JP2015057245A - Photoacoustic imaging device, photoacoustic imaging method, and program for executing photoacoustic imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical characteristic value distribution, such as an absorption coefficient in an analyte, with high accuracy.SOLUTION: A photoacoustic imaging device includes: an acoustic wave conversion section 1 that receives acoustic waves 81 and 82 generated upon irradiation of light 4 onto an analyte 6 and converts the acoustic waves 81 and 82 into electrical signals; and a processing section 2 that determines a light quantity distribution in the analyte 6 on the basis of a light quantity distribution or illuminance distribution of the irradiated light 4 on the surface of the analyte 6, and creates image data on the basis of the electrical signals and the light quantity distribution in the analyte 6.

Description

  The present invention relates to a photoacoustic imaging apparatus, a photoacoustic imaging method, and a program for executing the photoacoustic imaging method.

  Research on a photoacoustic imaging apparatus that obtains information in a subject by propagating light irradiated on the subject from a light source such as a laser is actively advanced mainly in the medical field. As one of such photoacoustic imaging techniques, Patent Document 1 proposes Photoacoustic Tomography (PAT: Photoacoustic Tomography).

PAT irradiates a living body (subject) with pulsed light generated from a light source, receives acoustic waves generated by absorption and propagation of light propagated and diffused in the subject, and analyzes the received acoustic waves This is a technique for visualizing information related to optical characteristics inside the living body, which is the subject, by processing.
Thereby, biological information such as optical characteristic value distribution in the subject, in particular, light energy absorption density distribution can be obtained.

In the PAT, the initial sound pressure P0 of the acoustic wave generated from the light absorber in the subject can be expressed by the following equation.
P0 = Γ · μa · Φ ・ ・ ・ Equation 1
Here, Γ is the Gruneisen coefficient, which is the product of the square of the volume expansion coefficient β and the speed of sound c divided by the constant pressure specific heat CP. Γ is known to take a substantially constant value when the subject is determined, μa is the light absorption coefficient of the absorber, Φ is the amount of light in the local area (the amount of light irradiated to the absorber, light Also called fluence).

  A time change of the sound pressure P that is the magnitude of the acoustic wave propagating through the subject is measured, and an initial sound pressure distribution is calculated from the measurement result. By dividing the calculated initial sound pressure distribution by the Gruneisen coefficient Γ, a product distribution of μa and Φ, that is, a light energy absorption density distribution can be obtained.

As shown in Expression 1, in order to obtain the distribution of the light absorption coefficient μa from the distribution of the initial sound pressure P0, it is necessary to obtain the distribution of the light quantity Φ in the subject. Assuming that light is propagated in the subject like a plane wave when a uniform amount of light is irradiated to a sufficiently large area with respect to the thickness of the subject, the distribution Φ of the amount of light in the subject is given by It can be shown.
Φ = Φ0 · exp (−μeff · d) Equation 2
Here, μeff is the average effective attenuation coefficient of the subject, and Φ0 is the amount of light incident on the subject from the light source (the amount of light on the surface of the subject). Further, d is a distance from the region of the subject surface (light irradiation region) irradiated with light from the light source to the light absorber in the subject.

  The light absorption coefficient distribution (μa) can be calculated from the light energy absorption density distribution (μaΦ) of Expression 1 using the light quantity distribution Φ shown in Expression 2.

US Pat. No. 5,713,356

  However, when the shape of the subject is not a simple shape or when the amount of light irradiated from the light source to the subject is not uniform, the area of the light irradiation region and the amount of irradiated light distribution on the surface of the subject are not uniform. For this reason, the light quantity distribution in the subject is not uniform in the in-plane direction with respect to the irradiation surface, and Formula 2 cannot be used. For this reason, in order to accurately obtain the optical characteristic value distribution in the subject, it is necessary to consider this non-uniformity.

  An object of the present invention is to obtain an optical characteristic value distribution such as an absorption coefficient in a subject with high accuracy.

  The present invention relates to an acoustic wave conversion unit that receives an acoustic wave generated by irradiating light on a subject and converts it into an electrical signal, and a light amount distribution or an illuminance distribution of the irradiated light on the surface of the subject. A photoacoustic comprising: a processing unit that determines a light amount distribution inside the subject based on the electrical signal and generates image data based on the light amount distribution inside the subject. An imaging device.

