JP2017018284A - Photoacoustic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoacoustic apparatus which, even when a variation occurs in a relative positional relationship between a subject and a photoacoustic wave reception unit during plural times of light irradiation, can acquire image data of the subject with the effect of the variation suppressed.SOLUTION: The photoacoustic apparatus according to the present invention, comprises an image data acquisition unit which: performs first-combination with two or more first image data sets to acquire first image data; performs second-combination with two or more second image data sets to acquire second image data; acquires position information after a position deviation of the first image data and the second image data, on the basis of the first image data and the second image data; and acquires position information after a position deviation of plural image data sets on the basis of the position information after a position deviation of the first image data and the second image data.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for acquiring image data using an acoustic wave generated by a photoacoustic effect.

  Photoacoustic imaging that acquires image data of an object using an acoustic wave (photoacoustic wave) emitted from within the object by photoacoustic effect by irradiating the object with light and absorbing the energy of the light Technology is being researched. In photoacoustic imaging, there is a method of synthesizing image data of an object obtained by each of a plurality of times of light irradiation.

  However, there is a possibility that the relative positional relationship between the object and the photoacoustic wave receiving unit varies between light irradiations. In this case, position shift due to the variation occurs in each image data corresponding to each light irradiation. As a result, the image data of the objects in which the positional deviation has occurred are combined, and the quality of the image data of the combined objects is deteriorated. In order to solve this problem, there is known a method of estimating and correcting a positional deviation amount (motion vector) of each image data by comparing the image data.

  However, the generated sound pressure of the photoacoustic wave is typically smaller than the sound pressure of the transmission ultrasonic wave used in the ultrasonic diagnostic apparatus. Therefore, the S / N of the image data of the target obtained by one light irradiation is smaller than the S / N of the image data obtained by the ultrasonic diagnostic apparatus that transmits and receives ultrasonic waves. Therefore, the estimation accuracy of the positional deviation amount of the image data obtained by comparing the image data of the object obtained by one light irradiation is low. In order to solve this problem, Patent Document 1 accurately estimates a positional shift amount by comparing image data of a target object obtained by a plurality of times of light irradiation, corrects the positional deviation, and then corrects the target object. Is disclosed.

JP 2014-140716 A

  However, there is a possibility that the relative positional relationship between the object and the photoacoustic wave receiver varies in multiple light irradiations for acquiring image data of one object in Patent Document 1. . In this case, there is a possibility that the quality of the image data of one object obtained by multiple times of light irradiation may deteriorate due to the fluctuation. Therefore, in the method disclosed in Patent Document 1, it is difficult to suppress the deterioration of quality due to the variation that occurs between multiple times of light irradiation for acquiring image data of one object.

  Therefore, the present invention suppresses the influence of the variation even in the case where the relative positional relationship between the object and the photoacoustic wave receiving unit varies during multiple times of light irradiation in photoacoustic imaging. An object is to provide a photoacoustic apparatus capable of acquiring image data of an object.

  The photoacoustic apparatus of the present invention includes a light irradiator, a receiver that outputs an electric signal by receiving a photoacoustic wave generated by irradiating the object with light emitted from the light irradiator, An image data acquisition unit that acquires image data of an object based on a signal group, the light irradiation unit irradiates the object multiple times, and the reception unit performs the multiple times By receiving photoacoustic waves generated by the light irradiation, a plurality of electrical signals corresponding to the plurality of times of light irradiation are output, and the image data acquisition unit is configured to output the plurality of electrical signals based on the plurality of electrical signals. A plurality of image data of the object corresponding to one light irradiation, and a first two or more images corresponding to two or more light irradiations performed in a first period from the plurality of image data Select the data and combine the first two or more image data into the first Thus, the first image data is acquired, and the combination of the image data is different from the first two or more image data from the plurality of image data, and is performed in a second period different from the first period. Selecting the second two or more image data corresponding to the two or more light irradiations obtained, and obtaining the second image data by second combining the second two or more image data; Based on the first image data and the second image data, position information after positional deviation of the first image data and the second image data is obtained, and the positions of the first image data and the second image data Based on the positional information after the shift, the positional information after the positional shift of the plurality of image data is acquired.

  According to the photoacoustic apparatus according to the present invention, in the photoacoustic imaging, even if the relative positional relationship between the object and the photoacoustic wave receiving unit varies during multiple light irradiations, the variation It is possible to acquire image data of an object in which the influence of the above is suppressed.

The figure which shows the photoacoustic apparatus which concerns on Embodiment 1. The figure which shows the position of the receiving part at the time of each light irradiation which concerns on Embodiment 1. FIG. The figure which shows the processing flow of the image data acquisition part which concerns on Embodiment 1. FIG. The figure which shows the pulse volume data which concern on Embodiment 1. The figure showing the pulse volume data of composition object concerning Embodiment 1. The figure which shows the synthetic | combination volume data which concerns on Embodiment 1. The figure which shows the positional offset amount of synthetic | combination volume data which concerns on Embodiment 1. FIG. The figure which shows the positional offset amount of the pulse volume data which concerns on Embodiment 1. The figure for demonstrating the positional offset correction process of the pulse volume data which concerns on Embodiment 1. FIG. The figure which shows another structural example of the photoacoustic apparatus which concerns on Embodiment 1. FIG. The figure which shows another process flowchart which concerns on Embodiment 1. FIG.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same component in principle, and description is abbreviate | omitted.

Embodiment 1
The photoacoustic apparatus according to this embodiment will be described with reference to FIG. The photoacoustic apparatus according to the present embodiment includes a light irradiation unit 100, a reception unit 200, a drive unit 300, a signal collection unit 400, an image data acquisition unit, a display unit 600, an input unit 700, and a control unit 800.

  Hereinafter, each structure of the photoacoustic apparatus which concerns on this embodiment is demonstrated.

(Light irradiation unit 100)
The light irradiation unit 100 includes a light source 110 that emits light and an optical system 120 that guides the light emitted from the light source 110 to the object 900.

  As the light source 110, a laser, a light emitting diode, or the like can be used. As the laser, various lasers such as a solid laser, a gas laser, a dye laser, and a semiconductor laser can be used. A pulsed laser such as an Nd: YAG laser or an alexandrite laser may be used as the light source 110. Further, a Ti: sa laser or an OPO (Optical Parametric Oscillators) laser that uses Nd: YAG laser light as excitation light may be used as the light source 110.

  The light source 110 may be a pulsed light source capable of generating pulsed light on the order of nanoseconds to microseconds. The light pulse width may be about 1 to 100 nanoseconds. Further, the wavelength of light may be in the range of about 400 nm to 1600 nm. In the case of imaging a blood vessel near the living body surface with high resolution, the wavelength at which absorption in the blood vessel is large (400 nm or more and 700 nm or less) may be used. On the other hand, when imaging a deep part of a living body, light having a wavelength (700 nm or more and 1100 nm or less) that is typically less absorbed in the background tissue (water, fat, etc.) of the living body may be used. Moreover, when measuring using light of a plurality of wavelengths, a light source capable of wavelength conversion may be used. When irradiating an object with a plurality of wavelengths, it is also possible to prepare a plurality of light sources that generate light of different wavelengths and irradiate each light source alternately. When multiple light sources are used, they are collectively expressed as light sources.

  Optical elements such as lenses, mirrors, and optical fibers can be used for the optical system 120. In order to irradiate with an expanded beam diameter of light, the light emitting portion of the optical system 120 may be configured with a diffusion plate or the like that diffuses light. On the other hand, in the photoacoustic microscope, in order to increase the resolution, the light emitting portion of the optical system 120 may be constituted by a lens or the like, and the beam may be focused and irradiated. Note that the light irradiation unit 100 may directly irradiate the object 900 from the light source 110 without including the optical system 120.

(Receiver 200)
The receiving unit 200 includes a receiving element group 210 including receiving elements 211 to 215 that output an electrical signal by receiving an acoustic wave, and a support body 220 that supports the receiving element group 210.

