JP6776397B2 - Information acquisition device - Google Patents

Description

The present invention relates to an acoustic wave acquisition device.

A general ultrasonic diagnostic apparatus can obtain information on the inside of a living body by transmitting ultrasonic waves and receiving ultrasonic waves reflected inside the living body. This makes it possible to detect a diseased part such as cancer, but in order to further improve the detection efficiency, imaging of physiological information of a living body, that is, functional information is drawing attention. Photoacoustic Tomography (PAT) using light and ultrasonic waves has been proposed as a means for imaging functional information.

Photoacoustic tomography uses the photoacoustic effect of irradiating a subject with pulsed light generated from a light source and generating acoustic waves (typically ultrasonic waves) by absorbing the light propagated and diffused within the subject. This is a technique for imaging the internal structure that is the source of acoustic waves. The time-dependent change of the received acoustic wave is detected at multiple points, the obtained signal is mathematically analyzed, that is, reconstructed, and the information related to the optical characteristic value inside the subject is visualized in three dimensions. ..

The resolution of the three-dimensional image obtained by photoacoustic tomography depends on the following depending on the arrangement of the acoustic detection elements. When a plurality of acoustic detection elements are arranged on a plane, the resolution (horizontal resolution) in the direction parallel to the arrangement plane can detect the dimensions of the receiving unit of each acoustic detection element and the acoustic detection element. It depends on both the frequency, and the resolution in the direction perpendicular to the arrangement plane (depth resolution) depends only on the frequency that can be detected by the acoustic detection element. In general, increasing the detectable frequency of the acoustic detection element is easier than reducing the size of the receiver, so the resolution in the direction perpendicular to the arrangement plane is higher than the resolution in the direction parallel to the arrangement plane. good. When a plurality of acoustic detection elements are arranged on a spherical surface, the information in the depth direction of all the acoustic detection elements is superimposed, so that the lateral resolution is equivalent to the depth resolution. That is, the resolution in all directions depends only on the frequency, and the arrangement has good resolution. In an arrangement between a plane and a spherical surface, such as arranging a plurality of acoustic detection elements on a plurality of planes provided at different angles, the resolution of the receiving part of the acoustic detection element increases as the plane approaches the spherical surface. It is less dependent on dimensions and has higher resolution.

Patent Document 1 is mentioned as an apparatus in which a plurality of acoustic detection elements are arranged on a spherical surface. In Patent Document 1, acoustic detection elements are spirally arranged on a hemisphere, and light irradiation and acoustic wave reception by the acoustic detection element are performed while rotating around a line connecting the poles of the hemisphere and the center of the sphere. By receiving the acoustic wave, the image is reconstructed using the signal output from the acoustic receiving element, and the image data is obtained.

U.S. Pat. No. 5,713,356

However, in the case of the spherical arrangement of the acoustic detection element shown in Patent Document 1, the resolution is best at the center of the sphere, the resolution decreases toward the periphery, and the resolution varies depending on the position. That is, in the central portion, the acoustic wave is vertically incident on all the acoustic detection elements, and the signals having the same phase are simultaneously incident, so that the signal is not dull. However, since the acoustic wave is obliquely incident on some acoustic detection elements in the portion other than the center, the signals having the same phase are incident with a time lag. Therefore, one of the causes is that the signal in the portion other than the central portion becomes dull.

Further, the directivity of the acoustic detection element is another cause. In the part other than the center, the traveling direction of the acoustic wave is angled with respect to the sound detection element, but since the sound detection element has directivity, the sensitivity decreases when the angle is set, and it is lost when the signal becomes noise or less. .. Therefore, the resolution is lowered by reducing the amount of information. In the planar type, when the acoustic detection element is arranged on a plane sufficiently wider than the measurement range, the resolution becomes uniform in the measurement range. In an arrangement between a plane and a sphere, such as arranging a plurality of planes, the range of uniform resolution gradually narrows as the transition from the plane to the sphere occurs. As described above, there is a trade-off relationship between high resolution and resolution uniformity.

The present invention has been made based on such problem recognition, and an object of the present invention is to reduce variations in resolution depending on the position.

