JP5496031B2 - Acoustic wave signal processing apparatus, control method thereof, and control program - Google Patents

Description

  The present invention relates to an acoustic wave signal processing apparatus, a control method thereof, and a control program.

Research on an optical imaging apparatus that obtains information in a subject such as a living body by using light emitted from a light source such as a laser is being actively promoted in the medical field.
One such optical imaging technique is photoacoustic tomography (PAT). Photoacoustic tomography is a technology that visualizes information related to optical property values inside a subject based on acoustic waves generated from living tissue that has absorbed the energy of light propagated and diffused within the subject due to the photoacoustic effect. is there. As an example of obtaining information related to the optical characteristic value, there is a method of detecting an acoustic wave at a plurality of locations surrounding the subject and mathematically analyzing the obtained signal.

  Information obtained by this technique, such as the initial sound pressure distribution or light energy absorption density distribution generated by light irradiation, can be used to identify the location of a malignant tumor associated with the growth of new blood vessels. In the following description, description of the light energy absorption density distribution is omitted, but is included in the description of the initial sound pressure distribution. Generation and display of such a three-dimensional reconstructed image based on the initial sound pressure distribution is useful for grasping the inside of a living tissue, and is expected to be useful for diagnosis in the medical field. However, since this is a developing technology, it is desired to generate an image with further reduced noise and artifacts.

  Here, the photoacoustic effect is a phenomenon in which when an object is illuminated with pulsed light, an acoustic wave (dense wave, typically ultrasound) is generated due to volume expansion in a region with a high absorption coefficient in the object to be measured. It is. In the present invention, an acoustic wave generated by volume expansion caused by irradiation with pulsed light is referred to as “photoacoustic wave”.

  In general, in photoacoustic tomography, the time variation of an acoustic wave is measured with an ideal acoustic detector (broadband, point detection) at various points on a closed spatial surface (especially a spherical measurement surface) that surrounds the entire subject. In theory, the initial sound pressure distribution generated by light irradiation can be completely visualized. Further, it is mathematically known that the initial sound pressure distribution generated by the light irradiation can be substantially reproduced if it is possible to measure the subject in a columnar shape or a flat shape even if it is not a closed space. Patent Document 1).

ここで、rは位置、tは時間であり、p(r,t)は音圧の時間変化、p₀(r)は初期音圧分布、cは音速である。δ(t)は光パルスの形状をあらわすデルタ関数である。 The following equation (1) is a partial differential equation that is the basis of PAT, and is called a “photoacoustic wave equation”. If this equation is solved, the sound wave propagation from the initial sound pressure distribution can be described, and it can be theoretically determined how and where the acoustic wave can be detected.

Here, r is the position, t is the time, p (r, t) is the time change of the sound pressure, p ₀ (r) is the initial sound pressure distribution, and c is the sound velocity. δ (t) is a delta function representing the shape of an optical pulse.

ここで、Ω₀は任意の再構成ボクセル（あるいはフォーカス点）に対する全体の測定エ
リアS₀の立体角である。 On the other hand, PAT image reconstruction is to derive the initial sound pressure distribution p ₀ (r) from the sound pressure pd (r _d , t) obtained at the detection point, which is mathematically called an inverse problem. The Universal Back Projection (UBP) method typically used in the PAT image reconstruction method is described below. By analyzing the photoacoustic wave equation of Equation (1) in the frequency space, the inverse problem for obtaining p ₀ (r) can be accurately solved. UBP expresses the result in time and space. Finally, the following equation (2) is derived.

Here, Ω ₀ is the solid angle of the entire measurement area S ₀ with respect to an arbitrary reconstructed voxel (or focus point).

ここでb(r₀,t)は投影データ、dΩ₀は任意の観測点Pに対する検出器dS₀の立体角である
。この投影データを式(3)の積分に従って逆投影することで初期音圧分布p₀(r)を得ることができる。 Furthermore, the following equation (3) is obtained by modifying the equation in an easily understandable manner.

Here, b (r ₀ , t) is projection data, and dΩ ₀ is a solid angle of the detector dS ₀ with respect to an arbitrary observation point P. The initial sound pressure distribution p ₀ (r) can be obtained by back-projecting this projection data according to the integration of equation (3).

ここで、θは検出器と任意の観測点Pとがなす角度である。 Note that b (r ₀ , t) and dΩ ₀ are expressed by the following equations (4) and (5).

Here, θ is an angle formed by the detector and an arbitrary observation point P.

このときb(r₀,t)は、以下の式(7)となる。

When the distance between the sound source and the measurement position is sufficiently larger than the size of the sound source (far field approximation), the following equation (6) is obtained.

At this time, b (r ₀ , t) is expressed by the following equation (7).

Thus, in the PAT image reconstruction, the projection signal b (r ₀ , t) is obtained by time differentiation of the detection signal p (r ₀ , t) obtained by the detector, and the inverse is performed according to equation (3). It is known that the initial sound pressure distribution p ₀ (r) can be obtained by projection (see Non-Patent Documents 1 and 2).

  However, the photoacoustic wave equation used to obtain Equation (3) is Equation (1), which is `` constant sound velocity '', `` measurement from all directions '', `` impulse-like optical excitation '', `` acoustic wave detection in a wide band ”,“ Acoustic wave detection at points ”, and“ continuous acoustic wave sampling ”. Realistically, it is not easy to realize a device that satisfies these assumptions.

For example, in an actual subject, it is difficult to obtain acoustic wave detection information on the entire closed space surface surrounding the whole subject. Further, in order to increase the acoustic wave measurement area, it is necessary to increase the size and number of elements of the acoustic detector, the signal processing of each element, and the control unit, leading to an increase in manufacturing cost. For this reason, a practical measurement device using the PAT technology is configured as a device that detects acoustic waves from a specific direction of the subject using a probe of a limited size. There are many.

  As an example of such an apparatus, as disclosed in Patent Document 1, a photoacoustic tomography of a flat plate measurement system has been devised. In this photoacoustic tomography, light is irradiated to a subject sandwiched between flat plates, and an acoustic wave is detected by an acoustic wave detector disposed on the flat plate. Here, the number of light irradiations and the number of times of acoustic wave reception may be performed a plurality of times. An acoustic wave signal or a value obtained by averaging each value calculated based on an acoustic wave signal may be calculated and used based on multiple times of light irradiation and acoustic wave reception.

  In addition, the method of detecting acoustic waves by bringing a flat probe into close contact with the subject allows detection of acoustic waves with less noise, and fixing the position of the subject and the probe during repeated detection. There is an advantage that the movement of the probe can be easily controlled.

  Furthermore, there is an image reconstruction method disclosed in Patent Document 2 as an image reconstruction method using the time domain method and the Fourier domain method, which has an effect similar to that of the present invention. Patent Document 2 describes a method for reducing artifacts from two types of reconstructed images obtained by two types of image reconstruction methods.

US Patent No. 5840023 Japanese Patent Application No. 2008-201902

PHYSICAL REVIEW E 71, 016706 (2005) REVIEW OF SCIENTIFIC INSTRUMENTS, 77, 042201 (2006)

However, when the image reconstruction process using the analytical solution is performed using information based on acoustic waves detected under non-ideal conditions as in the prior art, a large number of computational artifacts are generated in the reconstructed image. There is a problem.

  Such artifacts are always generated when image reconstruction is performed using an analytical solution based on acoustic waves detected under non-ideal conditions. Non-ideal conditions include that the acoustic wave detector is arranged on a flat plate and cannot be detected from all directions, and that it is not an ideal acoustic wave detector (broadband / point detection).