  As a member constituting each receiving element 211-215, a piezoelectric ceramic material typified by PZT (lead zirconate titanate), a polymer piezoelectric film material typified by PVDF (polyvinylidene fluoride), or the like is used. it can. Further, an element other than the piezoelectric element may be used. For example, a capacitive transducer (cMUT: Capacitive Micro-machined Ultrasonic Transducers), a transducer using a Fabry-Perot interferometer, or the like can be used. Note that any transducer may be employed as a receiving element as long as an electrical signal can be output by receiving an acoustic wave.

  The support 220 is preferably made of a metal material having high mechanical strength. In the present embodiment, the support body 220 has a hemispherical shell shape, and is configured to support the receiving element group 210 on the hemispherical shell. In this case, the directivity axis of each receiving element is collected near the center of curvature of the hemisphere. And when imaged using the electrical signal group output from these receiving elements, the image quality near the center of curvature is improved. The support 220 may have any configuration as long as it can support the receiving element group 210.

(Driver 300)
The driving unit 300 is a device that changes the relative position between the object 900 and the receiving unit 200. In the present embodiment, the drive unit 300 is a device that moves the support 220 in the XY directions, and is an electric XY stage equipped with a stepping motor.

  The driving unit 300 includes a motor such as a stepping motor that generates a driving force, a driving mechanism that transmits the driving force, and a position sensor that detects position information of the receiving unit 200. As the drive mechanism, a lead screw mechanism, a link mechanism, a gear mechanism, a hydraulic mechanism, or the like can be used. As the position sensor, a potentiometer using an encoder, a variable resistor, or the like can be used.

  The driving unit 300 is not limited to changing the relative position between the object 900 and the receiving unit 200 in the XY direction (two-dimensional), and may be changed to one-dimensional or three-dimensional.

  The driving unit 300 may fix the receiving unit 200 and move the target 900 as long as the relative position between the target 900 and the receiving unit 200 can be changed. When moving the target object 900, the structure etc. which move the target object 900 by moving the target object support part (not shown) which supports the target object 900 etc. can be considered. Moreover, you may move both the target object 900 and the receiving part 200. FIG.

  Moreover, the drive part 300 may move a relative position continuously, and may be moved by step and repeat. The driving unit 300 is preferably an electric stage, but may be a manual stage.

(Signal collection unit 400)
The signal collection unit 400 includes an amplifier 410 that amplifies an electrical signal that is an analog signal output from each receiving element 211-215, and an A / D converter that converts the analog signal output from the amplifier into a digital signal. . The digital signal output from the signal collection unit 400 is stored in the storage unit 510 in the image data acquisition unit 500. The signal collection unit 400 is also referred to as a data acquisition system (DAS). In this specification, an electric signal is a concept including both an analog signal and a digital signal.

(Image data acquisition unit 500)
The image data acquisition unit 500 is a device that stores the digital signal output from the signal collection unit 400 and acquires the image data of the object 900 based on the stored digital signal. Details of processing performed by the image data acquisition unit 500 will be described later.

In the present embodiment, image data is a general term for information at each position in a two-dimensional or three-dimensional space obtained based on an electrical signal group obtained by receiving a photoacoustic wave generated by a photoacoustic effect. Specifically, the image data includes photoacoustic wave generation sound pressure (initial sound pressure) [Pa], light energy absorption density [J / m ³ ], light absorption coefficient [1 / m], or a substance constituting the object. Information on the concentration of The information on the concentration of the substance is oxyhemoglobin concentration, deoxyhemoglobin concentration, total hemoglobin concentration, oxygen saturation, or the like. The total hemoglobin concentration is the sum of the oxyhemoglobin concentration and the deoxyhemoglobin concentration. Oxygen saturation is the ratio of oxyhemoglobin to total hemoglobin.

  The image data acquisition unit 500 includes a storage unit 510, a reconstruction unit 520, a selection unit 530, a synthesis unit 540, a projection data acquisition unit 550, and a position estimation unit 560. The storage unit 510 can be configured by a non-temporary storage medium such as a magnetic disk or a flash memory. The storage unit 510 may be a volatile medium such as a DRAM (Dynamic Random Access Memory). Note that the storage medium storing the program is a non-temporary storage medium.

  The units responsible for the calculation functions such as the reconstruction unit 520, the selection unit 530, the synthesis unit 540, the projection data acquisition unit 550, and the position estimation unit 560 are a processor such as a CPU or GPU (Graphics Processing Unit), an FPGA (Field Programmable Gate Array). ) It can be composed of an arithmetic circuit such as a chip. These units are not only composed of a single processor and arithmetic circuit, but may be composed of a plurality of processors and arithmetic circuits.

(Display unit 600)
The display unit 600 is a display such as a liquid crystal display or an organic EL (Electro Luminescence). This is an apparatus that displays an image based on the image data obtained by the image data acquisition unit 500, a numerical value at a specific position in the image data, and the like. The display unit 600 may display an image or a UI for operating the apparatus. Display unit 600 may be provided separately from the photoacoustic apparatus.

(Input unit 700)
The input unit 700 can be configured with a mouse, a keyboard, a touch panel, and the like that can be operated by the user. Note that the input unit 700 may be provided separately from the photoacoustic apparatus.

(Control unit 800)
The control unit 800 receives signals from various operations such as imaging start from the input unit 700 and controls each configuration of the photoacoustic apparatus. The control part 800 reads the program code stored in the memory | storage part, and controls the action | operation of each structure of a photoacoustic apparatus. The control unit 800 is configured by an arithmetic element such as a CPU.

  In addition, each structure of a photoacoustic apparatus may be comprised as a respectively different apparatus, and may be comprised as a single apparatus united. Moreover, you may be comprised as a single apparatus with which the some structure of the photoacoustic apparatus was united.

  Hereinafter, the operation of the photoacoustic apparatus in the present embodiment will be described.

  The light irradiation unit 100 irradiates the object 900 with light 130 at a repetition frequency of 20 Hz. Due to the photoacoustic effect caused by the light 130, an acoustic wave (photoacoustic wave) is generated in the object 900. Each receiving element 211-215 receives the photoacoustic wave and outputs an electrical signal, whereby the receiving unit 200 outputs an electrical signal group. The electrical signal output from each receiving element is a time-series signal representing the temporal variation of the pressure of the photoacoustic wave that reaches each receiving element.

  While the driving unit 300 moves the receiving unit 200, the light irradiation unit 100 irradiates the object 900 with light multiple times. That is, the driving unit 300 moves the receiving unit 200 during a period in which light irradiation is performed a plurality of times. As a result, the driving unit 300 can move the receiving unit 200 so that the receiving unit 200 is positioned at different positions when each light is irradiated. FIG. 2 shows an example of the position of the receiving unit 200 at the time of each light irradiation. The points in FIG. 2 plot the position of the bottom part of the support body 220 at the time of each light irradiation. The light irradiation unit 100 performed N times of light irradiation, and the reception unit 200 received photoacoustic waves at N locations. In FIG. 2, the number of times of light irradiation is 2050, and the average moving distance of the receiving unit 200 during light irradiation is about 1.5 mm.

  The receiving element group 210 outputs a plurality of electric signal groups corresponding to each of the plurality of times of light irradiation by receiving the photoacoustic wave generated by the light irradiation unit 100 irradiating the light a plurality of times. That is, the receiving element group 210 outputs an electrical signal group for the number of times of light irradiation of the light irradiation unit 100. Hereinafter, the plurality of electrical signal groups corresponding to each of the plurality of times of light irradiation are simply referred to as a plurality of electrical signal groups.

Hereinafter, a case where N times of light irradiation are performed will be described. Note that a received signal group obtained by the i-th light irradiation is denoted as P _{dp —} i (1 ≦ i ≦ N). The item with the subscript i represents an item corresponding to the i-th light irradiation. i is a positive integer and is also called a pulse index. An item with the subscript p represents an item corresponding to one light irradiation.

  The signal collection unit 400 converts a plurality of electrical signal groups that are analog signal groups output from the reception element group 210 into digital signal groups, and stores the digital signal groups in the storage unit 510.

