23. The standard deviation σ is expressed as a product of the speckle contrast and the average value of the light intensity from the equation (3) (σ = C <I>).

When the speckle contrast when applying ultrasonic waves is C _on and the speckle contrast when no ultrasonic waves are applied is C _off , Modulation Depth (
The quantity representing the degree of interaction called M) can be expressed by the following equation.

From this, the difference ΔC between C _off and C _on is as follows.

When the measurement object is a living tissue or the like, M is substantially constant (about 1/1000), and therefore ΔC is proportional to C _off .

ｔはエリアセンサーでの取り込み時間である。また、ΔＣも時間に応じて変化し、

となる。 On the other hand, the temporal flow biomolecular and blood flow, the temporal change C _off the C _{off (t)} is the value becomes smaller in accordance with the capture time of the area sensor 23. It can be associated with g ₂ (τ) obtained above by the following equation.

t is the capture time of the area sensor. ΔC also changes with time,

It becomes.

Here, for comparison with the noise amount σ _noise of the area sensor, when the speckle contrast is expressed in standard deviation, the difference Δσ in standard deviation between the application and non-application of the ultrasonic wave is as follows from the relationship with the equation (3). Can be represented.

  In the AOT measurement, this difference between when an ultrasonic wave is applied and when it is not applied is detected, and a Modulation Depth is calculated by the arithmetic processing unit 32. FIG. 3 schematically shows the above relationship. FIG. 3 is an intensity frequency distribution (histogram) in the area sensor 23. The bold line indicates the intensity distribution when no ultrasonic wave is applied, the dotted line indicates the intensity distribution when ultrasonic wave is applied, and the thin line indicates the noise distribution of the area sensor 23. In AOT, it is a necessary condition that the difference Δσ in standard deviation between application and non-application of ultrasonic waves is greater than or equal to the standard deviation of noise. The S / N in AOT measurement is as follows when Δσ is a signal (S) and Equation (2) is noise (N).

Therefore, by determining the capture time t = ts in the arithmetic processing unit 32 so that this value is maximized, AOT measurement with a high S / N can be performed. Note that since I ₀ and M are constants in the equation (9), it is only necessary to obtain t that maximizes t · C _off (t) / σ _noise (t).

In summary, the numerator of equation (9), that is, equation (8), can be obtained by equation (6) using the autocorrelation function g ₂ (τ) calculated in step 101. Further, the denominator of the formula (9) is the noise of the area sensor 23 obtained in step 102. Therefore, the measurement time ts that gives the maximum S / N in the AOT measurement can be obtained using the measurement results of steps 101 and 102. The above is step 104.

Step 104 is illustrated below. 4A to 4D schematically show the relationship of Expression (9). These figures are characteristics when the horizontal axis is time. In FIG. 4A, the thick line represents the speckle contrast C _off (t), and the thin line represents the light intensity I (t). The speckle contrast decays with time as shown in equation (6). Conversely, the light intensity increases linearly with time. FIG. 4B shows a formula (8) obtained by multiplying the two and adding Modulation Depth. Since Modulation Depth is constant with respect to time, the characteristic has one maximum value. FIG. 4C shows the noise (formula (2)) of the area sensor 23. As the light intensity increases with time, it increases approximately in the form of a square root. The ratio between FIG. 4B and FIG. 4C is shown in FIG. 4D. That is, this is S / N. In this case, it can be seen that S / N is maximum at about 0.05 seconds. This time is ts. As described above, ts can be obtained.

Next, the AOT measurement is performed by converging the ultrasonic wave at the place of step 105. In step 106, the position of the ultrasonic convergence position 4 is changed. When the ultrasonic generator 5 is made of an array-like element, the time for driving each element may be delayed and the delay state may be changed. In some cases, the position may be moved. During this time, the measurement may be performed at the measurement time ts obtained in step 103. However, when the light source or the detection position is changed in the determination 111, the light path in the measurement object 1 changes, so that g ₂ (τ) changes and the time ts at which the S / N becomes maximum also changes. Will be. Therefore, in this case, it is necessary to go back to step 101 and repeat the same operation. As a method of changing the light source or the detection position, the position of the optical fiber 12 with respect to the measurement object 1 may be shifted, or a plurality of optical fibers 12 may be attached at positions shifted in advance. If the light source or the detection position is not changed, the process returns to step 105 and AOT measurement is repeated.