For example, the projection data b (r ₀ , t) obtained in the UBP calculation process described above calculates a positive value that may be a sound source and a negative value that cancels out a non-sound source value during back projection. Is done. When calculated under ideal conditions such as using detection signals from all directions, the positive and negative values are canceled out, and a reconstructed image including only the value indicating the sound source is calculated. However, if the omnidirectional detection signal cannot be used, back projection is performed only with a part of the projection data at a biased position, so the initial sound pressure distribution p ₀ (r) is not actually a sound source. In the calculation, there is a value that cannot be denied the possibility of the sound source.

  When the reconstructed image is displayed and visually recognized, if the remaining value without denying the possibility of these sound sources exists at an intensity close to the position close to the detection target object, artifacts such as extending the detection target object may occur. Is displayed. In addition, such a value that cannot be denied the possibility of a sound source can be calculated at various positions depending on the size, number, and position of the detection target object. Therefore, many artifacts such as noise are displayed on the entire reconstructed image.

Furthermore, the fact that artifacts tend to form regular images depending on the area where image reconstruction is performed and the position of the detector also poses a problem when the reconstructed image is viewed. This is because in the reconstruction process based on the analytical solution, a regular calculation process for estimating the presence of a sound source using acoustic waves detected in a specific direction is repeated. For example, in the UBP method, a regular calculation process is repeated in which the existence of a sound source is estimated at a position corresponding to a hemisphere centered on the position of the detector element. For this reason, artifacts remaining in the reconstructed image tend to occur at regular positions, and are more difficult to discriminate than random noise.

  As a method for reducing such artifacts, a method using a more ideal acoustic wave detector can be given. However, an acoustic wave detector that can detect photoacoustic waves from all directions on a subject such as a human body does not actually exist. In addition, in a method of arranging an acoustic wave detector having a wider range of receiving surface or hemispherical shape or a plurality of acoustic wave detectors, the production cost is increased and a redundant configuration is required.

  These problems generally occur in an image information acquisition apparatus that performs an image reconstruction process using an analytical solution, regardless of an image reconstruction process method such as a time domain or a Fourier domain. In particular, in photoacoustic tomography that acquires a reconstructed image using photoacoustic waves and is useful for diagnosis as a medical image, it is a problem to obtain a reconstructed image with fewer artifacts.

  The present invention has been made in view of the above-described problems, and an object thereof is to obtain a reconstructed image with reduced artifacts without increasing production cost with an acoustic wave detector arranged on a flat plate.

In order to achieve the above object, the following configuration of the present invention is adopted. That is, an acoustic wave detector in which a plurality of elements that detect acoustic waves emitted from the subject are arranged, and an acoustic wave signal based on the acoustic waves detected by the plurality of elements of the acoustic wave detector, part or all A selection unit that sets an acoustic wave signal group by selecting an acoustic wave signal of the element; a calculation unit that obtains information related to the sound pressure of the acoustic wave at the point of interest using the acoustic wave signal group; and a determination unit And the selection unit sets a plurality of acoustic wave signal groups in which at least one of the combination of elements or the position of the elements is different from each other, and the determination unit For each of the information related to the sound pressure calculated by the calculation unit for each acoustic wave signal group, a first determination that determines whether the information is based on the presence of a sound source, and a result of the first determination At least one acoustic wave An acoustic wave signal processing apparatus characterized by performing a second determination that determines that a sound source is not present at a point of interest that is determined that information related to the sound pressure by a group of signals is not based on the presence of a sound source is there.

  The present invention also employs the following configuration. That is, a control method for an acoustic wave signal processing apparatus having an acoustic wave detector in which a plurality of elements that detect acoustic waves emitted from a subject are arranged, the acoustic waves detected by the plurality of elements of the acoustic wave detector A selection step of setting an acoustic wave signal group by selecting an acoustic wave signal of some or all elements from an acoustic wave signal based on the wave, and using the acoustic wave signal group, the sound pressure of the acoustic wave at the point of interest A calculation step for obtaining information related to the above, and a determination step, wherein the selection step sets a plurality of acoustic wave signal groups in which at least one of a combination of elements or a position of the elements is different from each other, Whether the determination step is based on the presence of a sound source for each of the information related to the sound pressure calculated by the calculation step for each of the plurality of acoustic wave signal groups with respect to the same attention point As a result of the first determination step to be determined and the first determination step, the attention point determined that the information related to the sound pressure by at least one acoustic wave signal group is not based on the presence of a sound source is A control method for an acoustic wave signal processing apparatus, comprising a second determination step for determining that no sound source exists.

  The present invention also employs the following configuration. That is, an acoustic wave based on an acoustic wave detected by a plurality of elements of the acoustic wave detector is added to an acoustic wave signal processing apparatus having an acoustic wave detector in which a plurality of elements for detecting an acoustic wave emitted from a subject is arranged. A step of selecting an acoustic wave signal of a part or all of the elements from the signal to set an acoustic wave signal group, and using the acoustic wave signal group, information related to the sound pressure of the acoustic wave of the target point A control program for an acoustic wave signal processing device that executes a calculating step and a determining step, wherein the selecting step includes a plurality of acoustic wave signal groups in which at least one of a combination of elements or a position of the elements is different from each other. The determination step is for each piece of information related to the sound pressure calculated by the calculation step for each of the plurality of acoustic wave signal groups with respect to the same point of interest. A first determination step for determining whether or not the sound pressure is based on the presence of a sound source, and information on the sound pressure based on at least one acoustic wave signal group based on the presence of the sound source as a result of the first determination step The attention point determined to be not is a control program for an acoustic wave signal processing device including a second determination step for determining that there is no sound source.

  According to the present invention, it is possible to obtain a reconstructed image with reduced artifacts without increasing production costs with an acoustic wave detector arranged on a flat plate.

The figure which shows the functional block of an image information acquisition apparatus. The block diagram of the computer which implement | achieves an information processing part by software. The figure which shows the structural example of an acoustic wave signal measurement part. The flowchart which shows the procedure which performs the image reconstruction of intermediate data. The flowchart which shows the procedure which performs image reconstruction based on intermediate data. The flowchart which shows the procedure which performs image reconstruction for every point. The conceptual diagram of the effective element with respect to an attention point.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the scope of the invention is not limited to the illustrated examples.

[Embodiment 1]
In the present embodiment, an image reconstruction method for obtaining an initial sound pressure distribution from a detected acoustic wave and generating a three-dimensional reconstruction image will be described. An image information acquisition apparatus that performs the image reconstruction method of the present embodiment is a photoacoustic wave diagnostic apparatus. Here, since the information necessary for image reconstruction is information related to sound pressure such as an initial sound pressure distribution obtained by processing the acoustic wave signal, the present invention can also be regarded as an acoustic wave signal processing device. . In that case, information obtained by the acoustic wave signal processing is separately imaged by a control device or the like and used for diagnosis. The present invention can also be understood as a control method or control program for an acoustic wave signal processing device.

  The photoacoustic wave diagnostic apparatus detects an acoustic wave emitted from a subject irradiated with light, and generates information related to sound pressure as three-dimensional reconstructed image data based on the acoustic wave signal. In the present embodiment, a plurality of acoustic wave signal groups having different numbers and positions of detection source elements are extracted from the acoustic wave signals detected by one imaging, and a plurality of three-dimensional reconstructed image data is obtained as intermediate data. Generate as A three-dimensional image data group (that is, voxel data) at the same position (attention point) of each three-dimensional reconstructed image is determined, and a reconstructed image is regarded as a sound source only when the value indicates a sound source in all voxel data. Generate. That is, when it is determined that one voxel data among the voxel data of the attention point generated from different acoustic wave signal groups is not a value indicating the sound source, the position in the subject corresponding to the attention point is It is determined that there is no light absorber serving as a sound source. In the following description, the initial sound pressure will be described as an example of “information related to sound pressure”, but the present invention is not limited to this. In the present invention, “information related to sound pressure” includes an initial sound pressure, a light energy absorption density, an absorption coefficient, and the like obtained from the initial sound pressure.

