JP7134657B2 - Photoacoustic measuring device - Google Patents

Description

The present invention relates to a photoacoustic measuring device.

One method of bioimaging uses the photoacoustic effect. The photoacoustic effect is a phenomenon in which when a living body is irradiated with laser light, molecules that have absorbed light energy in living tissue release heat, and volume expansion due to the heat generates acoustic waves. The acoustic waves generated in this manner are detected by an ultrasonic detection element using a piezoelectric material or the like. For example, Patent Literature 1 discloses an example of applying photoacoustic imaging to small animals.

Research is also underway to noninvasively measure the concentrations of components such as glucose and albumin present in blood using this photoacoustic effect. An example of this is disclosed in Patent Document 2. In the component concentration measuring method disclosed in Patent Document 2, when laser beams of two wavelengths are alternately input, an object to be measured generates sound waves according to the difference in the light absorption amount, and when the light absorption amounts are equal (absorption amount difference When there is no sound wave, the change in density of the object to be measured is measured from the state in which the difference in light intensity of the laser beams of two wavelengths changes depending on the density.

Japanese Patent Publication No. 2013-500091 JP 2016-154584 A

Since the acoustic waves generated by the photoacoustic effect are weak, it is difficult to stably measure the acoustic waves. Therefore, it is difficult to measure with the accuracy required for quantitative analysis. In Patent Document 2, a lock-in amplifier is used to detect weak acoustic waves. Although it is possible to accurately measure a weak signal by such signal processing, it leads to an increase in the size and cost of the measuring device. For example, in order to spread as a measuring device that can routinely measure glucose in a non-invasive manner, it is desirable to measure a weak signal with high precision using a device that is as inexpensive and small as possible.

In a photoacoustic measuring device according to one embodiment, a light source for irradiating a subject with light, a sound sensor for detecting an acoustic wave generated from the focus of the light, and a center of curvature of the sound sensor coinciding with the focus of the light or and a sound path length variable mechanism for adjusting so as to be positioned in the vicinity thereof. Other problems and novel features will become apparent from the description of the specification and the accompanying drawings.

It enables stable measurement of weak acoustic waves generated by the photoacoustic effect.

2 is a schematic configuration diagram of an acoustic wave receiving unit of Example 1. FIG. It is a figure which shows the modification of arrangement|positioning of a sound sensor. 1 is a schematic configuration diagram of a sound wave receiving section having a plurality of sound sensors; FIG. 4 is a schematic configuration diagram of a sound wave receiving section having an aspherical sound sensor; FIG. It is a figure explaining the adjustment method of a sound path length variable mechanism. It is a photoacoustic measurement flowchart in this Embodiment. 1 is a block diagram of a photoacoustic measuring device having an acoustic wave receiving unit of Example 1. FIG. FIG. 11 is a schematic configuration diagram of an acoustic wave receiving unit of Example 2; FIG. 11 is a block diagram of a photoacoustic measuring device having an acoustic wave receiving unit of Example 2; It is an example of a control table of the sound path length adjustment unit. 1 is a schematic configuration diagram of a sound sensor in which a light guide is provided in a light source; FIG.

The inventors have found that weak acoustic waves can be stably detected by providing an acoustic wave receiving section for detecting acoustic waves generated by the photoacoustic effect with a sound collecting structure.

FIG. 1 shows a schematic configuration example of an acoustic wave receiving section having a sound collecting structure according to the first embodiment. A light source 300 and a sound sensor 200 are provided so as to face each other with the subject 100 interposed therebetween. The subject 100 is, for example, a soft tissue such as a finger or an earlobe. The sound sensor 200 is a piezoelectric ceramic element such as a piezo element (PZT) and has a spherical shape. When the sound sensor 200 is attached to the earlobe, it can be made inconspicuous by attaching it to the back side of the earlobe. The sound sensor 200 is provided with an acoustic matching layer 201 and is in contact with the subject 100 via the acoustic matching layer 201 . The acoustic matching layer 201 is provided to match the acoustic impedance so that the acoustic wave passing through the object 100 is input to the sound sensor 200 with as little reflection as possible. Furthermore, by applying jelly between the acoustic matching layer 201 and the subject 100, reflection of acoustic waves between the subject 100 and the acoustic matching layer 201 can be suppressed. The sound sensor 200 is provided with a sound path length varying mechanism 400 that can move the position of the sound sensor 200 along a direction 410 .