  The present invention is also a photoacoustic imaging method for receiving an acoustic wave generated by irradiating a subject with light, converting the acoustic wave into an electrical signal, and generating image data from the electrical signal, the illumination being performed by the light source Determining a light amount distribution or illuminance distribution on the surface of the subject of the emitted light, determining a light amount distribution inside the subject based on the light amount distribution or illuminance distribution on the surface of the subject, and A photoacoustic imaging method comprising a step of generating image data based on an electrical signal and a light amount distribution inside the subject.

  According to the present invention, the light quantity distribution in the subject can be obtained with high accuracy, and the optical characteristic value distribution such as the absorption coefficient in the subject can be obtained with high accuracy.

Schematic diagram showing an example of the configuration of the photoacoustic imaging apparatus according to Embodiments 1 and 4 of the present invention Schematic diagram illustrating the problem of the present invention The flowchart which shows an example of the process of the photoacoustic imaging apparatus which concerns on Embodiment 1 of this invention. Schematic top view of an acoustic wave generating member used in the photoacoustic imaging apparatus according to Embodiment 1 of the present invention. The flowchart which shows an example of the process of the photoacoustic imaging apparatus which concerns on Embodiment 2 of this invention. The schematic diagram which shows an example of the process which determines the illumination intensity distribution in the surface in S14 of FIG. Schematic diagram showing an example of the configuration of a photoacoustic imaging apparatus according to Embodiment 3 of the present invention A flowchart which shows an example of processing of a photoacoustic imaging device concerning Embodiment 3 of the present invention. The flowchart which shows an example of the process of the photoacoustic imaging apparatus which concerns on Embodiment 4 of this invention.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In the present invention, the acoustic wave includes an acoustic wave including an acoustic wave, an ultrasonic wave, and a photoacoustic wave, and is an elastic wave generated inside the subject by irradiating the subject with light (electromagnetic waves) such as near infrared rays. Indicates. In addition, the photoacoustic imaging apparatus of the present invention is mainly intended for diagnosis of human or animal malignant tumors or vascular diseases, follow-up of chemical treatment, etc., and acquires biometric information inside the subject to obtain image data. It is a device to generate. Therefore, the subject is assumed to be a living body, specifically, a target site for diagnosis such as breasts, fingers, and limbs of a human body or an animal. The light absorber inside the subject has a relatively high absorption coefficient in the subject. For example, if the human body is a measurement target, there are many blood vessels or new blood vessels containing oxidized or reduced hemoglobin and a large amount thereof containing them. Includes malignant tumors.

(Embodiment 1)
FIG. 1A shows a configuration of a photoacoustic imaging apparatus according to the present embodiment.
The photoacoustic imaging apparatus according to the present embodiment includes an acoustic wave conversion unit 1 and a processing unit 2.
Furthermore, in the present embodiment, the acoustic wave generating member 10 is disposed on the surface of the subject 6 along the shape of the subject 6. The acoustic wave generating member 10 has an absorption coefficient different from that of the subject 6, and a member whose thickness, light absorption coefficient, and Gruneisen coefficient are measured in advance is used. Light 4 emitted from the light source 3 is irradiated onto a subject 6 such as a living body via an optical system 5 such as a lens, a mirror, or an optical fiber. When a part of the energy of light propagating through the inside of the subject 6 is absorbed by a light absorber 7 (resulting in a sound source) in a blood vessel or blood, the sound is absorbed by thermal expansion of the light absorber 7. A wave 81 (typically an ultrasonic wave) is generated. In addition, the acoustic wave 82 is generated from the acoustic wave generating member 10 in response to the light 4 emitted from the light source 3. The acoustic waves 81 and 82 are received by the acoustic wave converter 1 and converted into electrical signals. Then, based on the electrical signal and the light amount distribution on the surface of the subject 6 (hereinafter referred to as the surface light amount distribution) of the light irradiated by the light source 3 by the processing unit 2, the optical characteristic value distribution of the subject 6 and the like. Image data is generated. More specifically, the processing unit determines a light amount distribution in the subject 6 (hereinafter referred to as an internal light amount distribution) based on the surface light amount distribution, and generates image data based on the electrical signal and the internal light amount distribution. The The image data is displayed as an image on a display device 9 such as a liquid crystal display. In order to fix the subject 6 by the photoacoustic imaging apparatus, a fixing member 11 may be provided as shown in FIG. The fixing member is for defining the shape of a part of the subject. In other embodiments, a fixing member may be provided, although not particularly mentioned.

