JP2016077804A - Acoustic wave detection apparatus and acoustic wave detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acoustic wave detection apparatus capable of obtaining a high detection sensitivity at low cost.SOLUTION: The acoustic wave detection apparatus projects measurement light onto an interference film and measures the intensity of an acoustic wave incident to the interference film, based on the intensity of the measurement light reflected off the interference film, the acoustic wave detection apparatus comprising: an interference film formed of two opposing reflective layers; a first light source 13 for projecting light onto the interference film and capable of changing the wavelength of the light; a temperature adjusting unit 19 for adjusting the temperature at the interference film or a peripheral part of the interference film to a predetermined temperature; a wavelength control unit 20 which determines, based on the predetermined temperature, the wavelength of the measurement light to be projected from the first light source, and sets the determined wavelength to the first light source; a photodetector 16 for detecting the intensity of reflection, or the measurement light which is projected onto and reflected off the interference film; and a signal acquisition unit 17 for acquiring an electrical signal corresponding to an acoustic wave incident to the interference film, based on a change of the intensity of the reflection detected by the photodetector.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus for measuring the intensity of an acoustic wave.

  In recent years, research for imaging morphological information and physiological information in a subject, that is, functional information, has been advanced in the medical field. In recent years, photoacoustic tomography (PAT) has been proposed as one of such techniques.

  When light such as pulsed laser light is irradiated onto a living body that is a subject, an acoustic wave (typically, an ultrasonic wave) is generated when the light is absorbed by a living tissue in the subject. This phenomenon is called a photoacoustic effect, and an acoustic wave generated by the photoacoustic effect is called a photoacoustic wave. Since tissues constituting the subject have different optical energy absorption rates, the sound pressures of the generated photoacoustic waves are also different. In PAT, the generated photoacoustic wave is received by an acoustic wave detector, and the received signal is mathematically analyzed, whereby the optical characteristics in the subject, in particular, the distribution of light energy absorption density can be imaged. .

In photoacoustic tomography, since an acoustic wave having a different frequency is generated depending on an object in which light is absorbed, it is necessary to use an acoustic wave detector having a wide band.
As such an acoustic wave detector, a transducer using a piezoelectric phenomenon or a transducer using a change in capacitance is used. Recently, an acoustic wave detector using optical resonance has been developed. For example, when an acoustic wave is incident on the optical interference film in a state where light (hereinafter referred to as measurement light) is applied to the optical interference film, the intensity of the reflected light changes with a change in sound pressure. Therefore, a change in sound pressure of the acoustic wave can be detected by detecting the intensity of the reflected light using a light detection sensor such as a photodiode. A typical optical interference film is a Fabry-Perot interference film.

As an invention related to this, for example, Non-Patent Document 1 describes a device that moves an irradiation position of measurement light on a Fabry-Perot interference film and detects acoustic waves at a plurality of positions on the interference film. .
Such an acoustic wave detector using the resonance of light has a feature that it can detect a broadband acoustic wave, and thus can be said to be an acoustic wave detector suitable for photoacoustic tomography.

JP 2012-37479 A

Edward Zhang, Jan Laufer, and Paul Beard, "Backward-mode multiwavelength photoacoustic scanner using a planar Fabry-Perot polymer film ultrasound sensor for high-resolution three-dimensional imaging of biological tissues", 1 February 2008 Vol. 47, No. 4 APPLIED OPTICS.

  When detecting an acoustic wave generated in a subject and acquiring information in the subject based on the acoustic wave, it is required to increase the detection sensitivity of the acoustic wave as much as possible in order to improve the SN ratio.

On the other hand, an acoustic wave detector using a Fabry-Perot interference film is characterized in that the wavelength of measurement light capable of obtaining high detection sensitivity varies with temperature.
That is, in an environment where the temperature distribution of the interference film changes, the optimum wavelength of the measurement light cannot be uniquely determined.

  With respect to this problem, the apparatus described in Patent Document 1 adds a temperature adjustment mechanism to the Fabry-Perot interference film, and controls the temperature so that the change amount of the DC component of the measurement light is within a certain range. Yes. However, in practice, it is difficult to keep the entire surface of the interference film at a uniform temperature. Even if the entire surface of the interference film is kept at a uniform temperature, the optimum wavelength of the measurement light does not have a uniform value because the interference film has a variation in film thickness that occurs during the manufacturing process.

  Moreover, in the apparatus described in Non-Patent Document 1, the wavelength of the measurement light is adjusted each time according to the temperature change in order to maintain the detection sensitivity. Specifically, the measurement is performed while searching for a wavelength with high acoustic wave detection sensitivity by changing the wavelength with time and monitoring the change in the amount of reflected light from the interference film. However, when this method is used, another problem of causing a long measurement time occurs. In particular, when generating a three-dimensional image representing the distribution of optical characteristic values in a subject, it is necessary to acquire photoacoustic wave signals at multiple locations, so the wavelength search process must be performed at multiple locations, and measurement is performed. Will take a long time. When a living body is a measurement target, it is preferable to complete the measurement in as short a time as possible so that the target living body is not loaded.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide an acoustic wave detection device that can obtain high detection sensitivity at low cost.