An acoustic wave 101 is generated from the focus F of the light of the light source 300 (in the drawing, the spherical acoustic wave 101 is shown to spread from the focus F for simplification, but the inside of a blood vessel or the like in the subject 100 Due to the presence of structures and tissues with different densities, they do not actually spread concentrically as shown in the figure). In the acoustic wave receiving section of the present embodiment, the position of the sound sensor 200 is adjusted by the sound path length varying mechanism 400 so that the center of curvature C of the sound sensor 200 coincides with or is located near the focal point F of the light of the light source 300. By adjusting, it becomes possible to efficiently capture the generated acoustic wave 101 . As described above, the spread of the acoustic wave varies depending on the internal structure of the subject. Therefore, in some cases, the optimum point is not the theoretical focal position of light itself, but the vicinity of the focal position of light. “Coinciding with or near” means arranging the sound sensor at a position where the photoacoustic measuring device can capture the acoustic wave at a measurable level regardless of such changes in the acoustic wave.

FIG. 2 shows a modification regarding the arrangement of the sound sensor 200. As shown in FIG. As shown in FIG. 1, the acoustic wave 101 spreads inside the object 100 around the focal point F of the light. Therefore, the light source 300 and the sound sensor 200 do not have to face each other. In FIG. 2, the sound sensor 200a is an example in which the sound sensor is arranged on the surface 110 of the subject 100 in contact with the light source 300, and the sound sensor 200b is an example in which the sound sensor is arranged on another surface 111 of the subject 100. . Although not shown in the figure, each of the sound sensors 200a and 200b is provided with a sound path length variable mechanism for adjusting the position of the center of curvature C. configured to be movable by In the drawing, the sound sensors 200a and 200b have the same curvature. From the viewpoint of collecting acoustic waves, it is desirable to design the radius of curvature of the sensor 200a so as to be longer than the radius of curvature of the sound sensor 200a.

FIG. 3 shows still another modification, which is a schematic configuration example of a sound wave receiving section having a plurality of sound sensors. A second sound sensor 200 a is provided at a position facing the first sound sensor 200 , and the first sound sensor 200 and the second sound sensor 200 a are each controlled by the sound path length varying mechanism 401 to move the center of curvature along the direction 410 . C1 and the center of curvature C2 are configured to be movable. By using two sound sensors in this way, it becomes possible to capture more faint signals. Although this example shows an example in which two sound sensors are provided in a facing positional relationship, the present invention is not limited to this. For example, the sound sensor 200b shown in FIG. 2 may be used as the second sound sensor. Also, depending on the size of the subject 100, three or more sound sensors may be used.

FIG. 4 shows yet another variant, in which the sound sensor 210 is a piezoceramic element, such as a piezo element (PZT), having an aspherical shape, in this example an ellipsoidal shape. A second sound sensor 210a is provided at a position facing the first sound sensor 210, and the first sound sensor 210 and the second sound sensor 210a have a shape forming a part of an elliptical spherical surface 260. . The first sound sensor 210 and the second sound sensor 210a are configured to be movable along the direction 410 at the elliptical curvature center R1 and the elliptical curvature center R2 of the ellipsoidal surface 260 by the sound path length variable mechanism 402, respectively. In addition, the first sound sensor 210 and the second sound sensor 210a each change the curvature of the sound sensor (expanded or contracted along the direction 420) by the curvature variable mechanism 403, and the elliptical curvature center of the elliptical sphere 260 R1 and elliptical curvature center R2 are configured to be movable. Although the drawing shows an example in which both the sound path length varying mechanism 402 and the curvature varying mechanism 403 are provided, the configuration may be such that only one of them is provided.

In FIGS. 1 to 3, the acoustic wave 101 approximates the focal point of light and is shown as propagating on a spherical surface centering on the focal point F of the light. Instead, the focal point of the light generated by the acoustic wave is an ellipsoidal area (herein, this area is referred to as a "focal area") whose major axis is the optical axis direction of the light source 300 . When the spread of the focal region F' on the optical axis is relatively large, it is effective to approximate the propagation of the acoustic wave 101 as an ellipsoid rather than as a sphere. Moreover, even if the acoustic wave propagates in a spherical shape, the sound wave front may be distorted in an ellipsoidal shape due to non-uniformity of tissues in the living body. In such a case, by using an ellipsoidal sound sensor, it is possible to collect acoustic waves more effectively than a spherical sound sensor. At least one of the sound path length varying mechanism 402 and the curvature varying mechanism 403 is used so that both the elliptical curvature center R1 and the elliptical curvature center R2 are included in the focal region F′ of the light source 300 or located in the vicinity thereof. adjust. This allows the acoustic wave 101 generated in the light focal region F' to be efficiently captured by the first sound sensor 210 and the second sound sensor 210a.