In the image of the light energy absorption density distribution and the light absorption coefficient distribution, even if the light absorber 7 has the same shape, size, and absorption coefficient, if it exists at different positions in the subject 6, it is displayed with different brightness or color. End up. This is because the number of photons reaching each light absorber, that is, the local amount of light in the subject 6 is different. The reason why the local light amount in the subject 6 is different is considered that the surface light amount distribution of the subject 6 has an influence. FIG. 2 shows a state in which light is emitted from the light source 3 having the same amount of light to two regions (A, B) of the same area of the subject 6. As can be seen from FIG. 2, even if the amount of light emitted from the light source 3 is the same, the area of the light irradiation region on the surface of the subject is different, so that the illuminance differs between the region A and the region B.
Further, the light 4 emitted to the subject 6 via the light itself 3 or the optical system 5 also has a finite spread, and if the light intensity distribution is not uniform in this spreading direction, the light irradiation region (region) Even within C), the illuminance varies depending on the position. Equation 2 can be applied in the case of a uniform light amount (surface light amount distribution), but cannot be applied in the case where the light amount as described above is not uniform. The present invention corrects the light amount distribution in the subject using the surface light amount distribution of the subject irradiated with the light source, so that the same shape, size, and absorption coefficient are obtained in the finally obtained image. The same absorber can be displayed with approximately the same brightness or color.

  Next, the operation of the photoacoustic imaging apparatus of this embodiment will be described with reference to FIGS. 1 and 3.

  The object 6 is irradiated with light 4 from the light source 3, the acoustic wave 81 generated by the light absorber 7 in the object 6, and the acoustic wave 82 generated by the acoustic wave generating member 10 disposed on the surface of the object 6. Is received by the acoustic wave converter 1 (S10). The received acoustic wave is converted into an electrical signal by the acoustic wave conversion unit 1 (S11) and taken into the processing unit 2. The processing unit 2 performs amplification, A / D conversion, filter processing, and the like on the electrical signal (S12), and then calculates biological information such as the position and size of the light absorber 7 or the initial sound pressure distribution. Then, first image data is generated (S13).

  On the other hand, the processing unit 2 determines the surface light amount distribution of the subject 6 of the light irradiated by the light source 3 from the first image data obtained from the electrical signal (S14). Specifically, it is as follows.

  The acoustic wave 81 is generated by receiving light attenuated by propagating through the subject 6, whereas the acoustic wave 82 is generated on the surface of the subject 6 by receiving light that is hardly attenuated. In addition, the acoustic wave generating member 10 has a higher absorption coefficient than the subject. For this reason, the acoustic wave 82 generated on the surface of the subject 6 is larger than the acoustic wave 81 generated by the light absorber 7. Therefore, it is possible to extract a portion having a higher initial sound pressure than the other from the first image data (initial sound pressure distribution P0) obtained in S13. This portion corresponds to the boundary line between the subject 6 and the acoustic wave generating member 10, that is, the surface of the subject 6. More specifically, a line connecting portions of the initial sound pressure larger than a certain threshold value is a boundary line between the subject 6 and the acoustic wave generating member 10. While the surface of the subject 6 is determined, an initial sound pressure distribution (ΓbμbΦ0) along the boundary line can be obtained. Note that Γb and μb are the Gruneisen coefficient and the absorption coefficient of the acoustic wave generating member 10, respectively. By dividing the absorption coefficient Γb and μb of the acoustic wave generating member 10 from the initial sound pressure distribution (ΓbμbΦ0) along the boundary line, the surface light amount distribution Φ0 of the subject 6 of the light irradiated by the light source 3 is calculated. be able to.