In order to solve the above-described problem, an acoustic wave detection device according to the present invention includes:
An acoustic wave detection device for detecting the intensity of an acoustic wave incident on the interference film based on the intensity of the measurement light reflected on the interference film and irradiating the interference film with the measurement light. An interference film composed of layers; a light source that irradiates light to the interference film; a first light source capable of changing a wavelength of light; and a temperature that adjusts the temperature of the interference film or its peripheral part to a predetermined temperature An adjustment unit, a wavelength control unit that determines a wavelength of measurement light emitted from the first light source based on the predetermined temperature, and sets the wavelength of the measurement light to the first light source; A photodetector that detects the intensity of the reflected light reflected, and a signal acquisition unit that acquires an electrical signal corresponding to the acoustic wave incident on the interference film based on a change in the intensity of the reflected light detected by the photodetector. It is characterized by having.

Moreover, the acoustic wave detection method according to the present invention includes:
An interference film composed of two reflective layers facing each other, a light source for irradiating the interference film with light, a first light source capable of changing the wavelength of light, and detecting the intensity of light reflected by the interference film An acoustic wave detection method performed by an acoustic wave detection device having a photodetector and a temperature adjustment unit that adjusts a temperature of the interference film or a peripheral part thereof to a predetermined temperature, the interference film or the peripheral part thereof A temperature adjustment step for adjusting the temperature of the first light source to a predetermined temperature, and a wavelength control step for determining the wavelength of the measurement light emitted from the first light source based on the predetermined temperature and setting the wavelength to the first light source And an irradiation step of irradiating the interference film with the measurement light from the first light source, and an electric wave corresponding to the acoustic wave incident on the interference film based on a change in the intensity of the reflected light detected by the photodetector. A signal acquisition step for acquiring a signal. It is characterized in.

  ADVANTAGE OF THE INVENTION According to this invention, the acoustic wave detection apparatus which can obtain high detection sensitivity at low cost can be provided.

It is a system configuration figure of the photoacoustic measuring device concerning a first embodiment. It is a structural example of the temperature adjustment part in 1st embodiment. It is a figure explaining the detection sensitivity of an acoustic wave. It is an example of the optimal wavelength data in 1st embodiment. It is a process flowchart figure of the photoacoustic measuring device which concerns on 1st embodiment. It is a process flowchart figure of the photoacoustic measuring device which concerns on 2nd embodiment. It is a system block diagram of the photoacoustic measuring device which concerns on 3rd embodiment. It is a system block diagram of the photoacoustic measuring device which concerns on 4th embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The numerical values, materials, shapes, arrangements, etc. used in the description of the embodiments should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions, and do not limit the scope of the invention.

(First embodiment)
The photoacoustic measurement apparatus according to the first embodiment irradiates a subject with pulsed light, and receives and analyzes a photoacoustic wave generated in the subject due to the pulsed light. It is an apparatus for visualizing, that is, imaging, information related to optical characteristics. The information related to the optical characteristics in the subject is, for example, an initial sound pressure distribution, a light absorption energy density distribution, or an absorption coefficient distribution derived therefrom.

<System configuration>
The configuration of the photoacoustic measurement apparatus according to the present embodiment will be described with reference to FIG. The photoacoustic measurement device according to the present embodiment includes an excitation light source 11, a probe 12, a measurement light source 13, a scanning unit 14, a half mirror 15, a light detection unit 16, a processing unit 17, a display unit 18, a temperature adjustment unit 19, A control unit 20 is included.
Hereinafter, an outline of a method for acquiring subject information will be described while describing each means constituting the photoacoustic measurement apparatus according to the present embodiment.

The excitation light source 11 is means for generating pulsed light and irradiating the subject.
The excitation light source 11 is preferably a laser light source in order to obtain a large output, but a light emitting diode, a flash lamp, or the like can be used instead of the laser. When a laser is used as the light source, various lasers such as a solid laser, a gas laser, a dye laser, and a semiconductor laser can be used.
Ideally, an Nd: YAG-excited OPO laser, a dye laser, a Ti: sa laser, or an alexandrite laser that has a strong output and can continuously change the wavelength may be used. Also,
You may have two or more single wavelength lasers of a different wavelength.
The wavelength of the pulsed light is preferably a specific wavelength that is absorbed by a specific component among the components constituting the subject and is a wavelength at which the light propagates to the inside of the subject. Specifically, when the subject is a living body, the thickness is desirably 700 nm or more and 1100 nm or less. However, it is also possible to use a wavelength range wider than the above wavelength range, for example, a wavelength range of 400 nm to 1600 nm, and further a terahertz wave, microwave, and radio wave range.
In order to effectively generate photoacoustic waves, light must be irradiated in a sufficiently short time according to the thermal characteristics of the subject. When the subject is a living body, the pulse width of the pulsed light generated from the light source is preferably about 5 to 50 nanoseconds.
In addition, the excitation light source 11 does not necessarily need to be a part of the photoacoustic measuring device which concerns on this embodiment, and may be connected outside.