(Outline functional block diagram)
FIG. 1 shows a functional configuration of the photoacoustic wave diagnostic apparatus according to the present embodiment. As shown in FIG. 1, the photoacoustic wave diagnostic apparatus according to this embodiment includes an information processing unit 1000 and an acoustic wave signal measuring unit 1100. Examples of the device configuration for implementing each functional block are shown in FIGS. FIG. 2 is an example of a device configuration that implements the information processing unit 1000 of the photoacoustic wave diagnostic apparatus according to the present embodiment. FIG. 3 is an example of a device configuration that implements the acoustic wave signal measurement unit 1100.

The acoustic wave signal measurement unit 1100 transmits acoustic wave signal information including the acoustic wave signal detected by each element of the internal acoustic wave detector 1105 (FIG. 3) to the information processing unit 1000.
Here, the acoustic wave detector 1105 is, for example, a probe that detects acoustic waves. The acoustic wave signal information corresponds to information on the receiving element such as an acoustic wave signal and information on the position, sensitivity, and directivity of the element disposed on the receiving surface. Furthermore, information related to conditions at the time of acoustic wave signal acquisition such as imaging parameters for acoustic wave acquisition and other measurement information is also included. In the photoacoustic wave diagnostic apparatus, information regarding the control of the light source that emits the acoustic wave and the compression when the subject is compressed is also acquired as a condition when acquiring the acoustic wave signal. As will be described later, the acoustic wave detector converts the detected acoustic wave into an analog electric signal. The control unit 1102 (FIG. 3) adds at least amplification and digital conversion processing to the analog electric signal, and becomes an acoustic wave signal to be transmitted to the information processing unit.

Here, the information regarding the position of the element may be any information as long as it is information that allows the positional relationship between the object and the reconstruction region to be image reconstructed and the element to be grasped. For example, information such as the number of each element, the pitch of the element arrangement, the element position on the receiving surface, the position of the acoustic wave detector, the position and size of the subject, the position and size of the reconstruction area for image reconstruction, It is information such as the relative positional relationship of each.
The information acquired for each element is transmitted as information associated with the element identifier of the acoustic wave detector 1105.

  As for the information on the acoustic wave of the acoustic wave signal information, information on the acoustic wave signal may be transmitted, or information on the acoustic wave signal after correction such as sensitivity correction and gain correction of the element may be transmitted. . Alternatively, light may be emitted a plurality of times in one imaging process in the photoacoustic wave diagnostic apparatus, an average of acoustic wave signals obtained by each irradiation may be obtained, and transmitted as acoustic wave signal information.

In the acoustic wave signal information, information that does not hinder the implementation even as a static constant according to the configuration of the embodiment is stored in advance in the main memory 102 of the information processing unit 1000 or the magnetic disk 103 (FIG. 2). In this case, it may be used when the image reconstruction process is executed. However, information that is dynamically determined each time an image is taken is transmitted from the acoustic wave signal measuring unit 1100 to the information processing unit 1000 as part of the acoustic wave signal information.
For example, information regarding the position of the element on the receiving surface of the acoustic wave detector 1105 is stored in the information processing unit 1000 in advance after the element identifier is transmitted from the acoustic wave signal measuring unit 1100 to the information processing unit 1000. The position information may be referred to.

  The information processing unit 1000 performs a 3D image reconstruction process using the acoustic wave signal information obtained from the acoustic wave signal measurement unit 1100, and generates and displays a display image from the generated 3D reconstruction image. To do.

  Next, functional blocks of the information processing unit 1000 on the lower side of FIG. 1 will be described. The information processing unit 1000 includes an acoustic wave information acquisition unit 1001, an image reconstruction unit 1002, a display information generation unit 1003, and a display unit 1004.

  The acoustic wave information acquisition unit 1001 acquires the acoustic wave signal information transmitted from the acoustic wave signal measurement unit 1100 and transmits the acoustic wave signal information to the image reconstruction unit 1002 or stores it in the memory, so that the image reconstruction unit 1002 Make it available.

  The image reconstruction unit 1002 performs a three-dimensional image reconstruction using only an acoustic wave signal selected by a method described later for each point in a region where image reconstruction is performed, and performs a three-dimensional operation based on acoustic wave signal information. A reconstructed image (volume data) is generated. Here, as long as the image reconstruction process of the image reconstruction unit 1002 is a three-dimensional image reconstruction based on an analytical solution, the time domain method or the Fourier domain method is used in the first embodiment of the present invention. Can be applied. As will be described later, the image reconstruction unit serves as a selection unit, a calculation unit, a determination unit, and a determination unit of the present invention.

  In the photoacoustic wave diagnostic apparatus, a value indicating the light absorption coefficient distribution in the subject is calculated, and a reconstructed three-dimensional image is generated. Since the degree of light absorption varies within the subject depending on the wavelength of the light to be irradiated, the difference in composition within the subject can be displayed as a three-dimensional image.

Each information used in the reconstruction process may be included in the information transmitted from the acoustic wave measurement unit 1100 as acoustic wave signal information. If the information processing unit is configured as shown in FIG. Information stored in the magnetic disk 103 may be used. Furthermore, it is possible to specify by an operation instruction from the input unit 106 according to an instruction of the operator.
The generated three-dimensional reconstructed image is sent from the image reconstructing unit 1002 to the display information generating unit 1003.

The display information generation unit 1003 generates information to be displayed on the display unit 1004 from the generated three-dimensional reconstructed image. The display information can be any display information as long as the display information is generated based on the three-dimensional image information. Examples of display information include a two-dimensional image obtained by volume rendering, a multi-section conversion display method, a maximum value projection method, and the like. In addition, other display information such as statistical information can be generated from the information obtained from the three-dimensional image information.

  In the photoacoustic wave diagnostic apparatus, three-dimensional image information based on the absorption coefficient distribution value in the subject according to the wavelength of the irradiation light can be obtained. A variety of information can be generated by comparing these values with the wavelength dependence specific to the substance (glucose, collagen, oxidized / reduced hemoglobin, etc.) constituting the living tissue. That is, it is an image obtained by imaging the concentration distribution of a substance constituting a living body, information for displaying statistical information of each value as a numerical value, a graph, a histogram, or the like.

  The display unit 1004 is a graphic card for displaying the display information generated by the display information generation unit 1003, and a display device such as a liquid crystal display or a CRT display.

  In the description of the photoacoustic wave diagnostic apparatus that implements the image reconstruction method of the present invention, the acoustic wave signal measurement unit 1100 and the information processing unit 1000 are described separately. Specifically, a device configuration such as a measurement device such as digital mammography and a control device (or a PC) may be mentioned as an example. However, it goes without saying that the present invention can also be implemented as one image information acquisition device including the acoustic wave measurement unit 1100 and the information processing unit 1000. For example, it is possible to implement with a modality apparatus configuration such as a general ultrasonic diagnostic apparatus.

  FIG. 2 is a diagram illustrating a basic configuration of a computer for realizing the functions of the respective units of the information processing unit 1000 by software.

  The CPU 101 mainly controls the operation of each component of the information processing unit 1000. The main memory 102 stores a control program executed by the CPU 101 and provides a work area when the CPU 101 executes the program. The magnetic disk 103 stores an operating system (OS), device drivers for peripheral devices, various application software including a program for performing processing of a flowchart described later, and the like. The display memory 104 temporarily stores display data for the monitor 105.

  The monitor 105 is a CRT display or a liquid crystal monitor, for example, and displays an image based on data from the display memory 1204. The input unit 106 performs pointing input and character input by an operator such as a mouse and a keyboard. The operation of the operator in the embodiment of the present invention is performed from the input unit 106.