  The image data acquisition unit 500 acquires image data of an object based on a plurality of electrical signal groups stored in the storage unit 510. The image data acquisition unit 500 transmits the image data of the object to the display unit 600 and causes the display unit 600 to display an image based on the image data, a numerical value at a specific position in the image data, and the like. When the image data is three-dimensional, the image data acquisition unit 500 can display a tomographic image cut at an arbitrary cross section, a maximum intensity projection (MIP) image, or a volume-rendered image.

  Hereinafter, the process in which the image data acquisition unit 500 acquires the image data of the object will be described in detail according to the process flowchart shown in FIG.

(S210: Step of acquiring a plurality of pulse volume data)
The reconstruction unit 520 acquires a plurality of pieces of image data of the object corresponding to each of a plurality of times of light irradiation based on each of the plurality of electric signal groups stored in the storage unit 510. That is, the reconstruction unit 520 converts an electrical signal group representing a temporal change in pressure into image data of an object. Image data obtained by one light irradiation is also called pulse volume data. The pulse volume data is acquired in the form of volume data in which a value at the corresponding position is stored in each of two-dimensional or three-dimensionally arranged voxels (also called pixels in the case of two dimensions). The volume data can also be called a two-dimensional or three-dimensional volume, a two-dimensional or three-dimensional image, or a two-dimensional or three-dimensional tomographic image.

In the present embodiment, the reconstruction unit 520 has a plurality of initial sound pressure distribution data P corresponding to each of a plurality of times of light irradiation based on each of the plurality of electrical signal groups stored in the storage unit 510. _{0p_i} is acquired. The plurality of initial sound pressure distribution data P _{0p —} i is stored in the storage unit 510. In the present embodiment, a case will be described in which three-dimensional spatial distribution information of initial sound pressure is acquired as image data of an object. A value at each position of the initial sound pressure distribution data is expressed by a function expression such as P _{0p —} i (x, y, z). Hereinafter, the plurality of initial sound pressure distribution data P _{0p —} i corresponding to each of a plurality of times of light irradiation is also simply referred to as a plurality of initial sound pressure distribution data.

  As the reconstruction method, a known reconstruction method such as a time domain reconstruction method, a Fourier domain reconstruction method, a model-based reconstruction method (an iterative reconstruction method), or the like can be employed. For example, a time domain reconstruction technique called Universal Back-Projection (UBP) as described in PHYSICAL REVIEW E 71,016706 (2005) can be adopted.

  The reconstruction unit 520 acquires a plurality of initial sound pressure distribution data based on the position information of each receiving element at the time of each light irradiation in addition to the plurality of electrical signal groups. The reconstruction unit 520 can acquire the position information by reading the position information of each receiving element at the time of each light irradiation stored in advance in the storage unit 510. Further, the reconfiguration unit 520 may acquire the position information of each reception element by receiving the position information of the reception unit 200 from the position sensor provided in the drive unit 300 using light irradiation as a trigger.

FIG. 4 shows a part of the pulse volume data (P _0p _ 1 to P _0p _30) according to the present embodiment. Although the pulse volume data in the present embodiment is volume data in a three-dimensional space, the pulse volume data is represented on the XY plane for convenience of explanation on paper. In the present embodiment, the reconstruction area is set so that at least some areas of the temporally adjacent initial sound pressure distribution data overlap. In this embodiment, a 60 mm square cube region centered on the center of curvature of the hemispherical support 220 is a reconstruction region reconstructed based on one light irradiation, that is, one electrical signal group. In this case, the size (60 mm) of the reconstruction area by one light irradiation is larger than the moving amount (1.5 mm) of the receiving unit 200 during the light irradiation. Therefore, as shown in FIG. 4, two or more pulse volume data corresponding to continuous light irradiation are superimposed. The size and shape of the reconstruction area may be set in advance. The user may specify the size and shape of the reconstruction area using the input unit 700. The position of the upper left end of each pulse volume data with respect to the reference position O is set as the position of each pulse volume data. In Figure 4, showing the positional _POSP 0p _1 pulse volume data _P 0p _1 as an example. As shown in FIG. 2, since the position of the receiving unit 200 is different for each light irradiation, each pulse volume data obtained in the present embodiment shown in FIG. 4 is located at a position different from the reference position O. That is, in the present embodiment, the position of the pulse volume data is determined based on the position of the receiving unit set in advance at the time of light irradiation. Note that the position information of the receiving unit at the time of light irradiation may be acquired, and the position of the acquired pulse volume data may be determined based on the position information. Further, the position of the pulse volume data may be determined based on the position irradiated with light. Further, the position of the pulse volume data acquired in this step may be set in advance.

In this step, the reconstruction unit 520 acquires the optical fluence distribution data Φ [J / m ² ] in the object and the Gruneisen coefficient distribution data Γ [Pa · m ³ / J] in the object. May be. Then, the reconstruction unit 520 obtains the light absorption coefficient distribution data μ _a [1 / m] in the object by dividing the initial sound pressure distribution data by the light fluence distribution data and the Gruneisen coefficient distribution data. May be. In this case, the light absorption coefficient distribution data may be pulse volume data.

  For example, the reconfiguration unit 520 may include Proc. of SPIE Vol. As described in 7561 75617-1, the light fluence distribution data may be acquired by solving the light diffusion equation.

  Further, for example, since it is known that the value of the Gruneisen coefficient is determined almost uniquely when the type of the object is determined, the Gruneisen coefficient distribution data Γ corresponding to the object is stored in the storage unit 510 in advance. be able to. Then, the reconstruction unit 520 may acquire the Gruneisen coefficient distribution data Γ previously stored in the storage unit 510 by reading it.

  Note that the user may hold the receiving unit 200 having the holding unit and move the receiving unit 200. In addition, it is not necessary to move the receiving unit 200 during a period in which light irradiation is performed a plurality of times. Further, the reconstruction unit 520 may acquire image data of the entire imaging region based on an electrical signal group obtained by one light irradiation, and may repeat it for a plurality of times of light irradiation.

(S220: Step of selecting pulse volume data)
The selection unit 530 selects two or more pulse volume data corresponding to continuous light irradiation from a plurality of pulse volume data stored in the storage unit 510. The two or more pieces of pulse volume data selected here are collectively referred to as first aggregate data G _g _1.

In addition, the selection unit 530 uses a combination of pulse volume data different from the first aggregate data, and includes a part of the pulse volume data included in the first aggregate data. Select two or more corresponding pulse volume data. The two or more pieces of pulse volume data selected here are collectively referred to as second aggregate data G _g _2.

In this specification, the j-th set data is expressed as G _{g —} j (1 ≦ j ≦ M). The item with the subscript j represents an item corresponding to the j-th set data. j is a positive integer and is also called a set index. An item with the subscript g represents an item corresponding to one set data.

FIG. 5 shows a selection example of pulse volume data in this embodiment. Selecting unit 530 selects a single 10 initial sound corresponding to the light irradiation of 10 th from th pressure distribution data _P 0p _{_1~P} 0p _10 as first set data _G g _1. The selection unit 530 selects the five ten initial sound corresponding to the light irradiation of the 15th from the first pressure distribution data _P 0p _{_6~P} 0p _15 as second set data _G g _2. Here, in each set data, the initial sound pressure distribution data corresponding to the fifth to tenth light irradiation is selected as the common initial sound pressure distribution data. Similarly, the selection unit 530, an initial sound pressure distribution data corresponding to 10 times of the light irradiation, to select a plurality of sets data _{G g} _1~G _{g _M} By selecting shifted five times of the light irradiation amount be able to. That is, the aggregate data G _{g —} j includes initial sound pressure distribution data P _0p — (5j−4) to P _0p — (5j + 5). In the case of this embodiment, one set data is composed of ten electric signal groups, and a plurality of set data is formed while shifting by five electric signal groups. Therefore, the number of synthesized volume data (M) is smaller than the number of pulse volume data (N).