The pulsed light emitted from the excitation light source 11 is applied to the subject 101. The subject 101 is
It may be a part of a living body (for example, a breast), or a phantom that mimics the characteristics of a living body. When the subject 101 is a living body, a light absorber inside the living body, such as a tumor or a blood vessel, or a light absorber on the living body surface can be imaged. The light absorber (reference numeral 102) in or on the surface of the subject 101 generates a photoacoustic wave by absorbing a part of the energy when irradiated with pulsed light.

  The probe 12 is a Fabry-Perot acoustic wave probe. The probe 12 has an optical interference film composed of two opposing reflective layers. Specifically, the structure is such that two resonant mirrors sandwich a polymer film. When an acoustic wave enters the probe 12, the mirror on the side on which the acoustic wave is incident is deformed in the film thickness direction of the polymer film, and the distance between the two mirrors changes. By detecting this change in distance, the sound pressure of the incident acoustic wave can be detected. Specifically, light (measurement light) for measuring a change in the distance between the mirrors is irradiated from the surface opposite to the surface on which the acoustic wave is incident, and the light reflected by the measurement light (hereinafter referred to as reflection) Changes in light intensity). Thereby, a change in the sound pressure applied to the probe 12 can be detected.

  The measurement light source 13 is a tunable laser device that can change the wavelength of emitted laser light, and is a means for generating laser light having a wavelength determined by the control unit 20 described later. Laser light having a predetermined wavelength generated from the measurement light source 13 is used as measurement light. A method for determining the wavelength of the measurement light will be described later.

The photoacoustic measurement apparatus according to the present embodiment can set a position where the measurement light is irradiated (hereinafter referred to as an irradiation position) to an arbitrary position on the probe 12.
The scanning unit 14 is a unit that changes the irradiation position of the measurement light on the probe 12. The scanning unit 14 is configured by an optical member such as a movable mirror (for example, a galvanometer mirror), and by moving the optical member, the irradiation position of the measurement light is set at two or more points on the probe (on the interference film). Can be moved to

The measurement light applied to the surface of the probe 12 is reflected by the resonance mirror and enters the light detection unit 16 through the half mirror 15.
The light detection unit 16 is means for measuring the intensity of incident light (the photodetector and the signal acquisition unit in the present invention). When an acoustic wave enters the probe 12, the interval between the resonant mirrors changes, and the intensity of the reflected light changes. By measuring the intensity of the reflected light, the sound pressure fluctuation of the acoustic wave incident on the probe 12 can be converted into an electric signal. Hereinafter, the electric signal representing the sound pressure fluctuation of the acoustic wave is referred to as a photoacoustic signal. The light detection unit 16 may include means for amplifying the photoacoustic signal and means for converting an analog electric signal into a digital signal. In addition, the photoacoustic signal in this specification is a concept including both an analog electric signal obtained by the light detection unit 16 and a converted digital signal.

The photoacoustic signal generated by the light detection unit 16 is a signal that represents a change in the amount of reflected light at one point on the probe 12. The light detection unit 16 transmits the corresponding coordinates on the probe together with the photoacoustic signal to the processing unit 17.
In the present embodiment, the above-described operation is repeated while changing the irradiation position of the measurement light using the scanning unit 14. That is, a plurality of photoacoustic signals acquired at a plurality of positions on the probe 12 are transmitted to the processing unit 17.
In the following description, unless otherwise specified, measurement is used as a term indicating that the sound pressure of an acoustic wave incident on the probe 12 is converted into a photoacoustic signal.

The processing unit 17 temporarily stores information transmitted from the light detection unit 16 and generates (reconstructs) an image representing information in the subject, for example, an optical characteristic value distribution, based on the stored information. Means (information generating unit in the present invention). As a reconstruction method, there are a Fourier transform method, a universal back projection method (UBP method), a filtered back projection method, a phasing addition, and the like, and any method may be used. When there is a region where the film thickness is remarkably abnormal (for example, when a foreign object exists in the element), when reconstructing an image, processing is performed by excluding data obtained in the region. It may be.

  The display unit 18 is a device that displays information generated by the processing unit 17 as an image. Typically, a liquid crystal display or the like is used, but other types of displays such as a plasma display, an organic EL display, and an FED are used. There may be.