The I / F 107 is for exchanging various data between the information processing unit 1000 and the outside, and is configured by IEEE 1394, USB, an Ethernet port (“Ethernet” is a registered trademark), and the like. Data acquired via the I / F 107 is taken into the main memory 102.
The function of the acoustic wave signal measuring unit 1100 is realized via the I / F 107. The above components are connected to each other via a common bus 108 so that they can communicate with each other.

FIG. 3 is a diagram illustrating a photoacoustic wave diagnostic apparatus which is an example of the configuration of the acoustic wave signal measurement unit 1100.
The light source 1101 is a light source of irradiation light that irradiates a subject such as a laser or a light emitting diode. As the irradiation light, irradiation light having a wavelength expected to be strongly absorbed by a specific component among the components constituting the subject is used.

  The control unit 1102 controls the light source 1101, the optical device 1104, the acoustic wave detector 1105, and the position control unit 1106. The control unit 1102 also amplifies the electrical signal of the photoacoustic wave obtained by the acoustic wave detector 1105 and converts it from an analog signal to a digital signal. Various signal processing and various correction processes are performed. Further, an acoustic wave signal is transmitted from the acoustic wave signal measuring unit 1100 to an external device such as the information processing unit 1000 via an interface (not shown).

  The contents of laser control include control of laser irradiation timing, waveform, intensity, and the like. Regarding the control of the acoustic wave detector position control means 1106, the position of the acoustic wave detector 1105 is moved to an appropriate position.

  The control unit 1102 also performs various controls for measuring the photoacoustic wave signal detected by the acoustic wave detector 1105 in synchronization with the timing of laser irradiation. Further, signal processing is performed such that the average value of the acoustic wave signals for each element is calculated by averaging the acoustic wave signals for each element obtained by irradiating the laser several times.

  The optical device 1104 is, for example, a mirror that reflects light, a lens that collects or enlarges light, or changes its shape. As such an optical component, any optical component may be used as long as the light 1103 emitted from the light source is irradiated on the subject 1107 in a desired shape. As such an optical component, any optical component may be used as long as the light 1103 emitted from the light source is irradiated on the subject 1107 in a desired shape. A plurality of light sources 1101 and optical devices 1104 can be used.

  Note that the light 1104 emitted from the light source 1101 can be propagated using an optical waveguide or the like. An optical fiber is preferable as the optical waveguide. When there are a plurality of light sources and optical fibers are used, it is also possible to guide light to the surface of the living body by using a plurality of optical fibers for each light source. Alternatively, light from a plurality of light sources may be guided to one optical fiber, and all light may be guided to the living body using only one optical fiber.

  In such a configuration, when the subject 1107 is irradiated with light 1103 generated by the light source 1101 under the control of the control unit 1102 via the optical device 1104, the light absorber 1108 in the subject absorbs light, A photoacoustic wave 1109 is emitted. In this case, the light absorber 1108 corresponds to the sound source.

  The acoustic wave detector 1105 includes a transducer using a piezoelectric phenomenon, a transducer using optical resonance, a transducer using a change in capacitance, and the like. Any acoustic wave detector may be used as long as it can detect acoustic waves. The acoustic wave detector 1105 may detect an acoustic wave by directly contacting the subject 1107, or compresses the subject with a plate such as a flat plate 1110, and the photoacoustic of the subject compressed over the flat plate. The wave 1109 may be detected.

  The acoustic wave detector of the present embodiment will be described on the assumption that a plurality of elements (detection elements) are two-dimensionally arranged. By using such a two-dimensional array element, acoustic waves can be detected simultaneously at a plurality of locations, the detection time can be shortened, and influences such as vibration of the subject can be reduced. Moreover, it is desirable to use an acoustic impedance matching agent such as gel or water (not shown) for suppressing reflection of acoustic waves between the acoustic wave detector 1105 and the subject.

Here, the region where the object is irradiated with light and the acoustic wave detector 1105 may be movable. The optical device 1104 can be configured such that light generated from the light source can move on the subject. As a method for moving a region where light is irradiated onto a subject, there are a method using a movable mirror and the like, a method of mechanically moving a light source itself, and the like. Further, a position control means 1106 for moving the position of the acoustic wave detector 1105 is provided so that the acoustic wave detector can be moved. As an example of the position control means 1106, there is a method of moving on the flat plate 1110 by a motor based on information of the position sensor.

  The control unit 1102 controls the light irradiation region and the position of the acoustic wave detector 1105. In addition, the control unit 1102 can also control the acoustic wave detector 1105 to move in synchronization with a region (light irradiated to the subject) where the subject 1107 is irradiated with light. Since the light irradiation area is movable, it is possible to irradiate light in a wider range and to detect the photoacoustic wave with an acoustic wave detector at an appropriate position with respect to the irradiation area.

(Implementation procedure)
Next, a specific processing procedure executed by the photoacoustic wave diagnostic apparatus according to the present embodiment will be described with reference to the flowcharts of FIGS. 4 and 5.

  FIG. 4 is a flowchart showing a procedure of processing for generating a three-dimensional reconstructed image group based on a plurality of acoustic wave signal groups detected by receiving element groups having different numbers and positions in the present embodiment. FIG. 5 is a flowchart showing a procedure for generating a three-dimensional reconstructed image with reduced artifacts from a plurality of three-dimensional reconstructed image groups reconstructed for the same reconstructed region. This embodiment corresponds to a procedure for generating a plurality of three-dimensional reconstructed images reconstructed based on a plurality of acoustic wave signal groups detected by receiving elements having different element combinations and element positions. In the present invention, even if the acoustic wave signal group selected by the selection unit is the same element group, if the position of the element group differs due to the movement of the acoustic wave detector, the acoustic wave signal group before the movement and the movement Subsequent acoustic wave signal groups can be selected as different acoustic wave signal groups.

First, a procedure for reconstructing a three-dimensional image group based on a plurality of acoustic wave signal groups having different numbers of elements and positions will be described using the flowchart of FIG.
The flowchart in FIG. 4 is started from the time when the image processing of the image information acquisition apparatus that implements the image reconstruction method of the present invention is started.

  In step S <b> 401, when the acoustic wave signal measurement unit 1100 starts photoacoustic wave measurement processing, the light source 1101 irradiates the subject 1107 with laser light via the optical device 1104 under the control of the control unit 1102. Then, the photoacoustic wave emitted from the subject 1107 is detected by the acoustic wave detector 1105. When the photoacoustic wave is detected, the control unit 1102 generates acoustic wave signal information such as an acoustic wave signal detected for each parameter of the imaging and the acoustic wave detector 1105.

  Here, the acoustic wave signal information may include any information as long as it is information related to photoacoustic wave measurement. Moreover, when irradiating a laser beam several times by one imaging | photography, you may include the detected several acoustic wave signal with information, such as a laser irradiation frequency | count and irradiation time. Or in order to reduce noise, it is good also as information which added signal processing so that the average value of the acoustic wave signal at the time of each irradiation may be used as acoustic wave signal information.

  In step S <b> 402, the acoustic wave signal measurement unit 1100 transmits the generated acoustic wave signal information to the acoustic wave information acquisition unit of the information processing unit 1000. The acoustic wave information acquisition unit 1001 stores the acquired acoustic wave signal information in a storage device such as the main memory 102 or the magnetic disk 103 so that the image reconstruction unit 1002 can use it. Then, the acoustic wave signal information or information regarding the stored address is transmitted to the image reconstruction unit 1002.

  In step S403, the image reconstruction unit 1002 selects which element the acoustic wave signal is to be used for the image reconstruction process from among the acoustic wave signal information transmitted from the acoustic wave signal measurement unit 1100.