  Then, the internal light quantity distribution Φ in the subject 6 is determined based on the surface light quantity distribution of the subject 6 (S15). Specifically, using the shape of the surface of the subject 6 and the surface light amount distribution of the subject 6 obtained in S14 described above, the same light amount distribution as the surface light amount distribution Φ0 is formed on the surface of the subject 6 in the calculation space. Is arranged to calculate and determine the internal light quantity distribution Φ in the subject 6. At this time, the internal light quantity distribution is calculated using a light diffusion equation, a transport equation, and the like.

  Then, the processing unit 2 obtains second image data such as an absorption coefficient distribution based on the internal light quantity distribution Φ determined in S15 and the first image data (initial sound pressure distribution P0) obtained in S13. Generate (S16). That is, the absorption coefficient distribution can be calculated by using the internal light quantity distribution determined in S15 in Equation 1. The image represented by the second image data obtained in this way is displayed on the display device 9 (S17).

  Next, the configuration of the photoacoustic imaging apparatus of this embodiment will be described more specifically.

  The acoustic wave conversion unit has one or more elements that receive an acoustic wave and convert it into an electrical signal. The transducer uses a piezoelectric phenomenon, the transducer uses light resonance, and the transformer uses a change in capacitance. Consists of a duer, etc. Any element that can receive an acoustic wave and convert it into an electrical signal may be used. By arranging a plurality of acoustic wave receiving elements in one or two dimensions, it is possible to simultaneously receive acoustic waves at a plurality of locations, shorten the reception time, and reduce the influence of vibration of the subject. . By moving one element, it is possible to obtain a signal similar to that obtained by arranging a plurality of elements in two dimensions or one dimension. Further, it is preferable to apply an acoustic matching material such as a gel between the acoustic wave conversion unit and the subject in order to achieve acoustic matching.

  Typically, a workstation or the like is used as the processing unit, and image reconstruction (image data generation) processing or the like is performed by software programmed in advance. For example, software used in a workstation has a signal processing module that performs processing for obtaining a light amount distribution or illuminance distribution on the surface of an object and noise reduction processing using an electrical signal from inside or outside the photoacoustic imaging apparatus. Furthermore, the software used in the workstation has an image reconstruction module that performs image reconstruction. In PAT, noise reduction processing or the like is normally performed on signals received at each position as pre-processing before image reconstruction. In the image reconstruction module, image data is formed by image reconstruction, and as an image reconstruction algorithm, for example, back projection in the time domain or Fourier domain normally used in tomography technology is applied. The image data is data indicating biological information regardless of whether it is two-dimensional or three-dimensional. In the case of two-dimensional data, a plurality of pixel data are arranged. In the case of three-dimensional data, a plurality of voxel data are arranged. Is done. Pixel data and voxel data are obtained by image reconstruction of acoustic waves acquired at a plurality of positions. In the following description, three-dimensional image data will be described, but the present invention can also be applied to two-dimensional image data.

  The light source irradiates light having a specific wavelength that is absorbed by a specific component (for example, hemoglobin) among components constituting the living body. Specifically, the wavelength of light is preferably 500 nm or more and 1200 nm or less. In this case, it is easy to distinguish between an acoustic wave generated on the surface of the subject (for example, skin) and an acoustic wave generated on a light absorber (for example, hemoglobin) inside the subject in the processing described later. As the light source, at least one light source capable of generating pulse light of 5 to 50 nanoseconds is provided. Although a laser capable of obtaining a large output is preferable as the light source, a light emitting diode or the like can be used instead of the laser. As the laser, various lasers such as a solid laser, a gas laser, a dye laser, and a semiconductor laser can be used. Moreover, light may be irradiated from the acoustic wave conversion part side, and may be irradiated from the opposite side to an acoustic wave conversion part. Further, irradiation may be performed from both sides of the subject.

  The optical system is, for example, a mirror that reflects light, a lens that collects or enlarges light, or changes its shape. Such an optical system may be an optical waveguide or the like in addition to a mirror and a lens, and any optical system can be used as long as it can irradiate a subject with a light having a desired shape. Note that it is preferable to spread the light to a certain area by diffusing light with a lens. Moreover, it is preferable that the region where the subject is irradiated with light is movable on the subject. In other words, it is preferable that the light emitted from the light source is configured to be movable on the subject. By being movable, it is possible to irradiate light over a wider range. Further, it is more preferable that the region where the subject is irradiated with light moves in synchronization with the acoustic wave conversion unit. As a method of moving the region where light is irradiated to the subject, there are a method using a movable mirror and the like, a method of mechanically moving the light source itself, and the like.