Information acquiring apparatus according to the first aspect of the present invention is an information acquiring device you get information about the object based on the acoustic wave generated from a subject irradiated with light,
A scanning unit for changing the detector you output the received signal to receive an acoustic wave, the pre SL relative position of the detector relative to the subject through the matching member,
A signal processing unit for obtaining information about pre-Symbol object using the received signal,
A signal correction unit that corrects the received signal based on information on a first propagation distance in which the acoustic wave generated in the subject propagates in the subject and a second propagation distance propagating in the matching material. characterized in that it comprises a.
Further, the information acquisition method according to the second aspect of the present invention is an information acquisition method for acquiring information about the subject based on an acoustic wave generated from the subject irradiated with light.
A scanning step of changing the relative position of the detector with respect to the subject, a detection step of receiving the acoustic wave propagating from the subject through the matching material using the detector and outputting a received signal, and the received signal. Has a signal processing step of acquiring information about the subject using the
It is characterized in that the received signal is corrected based on information on a first propagation distance in which the acoustic wave generated in the subject propagates in the subject and a second propagation distance in which the matching material propagates. Information acquisition method.

According to the present invention, it is possible to reduce the variation in resolution depending on the position as compared with the conventional case.

It is a block diagram which shows the structure of the apparatus which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the scanning method which concerns on Embodiment 1 of this invention. It is a flowchart which shows the operation of the apparatus which concerns on Embodiment 1 of this invention. It is a conceptual diagram which showed the gradient of resolution and the effect by scanning. It is a figure which shows the modification of the apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the apparatus which concerns on Embodiment 2 of this invention. It is a schematic diagram which shows the apparatus which concerns on Embodiment 2 of this invention. It is a figure explaining the processing method of the apparatus which concerns on Embodiment 2 of this invention. It is a block diagram which shows the structure of the apparatus which concerns on Embodiment 2 of this invention. It is a flowchart which shows the operation of the apparatus which concerns on Embodiment 3 of this invention.

The present invention is characterized in that variations in resolution are reduced by moving at least one of a subject and an acoustic array detector in which a plurality of acoustic detection elements are arranged. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
This embodiment is a basic embodiment of the present invention. First, the components of the present embodiment will be described, and then the arrangement method and scanning method of the acoustic detection element, which are the features of the present invention, will be described. Then, the embodiment of this embodiment will be described, and finally, a possible variation will be described.

FIG. 1 is a block diagram showing components of the present embodiment. The acoustic wave acquisition device of the present embodiment includes a light source 1, a light irradiation device 2, an acoustic array detector 5, a scanning device 6, an electric signal processing device 7, a data processing device 8, and a display device 9. Hereinafter, each configuration and the subject will be described.

(light source)
The light source 1 is a device that generates pulsed light. A laser is desirable as a light source in order to obtain a large output, but a light emitting diode or the like may also be used. In order to effectively generate a photoacoustic wave, it is necessary to irradiate the light for a sufficiently short time according to the thermal characteristics of the subject. When the subject is a living body, it is desirable that the pulse width of the pulsed light generated from the light source 1 is several tens of nanoseconds or less. The wavelength of the pulsed light is in the near-infrared region called the window of the living body, and is preferably about 700 nm to 1200 nm. Light in this region can reach a relatively deep part of the living body, and information on the deep part can be obtained. If it is limited to the measurement of the surface portion of the living body, a visible light to near infrared region of about 500 to 700 nm may also be used. Further, it is desirable that the wavelength of the pulsed light has a high absorption coefficient with respect to the observation target.

(Light irradiation device)
The light irradiation device 2 is a device that guides the pulsed light generated by the light source 1 to the subject 3. Specifically, it is an optical device such as an optical fiber, a lens, a mirror, and a diffuser. In addition, these optical instruments may be used to change the shape and light density when guiding. The optical device is not limited to the ones listed here, and any optical device may be used as long as it satisfies such a function.