  Note that the selection unit 530 may select pulse volume data based on the image quality of each pulse volume. The selection unit 530 may select the pulse volume data so that the selected pulse volume data has a predetermined image quality or higher when synthesized. For the pulse volume data with high image quality, the selection unit 530 may select a smaller number of pulse volume data as one set compared with pulse volume data with low image quality. Here, the image quality is a signal level, S / N or contrast in volume data. For example, in the pulse volume data, it is assumed that a strong luminance value is observed in a region where a region of a subject where a strong photoacoustic wave has been imaged and a weak luminance value is observed in other regions. The selection unit 530 may calculate the signal level based on the average of luminance values in the pulse volume data, the variance of luminance values, and the like. Alternatively, the selection unit 530 may calculate the ratio between the component based on the photoacoustic wave and the noise component based on the luminance value of the pulse volume data, and calculate the S / N based on the ratio. In this case, for example, the selection unit 530 performs a spatial frequency analysis on the luminance value of the pulse volume data. Then, the selection unit 530 uses a component having a luminance value equal to or higher than a predetermined frequency as noise, sets a luminance value component at a frequency lower than that as a component based on photoacoustic waves, and calculates S / N based on the ratio of these components May be. As described above, the number of pulses to be combined can be adaptively changed according to the image quality of each pulse volume data. Therefore, it is possible to generate synthesized volume data whose image quality is equal to or higher than a predetermined level.

  In addition, when the change in the body motion of the object is known, the selection unit 530 may select the pulse volume data based on the size of the body motion. Specifically, the selection unit 530 can reduce the number of pulses to be selected when the body movement is large, and can increase the number of pulses to be selected when the body movement is small. Thereby, when the body movement of the subject is large, a small amount of pulse volume data is synthesized in S230 described later. Therefore, it is possible to suppress blur from being included in the volume data synthesized due to the influence of body movement. On the other hand, when the body movement of the object is small, a large number of pulse volume data is synthesized in S230 described later. Thereby, there is an effect that synthesized volume data in which the influence of noise included in the pulse volume data is reduced can be generated.

  As will be described later, the selected pulse volume data is synthesized. In order to suppress the blur of the volume data after synthesis, it is preferable that the positional deviation between the selected pulse volumes is small. Therefore, pulse volumes corresponding to two or more light irradiations among light irradiations performed within a predetermined period may be selected. The predetermined period corresponding to the first aggregate data is referred to as a first period, and the predetermined period corresponding to the second aggregate data is referred to as a second period. The predetermined period is determined by the size and period of the positional deviation. For example, you may select the pulse volume data contained in the period corresponding to 1/4 period of position shift. When assuming a position shift due to respiration, pulse volume data included within one second may be selected. When assuming a position shift due to relatively fast breathing, pulse volume data included within 0.5 seconds may be selected. Further, any combination of pulse volume data may be selected as long as pulse volume data within a predetermined period is selected. That is, it is not necessary to select continuous pulse volume data in terms of time.

(S230: Step of synthesizing selected pulse volume data)
The synthesizer 540 synthesizes two or more pulse volume data selected in S220 to obtain synthesized volume data.

Initial composite unit 540 in the present embodiment synthesizes the initial sound pressure distribution data _P 0p _{_1~P} 0p _10 included in the first set data _G g _1 selected by the selection unit 530, which is the first synthetic Sound pressure distribution data _{P0g_1} is acquired. The first synthesized initial sound pressure distribution data corresponds to first synthesized volume data (first image data). The synthesis for obtaining the first synthesis volume data is referred to as first synthesis.

FIG. 6A shows the first synthesized volume data P _0g _ 1 acquired by the first synthesis. In the present embodiment, the pulse volume data _P 0p _{_1~P} 0p _10 compositing target encompasses all, and, to a rectangular region having the smallest and the first combined volume data _P 0 g _1. Note that an arbitrary area including an area where at least two or more pulse volume data are superimposed may be used as the synthesized volume data. That is, the combined volume data area does not have to include all the pulse volume data to be combined.

Similarly to the pulse volume data, the position of the upper left edge of the drawing with respect to the reference position O is set as the position PosP _0g _1 of the first volume data.

Further, the combining unit 540 combines the initial sound pressure distribution data _P 0p _{_6~P} 0p _15 included in the second set data selected by the selection unit 530, a second synthesized initial sound pressure distribution data P _{0g_2} is acquired. The j-th synthesized initial sound pressure distribution data obtained by synthesizing the initial sound pressure distribution data included in the j-th set data is denoted as P _{0g —} j. The second synthesized initial sound pressure distribution data corresponds to second synthesized volume data (second image data). The synthesis for obtaining the second synthesis volume data is referred to as second synthesis.

6B shows a pulse volume data _P 0p _{_1~P} 0p _30 synthesis volume data _P 0g _{_1~P} 0g _5 obtained based on that shown in Figure 6A. In FIG. 6B, the solid line represents pulse volume data, and the broken line represents synthesized volume data.

6C illustrates only the synthesis volume data _P 0g _{_1~P} 0g _5 shown in Figure 6B. The solid lines represent the combined volume data P _{0g —} 1, P _{0g — 3} , P _{0g —} 5, and the broken lines represent P _{0g —} 2, P _{0g —} 4.

  In the present embodiment, the synthesizing unit 540 obtains synthesized volume data by averaging the selected pulse volume data. The averaging process (additional averaging) is performed by calculating the luminance of each pulse volume in an area where each pulse volume overlaps and dividing by the number of overlapping pulse volumes.

The synthesizer 540 may acquire the weight volume data Wg_j (x, y, z) together with the synthesized volume data P _{0g —} j. The weighted volume data Wg_j is volume data representing the number of superimposed pulse volume data at each position of the synthesized volume data P _{0g —} j (value when dividing in the case of averaging processing). The value of the synthesized volume data at the position obtained by synthesizing a lot of pulse volume data is considered highly reliable. That is, the weight volume Wg_j is regarded as a value representing the reliability of each position of the composite volume data.

  Note that the combining method is not limited to the averaging process, and any method can be used as long as volume data that accurately reproduces the characteristics of the object can be obtained as compared to one pulse volume data. However, the process of correcting the relative position fluctuation between the object 900 and the receiving unit 200 during light irradiation (for example, the process of changing the position of the pulse volume) is not included in the “synthesis” according to the present specification.

  For example, the synthesizing unit 540 may synthesize by adding each of the pulse volume data to be synthesized after weighting. Further, the synthesis unit 540 may calculate an addition value or an average value for the pulse volume data from which a value including much noise is excluded by an outlier removal method or the like.

  By these synthesis processes, noise included in each pulse volume data is reduced, and synthesized volume data that more accurately reproduces the characteristics of the object can be acquired.

  As in this embodiment, by selecting pulse volume data that is temporally continuous in S230, it is possible to synthesize pulse volume data with a small temporal change in this step. As a result, in this step, it is possible to obtain synthetic volume data in which the influence due to the relative positional relationship between the object and the photoacoustic wave receiver between the multiple light irradiations is suppressed as much as possible.

  In this step, synthesized volume data with improved quality can be obtained by synthesizing a plurality of low-quality pulse volume data. However, the synthetic volume data obtained in this step includes an influence due to a change in relative positional relationship between the object and the photoacoustic wave receiving unit between a plurality of times of light irradiation. Therefore, there is a possibility that the quality of the synthesized volume data is deteriorated due to the fluctuation. Hereinafter, a process for estimating the position of the pulse volume data from the estimated position of the synthesized volume data will be described in order to suppress this deterioration in quality.

  Note that the selection unit 530 may select the pulse volume data to be combined again based on the image quality of the combined volume data obtained in this step. Specifically, when the image quality of the combined volume data is smaller than the predetermined image quality, the selection unit 530 may add and reselect pulse volume data to be combined. Thereby, since the synthesized volume data can have a predetermined image quality or higher, the accuracy of estimating the position of the synthesized volume data in S250, which will be described later, is improved. Further, when the image quality of the combined volume data is equal to or higher than the predetermined image quality, the selection unit 530 may reduce and reselect the pulse volume data to be combined. Since the number of pulse volume data for achieving a predetermined image quality or higher can be reduced, it is possible to suppress the synthesis volume data from being blurred due to the influence of body movement.