  The temperature adjusting unit 19 is a means for maintaining the probe 12 and its peripheral part at a predetermined temperature. The configuration of the temperature adjusting unit 19 and a method for maintaining the temperature of the probe 12 will be described later.

  The control unit 20 is a unit (a wavelength control unit and a wavelength data storage unit in the present invention) that controls each unit described above. Specifically, the irradiation intensity, irradiation timing, irradiation position, and the like of the excitation light that irradiates the subject and the measurement light that irradiates the probe are controlled. It also controls the reception timing of acoustic waves. The control unit 20 may be realized by hardware designed exclusively, or may be realized by a software module. Further, it may be realized by a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), or the like, or may be realized by a combination thereof.

  In the photoacoustic measurement apparatus according to the present embodiment, the irradiation position of the measurement light is changed using the scanning unit 14. However, the measurement light may be configured to guide the measurement light to an arbitrary position on the probe 12. Other configurations may be adopted. For example, a configuration in which a light emitting element array capable of emitting light of a plurality of wavelengths is used as a measurement light source, and the irradiation position of the measurement light is changed by switching the light emitting element may be employed.

<Configuration of temperature control unit>
Next, a detailed configuration of the temperature adjusting unit 19 will be described with reference to FIGS. 2 (a) and 2 (b). FIG. 2 is a view of the probe 12 as viewed from the upper surface, that is, the surface on the side irradiated with the measurement light.
FIG. 2A shows an example of a configuration for exchanging heat using a fluid and maintaining the temperature of the probe. In the case of this example, the temperature adjustment unit 19 includes a heat exchanger 191, a pipe 192, and a fluid 193 that flows in the pipe 192. The fluid 193 is a liquid such as water or Galden or a gas such as air that circulates between the probe 12 and the heat exchanger 191. The pipe 192 is disposed so as to avoid an area irradiated with measurement light (hereinafter referred to as a measurement area) and border the periphery of the probe.
On the other hand, FIG. 2B is an example of a configuration in which temperature is maintained using a thermoelectric element such as Peltier. In the case of this example, the heat transfer element is installed outside the measurement region and performs heat exchange, as in FIG.

In the present embodiment, a predetermined temperature (hereinafter referred to as a target temperature) is set, and the temperature adjustment unit 19 performs control so that the probe becomes the target temperature. For example, when the subject is a human body, the target temperature can be a temperature close to the body temperature.
In order to enhance thermal conductivity, a paste or gel having high thermal conductivity may be disposed between the pipe and the probe or between the thermoelectric element and the probe.

By using the configuration as described above, the temperature of the probe can be kept uniform. However, when the size of the probe increases or the body temperature of the subject is low, temperature unevenness may occur in the measurement region. That is, depending on the position on the probe, the optimum wavelength of the measurement light may be shifted and the detection sensitivity may be reduced. Therefore, in the present embodiment, the control unit 20 acquires the optimum wavelength for measurement based on the set target temperature, and sets the wavelength of the laser light emitted from the measurement light source 13 using the acquired wavelength. .

<Relationship between acoustic wave detection sensitivity and temperature>
Before describing a specific method, the relationship between acoustic wave detection sensitivity and temperature in a Fabry-Perot probe will be described.

The Fabry-Perot probe acquires fluctuations in the distance between the interference mirrors caused by the sound pressure of the incident acoustic wave by detecting the reflected light intensity of the measurement light.
Here, the reflectance (I _r / I _i ) when the intensity of the measurement light applied to the probe 12 is I _i and the intensity of the reflected light is I _r can be expressed by equation (1). .

In the equation (1), R is the reflectance of the mirror included in the probe 12, and φ is the phase. Here, when the wavelength of the measurement light is λ, the refractive index of the spacer film laminated between the interference mirrors is n, and the distance between the mirrors is d, the relationship of Expression (2) is established. FIG. 3 is a graph showing this relationship.
φ = (4π / λ) × nd (2)

In the graph of FIG. 3, the horizontal axis represents the phase, and the vertical axis represents the reflectance. As can be seen from the graph, the phase at which the reflectance change with respect to the phase change becomes maximum is φ ₀ in the figure. By the way, as can be seen from the equation (2), the phase and the distance d between the mirrors have a linear relationship. Therefore, the change in the reflectivity is the largest when the phase becomes φ ₀ with respect to the minute fluctuation in the inter-mirror distance d. That is, when realizing such a phase φ ₀ , the acoustic wave detection sensitivity is maximized. That is, when a certain distance d between the mirrors is assumed, the wavelength λ _{0 at} which the detection sensitivity is highest can be expressed by Expression (3).
λ ₀ = (4π / φ ₀ ) × nd (3)

On the other hand, it is known that the inter-mirror distance d varies with temperature. Therefore, even if the wavelength that achieves the maximum sensitivity is determined at a certain temperature, if the temperature fluctuates, the acoustic wave detection sensitivity changes. When the dependence of the wavelength of measurement light (hereinafter referred to as the optimum wavelength) on which the detection sensitivity is maximized and the distance d between the mirrors with respect to the temperature T is expressed, Expression (4) is obtained.
λ ₀ (T) = (4π / φ ₀ ) × nd (T) (4)
Although the temperature dependence of the refractive index n of the spacer film is not shown, it is omitted here because it is considered to be sufficiently smaller than the temperature dependence of the inter-mirror distance d.