(Subject)
Subject 3 is the object of measurement. Specific examples include a living body such as a breast, and a phantom that simulates the acoustic and optical characteristics of a living body in adjusting a device. The acoustic characteristics are specifically the propagation velocity and the attenuation rate of the acoustic waves, and the optical characteristics are specifically the light absorption coefficient and the scattering coefficient. A light absorber having a large light absorption coefficient needs to be present inside the subject, and in a living body, hemoglobin, water, melanin, collagen, lipid, and the like serve as the light absorber. In the phantom, a substance simulating optical characteristics is enclosed inside as a light absorber. Further, in the present invention, the information distribution inside the subject generated by receiving the acoustic wave is the initial sound pressure distribution of the acoustic wave generated by light irradiation, or the light energy absorption density distribution derived from the initial sound pressure distribution. It also shows the absorption coefficient distribution and the concentration distribution of the substances that make up the structure. The concentration distribution of the substance is, for example, an oxygen saturation distribution or an oxidation / reduction hemoglobin concentration distribution.

(Matching layer)
The matching layer 4 is an impedance matching material for filling the space between the subject 3 and the acoustic array detector 5 and acoustically coupling the subject 3 and the acoustic array detector 5. The material is preferably a liquid having an acoustic impedance close to that of the subject 3 and the acoustic detection element and transmitting pulsed light. Specifically, water, castor oil, gel and the like are used. As will be described later, since the relative positions of the subject 3 and the acoustic array detector 5 change, it is preferable to place both the subject 3 and the acoustic array detector 5 in the solution forming the matching layer 4.

(Acoustic array detector)
The acoustic array detector 5 is a detector in which a plurality of acoustic detection elements that convert acoustic waves into electrical signals are assembled. The acoustic array detector 5 is installed on the surface of the matching layer 4 in contact with the solution so as to surround the subject 3. It is desirable that the acoustic detection element that receives the acoustic wave from the subject has high sensitivity and a wide frequency band, and specific examples thereof include an acoustic detection element using PZT, PVDF, cMUT, and a Fabry-Perot interferometer. .. However, it is not limited to those listed here, and any one that satisfies the function may be used.

(Scanning device)
The scanning device 6 is a device that scans (moves) the acoustic array detector 5 three-dimensionally. In the present embodiment, the subject 3 is fixed, and by using the XYZ stage as the scanning device 6, the acoustic array detector is moved (scanned), and the relative positions of the subject 3 and the acoustic array detector 5 are determined. Change. However, in the present invention, the relative positions of the subject 3 and the acoustic array detector 5 may change, and the acoustic array detector may be fixed and the subject may be scanned. When scanning a subject, it is conceivable that the subject is scanned by moving a support portion (not shown) that supports the subject. Further, both the subject 3 and the acoustic array detector 5 may be scanned. Further, although it is desirable that the scanning is performed continuously, it may be repeated in a fixed step. The scanning device is preferably an electric stage equipped with a stepping motor or the like, but a manual stage may also be used. However, the present invention is not limited to the ones listed here, and any one may be used as long as at least one of the subject 3 and the acoustic array detector 5 is configured to be movable.

(Scanning control device)
The scanning control device 601 controls the scanning device and relatively moves the subject 3 and the acoustic array detector 5. Specifically, the scanning control device 601 determines the moving speed and direction of the scanning device 6 and instructs the scanning device 6. Further, information on the moving speed and direction of the scanning device 6 is output to the data processing device 8.

(Electrical signal processing device)
The electric signal processing device 7 has a function of amplifying an analog electric signal (received signal) output from the acoustic array detector 5 and converting it into a digital signal (digital received signal). In order to acquire data efficiently, it is desirable to have as many analog-digital converters (ADCs) as the number of detection elements provided in the acoustic array detector, but one ADC should be connected and used one after another. May be good.

(Data processing device)
The data processing device 8 generates image data (image reconstruction) by processing the digital signal obtained by the electric signal processing device 7. Specific examples of the data processing device include a computer and an electric circuit. Examples of the image reconstruction method include a Fourier transform method, a universal back projection method, a filtered back projection method, and an iterative method. In the present invention, any image reconstruction method may be used.

(Display device)
The display device 9 displays the image data generated by the data processing device 8 as an image. Specific examples thereof include a liquid crystal display and an organic EL display. The display device may be provided separately from the acoustic wave acquisition device of the present invention.