The reconstruction unit 520 may acquire composite volume data based on two or more electrical signal groups obtained by light irradiation corresponding to two or more pulse volume data selected in S220. In this case, the electrical signal group may be selected by a method similar to the method of selecting the pulse volume data described in S220.
The reconstruction unit 520 may generate one volume data from two or more electric signal groups without generating pulse volume data for each electric signal group. Note that the size of the reconstruction area to which one electrical signal group is applied may be smaller than the entire imaging area as described in S210. The size of the reconstruction area to which one electrical signal group is applied may be the size of the entire imaging area. That is, the reconstruction unit 520 may apply each of all the electric signal groups to the entire imaging region.

(S240: Step of selecting composite volume data)
The position estimation unit 560 selects an arbitrary pair of composite volume data from the plurality of composite volume data obtained in S230. The k-th pair is denoted as R_k. Further, while the _P 0g _{_k1} synthetic volume data configuring a pair R_k, other and referred to as _P 0g _{_k2.} Hereinafter, in the present embodiment, a case where K pairs are selected will be described.

  In addition, it is preferable to make two synthetic volume data which have an overlap area | region into a pair. As a result, it is possible to avoid comparing the combined volume data that do not have a common feature in S250, which will be described later, thereby reducing redundant calculations. Furthermore, it is preferable that a pair of synthesized volume data having a large overlap area is paired. Therefore, for example, the position estimation unit 560 may select a pair in which the volume of the overlap region between the combined volume data is a predetermined value or more. In addition, for example, the position estimation unit 560 may select a pair in which the volume ratio of the overlap region to the combined volume data is equal to or greater than a predetermined value. In addition, a pair may be selected in which the overlapping areas of the pulse volume data in the synthesized volume data overlap each other.

  Further, for a certain synthetic volume data, synthetic volume data in which the aggregate index is included in a predetermined range may be selected as a pair target from the aggregate index of the synthetic volume data. Further, the composite volume data in which the set index is continuous, that is, temporally continuous may be selected as a pair target.

For example, in this embodiment, the position estimation unit _560, to the _{P 0g _j, P 0g _ (} j + 1) ~P 0g _ (j + 60) out of the _overlap region for the _P 0 g _j is 50% or more synthetic A pair is selected using volume data as a composition target.
(S250: Step of estimating the positional deviation amount of the composite volume data)
Subsequently, the position estimation unit 560 estimates the amount of positional deviation of each synthetic volume data due to a change in the relative positional relationship between the object and the photoacoustic wave receiving unit during light irradiation. Hereinafter, an example of a method for estimating the positional deviation amount of each synthetic volume data will be described.

The position estimation unit 560 acquires a similarity function F_k between P _{0g —} k1 and P _{0g —} k2 as shown in Expression (1).
F_k (x, y, z) = f _simil (P _{0g —} k, x, y, z) (1)
Here, the similarity function F_k is for one of the synthetic volume data _P 0g _{_k1} configuring a pair R_k, the relative positions of the other synthetic volume data _{P 0g _k2 (x, y,} z) only when is translated It is a function for calculating similarity. Here, the function _fsimil returns a high value as a function value when the similarity between images is high. Acquisition of the similarity function F_k refers to acquisition of a translation value (x, y, z) that is an argument of each function, that is, a function value when the relative position between image data is discretely changed within a predetermined range. Means. For example, acquisition of a set of (2L + 1) × (2L + 1) × (2L + 1) values returned by F_k for each of the values of x, y, and z being changed as integer values from −L to + L. means. More expediently, a similarity function F_k is derived as information closer to a continuous function using a set of (2L + 1) × (2L + 1) × (2L + 1) values, further using a bilinear method, a bicubic method, or the like, This may be acquired.

_{Incidentally,} as a reference only to translate the position (amount of movement of the receiving portion 200 between the light irradiation) relative position of the _P 0g _{_k2} for P 0g _{_k1,} discretely varying the position of the P 0g _k2 within a predetermined range The function value of the case may be acquired.

  For example, as a function for calculating the similarity, any similarity measure such as SSD (Sum of Squared Difference), SAD (Sum of Absolute Difference), mutual information, and cross-correlation can be applied. Further, for example, a similarity function may be acquired by extracting characteristic forms from the synthesized volume data and measuring the degree of coincidence with the positions. As the feature to be extracted, an anatomical feature such as a blood vessel, or a feature extracted by a known technique generally used in the image processing field such as edge detection or corner detection may be used. Further, higher-order local image features such as SIFT features and SURF features generally used in the technical field such as computer vision may be used as features to be extracted. According to these methods, it is considered that a more robust similarity function can be acquired with respect to a difference in luminance distribution between synthesized volume data, noise mixing, and the like.

  Note that the position estimation unit 560 multiplies the weighted volume data Wg_j described in S240 by the result of the similarity calculation of each position shown in Expression (1) (in the case of SSD, the calculation of the square of the difference between the pixel values). You may acquire a similarity function by processing. By this processing, the position estimation unit 560 can acquire a similarity function that strongly reflects the region of the synthetic volume data with high reliability.

  Further, when the similarity cannot be correctly calculated between the composite volume data to be subjected to similarity calculation, the result may not be used for the subsequent processing. As a case where the similarity cannot be calculated correctly, it is conceivable that the similarity is sufficiently small or does not change regardless of the translation. According to this process, the comparison result (similarity function) between the synthesized volume data in which the same features are sufficiently appearing can be selectively used for the subsequent processes.

Subsequently, as shown in Expression (2), the position estimation unit 560 acquires the translation amount M_k of the composite volume data P _{0g —} k2 with respect to the composite volume data P _{0g —} k1 that maximizes the function value of the similarity function F_k. .
M_k (x, y, z) = argmax {(F_k (x, y, z)}} Expression (2)
The position estimation unit 560 acquires the translation amount M_k that maximizes the function value of the similarity function F_k for each pair.

Subsequently, when estimating the position of the composite volume data, an evaluation function is defined so as to keep the translation amount M_k that is the individual optimum value for the pair R_k as much as possible. That is, an evaluation function is defined in which the value decreases as the position of P _{0g —} k2 with respect to P _{0g —} k1 moves away from the translation amount M_k. Equation (3) represents an example of the evaluation function E_k in this case.
_{E_k = (M_k- (PosP 0g _k1} -PosP 0g _k2)) 2
_{= (M_k (x) - (} PosP 0g _k1 (x) -PosP 0g _k2 (x))) 2
_{+ (M_k (y) - (} PosP 0g _k1 (y) -PosP 0g _k2 (y))) 2
_{+ (M_k (z) - (} PosP 0g _k1 (z) -PosP 0g _k2 (z))) 2
... Formula (3)
PosP _{0g —} k1 represents the position of P _{0g —} k1 with respect to the reference position. PosP _{0g —} k2 represents the position of P _{0g —} k2 with respect to the reference position. In defining the evaluation function, the similarity function F_k may be approximated to a quadratic function that fits the similarity function F_k. Further, when the similarity function F_k can be approximated to decrease according to a quadratic function around the translation amount M_k, the expression (3) is obtained from the positional relationship between P _{0g —} k1 and P _{0g —} k2 and the value of the similarity function F_k. Is a function that approximates around the translation amount M_k.

Subsequently, the position estimation unit 560 acquires the positions PosP ′ _{0g —} j of all the synthesized volume data with respect to the reference position when the cost function E defined as in Expression (4) is minimized.

コスト関数が最小化したときの、基準位置に対する合成ボリュームデータの位置は、対象物９００と受信部２００との相対的な位置関係の変動による位置ずれ後の合成ボリュームデータの位置情報を表す。

The position of the synthesized volume data with respect to the reference position when the cost function is minimized represents the position information of the synthesized volume data after the positional deviation due to the relative positional relationship between the object 900 and the receiving unit 200.

For example, the position estimation unit 560 solves the solution that minimizes the cost function E shown in Equation (4) (closest to 0) by the linear least square method. Thereby, the position PosP ′ _{0g —} j of each synthetic volume data can be calculated uniquely. In the cost function shown in Equation (4), the position PosP ′ _{0g —} j of each synthetic volume data can be uniquely determined by the linear least square method, and therefore the calculation cost is low.