The acoustic wave signal selected here may be, for example, an acoustic wave signal group of all the elements measured by one imaging, or an acoustic wave signal group detected by half of the elements. Sometimes used. Moreover, even if it is the acoustic wave signal group detected by the same number of elements, it may be the acoustic wave signal group detected by the element of a different position. If a two-dimensional probe in which M reception elements are arranged in the vertical direction and the N horizontal direction on the reception surface of the acoustic wave detector 1105 is used, a combination C (m, n) of elements that detect such an acoustic wave signal is used. ) Is expressed by the following equation (8).

  In the present embodiment, information on the number and position of receiving elements selected from this combination is recorded and associated with the reconstructed three-dimensional reconstructed image.

  However, the information on the number and position of reception elements to be recorded may be any record as long as the information can identify the reception element group that has detected the acoustic wave signal used for each image reconstruction process. For example, it can be implemented with element position information that can calculate the relative positional relationship between the identifier of each element of the acoustic wave detector 1105 and the reconstruction area. Further, information such as information indicating an area on the reception plane of the acoustic wave detector 1105 is not necessarily element information. It is also possible to create a table for managing the above combinations together with identifiers and store the identifiers.

  As described above, in step S403, the image reconstruction unit selects the number of detected elements and the type of position combination as the acoustic wave signal group used in the image reconstruction process in the subsequent step, and selects the selected element. Store number and location information. In the present embodiment, the first image reconstruction process starts with an image reconstruction process using acoustic wave signals detected by all the receiving elements. From the second time on, after using all cases of acoustic wave signal groups with the same number of elements and different positions, the image reconstruction process is repeated in the same manner with the number of elements reduced, and all combinations are performed.

  Here, in general, in image reconstruction processing of acoustic wave signals, it is possible to calculate a better initial sound pressure distribution value by performing image reconstruction processing based on acoustic wave signals detected by a probe having a large number of receiving elements. . Therefore, a better intensity value is often obtained for a reconstructed image located in a region that is a sound source of photoacoustic waves. For this reason, in this embodiment, a value obtained by performing image reconstruction processing using acoustic wave signals detected by all receiving elements is used as a representative value for determining the intensity value of the position serving as a photoacoustic wave sound source, not an artifact. This will be described as an example.

  However, when a more suitable value can be calculated as a representative value for determining the intensity value of the position of the sound source of the photoacoustic wave, it is not always necessary to use the acoustic wave signals of all the receiving elements. A value calculated by performing image reconstruction processing based on acoustic wave signal information of some of the receiving elements of the acoustic wave detector 1105 may be used as a representative value.

  In the present embodiment, the procedure is described in which the number of elements is repeated from the acoustic wave signals detected by all the elements, but the order of changing the number of elements and the positions of the elements is any order. May be. It can also be carried out in a range limited to combinations set in advance by user designation.

  In step S404, one point in the reconstruction area that is the target of image reconstruction is extracted as a point of interest. Here, the reconstruction area corresponds to the measurement range in the image information acquisition apparatus of the present invention, and is a three-dimensional area in which image reconstruction is performed.

  The measurement range of the apparatus serving as the reconstruction area can be set as long as it is a predetermined area where the subject is placed. Alternatively, a method of detecting and setting the region of the subject 1107 or a method of setting a region corresponding to the subject 1107 as a measurement range by a user operating from the UI may be used. Furthermore, when the measurement range is limited to a partial area of the subject 1107, the area inside the subject 1107 may be an area designated by three-dimensional coordinates.

  When the reconstruction area as described above is defined as volume data, extracting the attention point extracted in step S404 corresponds to extracting voxels on the volume data. In this case, the light absorption coefficient value calculated by the image reconstruction process based on the acoustic wave signal information of the photoacoustic wave can be handled as a voxel value of the voxel constituting the reconstruction area. In the following description, it is assumed that the three-dimensional reconstructed image is volume data, and the point of interest is a voxel constituting the volume data.

  The coordinate system used to designate these areas is a coordinate system in which one point on the apparatus is defined as an origin, and three axes orthogonal to each other are defined as an X axis, a Y axis, and a Z axis, respectively. In addition, when coordinate conversion can be performed using a means for appropriately aligning, it is possible to use a value specified in another coordinate system. For example, a point on the subject is defined as an origin, and values specified in a coordinate system in which three axes orthogonal to each other are defined as an X axis, a Y axis, and a Z axis are used after being transformed into a coordinate system on the apparatus. May be.

  Furthermore, the present embodiment may be implemented with the reconstruction area being a plane. A plane having an arbitrary position and orientation is defined as a reconstruction area, and only a point of interest on the plane is reconstructed. The reconstruction process is a calculation considering a three-dimensional position and orientation, but generates a three-dimensional reconstructed image composed only of attention points on a plane. Thus, by projecting and displaying only the region corresponding to the two-dimensional image, it is possible to deal with the two-dimensional image.

  In step S405, the image reconstruction unit 1002 extracts an acoustic wave signal detected by an element effective for the attention point extracted in step S404 from the receiving elements selected in step S403.

  Here, the effective element for the attention point is a receiving element at a position where the photoacoustic wave from the sound source can be detected within the directivity of the element when the sound source of the photoacoustic wave exists at the attention point. It is. That is, the sound source needs to be within the directivity range of the element. In general, an element arranged on the receiving plane of a probe detects an acoustic wave at any position, but the intensity is not suitable for practical use outside the range of directivity determined by the sensitivity of the element. A signal may be detected. Therefore, it is possible to obtain an acoustic wave signal detected with a practical element sensitivity by handling only an acoustic wave signal from a sound source within a directivity range determined by the element.

  FIG. 7 is a conceptual diagram of an effective element for the attention point described above. A method for determining effective elements will be described with reference to FIG.

The reception surface 701 of the acoustic wave detector in FIG. 7 is an example of the acoustic wave detector 1105 according to the present embodiment. On the receiving surface 701 of the acoustic wave detector, 25 elements for receiving acoustic waves are arranged on the receiving surface. When a region that falls within the directivity range of the element is calculated from the point of interest 702, a circular region centered on the foot of the perpendicular line 703 that falls on the reception surface of the reception surface 701 of the acoustic wave detector becomes the effective element region 704. In other words, the effective element region 704 indicates the existence range of elements that can include the attention point 702 in the directivity range. The element arranged on the effective element region 704 is selected as the effective element 705 on the reception surface of the reception surface 701 of the acoustic wave detector.

  As described above, in step S405, the image reconstruction unit 1002 extracts the position of the attention point in the reconstruction area. Then, an element is selected such that the receiving element determined in step S403 is in a position within the directivity range. Then, an acoustic wave signal detected by the receiving element at a position where the point of interest falls within the directivity range of the element is extracted.

  In step S406, the image reconstruction unit 1002 performs an image reconstruction process using the acoustic wave signal group extracted by the element effective for the point of interest extracted in step S405, and calculates the initial sound pressure value of the photoacoustic wave. calculate. Specifically, attention is paid to one of the voxels of the volume data corresponding to the reconstruction area, and the value calculated by the image reconstruction process is handled as the voxel value.

  Here, the image reconstruction process in this embodiment may be any reconstruction process as long as it is a reconstruction process based on an analytical solution and is a reconstruction process based on the time domain method. As an example, it can be implemented by reconstruction processing by the UBP method.

  In step S407, the image reconstruction unit 1002 determines whether the calculated value can be regarded as the value of the initial sound pressure by the sound source of the photoacoustic wave or an artifact.