FIG. 11 illustrates a modification of the light source 300 for making the light from the light source optimally incident on the subject 100. FIG. In FIG. 11, a light guide path 301 is provided in the acoustic matching layer 201 of the sound sensor 200c so as to take in the surroundings of the light source 300, and the tip of the light guide path is attached in a state that it slightly sinks into the subject 100 when the sound sensor 200c is attached. be done. When attached to the earlobe, it is preferable that the light guide path 301 has a shape and size that fits in a piercing hole. Although FIG. 11 shows an example in which a light source is combined with a sound sensor, the same effect can be obtained in the case of a single light source by similarly providing a light guide path.

In the acoustic wave receiving unit described above, by moving the position of the sound sensor or changing the curvature of the sound sensor, the position of the center of curvature of the sound sensor and the position of the focus of the light from the light source can be adjusted. It collects the acoustic waves that The sound path length variable mechanism is composed of a first member extending in the moving direction and a second member coupled to the sound sensor and fixable at any position on the first member. For example, a bolt (screw) may be used as the first member and a nut may be used as the second member, or a shaft may be used as the first member and a latch may be used as the second member. It is only necessary to move the second member along the first member to bring the center of curvature C of the sound sensor closer to the focus F of the light and fix it.

In this case, the sound path length variable mechanism adjusts the position of the sound sensor to the position where the reception intensity of the acoustic wave is maximized. A method of roughly adjusting the position of the sound sensor will be described with reference to FIG. Assuming that the distance between the focal point of light F and the sound sensor 200 is L, the time difference T between the light signal trigger 501 that generates light from the light source 300 and the received signal 502 received by the sound sensor 200 is L/c. It suffices to determine L. Strictly speaking, however, this is optimal when the subject 100 is a homogeneous tissue and the assumption holds that the acoustic wave 101 generated from the focal point F of the light spreads concentrically. . Therefore, it is desirable to simply obtain the magnitude of L by the method of FIG. 5 and adjust the position by finely adjusting the position of the sound sensor back and forth as necessary. Alternatively, if the variable curvature mechanism shown in FIG. 4 is provided, the variable curvature mechanism may be adjusted. The curvature variable mechanism can be realized, for example, by providing an ellipsoidal support mechanism for fixing the PZT, and by enabling the opening of the support mechanism to be fixed at an arbitrary position.

FIG. 6 shows the photoacoustic measurement method in this embodiment. After starting the measurement (step S01), the sound path length is adjusted (step S02). As described with reference to FIG. 5, the sound path length is obtained from the time difference between the optical signal trigger 501 and the received signal 502, and fine adjustment is performed as necessary. Completion of the adjustment is determined when the reception intensity of the acoustic wave at the adjusted sound path length becomes maximum (step S03). Photoacoustic measurement is performed with the adjusted sound path length (step S04), and processing according to the application is performed. Applications include measuring the glucose concentration of a subject from photoacoustic measurement results.

FIG. 7 shows a block diagram of a photoacoustic measuring device having an acoustic wave receiving unit of Example 1, which executes the flow of FIG. The photoacoustic measurement apparatus includes a signal processing unit 700 connected to a light source 300 and a sound sensor 200 (210), and a display for displaying analysis results by the signal processing unit 700 and inputting instructions to the signal processing unit 700. and an operation unit 750 . It should be noted that the display/operation unit 750 may be configured to make the user perceive using not only the display on the display, but also an audio alarm or vibration using a vibrator. The signal processing unit 700 can be implemented by one or more IC chips or FPGA, and includes an optical transmission unit 701, a sound wave reception unit 702, an analog/digital converter (ADC) 703, a measurement processing unit 704, and a sound path length measurement unit. 705 and an external I/F (Interface) 706 .