By repeatedly measuring as described above, AOT measurement information inside the measurement object 1 is acquired. The information is imaged in step 107 and the measurement is completed. The AOT measurement information here, the Modulation Depth or obtained from _{C off} and _{C on} the value or converting the Modulation Depth absorption and scattering coefficients, hemoglobin and fat by spectroscopic measurement, water, collagen, It is a value converted into a constituent in the living body such as melanin. These may be arranged in the image generation unit 34 and one or more of them may be displayed on the monitor 35.

(Second Embodiment)
A second embodiment of the present invention will be described. The configuration of the measurement system of this embodiment is basically the same as that of the first embodiment. The difference from the first embodiment is that the coherent light source 12 emits a short pulse light on the order of picoseconds ( ^10-12 seconds), measures the time response (time profile), and based on this, the intensity autocorrelation The function g ₂ (τ) is calculated and the time change of speckle contrast is obtained.

  FIG. 5 is a flowchart for explaining the operation of the second embodiment. In step 201, the measurement object 1 is irradiated with short pulse light of the order of picoseconds from the coherent light source 11 through the optical fiber 12. The light detected by the detector 25 is subjected to time response measurement by the arithmetic processing unit 32, and the optical path length distribution function P (l) is calculated.

In step 202, the intensity autocorrelation function g ₂ (τ) is obtained from the optical path length distribution function P (l) calculated in step 201 by the following procedure.

The autocorrelation function g ₁ (τ) of the electric field is defined below.

となる。τ_０が物体固有の相関時間であり、生体の場合は部位により数百マイクロ秒から数十ミリ秒であり、この値を用いてｇ_１（τ）を算出する。またｌ^＊は光子の平均自由行程である。ｌ^＊は等価散乱係数μｓ’の逆数となる。等価散乱係数は、Ｐ（ｌ）を解析解でフィッティングして求めた値を用いてもよく、拡散方程式を元に解いた値を用いてもよい。光の信号強度Ｔは

と記述できる。ここで、D=1/3（μａ+μｓ’）、ｚ_０＝１／μｓ’、μａは吸収係数、ｄは測定対象物１の厚さ、ｚは光の入射位置から観測点までの距離、ｃは光速である。時間ｔを光路長／光速（ｌ／ｃ）で表すことにより、光路長分布にすることができる。これよりμｓ’を求め、ｇ_１（τ）を算出することができる。 E (τ) is the electric field strength at time τ, and <> is the average operation.
G ₁ (τ) can be described by an optical path length distribution function P (l),

It becomes. τ ₀ is an object-specific correlation time, and in the case of a living body, it is several hundred microseconds to several tens of milliseconds depending on the part, and g ₁ (τ) is calculated using this value. L ^* is the mean free path of photons. l ^* is the reciprocal of the equivalent scattering coefficient μs ′. As the equivalent scattering coefficient, a value obtained by fitting P (l) with an analytical solution may be used, or a value solved based on a diffusion equation may be used. The signal strength T of light is

Can be described. Here, D = 1/3 (μa + μs ′), z ₀ = 1 / μs ′, μa is the absorption coefficient, d is the thickness of the measurement object 1, and z is the distance from the incident position of the light to the observation point. , C is the speed of light. By expressing the time t as optical path length / light speed (l / c), an optical path length distribution can be obtained. From this, μs ′ can be obtained and g ₁ (τ) can be calculated.

The autocorrelation function g ₂ of the autocorrelation function g ₁ (τ) and the scattered light intensity of the electric field intensity _(tau) satisfy the following relationship.

βは測定系に依存するパラメータであり、理想的な場合には１となる。

β is a parameter depending on the measurement system, and is 1 in an ideal case.

Using the above equations (11) to (13), the intensity autocorrelation function g ₂ (τ) can be calculated from the optical path length distribution function P (l) obtained by measurement.

The means for obtaining C _off (t) from g ₂ (τ) and obtaining the time ts when the S / N becomes the highest together with the noise amount of the area sensor 23 and the AOT measurement procedure are the same as in the first embodiment. .