Next, a method of arranging the acoustic detection element 501 and a scanning method of the acoustic array detector 5, which are the features of the present invention, will be described. The arrangement method when carrying out the present invention will be described with reference to FIG. The inner wall (subject side) of the plurality of acoustic detection elements 501 is fixed to a hemispherical container, and the receiving surface faces the center of the hemisphere. In the case of the arrangement as shown in FIG. 2, in the image obtained by performing universal back projection, the center point of the hemisphere has the highest resolution, and the resolution decreases according to the distance from the center. Even when the plurality of acoustic detection elements 501 are not arranged on the spherical surface, the maximum resolution region is uniquely determined by the arrangement of the plurality of acoustic detection elements 501.

Here, in the present invention, a high-resolution region near the center point, which is the highest resolution region, is defined as a high-resolution region 301. The range of the high resolution region 301 is determined by how much difference is allowed with respect to the maximum resolution. For example, when the arrangement of the acoustic detection elements is spherical, the diameter r of the high resolution region 301 is represented by the following equation (1).

Here, R is an acceptable resolution, RH is the maximum resolution, r0 is the diameter of the sphere on which the acoustic detection element is arranged, and Φd is the diameter of the acoustic detection element 501. The relative position between this high-resolution region and the subject is changed, and reconstruction is performed to make the resolution uniform. In the present invention, by changing the relative position between the highest resolution region and the subject, as a result, the relative position between the high resolution region and the subject is changed.

Further, in the present invention, the sphere is not only a perfect true sphere but also an ellipsoid represented by the following equation (2) (a shape obtained by expanding the ellipse into three dimensions and having a quadric surface). Also includes.

Here, a, b, and c correspond to half the diameters in the x-axis, y-axis, and z-axis directions, respectively. The ellipsoid with a = b = c is a true sphere. An ellipse in which any two of a, b, and c are equal is a spheroid obtained by rotating the ellipse around the axis of the ellipse, and the sphere of the present invention also includes a spheroid. The ellipsoid, like the sphere, is symmetric with respect to the xy, yz, and zx planes.

In the measurement, the inside of the hemisphere of the acoustic array detector 5 is filled with the solution to be the matching layer 4, and the subject is placed in the solution. The laser beam 201 is irradiated from the lower part (pole) of the hemispherical container so as to hit the subject. The acoustic array detector 5 is scanned by the XYZ stage, which is a scanning device 6, and its position with respect to the subject changes relatively. As a result, the high resolution region 301 scans in the subject. At this time, in order to make the resolution uniform, it is desirable to scan in a direction in which the resolution is not uniform, that is, in a direction in which the resolution has a gradient. This effect will be described later.

FIG. 3 shows a specific scanning method. FIG. 3A is the initial position, and the received signal is acquired while scanning the entire acoustic array detector 5 in the direction of the arrow (left side of the paper) using the XYZ stage. When the position shown in FIG. 3B is reached, the entire acoustic array detector 5 is scanned under the paper to reach the state shown in FIG. 3C. Subsequently, scanning and signal acquisition are performed until the positional relationship shown in FIG. 3D is reached. After performing this in the entire area in one plane (in the XZ plane), the position of the acoustic array detector 5 is shifted in the depth direction (Y direction) of the paper surface, and scanning and signal acquisition are performed in the same manner.

Next, the measurement method in this embodiment will be described with reference to FIG. First, the light irradiation device 2 irradiates the subject with pulsed light (S1). The acoustic wave excited by the light absorber in the subject by the irradiated pulsed light is received by the acoustic detection element 501 and converted into a received signal. Then, it is converted into a digital signal by the electric signal processing device 7 (S2). At the same time, the data processing device 8 acquires the scanning position information corresponding to the obtained digital signal from the scanning control device 601 (S3).

Next, the scanning control device 601 determines whether or not the high resolution region 301 has finished scanning the entire measurement region (S4). The entire measurement area does not mean the entire subject 3, but the measurement target area may be arbitrarily specified. When the scanning is not completed, the acoustic array detector is scanned while the positional relationship between the acoustic detection elements 501 is fixed (S5), and the irradiation of the pulsed light and the signal acquisition of the acoustic wave are repeated. “Fixing the positional relationship between the acoustic detection elements” means that the arrangement positions of the plurality of acoustic detection elements 501 on the acoustic array detector 5 are not moved.