The measurement processing unit 704 controls the overall photoacoustic measurement shown in FIG. 6, receives instructions from the user from the operation unit 750 via the external I/F 706, and executes measurement. The measurement processing unit 704 issues an optical signal trigger to the optical transmission unit 701, and the optical transmission unit 701 receives the optical signal trigger and causes the light source 300 to emit light. Acoustic waves received by the sound sensor 200 are amplified by the sound wave receiving section 702 and converted into digital signals by the ADC 703 . The received signal is analyzed by the measurement processing unit 704 to measure the glucose concentration, for example, and displayed on the display unit 750 via the external I/F 706 .

Further, the sound path length measurement unit 705 receives as input the timing information for issuing the optical signal trigger and the timing information for receiving the acoustic wave in the sound sensor 200, and generates sound sensor position adjustment information for the sound path length varying mechanism described with reference to FIG. do. The generated sound sensor position adjustment information is notified to the user via the display unit 750 via the external I/F 706 . When performing fine adjustment, it is preferable to display the reception intensity of the acoustic wave on a monitor or display the volume and pitch of an alarm sound so that the user can easily perform the adjustment.

FIG. 8 shows a schematic configuration example of an acoustic wave receiving section having a sound collecting structure according to the second embodiment. Components having the same function are denoted by the same reference numerals, and overlapping descriptions are omitted. A light source 300 and a sound sensor array 800 are provided so as to face each other with the subject 100 interposed therebetween. The sound sensor array 800 is obtained by arranging piezoelectric ceramic elements 801-1 to 801-6 such as piezoelectric elements (PZT) one-dimensionally or two-dimensionally on a flexible resin substrate. Note that the number of elements forming the sound sensor array is not particularly limited. Thereby, a sound sensor array conforming to the shape of the subject 100 can be realized. When the sound sensor array 800 is attached to the earlobe, it can be made inconspicuous by attaching it to the back side of the earlobe. In order to suppress the reflection of acoustic waves as in the first embodiment, the sound sensor array 800 is provided with an acoustic matching layer 810 and is in contact with the subject 100 through the acoustic matching layer 810 . Furthermore, by applying jelly between the acoustic matching layer 810 and the subject 100, reflection of acoustic waves between the subject 100 and the acoustic matching layer 810 can be suppressed. Also, as described with reference to FIG. 11, it is desirable to provide a light guide path so as to take in the surroundings of the light source.

If the shape of the sound sensor array 800 conforms to the shape of the subject 100 in this way, the radius of curvature usually becomes large. If the center of curvature C of the sound sensor array 800 is greatly separated from the light focus F of the light source 300, acoustic waves cannot be effectively collected as described in the first embodiment. Therefore, in the second embodiment, a sound path length variable mechanism 820 is provided to delay the signals from the sound sensor elements 801-1 to 801-6, respectively, and the center of curvature of the sound sensor array 800 is moved. As shown in FIG. 8, the acoustic path length variable mechanism 820 delays the acoustic wave received signals from the sound sensor elements 801-1 to 801-6 by τ ₁ to τ ₆ respectively, and synthesizes the delayed received signals. do. This allows the center of curvature C' of the resulting sound sensor array 800 to be positioned at or near the focal point F of the light.

A piezoelectric film may be used as the sound sensor element of the sound sensor array 800 instead of the piezoelectric ceramic element. As such a piezoelectric film, a PVDF (polyvinylidene fluoride) film and the like are known. By using a piezoelectric film, the sound sensor array 800 can be configured more flexibly, and the sound sensor array can be brought into close contact with the subject 100 .

Note that FIG. 8 shows an example in which the light source 300 and the sound sensor array 800 are arranged to face each other with the subject 100 interposed therebetween, but the present invention is not limited to this. Modifications similar to those shown in FIGS. 2 to 4 are possible with respect to the first embodiment. The sound sensor array of the first embodiment is replaced with the sound sensor array of the second embodiment, and the mechanical sound path length varying mechanism of the first embodiment is replaced with the electrical sound path length varying mechanism of the second embodiment.

The photoacoustic measurement method in this embodiment is also as shown in FIG. However, as will be described later, the sound path length adjustment method (step S02) is different from that of the first embodiment.