  The acoustic wave generating member has an absorption coefficient, is disposed on the surface of the subject, and has a known thickness, light absorption coefficient, and Gruneisen coefficient. The acoustic wave generating member generates an acoustic wave by absorbing light emitted from the light source, and enables calculation of the surface shape of the subject and the surface light amount distribution of the subject. The acoustic wave generating member is made of a material having an absorption coefficient of light generated by the acoustic wave larger than the average absorption coefficient of the subject. Specifically, the size of the light absorption coefficient is preferably 0.005 mm −1 or more and 0.100 mm −1 or less. When the absorption coefficient is larger than 0.100 mm-1, light that enters the subject 6 is reduced, and acoustic waves generated inside the subject are reduced. Further, if the absorption coefficient is smaller than 0.005 mm-1, it becomes smaller than the average absorption coefficient inside the subject, so that it becomes difficult to distinguish the acoustic wave obtained from the inside and the surface of the subject, and the surface of the subject. It becomes difficult to calculate the shape of. Preferably, the magnitude of the light absorption coefficient is 0.010 mm-1 or more and 0.080 mm-1 or less. Further, it is preferable to use a material having a Gruneisen coefficient of 0.8 or more and 1.5 or less. The average Gruneisen coefficient of the subject is about 0.5. The acoustic wave generating member may be a member in which particles of an absorber having a known absorption coefficient are arranged in a spot shape as shown in FIG. 4 (a), and the absorber is a lattice as shown in FIG. 4 (b). It may be arranged in a shape. The acoustic wave generating member may be a member in which fine particles of the absorber are uniformly arranged in a film shape. The acoustic wave generating member may be an acoustic matching material such as a gel having a known absorption coefficient.

(Embodiment 2)
The photoacoustic imaging apparatus according to the present embodiment has a configuration in which no acoustic wave generating member is disposed in the photoacoustic imaging apparatus according to the first embodiment. In the present embodiment, the surface shape is calculated using acoustic waves generated due to discontinuous optical characteristics (for example, absorption coefficient) between the subject 6 and its surroundings (for example, air or a fixed member). Then, the illuminance distribution on the surface of the subject (hereinafter referred to as the surface illuminance distribution) is calculated based on the calculation result of the surface shape and the intensity distribution of the light emitted from the light source. Hereinafter, an example in which air is present around the subject will be described.

  In the air and the subject 6, the absorption coefficient and the Gruneisen coefficient are discontinuous. For this reason, since light is absorbed at the boundary surface between them, that is, the surface of the subject, an acoustic wave 82 is generated from the surface of the subject 6. The acoustic wave converter 1 receives the acoustic wave 81 generated from the light absorber 7 and the acoustic wave 82 and converts the acoustic wave into an electrical signal.

  Next, the operation of the photoacoustic imaging apparatus of this embodiment will be described with reference to FIG.

  The subject 6 is irradiated with light 4 from the light source 3, and the acoustic wave 81 generated by the light absorber 7 in the subject 6 and the acoustic wave 82 generated on the surface of the subject 6 are received by the acoustic wave conversion unit 1. (S10). The received acoustic wave 81 is converted into an electrical signal by the acoustic wave conversion unit 1 (S11) and taken into the processing unit 2. After performing the filtering process on the electrical signal (S12), the processing unit 2 calculates biological information such as the position and size of the light absorber 7, or the light energy absorption density distribution and the initial sound pressure distribution, and the first Image data is generated (S13).

  On the other hand, the processing unit 2 determines the shape of the subject 6 from the first image data obtained from the electrical signal (S20). Specifically, it is as follows.