  Note that the cost function optimization is not limited to the optimization of the cost function by the linear optimization described above, and any known method may be used. For example, the optimization may be performed by a nonlinear optimization method such as a steepest descent method or a Newton method by repeated calculation. That is, the position estimation unit 560 obtains position information after positional deviation of the composite volume data with respect to the reference position by searching for the position of each composite volume data that minimizes the cost function.

  Note that the cost function may be defined so as to regularize the fluctuation (movement) between the light irradiations at the positions of the respective synthetic volume data assumed. When the breast is considered as an object, it is assumed that movement due to respiration is dominant. In this case, the movement of the object is a movement of about several mm at the maximum, and the movement is assumed to be continuous and smooth in time. In addition, the movement is assumed to be a periodic movement. As described above, it is possible to apply regularization to suppress the movement that deviates from the assumed movement of the object.

  Any method of regularization may be used. For example, regularization can be achieved by adding a predetermined weighting factor to the total amount of variation (movement distance) of the object in the derivation process and adding it to the cost function. Moreover, you may add the sum total of the time differentiation (acceleration) of the fluctuation | variation of a target object to a cost function. Further, a value calculated based on the frequency component value of the fluctuation of the object may be added to the cost function. Alternatively, a typical variation method of the object may be prepared as a model, and a difference from the variation in the model may be added to the cost function as a cost.

  “Minimize the cost function” is not only when the cost function is strictly minimized, but also when the cost function value is equal to or less than a predetermined value when the solution candidate is changed. This includes the case where the amount of change of the value becomes equal to or less than a predetermined value. That is, the position estimation unit 560 may determine that the cost function is minimized when the cost function satisfies a predetermined condition. In addition, the user may use the input unit 700 to indicate that the cost function has been minimized. In this case, the position estimation unit 560 determines that the cost function has been minimized in response to an instruction from the input unit 700.

Subsequently, the position estimation unit 560 acquires the positional deviation amount M _{g —} j of the combined volume data when the cost function is minimized with respect to the combined volume data obtained in S230. This misregistration amount M _{g —} j represents the misregistration amount of each synthetic volume data due to a change in the relative positional relationship between the object 900 and the receiving unit 200.

7, the position _POSP 0 g _2 of resulting synthetic volume data _P og _2 in S230, (the position of the displacement-) 'position POSP of _og _2' _og _2 synthesis volume data P when the cost function is minimized It shows. In FIG. 7, the combined volume data P _og _2 obtained in S230 is represented by a solid line, and the synthesized volume data P ′ _og _2 when the cost function is minimized is represented by a broken line.

  In this step, any method may be used as long as the amount of positional deviation of each synthetic volume data due to a change in the relative position between the object 900 and the receiving unit 200 can be acquired.

  In this step, it is possible to accurately estimate the positional deviation amount of the synthesized volume data by using the synthesized volume data whose quality is improved compared to the pulse volume data.

(S260: Step of estimating positional deviation amount of pulse volume data)
The position estimation unit 560 estimates the positional deviation amount M _{p —} i of each pulse volume data based on the positional deviation amount M _{g —} j of each synthetic volume data estimated in S250. That is, the position estimation unit 560 estimates a positional deviation with respect to the position of the pulse volume data set in S210.

  The position estimation unit 560 can assign the positional deviation amount of the synthetic volume data estimated in S250 as the positional deviation amount of the pulse volume data associated with the synthetic volume data. The misregistration amount of other pulse volume data can be estimated by the position estimation unit 560 performing interpolation processing on the misregistration amount of the assigned pulse volume data. As the interpolation processing method, a known method such as linear interpolation or spline interpolation can be employed. Further, the interpolation processing may be performed with a restriction that does not calculate a position that deviates from the assumed movement of the object described in S250.

  Of the pulse volume data targeted for synthesis, any pulse volume data may be used as pulse volume data associated with the synthesized volume data.

  For example, when the number of pulse volume data to be synthesized is an odd number, the pulse volume data located at the center in time may be associated with the synthesized volume data.

Further, for example, when the number of pulse volume data to be synthesized is an even number as in the present embodiment, any pulse volume data that is temporally located near the center may be associated with the synthesized volume data. For example, when 10 pulse volume data are to be combined as in this embodiment, the positional deviation amount M _{g —} j of the synthesized volume data P _{0g —} j is used as the positional deviation amount M _{p —} 5 i of the pulse volume data P _{0p —} 5j. It may be assigned.

Further, when the number of pulse volume data to be synthesized is an even number, virtual pulse volume data located at the center in time may be associated with the synthesized volume data. For example, when 10 pulse volume data are to be combined as in the present embodiment, the positional shift amount of the combined volume data P _{0g —} j is set to the positional shift amount of the virtual pulse volume data with the pulse index of 5.5j. It may be assigned.

  Further, when combining with weighting, the pulse volume data weighted with the highest weighting coefficient among the pulse volume data to be combined may be associated with the combined volume data. Further, among the pulse volume data to be synthesized, the pulse volume data having a median weighting factor may be associated with the synthesized volume data.

  FIG. 8 shows an example of processing for estimating the positional deviation amount of the pulse volume data in the present embodiment.

FIG. 8A is a diagram showing the amount of misalignment with respect to pulse volume data before performing misalignment correction described later by arrows. First, as shown in FIG. 8A, the position estimation unit 560 assigns the positional deviation amount M _g _2 of the combined volume data P _0g _2 to the positional deviation amount M _p _10 of the hatched pulse volume data P _0p _10. The position estimation unit 560 also assigns the misregistration amount M _{g —} j of the other combined volume data P _{0g —} j to the misregistration amount M _{p —} 5j of the pulse volume data P _{0p —} 5j. In this embodiment, since M _g _1 is 0, M _p _5 is also 0. In FIG. 8A, the position PosP ′ _{op —} 10 after the positional deviation of the pulse volume data is shown.

Subsequently, as illustrated in FIG. 8B, the position estimation unit 560 obtains the translation amount other than the hatched pulse volume data P _{0p —} 5j by linearly interpolating the displacement amount M _{p —} 5j. In FIG. 8B, the positional deviation amount M _{p —} 5j is represented by a solid line, and the positional deviation amount estimated by interpolation other than the positional deviation amount M _{p —} 5j is represented by a dotted line. That is, the amount of positional deviation of each pulse volume data can be estimated by interpolating the amount of positional deviation so as to connect the positions PosP ′ _{op —} i after the positional deviation of the pulse volume data. Incidentally, the position obtained by interpolating _{og _j} 'position PosP of _{og _j'} synthesis volume data P after optimization, may be estimated as the position of the displacement-pulse volume data. Further, the positional deviation amount of the pulse volume data may be acquired based on the position after the positional deviation of the pulse volume data obtained in this way.

  Through the above processing, the positional deviation amount of each pulse volume data can be acquired based on the positional deviation amount of each synthetic volume data.

  In this step, the positional deviation amount of the pulse volume data can be estimated based on the positional deviation amount of the synthesized volume data estimated with high accuracy. As a result, the estimation accuracy of the positional deviation amount of the pulse volume data is high as compared with the case where the positional deviation amount is estimated directly from the low-quality pulse volume data.

  Further, as described above, in the present embodiment, the number (M) of synthesized volume data is smaller than the number (N) of pulse volume data. In this case, the method of estimating the positional deviation of the total synthesized volume data by comparing the synthesized volume data is more than the technique of estimating the positional deviation of the total pulse volume data by comparing the pulse volume data. The calculation amount is small. For this reason, the method of estimating the amount of positional deviation of all pulse volume data based on the amount of positional deviation of all synthesized volume data obtained by the latter is better than the method of estimating the positional deviation of all pulse volume data by the former. Calculation cost can also be reduced.

(S270: Step of synthesizing a plurality of pulse volume data after positional deviation correction)
The synthesizing unit 540 performs processing (translation processing) for correcting the position of each pulse volume data by the positional deviation amount estimated in S260, and then synthesizes them to generate third synthesized volume data (third Image data). That is, the third synthesized volume data is obtained by synthesizing the pulse volume data arranged at the position after the positional deviation. The synthesis for obtaining the third synthesis volume data is referred to as third synthesis.