  Here, the value that cannot be regarded as a sound source of a photoacoustic wave is that the calculated value of the image reconstruction process at the point of interest in the reconstruction area is not only the acoustic wave signal by the photoacoustic wave, but also other acoustic waves and system noise. This value is indistinguishable from the effect of. When calculating based on the photoacoustic wave detected in an ideal environment, zero is calculated at a position where there is no sound source of the photoacoustic wave. However, in actual measurement, noise on the system of the apparatus to which the acoustic wave detector 1105 is attached is included in the detected photoacoustic wave signal information. In addition, values due to factors other than light absorption may be included due to various factors, such as acoustic waves emitted from the subject and directly received.

  Therefore, for example, in a method such as threshold processing, a value greater than or equal to a predetermined value determined by the system configuration is treated as a value that may be a photoacoustic sound source, and a value less than or equal to the predetermined value is Judge as not. The determination process in step S407 corresponds to the first determination of the present invention.

  If it is determined in step S407 that there is no photoacoustic sound source, the process of step S408 is performed. In step S <b> 408, the image reconstruction unit 1002 indicates that the initial sound pressure value of the reconstruction process is not a photoacoustic sound source, and can be distinguished from other calculated values that may be photoacoustic sound sources. Replace with (for example, zero).

  Here, in this embodiment, the procedure for replacing the calculated value of the initial sound pressure in the image reconstruction process will be described, but a method that does not replace the calculated value may be used. For example, a method of preparing a flag indicating whether or not to be regarded as a photoacoustic wave sound source for each position of the attention point may be used. In this case, even if the method of determining the presence or absence of the photoacoustic sound source with reference to the flag for each position of the target point instead of determining whether the calculated value is zero or non-zero in this embodiment, Embodiments can be implemented.

If it is determined in step S407 that the value is calculated from the photoacoustic wave acoustic wave signal, the process of step S409 is performed. In step S409, the image reconstruction unit 1002 determines the value after the determination in step S407 as a voxel value indicating the initial sound pressure value at the point of interest, and temporarily stores it. The information to be stored may be any method as long as the calculated value can be stored in association with the three-dimensional coordinates of the target point. For example, in the case of a voxel previously associated with information of three-dimensional coordinates, a method may be used in which only voxel identifiers and voxel values are stored in an array.

  In step S410, the image reconstruction unit 1002 determines whether or not there is an attention point that has not been subjected to image reconstruction processing in the reconstruction area. When there is an unprocessed attention point, the initial sound pressure values at all points in the reconstruction area are determined by repeating the processing from step S404 to step S410. If it is determined in step S410 that there is no unprocessed attention point, the process proceeds to step S411.

  In step S411, the image reconstruction unit 1002 stores the initial sound pressure value group determined in the processing from step S404 to step S410. At this time, information relating to the number of elements and the position of the elements selected in step S403 and information associated with the three-dimensional reconstructed image based on the acoustic wave signal information group are also stored.

  In step S412, the image reconstruction unit 1002 refers to the information of the element group that has already undergone the image reconstruction process, and selects the acoustic wave signal information of another element group that has not been subjected to the image reconstruction process. It is determined whether to perform image reconstruction. Here, the other receiving element group refers to a receiving element group in which the number of elements is different from the receiving element group for which the candidate for the three-dimensional reconstructed image has been calculated in step S411, or the position of the element is different. Including. In the present embodiment, the process is repeated until all element groups are combined.

  Here, in the present embodiment, the method of repeating until all the combinations of receiving elements having different numbers and positions of elements are covered has been described. However, a table or identifier indicating the type of element group may be provided in advance, and the reconfiguration process may be performed only for the specified type of receiving element group.

  In step S412, when three-dimensional image candidates are generated based on acoustic wave signal information of all receiving element groups that perform image reconstruction, three-dimensional reconstruction is performed based on acoustic wave signal groups having different numbers of elements and positions of elements. The image group generation process ends.

  As described above, a three-dimensional reconstructed image group based on a plurality of acoustic wave signals detected by receiving element groups having different numbers and positions of elements in the present embodiment can be generated by the procedure as shown above. These are used in the following procedure as intermediate data for generating volume data of a three-dimensional reconstructed image with reduced artifacts in this embodiment.

  In this way, when image reconstruction processing is performed using different combinations of acoustic wave signal groups detected by different numbers and positions of elements, artifact images that are not photoacoustic wave sound sources in the reconstructed images are at different positions. To occur.

  In general, in a reconstructed image generated by image reconstruction based on an analytical solution, an increase or decrease in an acoustic wave signal detected at a different position affects both a region where there is a possibility of a photoacoustic wave sound source and a region where it is not. That is, for each acoustic wave signal detected by elements at different positions, there is a position where the possibility of the sound source cannot be denied and an artifact is generated, and a position where the possibility of the sound source is denied. Therefore, even if reconstruction processing is performed by the same method, if the acoustic wave signal to be used is detected at a different position, the calculation result of the initial sound pressure value in the reconstruction image is made different. . In an ideal environment, these effects are completely offset. However, if it is not an ideal environment, it is not a photoacoustic wave sound source, but in the calculation of the image reconstruction process, there may be a case where a calculated value that cannot completely deny the possibility of the sound source remains. It will remain.

Therefore, in the present embodiment, as described above, for the acoustic wave signals detected at the same time in the same imaging process, image reconstruction is performed a plurality of times based on acoustic wave signal groups with different numbers and positions of receiving elements. Do. Thereby, it is possible to generate a reconstructed image group having different areas that are offset from the range of influence of each element on the calculation result. While these are reconstruction processes based on the same measurement data in the same reconstruction area, the presence or absence of artifacts at individual points of interest differs for each reconstructed image.
On the other hand, no matter which combination of acoustic wave signal information groups is used, the photoacoustic sound source position is always calculated based on the photoacoustic wave, so it cannot disappear from any reconstructed image. Absent.

  Using the above properties, a plurality of acoustic wave signal groups having different element combinations and element positions are set, and the same position is set between a plurality of reconstructed image groups generated from the respective acoustic wave signal groups. Determine the value. Then, it is found that a position determined as not an acoustic wave sound source in any one of the reconstructed images is not at least an acoustic wave sound source. In other words, all the reconstructed images can be regarded as artifacts except for positions where there is a value estimated as a sound source. By excluding the positions regarded as artifacts, it is possible to generate a reconstructed image with reduced artifacts compared to a reconstructed image based on a single acoustic wave signal group.

Next, a procedure for generating a three-dimensional reconstructed image with reduced artifacts from a three-dimensional reconstructed image group based on acoustic wave signals detected by receiving element groups having different numbers and positions using the flowchart of FIG. explain.
The flowchart in FIG. 5 starts in a situation where a volume data group of a three-dimensional reconstructed image, which is intermediate data in the present embodiment, has been generated.

  In step S501, the image reconstruction unit 1002 extracts one point in the reconstruction area as a point of interest. For example, for each volume data of a three-dimensional reconstructed image that is intermediate data, unprocessed voxels at the same position in the reconstruction area are extracted one by one.

  In step S502, the image reconstruction unit 1002 refers to all voxel values for voxels at the same position extracted from the respective intermediate data. Then, it is determined whether a value indicating that it is not a photoacoustic wave sound source is included in the voxel values at the same position in each intermediate data.

  If even one value indicating that it is not a photoacoustic wave sound source is included in step S502, the process proceeds to step S503. In step S503, the image reconstruction unit 1002 determines the voxel value at the determined position in the volume data of the reconstructed image to be finally calculated as a zero value indicating that it is not a photoacoustic wave sound source.

  If it is determined in step S502 that the voxel values of all candidate data are values that can be photoacoustic sound sources, the process proceeds to step S504. In step S504, the image reconstruction unit 1002 determines the voxel value of the intermediate data used as the representative value as the voxel value at this position. As a result of this processing, the initial sound pressure value at the position estimated as the position of the sound source of the photoacoustic wave is uniform, although it is a three-dimensional reconstruction process using a plurality of types of acoustic wave signal information groups. The most desirable value can be reflected under the same shooting conditions. The determination process in step S502 corresponds to the second determination of the present invention.