The acoustic wave 82 generated on the surface of the subject 6 is generated in response to light that is hardly attenuated, and therefore is larger than the acoustic wave 81 generated by the light absorber 7. Therefore, it is possible to extract from the first image data (initial sound pressure distribution) obtained in S13 a portion where the initial sound pressure is higher than others.
This portion corresponds to the boundary line between the subject 6 and air, that is, the surface of the subject 6. More specifically, a line connecting portions of the initial sound pressure larger than a certain threshold value is a boundary line between the subject 6 and air.

  On the other hand, when the absorption rate (absorption coefficient) at the boundary between the subject 6 and air (around the subject 6) is known, the initial sound pressure distribution along this boundary line is the same as in the first embodiment. Thus, the surface illuminance distribution of the subject 6 of the light irradiated by the light source 3 can be calculated.

  However, when the absorption rate (absorption coefficient) at the boundary between the subject 6 and air is not known, the surface illuminance distribution of the irradiated light on the subject 6 is calculated from the initial sound pressure distribution along the boundary line. Since this is not possible, the following processing is performed.

  The processing unit 2 determines the surface illuminance distribution of the subject 6 of the light 4 irradiated by the light source 3 based on the shape of the subject 6 and the intensity distribution of the light 4 irradiated from the light source 3 (S14). A specific example is as follows.

  The intensity distribution of the light 4 emitted from the light source 3 is a light intensity distribution in the in-plane direction perpendicular to the depth direction of the subject 6 and is measured in advance. This will be specifically described with reference to FIG. In FIG. 6, the shape of the subject 6 includes a position z in the depth direction of the subject 6, a position x in the in-plane direction perpendicular to the depth direction of the subject 6, and an inclination θ (x ). A light intensity distribution in the in-plane direction perpendicular to the depth direction of the subject 6 of light 4 is defined as A (x). It is assumed that the light travels straight with respect to the outside of the subject 6. The inclination distribution θ (x) with respect to the light 4 on the surface on the surface of the subject 6 irradiated with light can be calculated based on the normal direction calculated from the surface shape of the subject 6. The surface illuminance distribution of the subject 6 can be calculated by applying cos θ (x) to the light intensity distribution A (x) at each position (x, z).

  In the above example, it is assumed that the light travels straight with respect to the outside of the subject 6. However, in the external region of the subject 6, the surface of the subject 6 is reached using a light transport equation, Monte Carlo / light propagation simulation, or the like. The surface illuminance distribution can also be obtained by solving the propagation of the light 4.

  Based on this surface illuminance distribution, the internal light quantity distribution in the subject 6 is determined (S15). Specifically, using the shape of the subject 6 obtained in S20 and the surface illuminance distribution of the subject 6 obtained in S14, the same amount of light as the surface illuminance distribution is formed on the surface of the subject in the calculation space. A virtual light source having a distribution is arranged to calculate and determine the internal light quantity distribution. At this time, the internal light quantity distribution is calculated using a light diffusion equation, a transport equation, a Monte Carlo / light propagation simulation, or the like.

  Then, the processing unit 2 generates second image data such as an absorption coefficient distribution based on the internal light amount distribution in the subject 6 determined in S15 and the first image data obtained in S13 ( S16). That is, the absorption coefficient distribution can be calculated by using the internal light quantity distribution determined in S15 in Equation 1. The image represented by the second image data obtained in this way is displayed on the display device 9 (S17).

  Embodiment 3 FIG. 7 is a diagram showing a configuration of a photoacoustic imaging apparatus according to Embodiment 3 of the present invention. This embodiment is different from the second embodiment in that the measurement unit 30 is provided. Other configurations are the same as those of the second embodiment. The measuring unit 30 is for measuring the shape of the subject.

  The measurement unit 30 can use an imaging device such as a CCD camera, for example. In this case, the processing unit 2 calculates the outer shape and thickness of the subject 6 from the captured image, and determines the shape of the subject 6. Further, the measurement unit 30 may be an acoustic wave conversion unit (so-called ultrasonic echo acoustic conversion unit) that transmits an acoustic wave and receives an acoustic wave. Note that the acoustic wave conversion unit 1 may serve as the function or may be provided separately.

  Next, the operation of the photoacoustic imaging apparatus of this embodiment will be described with reference to FIG. In the second embodiment, the shape of the subject 6 is determined from the electrical signal (first image data) (S20), whereas the operation of the photoacoustic imaging apparatus of the present embodiment is performed by the subject obtained by the measurement unit. A difference is that the shape of the subject is determined from the sample image (S30). Other operations are the same as those in the second embodiment.