As a factor that causes the temperature of the probe to fluctuate, for example, heat transfer caused by a temperature difference between the probe and the living body that is the subject can be cited. Another factor is the change in environmental temperature.
When a plurality of measurement positions are set on the probe and measurement is performed at each measurement position, variations in detection sensitivity occur at each measurement position for the reasons described above. For this reason, in this embodiment, the temperature adjustment unit 19 is used to maintain the temperature of the probe uniformly, thereby suppressing fluctuations in detection sensitivity.

<Optimum wavelength data>
On the other hand, even when the probe is kept at a constant temperature, the optimum wavelength is not always the same at all measurement positions on the probe. This is because the film thickness of the interference film is not completely uniform, and there are variations during manufacturing. Therefore, in the present embodiment, the optimum wavelength under a predetermined temperature condition is stored in a table format in association with the position on the probe, and the measurement light is irradiated using the data (hereinafter, optimum wavelength data). Determine the wavelength. FIG. 4 is an example of optimum wavelength data.
In the optimum wavelength data table, the wavelength with the highest sensitivity at a predetermined measurement temperature is recorded at a plurality of measurement positions set on the probe. By maintaining the temperature of the probe at a predetermined measurement temperature and determining the wavelength of the measurement light each time while referring to the table, measurement can be performed with good detection sensitivity at all measurement positions. It becomes like this.

  Next, a method for creating optimum wavelength data will be described. The optimum wavelength data is created by executing the following steps. In this specification, the measurement for acquiring the characteristic information in the subject is referred to as main measurement, and the measurement for determining the optimum wavelength (calibration measurement) as described here is referred to as auxiliary measurement. .

First, after maintaining the temperature of the probe at a predetermined temperature, light for performing auxiliary measurement (hereinafter referred to as auxiliary measurement light) is irradiated to an arbitrary measurement position on the probe, The change in the amount of reflected light is recorded while changing the wavelength. Note that, in the auxiliary measurement, control of the measurement position, control of the wavelength, acquisition of the amount of reflected light, and the like are performed by the control unit 20 as in the main measurement.
Next, from the relationship between the wavelength of the irradiated auxiliary measurement light and the intensity of the detected reflected light, the wavelength for realizing the phase φ ₀ described above is obtained. The wavelength obtained here is the optimum wavelength at the target measurement position.
Then, by performing the same auxiliary measurement while moving the measurement position, a set of optimum wavelengths is obtained, a table is generated, and finally stored in the control unit 20 as optimum wavelength data.

The timing for generating or regenerating the optimum wavelength data is appropriate at the time of shipment of the apparatus, at the time of starting up the apparatus, or at the time of maintenance of the apparatus. When generating optimum wavelength data at the time of starting up the apparatus, it is preferable to perform it before the first measurement after turning on the main power. Alternatively, it may be performed when the apparatus is not used for a certain period. Alternatively, optical characteristics may be measured using a known phantom, and optimum wavelength data may be generated when a predetermined signal sensitivity is not achieved.
During the auxiliary measurement, it is preferable to notify the user that the main measurement cannot be performed and to prevent the main measurement from starting.

<Method of photoacoustic measurement>
Next, a method by which the photoacoustic measurement apparatus according to the present embodiment acquires characteristic information in the subject will be described with reference to FIG. 5 which is a processing flowchart.
First, in step S <b> 1, the temperature of the probe 12 is adjusted to the target temperature by the temperature adjustment unit 19. The target temperature is preferably a temperature close to the temperature of the subject. For example, when the subject is a human body, a value close to the human body temperature or skin temperature is suitable.
Next, in step S2, the probe 12 is brought close to the subject and measurement is started.

Next, in step S <b> 3, a position (hereinafter referred to as a measurement position) on the probe to which the measurement light is irradiated is determined, and the measurement light irradiation position is moved to the measurement position using the scanning unit 14.
Next, in step S4, referring to the stored optimum wavelength data, the optimum wavelength corresponding to the measurement position is acquired. The acquired optimum wavelength is set in the measurement light source 13.
Next, in step S5, the measurement light having the wavelength set in step S4 is irradiated to the measurement position on the probe 12, and the subject is irradiated with the pulsed light generated by the excitation light source 11. The irradiated measurement light is reflected by the probe 12, and the intensity (light quantity) of the reflected light is detected by the light detection unit 16. The light amount detection performed by the light detection unit 16 is performed in synchronization with the light emission trigger signal output from the excitation light source 11. A change in the amount of reflected light (photoacoustic signal) detected by the light detection unit 16 is accumulated in a memory inside the processing unit 17.
In step S6, it is determined whether or not it is necessary to perform measurement at another measurement position. If there is an unprocessed measurement position, the process proceeds to step S3 and measurement is continued. When all the measurements are completed, the process proceeds to step S7.