FIG. 9 shows an example of misalignment correction processing (translation processing) in this step.
9A shows a portion of the pulse volume data before the translation process in the present embodiment _(P 0p _{_23~P} 0p _25). Dashed lines _represent the characteristics 701 of the outer and the _P 0p _25 of P 0p _25. The solid line represents the outer and inner features 711 of P _0p —24. The dotted line represents the outer and inner features 721 of P _0p —23. Note that the feature 701, the feature 711, and the feature 721 all represent the same feature. In the state of FIG. 9A, the features in each pulse volume data are located at different positions.

FIG. 9B shows the pulse volume data P ′ _{0p —} 25 after translation of the pulse volume data P _{0p —} 25 before translation by the positional deviation amount M _p —25 estimated in S260. FIG. 9C shows the pulse volume data P ′ _{0p —} 24 after the translation of the pulse volume data P _{0p —} 24 before translation by the displacement amount M _p —24 estimated in S260. FIG. 9D shows the pulse volume data P ′ _{0p —} 23 after translation of the pulse volume data P _{0p —} 23 before translation by the positional deviation amount M _{p —} 23 estimated in S260.

FIG. 9E shows how pulse volume data P ′ _{0p —} 23, P ′ _{0p —} 24, and P ′ _{0p —} 25 after translation are superimposed. In FIG. 9E, features 701, 711, and 721 in each pulse volume data overlap at substantially the same position. The synthesizing unit 540 can acquire the aligned volume data by synthesizing each piece of pulse volume data subjected to translation processing as shown in FIG. 9E. The aligned volume data corresponds to third synthesized volume data. “Alignment” refers to performing both misalignment correction processing (translation processing) and composition processing.

  For the region in which the pulse volume data is superimposed in this step, the synthesis method described in S240, the synthesis method that leaves only arbitrary pulse volume data, or the like can be applied.

  In this step, the composition can be performed after correcting the positional deviation of each pulse volume data based on the positional deviation amount accurately estimated using the synthesized volume data. Thereby, image data (positioned volume data) in which the influence of fluctuations in the relative positional relationship between the object during light irradiation and the photoacoustic wave receiver included in the synthesized volume data is suppressed is obtained. Can be acquired.

  Note that the above processing can be applied even when the receiving unit 200 does not move between light irradiations. That is, the above processing can be applied even when the photoacoustic apparatus does not include the driving unit 300. Also in this case, it is possible to acquire image data in which the influence of the change in the relative positional relationship between the object and the photoacoustic wave receiving unit during multiple light irradiations is suppressed.

[Example of misalignment correction considering rotation or deformation]
In this embodiment, the example in which translation arises as a fluctuation | variation of the relative positional relationship of a target object and a receiving part was demonstrated. However, the present invention can be similarly applied to a case where rotation or deformation occurs as the fluctuation.

  For example, when considering rotation, in S250, the position estimation unit 560 can estimate the position and rotation amount (position shift amount) of each synthetic volume data using the rotation amount as an argument in addition to the translation amount. Subsequently, in S260, the position estimation unit 560 can estimate the position and rotation amount (position shift amount) of each pulse volume data based on the position and rotation amount (position shift amount) of each composite volume data. . Subsequently, in S270, the position estimation unit 560 performs a third synthesis on each pulse volume data based on the estimated position and rotation amount, and then performs a third synthesis on the third synthesis volume. Data can be acquired. Note that only the rotation amount may be used as the positional deviation amount.

  For example, when considering deformation, the position estimation unit 560 estimates the displacement amount at S250 using as an argument the displacement amount (at least one of translation and rotation amount) at each point set in the composite volume data in S250. be able to. Subsequently, in S260, the position estimation unit 560 can estimate the displacement amount at each point of each pulse volume data based on the displacement amount at each point of each synthetic volume data. Subsequently, in S270, the position estimation unit 560 obtains the third synthesized volume data by performing the third synthesis after performing the deformation process (position shift correction process) on each pulse volume data based on the estimated displacement amount. can do. For example, the amount of displacement between synthesized volume data can be calculated by a technique that expresses deformation such as Free Form Deformation (hereinafter referred to as FFD) or Thin Plate Spline. Through these processes, high-quality third synthesized volume data can be acquired in consideration of higher-order fluctuations including deformation.

[Example of holding an object]
The photoacoustic apparatus may include an object holding unit 1000 that holds the object 900 as shown in FIG. In FIG. 10, an object 900 is a breast of a living body 1200 that is in a prone position on a bed 1100. The object holding unit 1000 is a member for suppressing the movement of the object 900. For example, as the material of the object holding unit 1000, polymethylpentene, polyethylene terephthalate, or the like can be used. As shown in FIG. 10, when the object 900 is irradiated with the light 130 via the object holding unit 1000, the object holding unit 1000 may be transparent to the light 130. The object holding unit 1000 may be configured such that the holding surface of the object holding unit 1000 and the outer shape of the object 900 substantially coincide.

  For example, when the movement of the object 900 is limited to a specific direction by the object holding unit 1000, the position estimation unit 560 may perform only the displacement correction in the specific direction. That is, the positional deviation correction may be performed without considering the positional deviation other than the direction in which the positional deviation is suppressed by the object holding unit 1000. Thereby, it is possible to reduce the processing amount required for the positional deviation correction.

  In addition, although the example which images the breast in the state where the living body 1200 is in the prone position is described in FIG. 10, the photoacoustic apparatus according to the present embodiment is not limited to the prone position, and images the target object 900 in all positions. Can do.

[Display example of pulse volume data]
In the present embodiment, an example is described in which acquisition of pulse volume data is started after measurement of photoacoustic waves by all-light irradiation is completed. However, pulse volume data may be acquired sequentially each time light irradiation is performed. In the latter case, the acquired pulse volume data may be sequentially displayed on the display unit 600. As a result, the user can check the acquired pulse volume data before completing all measurements. At this time, the region where the pulse volume data is superimposed may be synthesized by the synthesis method described in S270.

[Example of position estimation based on MIP image]
In S250, after converting the three-dimensional image data into the two-dimensional projection data, the position of each synthesized volume data after the positional deviation with respect to the reference position may be estimated. Hereinafter, an example of the process will be described.

The projection data acquisition unit 550 acquires MIP data as projection data obtained by projecting the synthesized initial sound pressure distribution data P _{0g —} j (x, y, z) in the X direction, the Y direction, and the Z direction. . The MIP data projected in the X direction is two-dimensional spatial distribution information represented by the Y axis and the Z axis, and is expressed as I _{xg —} j (y, z). The MIP data projected in the Y direction is two-dimensional spatial distribution information represented by the Z axis and the X axis, and is expressed as I _{ig —} j (z, x). The MIP data projected in the Z direction is two-dimensional spatial distribution information represented by the X axis and the Y axis, and is expressed as I _{zg —} j (x, y). In addition, the value at each position of each MIP data is expressed by a function expression such as I _{xg —} j (y, z), I _{yg —} j (z, x), I _{zg —} j (x, y).

  Note that projection methods other than MIP images may be employed as long as the three-dimensional image data can be converted into two-dimensional image data. For example, instead of the MIP image, a minimum intensity projection (MinP) image may be generated and used. Further, projection data may be acquired by adding a plurality of slides in the projection direction.

Next, the position estimating unit 560, XY plane, YZ plane, for each of the ZX _plane, obtains the similarity between the MIP data MIP data and _P 0g _{_k2} of P 0g _k1. That is, the position estimation unit 560 acquires the similarity as shown in Expressions (5) to (7).
FX — k (y, z) = f _simil (I _{xg —} k, y, z) (5)
_{FY_k (x, z) = f} simil (I yg _k, x, z) ··· (6)
FZ_k (x, y) = f _simil (I _{zg —k} , x, y) (7)
Here, FX_k (y, z) is obtained by translating the relative position of the other MIP data with respect to one MIP data constituting the pair R_k by (y, z) for the MIP data represented by the YZ plane. It is a function for calculating similarity. FY_k (x, z) is a function related to the ZX plane, and FZ_k (x, y) is a function related to the XY plane. Note that the method described in S250 can be used as a method for calculating the similarity.