In S5, it is preferable that the scanning and the acquisition of the received signal are performed at regular time intervals. In particular, the acoustic array detection so that the pulsed light is irradiated at least once while the relative position between the high resolution region 301 and the subject 3 changes by a distance equal to the size (diameter) of the high resolution region. It is preferable to move the vessel 5. This means that the received signal is acquired at least once while the high resolution region travels a distance equal to the size of the high resolution region.

The shorter the scanning distance from one light irradiation to the next light irradiation, the more uniform the resolution can be, but the smaller the scanning distance (that is, the slower scanning speed), the longer the measurement takes. .. Therefore, the scanning speed and the acquisition time interval of the received signal may be appropriately set in consideration of the desired resolution and the measurement time.

Further, the scanning is performed three-dimensionally and in a direction having a resolution gradient. Scanning is performed over the entire measurement area, and when scanning is completed, the data processing device 8 executes image reconstruction based on the obtained digital signal and scanning position information (S6). The universal back projection used for image reconstruction performs preprocessing such as differentiation and noise filter on the obtained digital signal, and performs back projection in which this is propagated in the reverse direction from the position of the acoustic detection element 501. This is done for the acoustic array detectors at all scanning positions and the propagated processing signals are superimposed. By this process, the information distribution in the subject such as the absorption coefficient distribution is acquired as image data. Finally, the data processing device 8 outputs the obtained image data to the display device 9, and the display device 9 displays the image (S7).

FIG. 5 is a schematic diagram showing the effect of uniform resolution depending on the scanning direction. The shade of color represents the resolution obtained at that position. The darker the color, the higher the resolution, and the lighter the color, the lower the resolution. In FIG. 5A, there is a resolution gradient in the lateral direction. When scanning is performed in a direction in which the resolution has a gradient, the lateral resolution is made uniform with high resolution except for a certain rightmost region at the end point of scanning as shown in FIG. 5 (b).

On the other hand, FIG. 5C has a resolution gradient in the vertical direction, but when scanning is performed in a direction in which there is no gradient in the resolution, the resolution in the vertical direction is not uniform as in FIG. 5D. In the present embodiment, since the acoustic detection element 501 is arranged on a spherical surface, the resolution gradient is in all directions from the center of the sphere, and the scanning direction may be any direction.

Next, a possible variation of the present invention (a modification of the present embodiment) will be described. The scanning device 6 may include rotation as well as linear scanning as long as it can perform three-dimensional scanning. Specifically, the motion of rotating the acoustic array detector 5 around the optical axis of the laser beam shown in FIG. 2 may be combined with linear scanning. Further, it is desirable that the scanning is performed so that the path is short.

In order to make the resolution of the entire subject uniform, the size of the hemispherical container as the acoustic array detector 5 should be at least twice the size of the subject so that the high resolution region can scan the entire subject. It is desirable to have. That is, when the holding member for holding the subject (subject holder 10 shown in FIG. 8 described later) is used, the inner diameter of the acoustic array detector 5 (the diameter of the hemisphere provided with the acoustic detection element) becomes , It is preferable that the diameter is twice or more the outer diameter of the holding member.

Furthermore, since the volume of the subject in the solution, which is the matching layer, changes when three-dimensional scanning is performed, the injection port for injecting the solution and the solution so as to keep the liquid level of the matching layer solution constant. It is desirable to provide an outlet for discharging the solution and adjust the amount of the solution.

It is desirable that the arrangement of the plurality of acoustic detection elements 501 is spherical, but the arrangement is not limited to the spherical shape, and if the arrangement of the plurality of acoustic detection elements is a detector having variations in resolution (spatial resolution). Applicable. Specifically, the plurality of acoustic detection elements may be arranged so that the receiving surface faces the subject side, and may be arranged on a curved surface or a plane so that a predetermined maximum resolution region can be obtained. That is, in the present invention, the receiving surfaces of at least some of the plurality of acoustic detection elements may be arranged so as to have different angles. In other words, it is preferable that some of the acoustic detection elements 501 out of the plurality of acoustic detection elements 501 are arranged in a concave shape with respect to the subject so that the receiving surfaces are arranged at different angles. Of course, as the arrangement of the plurality of acoustic detection elements approaches the spherical surface, the resolution becomes less dependent on the dimensions of the receiving portion of the acoustic detection elements, and the resolution becomes higher.