  In step S7, the processing unit 17 performs image reconstruction using the accumulated photoacoustic signal, and generates a three-dimensional image representing the light energy absorption density distribution inside the subject. Further, after performing appropriate image processing, the image is output to the display unit 18.

  As described above, in the first embodiment, the optimum wavelength under a predetermined temperature condition is stored as optimum wavelength data in association with the position on the probe, and the wavelength of measurement light is used using the optimum wavelength data. To decide. With this configuration, it is possible to prevent a decrease in detection sensitivity due to variations in the film thickness of the Fabry-Perot interference film. In addition, since it is not necessary to search for the optimum wavelength every measurement position, the measurement time can be shortened.

(Second embodiment)
In the first embodiment, the optimum wavelength data is generated by performing calibration in advance, and the optimum wavelength is determined using the optimum wavelength data. However, in actual measurements, the subject may come into contact with the probe, or the temperature distribution on the probe may change due to environmental changes. There may be a deviation from the optimum wavelength.
In order to cope with this problem, the second embodiment does not use the optimum wavelength acquired from the optimum wavelength data as it is, but sweeps (scans) the wavelengths before and after the optimum wavelength to obtain a truly optimum wavelength. It is an embodiment.
Since the system configuration diagram of the photoacoustic measurement apparatus in the second embodiment is the same as that in the first embodiment, detailed description thereof will be omitted, and only differences in processing from the first embodiment will be described.

  In the second embodiment, the content of the process performed in step S4 is different from the first embodiment. FIG. 6 is a flowchart for explaining in detail the processing content of step S4 in the second embodiment. Hereinafter, the processing content of step S4 is demonstrated.

The process performed in step S41 is the same as the process performed in step S4 in the first embodiment. That is, referring to the stored optimum wavelength data, the optimum wavelength corresponding to the measurement position is acquired.
Next, wavelength sweep is performed in step S42. The wavelength sweep in this specification refers to an operation of setting a predetermined wavelength range and irradiating the measurement light from the measurement light source 13 a plurality of times while changing the wavelength within the range to obtain the intensity of the reflected light. Point to.

A range in which the wavelength sweep is performed (hereinafter, sweep range) will be described. Here, assuming that the film thickness d in the equation (4) is directly proportional to the temperature, the relationship between the optimum wavelength and the temperature can be approximated to a linear function. Here, the slope of the linear function is a [nm / ° C.]. The slope a is the phase φ ₀
And the refractive index n of the spacer film of the probe and the thermal expansion coefficient of the spacer film.
Further, the inclination a may be obtained by actual measurement. For example, it is possible to calculate the optimum wavelength for each temperature while changing the temperature of the probe 12 by the temperature adjustment unit 19 and derive the optimum wavelength from the obtained gradient of the optimum wavelength.

The sweep range can be determined based on the optimum wavelength λ ₀ acquired in step S41. For example, if the temperature range assumed on the probe is ± ΔT, ± ΔT with respect to λ ₀
The range of / a [nm] may be swept. That is, the sweep range is (λ ₀ −ΔT / a) ≦ λ ₀ ≦ (λ ₀ + ΔT / a). In the present example, to determine the sweep range around the lambda _0, if it contains lambda ₀ the sweep range, necessarily lambda ₀ is not necessarily the center value. Further, as long as the sweep range can be narrowed based on λ ₀ , the sweep range may be determined by other methods.

  Finally, in step S43, the final wavelength is determined based on the intensity of the reflected light obtained as a result of the wavelength sweep. Other steps are the same as those in the first embodiment.

As described above, in the present embodiment, the sweep range of the measurement light is set based on the optimum wavelength λ ₀ corresponding to the target temperature. When performing wavelength sweeping unconditionally as in the device described in Non-Patent Document 1, it is necessary to increase the sweep range, but in this embodiment, the sweep range is narrowed down based on λ ₀ corresponding to the target temperature. Therefore, the measurement time can be shortened.
For example, when the difference between the temperature of the skin and the temperature of air is 10 ° C., in the conventional apparatus, it is necessary to sweep the range of 10 ° C. at the maximum, but the probe after the temperature is adjusted When the difference between the minimum temperature and the maximum temperature is 1 ° C. at maximum, it is sufficient to sweep only the range of 1 ° C. That is, the time required for the wavelength sweep can be reduced to 1/10 at the maximum.