FIG. 9 shows a block diagram of a photoacoustic measuring device having an acoustic wave receiving unit of Example 2, which executes the flow of FIG. The photoacoustic measurement apparatus includes a signal processing unit 900 connected to a light source 300 and a sound sensor array 800, and a display unit for displaying analysis results by the signal processing unit 900 and inputting instructions to the signal processing unit 900. and an operation unit 750 . The signal processing unit 900 can be implemented by one or more IC chips or FPGA, and includes an optical transmission unit 901, a sound wave reception unit 902, an analog/digital converter (ADC) 903, a measurement processing unit 904, and a sound path length adjustment unit. 905 , sound path length variable mechanism 820 , and external I/F 906 .

A measurement processing unit 904 controls the entire measurement shown in FIG. 6, receives an instruction from the operation unit 750 by the user via the external I/F 906, and executes measurement. The measurement processing unit 904 issues an optical signal trigger to the optical transmission unit 901, and the optical transmission unit 901 receives the optical signal trigger and causes the light source 300 to emit light. Acoustic waves received by the plurality of sound sensor elements 801 are amplified by the sound wave receiving section 902 and converted into digital signals by the ADC 903 . The received signal is analyzed by the measurement processing unit 904 to measure the glucose concentration, for example, and displayed on the display unit 750 via the external I/F 906 .

Note that the sound path length adjustment unit 905 holds a control table 1001 shown in FIG. The control table 1001 includes, for example, a plurality of radii of curvature (sound path lengths) L of the sound sensor array 800 and delay amounts τ ₁ to τ of received signals of acoustic waves from the sound sensor elements 801-1 to 801-6 corresponding to L. ₆ is stored. The sound path length adjustment unit 905 finds a combination that maximizes the reception intensity of the acoustic waves synthesized by delaying the signals from the sound sensor elements 801-1 to 801-6 in accordance with the control table 1001, and sets it in the sound path length variable mechanism 820. do. At the time of photoacoustic measurement, the signals received from the sound sensor elements 801-1 to 801-6 are delayed by the delay amount set by the sound path length adjustment unit 905, and the signals are synthesized and input to the measurement processing unit 904 as received signals. . In this example, the sound path length is adjusted using the digitized received signal, but the analog received signal amplified by the sound wave receiving section 902 may be used.

Common matters regarding the photoacoustic measurement apparatus or the photoacoustic measurement method according to the first and second embodiments will be described below.

The wavelength of the light emitted by the light source can be selected from ultraviolet light to infrared light depending on the purpose of measurement. However, there is a preferred wavelength of light depending on the light absorptivity of the subject and the in vivo physical properties to be measured, such as the concentrations of hemoglobin, oxygen, and glucose in blood. In the case of glucose measurement, the infrared region of 1000 nm to 2000 nm is the preferred frequency region due to the large absorption rate. In addition, when short pulse light is used for light irradiation, it may be preferable to use the ultraviolet region, which has good energy efficiency for light convergence. Considering the absorption rate of hemoglobin and the like, it may be preferable to use a wavelength in the visible light region.

Either pulse light or continuous light may be used for light irradiation. Considering the time constant of light absorption when pulsed light is used, it is considered that the volume expansion due to light absorption occurs in a sufficiently short time, and the stress confinement condition is about 1 μs. Therefore, the duration of the light pulse is preferably 1 μs or less. Irradiating this light pulse at a pulse repetition frequency (PRF) of, for example, several kHz to several 100 kHz is one preferable light irradiation pulse irradiation method.

On the other hand, when a continuous wave is used, sound is generated by changing the irradiation intensity of light in the time direction, because DC-like application does not generate sound. For example, an acoustic wave corresponding to the frequency of the sine wave can be obtained by vibrating the irradiation intensity of light in the time direction with a sine wave. For example, the modulation frequency of the irradiation intensity of light is preferably from several tens of kHz to 10 MHz.

Since the frequency of the photoacoustic wave generated by the photoacoustic effect depends on the pulse shape and wavelength of the irradiated light, the optimum frequency for the system differs. However, considering the attenuation rate of sound wave propagation in the living body, restrictions on the size of the sound sensor, etc., a frequency of several 10 kHz or more and 10 MHz or less is preferable. This roughly coincides with the modulation frequency of the irradiation intensity of light described above. When measuring glucose in a soft tissue such as an earlobe, a relatively low frequency band of several tens of kHz or more and 1.0 MHz or less is preferable.

Note that when measuring in vivo physical property values such as glucose concentration using a soft tissue such as an earlobe as a subject, the thickness of the subject is about several millimeters. 3 and 4, the distance between the sound sensors is preferably about 0.5 mm to 20 mm. Also, when using a single sound sensor (sound sensor array), it is arranged so that the depth of light irradiation is about 10 mm or less. Almost no light energy reaches depths greater than 10 mm.