FIG. 6 shows some examples of arrangements of acoustic detection elements applicable to the present invention. In FIGS. 6A and 6B, the plurality of acoustic detection elements 501 are arranged along a curved surface of a part of a spherical surface. Here, in the present invention, the curved surface includes not only a completely smooth curved surface but also a curved surface having irregularities in a part thereof. With the configuration shown in FIGS. 6A and 6B, the light irradiation device 2 and the like can be flexibly installed. In FIG. 6C, the plurality of acoustic detection elements 501 are arranged along a curved surface that is not a spherical surface. In such cases, the trade-off between resolution and resolution uniformity can be adjusted. In FIG. 6D, the plurality of acoustic detection elements 501 are arranged in two linear shapes (planar shapes). In the case of such an example, since the acoustic wave detection elements are arranged linearly at two different angles so as to surround the subject, a region having uniform resolution can be widened and the scanning step can be increased. it can.

Further, in FIGS. 6 (b) and 6 (d), two examples are shown in which the number of curved surfaces or planes on which the acoustic detection elements are arranged is two, but the present invention may be arranged on a larger number of surfaces. Of course, it may be one continuous surface. A desired number of acoustic detection elements may be provided.

In the present embodiment, the resolution of the image obtained in the entire measurement region is higher than the high resolution and lower than the maximum resolution by the above configuration and processing method, but the range of variation in the resolution can be narrowed. That is, it is possible to increase the region where the resolution is uniform.

[Embodiment 2]
(Signal attenuation correction)
In this embodiment, a mode for correcting a received signal will be described. When the acoustic wave propagates in the subject or in the matching layer, the intensity of the acoustic wave is attenuated. Further, the distance propagating in the subject and the distance propagating in the matching layer in the path from the generated position of the generated acoustic wave to the acoustic detection element 501 differ depending on the scanning position of the acoustic array detector 5. If the subject and the matching layer are each composed of a living body and water, or if the attenuation rates are different from each other, the contrast may not be calculated correctly. Therefore, in the present embodiment, a method for correcting different intensity attenuation will be described.

Each configuration of the acoustic wave acquisition device of this embodiment is shown in FIG. It differs from each configuration shown in the first embodiment in that a subject holder 10 is added as a holding member for holding the subject. Further, the treatment method in the data processing device 8 is different. Since the other configurations are the same as those in the first embodiment, the description thereof will be omitted. As shown in FIG. 8, the subject holder 10 holds the subject 3 and defines the shape of the subject. It is desirable that the holding member is thin and hard, and has an acoustic impedance close to that of the subject or the matching layer 4. It is better if the acoustic impedance is a value between the subject and the matching layer. Specifically, polymethylpentene and the like can be considered. The thickness of the holding member is preferably 0.1 mm or more and 5 mm or less.

In the measurement method of the present embodiment, the image reconstruction process (S6 in FIG. 4) in the data processing device 8 is different from that of the first embodiment. In the present embodiment, the boundary between the subject 3 and the matching layer 4 can be known from the shape of the subject holder 10, and the distance is converted into time to know the subject region and the matching layer region even in the acquired signal. be able to. Here, since the subject holder 10 is sufficiently thin, it is assumed that the propagation of the acoustic wave in the subject holder 10 can be ignored.

Normally, when paying attention to one acoustic detection element 501, the attenuation can be corrected correctly by dividing the signal corresponding to each region by the acoustic attenuation factor for each region. However, as shown in FIG. 9, the signal obtained by one acoustic detection element 501 is a superposition of signals from a plurality of voxels. The time of the boundary differs depending on the voxel of interest, and the position of the boundary is not uniquely determined in the signal. Therefore, when the voxel 1 of interest is reconstructed, the boundary 1 derived from the positional relationship between the voxel and the acoustic detection element 501 is set, and the signal is divided and corrected by the attenuation factor corresponding to each region based on the boundary 1. The signals of the other acoustic detection elements are also corrected in the same manner, and they are subjected to preprocessing such as differentiation and superimposition to generate voxel data of the voxel 1 of interest. In the case of the attention voxel 2, the boundary 2 is set in the same manner, and the correction is performed based on the boundary 2.