  In the second embodiment, the optimum wavelength is determined by performing the wavelength sweep for each measurement position. However, the wavelength sweep may be performed at least at a part of the plurality of measurement positions, and not all of them are required. It does not need to be done at the measurement position. Even when wavelength sweeping is performed, it is not always necessary to refer to the optimum wavelength data every time.

(Third embodiment)
In the first and second embodiments, the probe 12 is brought into direct contact with the subject. In contrast, the third embodiment is an embodiment in which a gel for matching acoustic impedance, maintained at a desired temperature, is interposed between the probe 12 and the subject.
FIG. 7 is a system configuration diagram of the photoacoustic measurement apparatus according to the third embodiment. The same means as those in the first and second embodiments are denoted by the same reference numerals, and description thereof is omitted.

In the third embodiment, an acoustic matching gel 701 is inserted between the subject and the probe 12. The acoustic matching gel 701 is a gel for suppressing reflection of acoustic waves generated due to a difference in acoustic impedance at the interface between the subject and the probe.
The acoustic matching gel 701 is stored in the storage container 702 and is maintained at the same temperature as the probe by the heat retaining device 703.

In the third embodiment, in step S1, the temperature of the probe is adjusted to the target temperature, and the acoustic matching gel 701 stored in the storage container 702 is adjusted to the same temperature.
Further, after the subject is set in step S2, the acoustic matching gel is supplied between the probe and the subject. The acoustic matching gel may be applied to the surface of the probe or the subject, for example, or when there is a closed space between the probe and the subject, the acoustic matching gel may be supplied so as to fill the closed space. .
Since other steps are the same as those in the first and second embodiments, the description thereof will be omitted.

  Thus, in the third embodiment, the temperature of the acoustic matching gel is maintained at the same temperature as that of the probe. Thereby, the fall of the detection sensitivity by a temperature difference between a probe and an acoustic matching gel can be suppressed.

(Fourth embodiment)
In the first to third embodiments, the photoacoustic measurement apparatus that generates an acoustic wave by irradiating a subject with pulsed light has been described. On the other hand, the present invention can also be applied to an apparatus (acoustic measurement apparatus) that acquires information in a subject by transmitting an acoustic wave to the subject and detecting the reflected acoustic wave. The fourth embodiment is an embodiment in which the present invention is applied to an acoustic measurement device.

  FIG. 9 is a system configuration diagram of an ultrasonic measurement apparatus according to the fourth embodiment. The ultrasonic measurement apparatus according to this embodiment is an apparatus that images an interface in a subject that has a difference in acoustic impedance by transmitting the ultrasonic wave to the subject and detecting the reflected ultrasonic wave. . The same means as those in the first and second embodiments are denoted by the same reference numerals, and description thereof is omitted.

The ultrasonic measurement apparatus according to this embodiment includes a transducer 901 that transmits ultrasonic waves toward a subject. In the present embodiment, the control unit 20 has a function of controlling the waveform of the ultrasonic wave transmitted from the transducer 901.
In the present embodiment, the probe 12 is a means for receiving ultrasonic waves reflected in the subject. That is, it is possible to detect the sound pressure of an ultrasonic wave reflected at the interface of a tissue having a different acoustic impedance from the surroundings, such as a tumor.

Note that the processing for generating an image based on the detected ultrasonic wave is the same as that in the first embodiment, and thus the description thereof is omitted.
According to the fourth embodiment, in an apparatus (acoustic measurement apparatus) for imaging an interface existing in a subject and having a difference in acoustic impedance, as in the first to third embodiments, the measurement time is shortened. And improved detection sensitivity.

(Modification)
The description of each embodiment and the description of the examples are exemplifications for explaining the present invention, and the present invention can be appropriately modified or combined in a range not departing from the gist of the invention.
For example, the present invention can be implemented as a photoacoustic measurement device or an acoustic measurement device that includes at least a part of the above processing. Moreover, it can also implement as a photoacoustic measuring device and the control method of an acoustic measuring device including at least one part of the said process. Moreover, it can also implement as an acoustic wave detection apparatus single-piece | unit, and can also be implemented as an acoustic wave detection method which the said acoustic wave detection apparatus performs. The above processes and means can be freely combined and implemented as long as no technical contradiction occurs.

  In the first to third embodiments, the excitation light is emitted from a direction that does not become a shadow of the probe 12, but the excitation light having a wavelength that passes through the mirror of the probe 12 is used. The subject may be irradiated with excitation light through the child.

  Further, an acoustic coupling medium other than those exemplified may be disposed between the subject and the probe. For example, a subject may be placed in a water tank, and the probe 12 may be closely attached to the water surface for measurement.