(Embodiment 4)
A photoacoustic imaging apparatus according to this embodiment will be described with reference to FIG. The photoacoustic imaging apparatus according to the present embodiment uses a container 40 that defines the shape of the subject 6 instead of the acoustic wave generating member 10 in the photoacoustic imaging apparatus according to the first embodiment. Other configurations are the same as those of the first embodiment.

  In this embodiment, since the shape of the subject 6 is uniquely determined, the surface illuminance distribution of the subject 6 of the light 4 irradiated from the light source 3 on the surface of the subject 6 is uniquely determined. Specifically, a plurality of containers having different shapes and sizes are prepared, one container 40 is selected from the plurality of containers according to the subject 6, and the subject 6 is placed in the container 40. And perform PAT measurement.

  On the other hand, in each container, a surface illuminance distribution data table including surface illuminance distribution data to be irradiated on the surface of the subject 6 when the container is used is obtained in advance. Is stored in the processing unit 2. Then, along with the selection of the container, the surface illuminance distribution data of the subject 6 when the corresponding container is used can be extracted from the table. In addition, the container which can change the magnitude | size and shape of the capacity | capacitance of a container may be sufficient, without preparing several containers. In this case, the surface illuminance distribution irradiated on the surface of the subject 6 when the size or shape of the capacity is changed is obtained in advance, and the surface illuminance distribution data when the processing unit changes the size or shape of the capacity is used. A surface illuminance distribution data table may be held.

  Next, the operation of the photoacoustic imaging apparatus of this embodiment will be described with reference to FIG.

  First, one container 40 is selected from a plurality of containers according to the size and shape of the subject, and the subject 6 is placed in the container 40.

  Next, the subject 4 is irradiated with the light 4 from the light source 3, and the acoustic wave 81 generated by the light absorber 7 in the subject 6 is received by the acoustic wave conversion unit 1 (S10). The received signal of the acoustic wave 81 is converted into an electric signal by the acoustic wave conversion unit 1 (S11) and taken into the processing unit 2. After performing the filtering process on the electrical signal (S12), the processing unit 2 calculates biological information such as the position and size of the light absorber 7 or the initial sound pressure distribution, and generates first image data. (Image reconstruction, S13).

  On the other hand, the processing unit 2 selects and reads the surface illuminance distribution data in the container 40 selected from the surface illuminance distribution data table held in the processing unit 2 (S40), and the subject of the light irradiated by the light source is selected. The surface illuminance distribution is determined (S14).

  Based on this surface illuminance distribution, the internal light quantity distribution in the subject 6 is determined (S15). Specifically, using the shape of the subject 6 defined by the container and the surface illuminance distribution of the subject obtained in S14, the same illuminance distribution as the surface illuminance distribution on the surface of the subject in the calculation space. An internal light quantity distribution is calculated and determined by arranging a virtual light source having At this time, the internal light quantity distribution is calculated using a light diffusion equation, a transport equation, a Monte Carlo / light propagation simulation, or the like.

  Then, the processing unit 2 generates second image data such as an absorption coefficient distribution based on the internal light quantity distribution determined in S16 and the first image data obtained in S13 (S16). That is, the absorption coefficient distribution can be calculated by using the internal light amount distribution determined in S16 in Equation 1. The image represented by the second image data obtained in this way is displayed on the display device 9 (S17).

  If the diffusion of light in the subject 6 can be predicted in advance, an internal light quantity distribution data table in the subject 6 can be prepared instead of the surface illuminance distribution data table. In this case, not the surface illuminance distribution data but the internal light amount distribution data is read in S40, and the process of S14 can be used in S40.

(Embodiment 5)
The present invention can also be realized by executing the following processing. That is, the software (program) that realizes the functions of the first to fourth embodiments described above is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus is programmed. Is read and executed.