According to the present embodiment, even if different boundaries are set for the same received signal, it is correctly corrected by superimposing the received signals of the plurality of acoustic detection elements 501. Therefore, the contrast can be calculated correctly even when the acoustic attenuation factor of the subject and the matching layer are different.

Further, in the present embodiment, the boundary between the subject 3 and the matching layer 4 is grasped from the shape of the subject holder 10, but instead, the outer shape of the subject is measured by the shape measuring device 11 as shown in FIG. A method of acquiring the boundary position and correcting the contrast is also conceivable. In this method, since there is no contact with the subject by the subject holder 10, the burden on the subject is reduced.

[Embodiment 3]
(Refraction correction)
The present embodiment is characterized in that the signal is corrected in consideration of the refraction of the acoustic wave at the interface. It is desirable that the matching layer 4 has an acoustic impedance close to that of the subject 3, but in reality it is difficult to make a perfect match. Therefore, since the acoustic impedance is the product of the propagation speed of the acoustic wave and the density, the matching layer 4 and the subject 3 may have different propagation speeds of the acoustic wave. In that case, refraction of the acoustic wave occurs, and the resolution is lowered. Here, a method of correcting refraction and improving the resolution will be described.

The configuration of this embodiment is the same as that of the second embodiment shown in FIG. 7, and the subject holder 10 is provided as a holding member for holding the subject. Further, the treatment method in the data processing device 8 is different from that of the first and second embodiments. Since the other configurations are the same as those of the first and second embodiments, the description thereof will be omitted.

The measurement method of the present embodiment differs from the image reconstruction process (S6 in FIG. 4) in the data processing device 8. In the image reconstruction process, the back projection in which the preprocessed signal is propagated in the reverse direction from the detection element and superposed is considered in consideration of the refraction that occurs at the interface between the subject and the matching layer during the back projection. Make corrections. Since the speed of sound of the subject and the matching layer is required to correct this refraction, it is advisable to measure it in advance.

Similar to the second embodiment, the boundary (interface) between the subject and the matching layer can be known from the shape of the subject holder 10, and the angle of incidence can be known from that. Further, since the sound velocity of the subject and the matching layer is known, the refractive index is derived from the sound velocity ratio. Since the index of refraction and the angle of incidence are known, the angle of refraction can be known from Snell's law. Therefore, when the processed signal is back-projected, it is propagated at the refraction angle calculated at the boundary instead of going straight, and superimposition is performed to generate image data. Also in this embodiment, since the subject holder 10 is sufficiently thin, the propagation of the acoustic wave in the subject holder 10 can be ignored.

According to this embodiment, it is possible to correct the resolution decrease due to refraction caused by the difference in sound velocity. Further, as in the second embodiment, the boundary between the subject 3 and the matching layer 4 can be measured by using the shape measuring device 11 instead of the subject holder 10.

[Embodiment 4]
(Displayed in real time)
The reconstruction shown in the first embodiment is to perform the reconstruction collectively after acquiring all the signals, but if the measurement time is long, the measurement result cannot be confirmed until the end. Moreover, if the measurement fails, time is wasted. Therefore, in the present embodiment, a method of displaying the result in real time will be described.

The configuration of the present embodiment is the same as the configuration of the first embodiment shown in FIG. 1, but the processing in the data processing device 8 is different.

The measuring method of this embodiment will be described with reference to FIG. First, the subject is irradiated with pulsed light (S1). The acoustic wave excited by the pulsed light is received by the acoustic detection element 501, converted into an analog received signal, and converted into a digital signal by the electric signal processing device 7 (S2). Further, the data processing device 8 acquires the scanning position information corresponding to the obtained digital signal from the scanning control device 601 (S3). The data processing device 8 uses the obtained signal to reconstruct the high resolution region (S8). Further, the data processing device 8 outputs the image data reconstructed at a position corresponding to the high resolution region at that time to the display device, and the display device displays the image (S9).