  Further, in the first to third embodiments, an example in which pulsed light having a single wavelength is irradiated as excitation light has been described, but optical light in a subject obtained by irradiating pulsed light having a plurality of wavelengths is obtained. Based on the coefficient, the concentration distribution of the substance constituting the tissue of the subject may be acquired. For example, photoacoustic signals and spectral information acquired at multiple wavelengths can be obtained from the concentration of a substance in a subject, particularly the concentration of oxygen in blood in blood vessels and the concentration distribution of fat, collagen, glucose, hemoglobin, etc. Can be used to calculate.

In each embodiment, the optimum wavelength data is held in a table format, but may be held in other formats. For example, you may hold | maintain by numerical formula etc.

  DESCRIPTION OF SYMBOLS 12 ... Probe, 13 ... Measurement light source, 16 ... Light detection part, 19 ... Temperature adjustment part, 20 ... Control part

Claims (8)

An acoustic wave detection device that irradiates the interference film with measurement light and detects the intensity of the acoustic wave incident on the interference film based on the intensity of the measurement light reflected by the interference film,
An interference film composed of two reflective layers facing each other;
A light source for irradiating the interference film with light, the first light source capable of changing the wavelength of the light; and
A temperature adjusting unit for adjusting the temperature of the interference film or its peripheral part to a predetermined temperature;
A wavelength controller configured to determine the wavelength of measurement light emitted from the first light source based on the predetermined temperature and set the first light source;
A photodetector for detecting the intensity of the reflected light reflected by the interference film from the measurement light;
A signal acquisition unit that acquires an electrical signal corresponding to an acoustic wave incident on the interference film based on a change in intensity of reflected light detected by the photodetector;
An acoustic wave detection device comprising: The first light source can irradiate measurement light to two or more different locations on the interference film,
A wavelength data storage unit that stores wavelength data that is data that associates the wavelength of the measurement light corresponding to the predetermined temperature with the irradiation position of the measurement light on the interference film;
The wavelength control unit determines a wavelength of measurement light to be set in the first light source based on the wavelength data and an irradiation position of the measurement light on the interference film. The acoustic wave detection apparatus described. The wavelength controller is
Means for determining a range that the wavelength of the measurement light can take based on the wavelength data and an irradiation position of the measurement light on the interference film;
Means for irradiating the interference film multiple times as auxiliary measurement light with light corresponding to a plurality of wavelengths included in the range using the first light source;
Means for determining the wavelength of the measurement light set in the first light source based on the intensity of the reflected light reflected from the interference film by the auxiliary measurement light;
The acoustic wave detection device according to claim 2, comprising: A second light source for irradiating the subject with excitation light;
The acoustic wave detection device according to any one of claims 1 to 3, wherein an electrical signal corresponding to an acoustic wave generated from the subject due to the excitation light is acquired;
Based on the electrical signal acquired by the acoustic wave detection device, an information generation unit that acquires characteristic information in the subject;
A photoacoustic measuring device comprising: A transducer for irradiating the subject with acoustic waves;
The acoustic wave detection device according to any one of claims 1 to 3, wherein an electrical signal corresponding to an acoustic wave reflected in the subject is acquired;
Based on the electrical signal acquired by the acoustic wave detection device, an information generation unit that acquires characteristic information in the subject;
An acoustic measurement device comprising: An interference film composed of two reflective layers facing each other, a light source for irradiating the interference film with light, a first light source capable of changing the wavelength of light, and detecting the intensity of light reflected by the interference film An acoustic wave detection method performed by an acoustic wave detection device having a photodetector and a temperature adjustment unit that adjusts the temperature of the interference film or its peripheral part to a predetermined temperature,
A temperature adjusting step of adjusting the temperature of the interference film or its peripheral portion to a predetermined temperature;
A wavelength control step of determining a wavelength of measurement light emitted from the first light source based on the predetermined temperature and setting the wavelength to the first light source;
An irradiation step of irradiating the interference film with the measurement light from the first light source;
A signal acquisition step of acquiring an electrical signal corresponding to an acoustic wave incident on the interference film based on a change in intensity of reflected light detected by the photodetector;
The acoustic wave detection method characterized by including. The first light source is an acoustic wave detection method performed by an acoustic wave detection device capable of irradiating measurement light to two or more different locations on the interference film,
Further including the step of obtaining wavelength data, which is data relating the wavelength of the measurement light corresponding to the predetermined temperature with the irradiation position of the measurement light on the interference film,
In the wavelength control step, a wavelength of measurement light to be set in the first light source is determined based on the wavelength data and a measurement light irradiation position on the interference film. The acoustic wave detection method as described. The wavelength control step includes
Determining a range of wavelengths of the measurement light based on the wavelength data and an irradiation position of the measurement light on the interference film;
Using the first light source, irradiating the interference film multiple times as auxiliary measurement light with light corresponding to a plurality of wavelengths included in the range;
Determining the wavelength of the measurement light to be set in the first light source based on the intensity of the reflected light reflected by the interference film from the auxiliary measurement light;
The acoustic wave detection method according to claim 7, comprising:

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