When the voxel value at the point of interest is determined in step S503 or step S504, the process proceeds to step S505.
In step S505, it is determined whether voxels at other positions that are unprocessed attention points remain. If voxels at other positions are unprocessed, the processes from step S501 to S504 are repeated. When the voxel values are determined for all attention points, the process proceeds to step S506.

  In step S506, the image reconstruction unit 1002 records (stores in a memory or a magnetic disk) volume data of a three-dimensional reconstruction image from which artifacts have been removed for each point of interest.

  The volume data of the three-dimensional reconstructed image obtained by the above procedure is far more artifact than when reconstructing an image using an acoustic wave signal related to one type of receiving element group detected by photographing under the same conditions. A three-dimensional reconstructed image with a small amount can be obtained. When a three-dimensional reconstructed image with reduced artifacts is generated, the process proceeds to step S507, and display information is generated.

  In step S507, the display information generation unit 1003 generates display information from the calculated volume data of the three-dimensional reconstructed image, and sends the display information to the display unit 1004. Examples of display information include shooting conditions, shooting parameters of the acoustic wave signal measurement unit, statistical information, analysis information, two-dimensional cross-sectional images for display, display images by volume rendering, and the like.

In step S508, the display unit 1004 displays the display information generated from the volume data of the three-dimensional reconstructed image generated in step S507.
Through the procedure described above, a three-dimensional reconstructed image with reduced artifacts is presented to the user.

  The reconstructed image based on the value of the initial sound pressure distribution generated by the above procedure can be presented by imaging the acoustic characteristics of the subject based on the intensity of the acoustic wave sound source. In particular, in a photoacoustic wave diagnostic apparatus, the shape of a substance that emits an acoustic wave by absorbing a specific wavelength can be imaged and displayed. By using the image reconstruction method of the present invention, it is possible to present a more accurate three-dimensional image with fewer artifacts.

  In the present embodiment, the display information generation unit 1003 and the display unit 1004 have been described as an example of displaying a reconstructed image with reduced artifacts based on the detected acoustic wave signal. Not limited. For example, it goes without saying that the image reconstruction method of the present invention can be applied even to a procedure in which a file is saved instead of being displayed, or sent to another device by communication.

  Further, in the present embodiment, an example is described in which image reconstruction is performed using an image reconstruction technique based on the time domain method to generate a three-dimensional reconstructed image group as intermediate data and the image reconstruction technique of the present invention is applied. did. However, the present embodiment can also be implemented using an image reconstruction technique based on the Fourier domain method. In the case of the Fourier domain method, an image reconstruction method is performed for each selected acoustic wave signal information, as in the present embodiment, although not for each point of interest. A three-dimensional reconstructed image group based on the generated acoustic wave signal information having different numbers of elements and positions may be prepared as intermediate data, and the steps S501 to S508 in FIG.

  Furthermore, in the present embodiment, the photoacoustic wave that irradiates light is detected and the initial sound pressure distribution and the three-dimensional reconstructed image of the light absorption energy have been described as examples. However, the present embodiment is not limited to this. For example, an image reconstruction process based on a detected acoustic wave signal can be applied to an image reconstruction method based on a general acoustic wave instead of a photoacoustic wave.

[Embodiment 2]
In the first embodiment, a three-dimensional reconstructed image is generated as intermediate data, and a reconstructed image with reduced artifacts is generated from the generated three-dimensional reconstructed image group.

  In the present embodiment, an image reconstruction method for obtaining an initial sound pressure distribution from a detected acoustic wave and generating a three-dimensional reconstruction image will be described. The image information acquisition apparatus in the present embodiment is the same photoacoustic wave diagnostic apparatus as that in the first embodiment. However, unlike the first embodiment, this embodiment does not generate a three-dimensional reconstructed image as intermediate data.

  In the present embodiment, an artifact is determined for each point of interest to be reconstructed in the reconstruction area, and a redundant calculation process is omitted, so that a three-dimensional reconstructed image having the same effect of reducing artifacts as in the first embodiment. Can be obtained at high speed.

(Outline functional block diagram)
Since the photoacoustic wave diagnostic apparatus according to the present embodiment has the same configuration as that of the first embodiment, the description thereof is omitted.

(Implementation procedure)
FIG. 6 is a flowchart showing a processing procedure of the present embodiment. A specific process procedure executed by the photoacoustic wave diagnostic apparatus according to the present embodiment will be described with reference to the flowchart of FIG. The flowchart of FIG. 6 is started from the time when the image processing of the image information acquisition apparatus that implements the image reconstruction method of the present invention is started.

  The processing of the acoustic wave signal measurement unit 1100 in step S601 and the processing of the acoustic wave information acquisition unit 1001 in step S602 are the same as steps S401 and S402 in the first embodiment, and thus detailed description thereof is omitted.

  In step S603, the image reconstruction unit 1002 extracts one point of the reconstruction area that is a target of image reconstruction as a point of interest. That is, one unprocessed voxel is extracted when the reconstruction area is defined as volume data.

  In step S604, the image reconstruction unit 1002 extracts an effective element for the point of interest. That is, when a sound source is present at the position of the voxel extracted in step S603, unlike in the first embodiment, an element at a position that can be received within the directivity range of the element is defined on the reception surface of the acoustic wave detector 1105. Extract from all elements.

  In step S <b> 605, as in step S <b> 403 of the first embodiment, the acoustic wave signal relating to which element is used for image reconstruction processing is selected from the acoustic wave signal information transmitted from the acoustic wave signal measuring unit 1100. However, in step S403 of the first embodiment, all elements of the acoustic wave detector 1105 are selected, whereas in the present embodiment, selection is made from acoustic wave signal groups detected by effective elements for each target point. Is different. However, depending on the point of interest, when the effective elements are all elements, the selection process is the same as step S403 in the first embodiment.

  In step S606, the image reconstruction unit 1002 performs image reconstruction processing on the voxel that is the target point extracted in step S504, based on the acoustic wave signal detected by the element selected in step S605.

  Here, the image reconstruction process in this embodiment may be any reconstruction process as long as it is a reconstruction process based on an analytical solution and is a reconstruction process based on the time domain method. As an example, it can be implemented by reconstruction processing by the UBP method.

In step S607, the image reconstruction unit 1002 determines whether the value calculated by the image reconstruction processing of the voxel at the point of interest in step S606 can be regarded as the initial sound pressure value by the sound source of the photoacoustic wave, or is an artifact. .
Since this determination process is the same as the process in step S407 of the first embodiment, a description thereof will be omitted.

  If it is determined in step S607 that there is no photoacoustic sound source, the process of step S608 is performed. If it is determined in step S607 that there is no photoacoustic wave sound source, the image reconstruction process using the remaining acoustic wave signal group in the same voxel is not performed, and the process proceeds to the reconstruction process in the next voxel of interest. Can do. Therefore, as in the first embodiment, the time until the end of the generation of the three-dimensional reconstructed image can be shortened as compared with the case where the calculation processing is performed on all the combinations of the set of acoustic wave signals for all the voxels. .

  Since the process of step S608 is the same process as the process of step S408 of the first embodiment, a description thereof will be omitted.

When it is determined in step S607 that the value is calculated from the photoacoustic wave acoustic wave signal, the process of step S609 is performed.
In step S609, the image reconstruction unit 1002 stores the calculated initial sound pressure value candidate values. As long as this candidate value is determined to be a value that is considered to have been calculated from the acoustic wave signal of the photoacoustic wave, the present embodiment can be implemented regardless of how it is determined. As an example, there is a method in which a calculated value of reconstruction processing based on acoustic wave signals detected by all effective elements is used as a candidate value. The acoustic wave signal group that can calculate the most desirable value as a reconstructed image by the photoacoustic wave sound source in the selection range in step S605 may be stored as a candidate value.