(Third embodiment)
A third embodiment of the present invention will be described. The configuration of the measurement system of this embodiment is basically the same as that of the first embodiment. The difference from the first embodiment is that the coherent light source emits frequency-modulated light, measures the phase and amplitude, calculates the autocorrelation function g ₂ (τ) of the intensity based on this, and This is the point to obtain the time change of the contrast.

  In the present embodiment, the coherent light source emits light modulated at the frequency f. The frequency f is usually several tens to several hundreds MHz. The irradiated frequency-modulated light is detected by the detector 25 after being repeatedly absorbed and scattered inside the measurement object 1. By measuring the phase and amplitude of the detected modulated light, information inside the measurement object 1 can be extracted.

  FIG. 6 is a flowchart for explaining the operation of the third embodiment. In step 301, an absorption coefficient μa and an equivalent scattering coefficient μs ′ are obtained from the amplitude and phase obtained by the measurement. Although this embodiment uses an approximate solution derived from the light diffusion equation, the present invention can also be applied to a stricter solution.

The light intensity I (r, t) [photon / sec · mm ² ] at time t at a position r from the point light source in the uniform absorption scatterer is given by the following equation.

Here, I _DC is a bias component [photon / sec · mm ² ] of the detected light intensity, ε is an arbitrary phase term, A is the number of incident photons incident on the measurement object 1 [photon / sec], and D is a diffusion coefficient. [Mm] and ν are light speeds [mm / sec] inside the absorbing scatterer. Μa is an absorption coefficient [mm ^−
1 ] and μs ′ are equivalent scattering coefficients [mm ⁻¹ ], and ω is an angular frequency [rad / sec] of a modulated wave modulated by ultrasonic waves (ω = 2πf where f is a modulation frequency).

If the amplitude I _AC (r, t) and the phase Φ (r, t) are measured, the absorption coefficient μa and the equivalent scattering coefficient μs ′ can be calculated from the equations (14) and (15). By substituting these determined μa and μs ′ into the equation (12), the optical path length distribution function P (l) can be determined.

Means for obtaining g ₁ (τ) and g ₂ (τ) from the obtained P (l), estimating C _off (t), and obtaining the time ts when the S / N is highest from the noise amount of the area sensor 23, and AOT The measurement procedure is the same as in the second embodiment.

FIG. 1 is a diagram illustrating a configuration of a measurement system according to the first to third embodiments. FIG. 2 is a flowchart showing the flow of AOT measurement processing in the first embodiment. FIG. 3 is a diagram comparing the intensity frequency distribution and the noise frequency distribution in the area sensor. FIG. 4 is a diagram showing the relationship of S / N calculation. FIG. 5 is a flowchart showing a flow of AOT measurement processing in the second embodiment. FIG. 6 is a flowchart showing a flow of AOT measurement processing in the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement object 2 Measurement container 3 Matching material 4 Ultrasonic convergence position 5 Ultrasonic generator 10 Control part 11 Signal generator 12 Light source 13 Optical fiber 21 Outgoing opening 22 Beam splitter 23 Area sensor 24 Opening 25 Detector 31 Signal extraction part 32 Arithmetic processor 33 Memory 34 Image generator 35 Monitor

Claims (13)