DESCRIPTION OF SYMBOLS 1 Acoustic wave conversion part 2 Processing part 3 Light source 4 Light emitted from a light source 6 Subject 81,82 Acoustic wave

The present invention relates to an acoustic wave converter that receives an acoustic wave generated by irradiating a subject with light and converts it into an electrical signal, acquires image data based on the electrical signal, and based on the image data Information on the shape of the subject is obtained, and based on the information on the shape of the subject and the information on the intensity distribution of light irradiating the subject, the subject of the light irradiated on the subject is obtained. Information on the light amount distribution or illuminance distribution on the surface of the specimen is acquired, and the subject is based on the information on the light quantity distribution or illuminance distribution on the surface of the subject of the light irradiated on the subject and the electrical signal. And a processing unit that acquires information on an optical characteristic value distribution inside the subject information acquisition apparatus.

The present invention also includes a step of receiving an acoustic wave generated by irradiating a subject with light and converting it to an electrical signal, a step of acquiring image data based on the electrical signal, Acquiring the information on the shape of the subject based on the information on the shape of the subject, and the intensity distribution of the light that irradiates the subject based on the information on the shape of the subject. Based on the step of obtaining information on the light amount distribution or illuminance distribution on the surface of the subject, the information on the light amount distribution or illuminance distribution on the surface of the subject of the light irradiated on the subject, and the electrical signal And a step of acquiring information on an optical characteristic value distribution inside the subject.

Claims (16)

An acoustic wave converter that receives an acoustic wave generated by irradiating the subject with light and converts it into an electrical signal;
A light amount distribution inside the subject is determined based on a light amount distribution or an illuminance distribution of the irradiated light on the surface of the subject, and based on the electrical signal and the light amount distribution inside the subject. And a processing unit that generates image data.   The photoacoustic imaging apparatus according to claim 1, wherein the light amount distribution on the surface of the subject is determined from the electrical signal.   The photoacoustic imaging apparatus according to claim 1, wherein an illuminance distribution on the surface of the subject is determined based on a shape of the subject.   The photoacoustic imaging apparatus according to claim 1, wherein the illuminance distribution on the surface of the subject is determined by the shape of the subject and the intensity distribution of light emitted from the light source.   The photoacoustic imaging apparatus according to claim 3 or 4, wherein the shape of the subject is determined from the electrical signal.   The processing unit holds a plurality of illuminance distribution data on the surface of the subject, selects one from the illuminance distribution data on the surface of the subject based on the shape of the subject, and the subject The photoacoustic imaging apparatus according to claim 3, wherein an illuminance distribution on the surface of the light is determined. A measurement unit for measuring the shape of the subject;
The photoacoustic imaging apparatus according to claim 3 or 4, wherein the shape of the subject is a shape of the subject measured by the measurement unit.   The photoacoustic imaging apparatus according to claim 1, further comprising an acoustic wave generating member disposed along a shape of the subject on a surface of the subject. A photoacoustic imaging method for receiving an acoustic wave generated by irradiating a subject with light and converting it into an electrical signal, and generating image data from the electrical signal,
Determining a light amount distribution or an illuminance distribution on the surface of the subject of light irradiated by the light source;
Determining a light amount distribution inside the subject based on a light amount distribution or an illuminance distribution on the surface of the subject;
A photoacoustic imaging method comprising: generating image data based on the electrical signal and a light amount distribution inside the subject.   The photoacoustic imaging method according to claim 9, wherein the light amount distribution on the surface of the subject is determined from the electrical signal.   The photoacoustic imaging method according to claim 9, wherein the illuminance distribution on the surface of the subject is determined based on the shape of the subject.   The photoacoustic imaging method according to claim 9, wherein the illuminance distribution on the surface of the subject is determined by the shape of the subject and the intensity distribution of light emitted from the light source.   The photoacoustic imaging method according to claim 11 or 12, wherein the shape of the subject is determined from the electrical signal.   The photoacoustic imaging method according to claim 11 or 12, wherein the illuminance distribution on the surface of the subject is selected from illuminance distribution data on the surfaces of the plurality of subjects that are held in advance. Measuring the shape of the subject,
The photoacoustic imaging method according to claim 11 or 12, wherein the shape of the subject is a shape of the subject to be measured.   The program for making a computer perform each process of the photoacoustic imaging method of any one of Claim 9 thru | or 15.

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