  In step S610, when there is an unprocessed acoustic wave signal group, the image reconstruction unit 1002 proceeds to the process of step S605 again. And another acoustic wave signal group is selected and the process of step S605-610 is repeatedly implemented.

  In step S610, for all combinations of acoustic wave signal groups in the same voxel, image reconstruction processing of all acoustic wave signal information groups is performed, and if it is not determined that the sound source is not a photoacoustic wave source, The process proceeds to step S611.

  In step S611, the image reconstructing unit 1002 uses either the value that can be identified as not the sound source replaced in step S608 or the initial sound pressure value set as the candidate value in step S609, and the voxel value of the target point. Determine and save.

  When the voxel value is determined for one attention point, in step S612, it is determined whether or not there is an unprocessed attention point in the reconstruction area. If there is an unprocessed attention point, the processing from step S603 to step S611 is repeated to determine the voxel value at each attention point. When all the voxel values are determined, the process proceeds to step S613.

  In step S613, the processing of the display information generation unit 1003 is the same processing as step S507 of the first embodiment, and thus detailed description thereof is omitted.

  In step S614, the processing of the display unit 1004 is the same processing as step S508 of the first embodiment, and thus detailed description thereof is omitted.

Through the above procedure, it is possible to efficiently generate a reconstructed image with reduced artifacts, and it is possible to generate a reconstructed image at a higher speed while having a reduction effect similar to that of the first embodiment. it can.

  In the present embodiment, the procedure for performing image reconstruction immediately after detection of acoustic waves has been described. However, it is not always necessary to reconstruct and display an image immediately after detection of an acoustic wave. The acoustic wave signal information may be stored and the reconstruction method of the present invention may be performed when it is desired to display again. Moreover, you may reconfigure | reconstruct a part of area | region which can reconstruct an image with acoustic wave signal information. For example, in the acoustic wave signal information that can be reconstructed in a large three-dimensional region, the user designates only the region occupied by each cross-sectional image to be displayed as the reconstructed region, so that the present invention is provided each time each cross-sectional image is displayed. It is also possible to apply the image reconstruction method.

  A method using both the present embodiment and the procedure of the first embodiment is also possible. For example, a three-dimensional reconstructed image using an image reconstruction technique of the Fourier domain method is generated based on acoustic wave signal information selected based on the difference in the number of elements and the position of the elements. In addition, a three-dimensional reconstructed image reconstructed by the procedure of this embodiment based on the time domain method is generated. Then, the steps S501 to S508 in FIG. 5 in the first embodiment are performed using the three-dimensional reconstructed image group obtained by the Fourier domain method and the reconstruction method of the present embodiment as intermediate data. In this case, the artifact reduction effect is further increased by the synergistic effect of the effect of using a plurality of pieces of acoustic wave signal information having different numbers of elements and positions of the element of the present invention and the effect of using different reconstruction methods.

  1000: Information processing unit, 1001: Acoustic wave information acquisition unit, 1002: Image reconstruction unit, 1100: Acoustic wave signal measurement unit, 1105: Acoustic wave detector

Claims (8)

An acoustic wave detector in which a plurality of elements that detect acoustic waves emitted from the subject are arranged;
A selection unit that sets an acoustic wave signal group by selecting an acoustic wave signal of some or all elements from an acoustic wave signal based on an acoustic wave detected by a plurality of elements of the acoustic wave detector;
Using the acoustic wave signal group, a calculation unit for obtaining information related to the sound pressure of the acoustic wave at the point of interest;
A determination unit;
Have
The selection unit sets a plurality of acoustic wave signal groups in which at least one of the combination of elements or the position of the elements is different from each other,
The determination unit determines whether each of the information related to the sound pressure calculated by the calculation unit for each of the plurality of acoustic wave signal groups with respect to the same point of interest is based on the presence of a sound source. And the point of interest determined that the information related to the sound pressure based on the at least one acoustic wave signal group is not based on the presence of the sound source based on the result of the determination and the first determination. An acoustic wave signal processing apparatus that performs a second determination. Of the plurality of elements of the acoustic wave detector, further comprising a determination unit that determines an effective element that is an element in which the point of interest falls within a directivity range,
The acoustic wave signal processing apparatus according to claim 1, wherein the selection unit selects an acoustic wave signal of the effective element and sets an acoustic wave signal group. In the first determination, when the information related to the sound pressure calculated by the calculation unit is larger than a predetermined threshold in the first determination, the information related to the sound pressure is based on the presence of a sound source. The acoustic wave signal processing device according to claim 1, wherein the acoustic wave signal processing device is determined. In the second determination, the determination unit determines that the result of the first determination is based on the presence of a sound source in the information related to the sound pressure corresponding to any acoustic wave signal group. The acoustic wave signal processing apparatus according to claim 3, wherein it is determined that a sound source exists at the position of the point of interest. The selection unit selects all of the acoustic wave signals of the effective element as one of the acoustic wave signal groups,
For the attention point determined by the determination unit that the sound source is present at the position of the attention point, the calculation unit has the sound pressure calculated using all of the acoustic wave signals of the effective element and the image data of the subject. The acoustic wave signal processing device according to claim 2, wherein the acoustic wave signal processing device is data used when generating the sound wave. 6. The acoustic wave emitted from the subject is a photoacoustic wave generated using a light absorber in the subject that has received light from the light source as a sound source. The acoustic wave signal processing apparatus according to claim 1. A method for controlling an acoustic wave signal processing apparatus having an acoustic wave detector in which a plurality of elements that detect acoustic waves emitted from a subject are arranged,
A selection step of selecting an acoustic wave signal of a part or all of the elements from an acoustic wave signal based on an acoustic wave detected by a plurality of elements of the acoustic wave detector and setting an acoustic wave signal group;
Using the acoustic wave signal group, a calculation step for obtaining information related to the sound pressure of the acoustic wave at the point of interest;
A determination step;
Have
The selection step is to set a plurality of acoustic wave signal groups in which at least one of the combination of elements or the position of the elements is different from each other.
The determination step determines whether each of the information related to the sound pressure calculated by the calculation step for each of the plurality of acoustic wave signal groups with respect to the same attention point is based on the presence of a sound source. As a result of the determination step and the first determination step, the attention point determined that the information related to the sound pressure by the at least one acoustic wave signal group is not based on the presence of the sound source does not exist. The control method of the acoustic wave signal processing apparatus characterized by including the 2nd determination step determined as follows. In an acoustic wave signal processing apparatus having an acoustic wave detector in which a plurality of elements that detect acoustic waves emitted from a subject are arranged,
A selection step of selecting an acoustic wave signal of a part or all of the elements from an acoustic wave signal based on an acoustic wave detected by a plurality of elements of the acoustic wave detector and setting an acoustic wave signal group;
Using the acoustic wave signal group, a calculation step for obtaining information related to the sound pressure of the acoustic wave at the point of interest;
A determination step;
A control program for an acoustic wave signal processing apparatus,
The selection step is to set a plurality of acoustic wave signal groups in which at least one of the combination of elements or the position of the elements is different from each other.
The determination step determines whether each of the information related to the sound pressure calculated by the calculation step for each of the plurality of acoustic wave signal groups with respect to the same attention point is based on the presence of a sound source. As a result of the determination step and the first determination step, the attention point determined that the information related to the sound pressure by the at least one acoustic wave signal group is not based on the presence of the sound source does not exist. A control program for an acoustic wave signal processing device, comprising a second determination step for determining

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