A coherent light source for irradiating the measurement target with coherent light, and
An area sensor for detecting speckles of light emitted from the measurement object;
Ultrasonic irradiation means for irradiating the measurement object with ultrasonic waves;
An acousto-optic tomography measuring apparatus for performing acousto-optic tomography measurement,
Exit light detection means for detecting the exit light from the measurement object;
The temporal change C _off (t) of the speckle contrast and the noise amount σ _noise (t) of the area sensor are calculated from the detection result by the emitted light detection means, and the temporal change of the calculated speckle contrast is calculated. Based on C _off (t) and the noise amount σ _noise (t) of the area sensor, the area so that the S / N of the speckle detection signal by the area sensor at the time of the acousto-optic tomography measurement is maximized. Measurement time determining means for determining a measurement time ts of the speckle by the sensor;
An acousto-optic tomography measuring apparatus comprising: The acousto-optic tomography measurement apparatus according to claim 1, wherein the measurement time determination unit determines t that maximizes t · C _off (t) / σ _noise (t) as the measurement time ts. The measurement time determining means obtains a correlation between the intensities of light emitted from the measurement object when the measurement object is irradiated with coherent light from the coherent light source, and the speckle contrast time is determined based on the correlation. The acousto-optic tomography measurement apparatus according to claim 1, wherein a typical change C _off (t) is calculated. The measurement time determining means measures a time profile of light emitted from the measurement object when the measurement object is irradiated with short pulse light from the coherent light source, and the speckle contrast is based on the time profile. The time-dependent change C _off (t) of is calculated. The acousto-optic tomography measurement apparatus according to claim 1 or 2, wherein: The measurement time determining means calculates an absorption coefficient and a scattering coefficient of the measurement object based on light emitted from the measurement object when the measurement object is irradiated with frequency-modulated light from the coherent light source, The acoustooptic tomography measurement apparatus according to claim 1, wherein a temporal change C _off (t) of the speckle contrast is calculated based on the absorption coefficient and the scattering coefficient. The acoustooptic tomography measurement apparatus according to any one of claims 1 to 5, wherein the emission light detection means is a photomultiplier tube or an avalanche photodiode. When the pixel area of the area sensor is p, the area of the exit aperture from which light is emitted from the measurement object is As, and the wavelength of the coherent light is λ,
The optical distance between the area sensor and the exit aperture is z expressed by the following equation:
The opening of the area p is provided in the said emission light detection means, and the optical distance between the said emission light detection means and the said emission opening is z. The any one of Claims 1-6 characterized by the above-mentioned. 2. An acousto-optic tomography measuring device according to 1.

A coherent light source for irradiating the measurement target with coherent light, and
Ultrasonic irradiation means for irradiating the measurement object with ultrasonic waves;
An area sensor for detecting speckles of light emitted from the measurement object;
Exit light detection means for detecting the exit light from the measurement object;
An acousto-optic tomography measuring method performed by an acousto-optic tomography measuring device having:
An emission light detection step of measuring the emission light from the measurement object;
Calculating a temporal change C _off (t) of speckle contrast from the detection result of the emission light detection step;
Calculating a noise amount σ _noise (t) of the area sensor;
Based on the calculated temporal change C _off (t) of the speckle contrast and the noise amount σ _noise (t) of the area sensor, the detection signal of the speckle detection signal by the area sensor at the time of acousto-optic tomography measurement A measurement time determining step of determining the speckle measurement time ts by the area sensor so that S / N is maximized;
An acousto-optic tomography measurement method, comprising: an acousto-optic tomography measurement step of performing acousto-optic tomography measurement with a measurement time by the area sensor as ts. The acoustooptic tomography measurement method according to claim 8, wherein in the measurement time determination step, t at which t · C _off (t) / σ _noise (t) is maximized is determined as the measurement time ts. In the step of calculating the temporal change C _off (t) of the speckle contrast, a correlation of the intensity of light emitted from the measurement object when light is irradiated from the coherent light source to the measurement object is obtained. The temporal change C _off (t) of the speckle contrast is calculated based on the correlation. The acoustooptic tomography measurement method according to claim 8 or 9, wherein: In the step of calculating the temporal change C _off (t) of the speckle contrast, a time profile of light emitted from the measurement object when the measurement object is irradiated with short pulse light from the coherent light source is calculated. 10. The acousto-optic tomography measurement method according to claim 8, wherein measurement is performed and the temporal change C _off (t) of the speckle contrast is calculated based on the time profile. In the step of calculating the temporal change C _off (t) of the speckle contrast, when the measurement object is irradiated with frequency-modulated light from the coherent light source, the speckle contrast is calculated based on the light emitted from the measurement object. The absorption coefficient and the scattering coefficient of the measurement object are calculated, and the temporal change C _off (t) of the speckle contrast is calculated based on the absorption coefficient and the scattering coefficient. The acoustooptic tomography measuring method as described. The acoustic according to any one of claims 8 to 12, wherein in the emission light detection step, the emission light from the measurement object is detected using a photomultiplier tube or an avalanche photodiode. Optical tomography measurement method.

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