Next, the scanning control device 601 determines whether or not the high resolution region has finished scanning the entire measurement region (S4). If it is not finished, the acoustic array detector 5 is scanned (S5). After that, S1, S2, S3, S8, and S9 are repeated. Since the scanning step is smaller than the high resolution area, the image display areas overlap in the first measurement and the second measurement. Therefore, it is desirable to take the average value of the superimposed region to generate image data. By repeating this, the image can be displayed in real time. However, since the number of signals used for reconstruction is small and the amount of information is small, the image quality is inferior to that of the first embodiment. Therefore, after the scanning is completed, the data processing device 8 reconstructs using all the signals (S6), overwrites the image data, and displays the image data (S7).

According to this embodiment, measurement can be performed while confirming the result in real time.

1 Light source 2 Light irradiation device 3 Subject 4 Matching layer 5 Acoustic array detector 6 Scanning device 7 Electrical signal processing device 8 Data processing device 9 Display device 10 Subject holder 11 Shape acquisition device

Claims (17)

An information acquisition device that acquires information about a subject based on an acoustic wave generated from the subject irradiated with light.
A detector that receives an acoustic wave via a matching material and outputs a received signal, and a scanning unit that changes the relative position of the detector with respect to the subject.
A signal processing unit that acquires information about the subject using the received signal, and
A signal correction unit that corrects the received signal based on information on a first propagation distance in which the acoustic wave generated in the subject propagates in the subject and a second propagation distance propagating in the matching material. An information acquisition device characterized by being equipped with. The information acquisition device according to claim 1, wherein the first propagation distance and the second propagation distance change with a change in the relative position. The information acquisition device according to claim 1 or 2, wherein the received signal is corrected so as to reduce a change in the received signal due to a change in the relative position. The information acquisition device according to any one of claims 1 to 3, wherein the received signal changes depending on the difference in the acoustic attenuation rate between the matching material and the subject. The signal processing unit generates a plurality of image data corresponding to light irradiation at each of the plurality of relative positions based on an acoustic wave generated by irradiating the subject with light at a plurality of relative positions. The information acquisition device according to any one of claims 1 to 4, wherein the information acquisition device is characterized. The information acquisition device according to any one of claims 1 to 5, wherein the signal processing unit includes the signal correction unit. The information acquisition device according to any one of claims 1 to 6, further comprising a propagation distance acquisition unit that acquires information on the propagation distance corresponding to each of the subject and the matching material. The information acquisition device according to claim 7, wherein the propagation distance acquisition unit includes a shape acquisition unit that acquires the shape of the subject or the shape of a holding member that holds the subject. The information acquisition device according to any one of claims 1 to 8, wherein the matching material acoustically couples the subject and the detector. The information acquisition device according to any one of claims 1 to 9, wherein the detector includes a plurality of detection elements so that the directions of the respective receiving surfaces are gathered. The information acquisition device according to any one of claims 1 to 10, wherein the scanning unit moves at least one of the subject and the detector. An information acquisition method for acquiring information about a subject based on an acoustic wave generated from the subject irradiated with light.
A scanning step of changing the relative position of the detector with respect to the subject, a detection step of receiving an acoustic wave propagating from the subject through the matching material using the detector and outputting a received signal, and the received signal. It has a signal processing step of acquiring information about the subject by using it, and has a first propagation distance in which the acoustic wave generated in the subject propagates in the subject and a second propagation in the matching material. An information acquisition method, characterized in that the received signal is corrected based on the information regarding the propagation distance of the signal. The information acquisition method according to claim 12, wherein the first propagation distance and the second propagation distance change with a change in the relative position. The information acquisition method according to claim 12 or 13, wherein the received signal is corrected so as to reduce a change in the received signal due to a change in the relative position. The information acquisition method according to any one of claims 12 to 14, wherein the received signal changes depending on the difference in the acoustic attenuation rate between the matching material and the subject. Information acquisition method according to any one of claims 12 to 15 wherein the signal processing step is characterized in that it comprises a signal correction process. In the signal processing step, a plurality of image data corresponding to light irradiation at each of the plurality of relative positions is generated based on an acoustic wave generated by irradiating the subject with light at a plurality of relative positions. The information acquisition method according to any one of claims 12 to 16, wherein the information acquisition method is characterized.

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