Although the invention made by the present inventors has been specifically described above based on the embodiment, the invention is not limited to the embodiment, and can be variously modified without departing from the gist of the invention. be.

For example, the light absorptance varies depending on the color of the subject's skin and changes in the environment. For this reason, it is conceivable to perform calibration according to the light absorptance. In this case, the absorption coefficient of the subject is calculated by calculating the ratio between the sound pressure value of the acoustic wave received by attaching the acoustic wave receiving unit to the subject and the sound pressure value measured in advance using a reference material such as water. can be approximated. Since the absorption coefficient has a one-to-one correspondence with the wavelength of light, it is possible to estimate the optimum wavelength of light in consideration of the disturbance and the subject. This value may be used to slightly modify the wavelength of light emitted by the light source. At this time, if the light source cannot change the wavelength of light, in the sound path length adjustment shown in FIG. , by calibrating using an internal arithmetic circuit, etc., it is possible to calculate the optimum sound path length according to the disturbance, and to modify the control table (see Fig. 10) that sets the delay amount of each sound sensor element. You can add it.

Further, in the photoacoustic measurement apparatus of the present embodiment, analog signal processing and analog-to-digital conversion processing of the signal processing unit may be left, and other processing may be implemented by a PC (Personal Computer). In addition, the signal processing unit and the display/operation unit may be mounted as a device built into an integrated housing. may As a result, it can also be established as an IoT device that can be remotely controlled wirelessly even in remote locations via the Internet, the Web, and the cloud.

100: Subject, 101: Acoustic wave, 200, 210: Sound sensor, 201, 810: Acoustic matching layer, 300: Light source, 301: Light guide path, 400, 401, 402: Sound path length variable mechanism, 403: Curvature variable mechanism, 700, 900: signal processing unit, 701, 901: optical transmission unit, 702, 902: sound wave reception unit, 703, 903: ADC, 704, 904: measurement processing unit, 705: sound path length measurement unit, 706, 906: external I/F, 750: display/operation unit, 800: sound sensor array, 801: sound sensor element, 820: sound path length varying mechanism, 905: sound path length adjustment unit, 1001: control table.

Claims (4)

a light source for irradiating a subject with light;
a sound sensor that detects acoustic waves generated from the focus of the light;
a sound path length variable mechanism that adjusts the center of curvature of the sound sensor to coincide with or be positioned in the vicinity of the focus of the light ;
Having a plurality of sound sensors,
The photoacoustic measuring device , wherein the sound path length varying mechanism adjusts each of the plurality of sound sensors so that the center of curvature of the sound sensor coincides with or is positioned near the focus of the light. a light source for irradiating a subject with light;
a sound sensor that detects acoustic waves generated from the focus of the light;
a sound path length variable mechanism that adjusts the center of curvature of the sound sensor to coincide with or be positioned in the vicinity of the focus of the light;
Having the sound sensor and another sound sensor arranged to face each other with the subject sandwiched therebetween;
each of the sound sensor and the another sound sensor has a shape that forms a part of an elliptical sphere when the sound sensor and the another sound sensor are arranged to face each other;
The acoustic wave is generated from a region whose major axis direction is the optical axis direction of the light source,
The photoacoustic measuring device, wherein the sound path length varying mechanism adjusts the two elliptical curvature centers of the elliptical sphere so that they are included in the region or positioned in the vicinity thereof. In claim 2 ,
Having a curvature variable mechanism for changing the curvature of the sound sensor and the another sound sensor,
The curvature variable mechanism is a photoacoustic measuring device that adjusts the two elliptical curvature centers of the elliptical sphere so that they are included in the region or located in the vicinity thereof. In any one of claims 1 to 3 ,
a signal processing unit connected to the light source and the sound sensor;
The signal processing unit is
a measurement processing unit that controls photoacoustic measurement;
an optical transmission unit that receives an optical signal trigger from the measurement processing unit and causes the light source to emit light;
a sound wave receiving unit that amplifies a received signal of the acoustic wave received by the sound sensor;
and a sound path length measuring unit,
The sound path length measuring unit measures the focal point of the light that maximizes the received intensity of the acoustic wave and the A photoacoustic measuring device that determines the distance to the sound sensor.

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