Next, the position estimating unit 560, as shown in equation (8) ~ (10), YZ plane, ZX plane, for each of the XY plane, the function value is _maximized, translation of _P 0 g _k for P 0g _k1 The quantities MX_k, MY_k, MZ_k are calculated.

例えば、式（１１）に示すように、並進量ＭＸ＿ｋ，ＭＹ＿ｋ，ＭＺ＿ｋの各座標軸の成分の平均値を、類似度が最大となる、Ｐ_０ｇ＿ｋ１に対するＰ_０ｇ＿ｋの三次元の並進量Ｍ＿ｋの各成分値とする。

For example, as shown in equation (11), translation amount MX_k, MY_k, the average value of the components of each coordinate axis of MZ_k, similarity is the _maximum, the three-dimensional translation amount M_k of _P 0 g _k for P 0g _k1 Each component value.

続いて、位置推定部５６０は、式（１１）に示す並進量Ｍ＿ｋを用いて、Ｓ２５０で説明したように、式（４）に示すコスト関数が最小化したときの各合成ボリュームデータの位置を推定することができる。

Subsequently, the position estimation unit 560 uses the translation amount M_k shown in Expression (11) to determine the position of each synthetic volume data when the cost function shown in Expression (4) is minimized as described in S250. Can be estimated.

  With the above processing, the position of each synthetic volume data with respect to the reference position can be acquired based on the two-dimensional image data converted from the three-dimensional image data. By converting the 3D image data to the 2D image data, the position of the synthesized volume data after the positional deviation can be acquired with a lower calculation cost compared to the case of performing the processing with the 3D image data as it is.

[Example of position correction for received position information]
The photoacoustic apparatus according to the present embodiment may correct the position information of each receiving element at the time of each light irradiation, which is used to acquire the initial sound pressure distribution data, based on the amount of positional deviation corresponding to each light irradiation. . That is, the photoacoustic apparatus according to the present embodiment may correct photoacoustic wave reception position information at the time of each light irradiation. The process for correcting the positional deviation of the received position information will be described in detail according to the process flowchart shown in FIG. Steps similar to those shown in FIG. 3 are given the same reference numerals, and descriptions thereof are omitted. (S280: Step of correcting position information of receiving element)
First, the reconfiguration unit 520 acquires position information of each receiving element when the positional deviation is not considered. For example, the reconstruction unit 520 can acquire the position information when the positional deviation is not taken into consideration by reading the position information of each receiving element at the time of each light irradiation stored in the storage unit 510 in advance. Also, the reconstruction unit 520 acquires the position information of each receiving element when the positional deviation is not taken into account by receiving the position information of the receiving unit 200 from the position sensor provided in the driving unit 300 using light irradiation as a trigger. May be.

  Subsequently, the reconstruction unit 520 corrects the position corresponding to the positional information of each receiving element when the positional deviation in each light irradiation is not taken into account by the positional deviation amount of the pulse volume data obtained in S260 (translation processing). To do. Thereby, the reconstruction part 520 can acquire the positional information on each receiving element in which the positional deviation is corrected in each light irradiation. In other words, the reconstruction unit 520 acquires the positional information after the positional deviation of the receiving element based on the positional deviation amount of the pulse volume data obtained in S260.

(S290: Step of acquiring volume data based on the corrected position information of the receiving element)
Based on the electrical signal group of the plurality of electrical signal groups stored in the storage unit 510 and the positional information after the positional shift of each receiving element acquired in S280, the reconstruction unit 520 performs image processing as volume data. Get the data. In this step, as described in S210, the reconstruction unit 520 reconstructs a region smaller than the entire imaging region from the electrical signal group corresponding to one light irradiation, and this is used for all the light irradiations. One volume data may be generated by repeating. In addition, the reconstruction unit 520 may generate one volume data by reconstructing the entire imaging region from the electrical signal group corresponding to any light irradiation.

  In this embodiment, without generating pulse volume data in S210, a desired combination of electrical signal groups is selected in S220, and synthesized volume data is generated in S230 using the selected electrical signal group. Also good. In this case, the electrical signal group may be selected by a method similar to the method of selecting the pulse volume data described in S220.

[Examples other than photoacoustic devices]
As mentioned above, although one Embodiment of this invention was described in the example using a photoacoustic apparatus, the application range of this invention is not restricted to this. The present invention can be applied to any apparatus that acquires position information of a plurality of image data based on a plurality of image data. For example, the position information acquisition method of the present invention may be applied to a plurality of ultrasonic image data obtained by an ultrasonic diagnostic apparatus that acquires image data by transmitting and receiving ultrasonic waves. In addition, the present invention is not limited to image data obtained using acoustic waves, and a plurality of images obtained using light by, for example, a diffuse optical tomography (DOT) device or an optical interference tomography (OCT) device. The position information acquisition method of the present invention may be applied to data. In addition, the position information acquisition method of the present invention may be applied to a plurality of image data obtained using X-rays by an X-ray fluoroscopic image acquisition apparatus, an X-ray tomogram acquisition apparatus, or the like.

[Other Examples]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

DESCRIPTION OF SYMBOLS 100 Light irradiation part 200 Reception part 500 Image data acquisition part

Claims (20)

A light irradiation unit;
A receiving unit that outputs an electrical signal by receiving a photoacoustic wave generated by irradiating an object with light emitted from the light emitting unit;
An image data acquisition unit that acquires image data of the object based on the electrical signal group;
The light irradiation unit irradiates the object with light a plurality of times,
The receiving unit outputs a plurality of electrical signals corresponding to the plurality of times of light irradiation by receiving photoacoustic waves generated by the plurality of times of light irradiation,
The image data acquisition unit
Based on the plurality of electrical signals, obtain a plurality of image data of the object corresponding to the plurality of times of light irradiation,
Selecting from the plurality of image data first two or more image data corresponding to two or more light irradiations performed in a first period;
First image data is obtained by first combining the first two or more image data,
The combination of image data is different from the first two or more image data from the plurality of image data, and corresponds to two or more light irradiations performed in a second period different from the first period. Select the second two or more image data,
Second image data is obtained by second combining the second two or more image data,
Based on the first image data and the second image data, the positional information after the positional deviation of the first image data and the second image data is obtained,
A photoacoustic apparatus, wherein positional information after positional deviation of the plurality of image data is acquired based on positional information after positional deviation of the first image data and the second image data. The image data acquisition unit acquires third image data by third combining the plurality of image data arranged at a position corresponding to the position information after the positional shift of the plurality of image data. The photoacoustic apparatus according to claim 1. The image data acquisition unit selects, from the plurality of image data, the first two or more image data corresponding to two or more continuous light irradiations performed in the first period. The photoacoustic apparatus according to claim 1, wherein: 4. The image data acquisition unit according to claim 1, wherein the image data acquisition unit selects the first two or more image data based on an image quality of the first image data. 5. Photoacoustic device. 5. The light according to claim 1, wherein the image data acquisition unit selects the first two or more image data based on image quality of the plurality of image data. Acoustic device. An object holding unit for holding the object so as to suppress displacement of the object in a specific direction;
The image data acquisition unit does not consider the positional deviation of the first image data and the second image data in the specific direction, and the positional deviation of the first image data and the second image data. The photoacoustic apparatus according to any one of claims 1 to 5, wherein subsequent position information is acquired. 2. The image data acquisition unit acquires position information after displacement of at least one of translation, rotation, and deformation of the first image data and the second image data. 7. The photoacoustic apparatus according to any one of items 1 to 6. The image data acquisition unit acquires position information after positional deviation of the plurality of image data by performing interpolation processing on positional information after positional deviation of the first image data and the second image data. The photoacoustic apparatus according to claim 1, wherein: A light irradiation unit;
A receiving unit that outputs an electrical signal by receiving a photoacoustic wave generated by irradiating an object with light emitted from the light irradiation unit;
An image data acquisition unit that acquires image data of the object based on the electrical signal;
The light irradiation unit irradiates the object with light a plurality of times,
The receiving unit outputs a plurality of electrical signals corresponding to the plurality of times of light irradiation by receiving photoacoustic waves generated by the plurality of times of light irradiation,
The image data acquisition unit
Selecting a first two or more electrical signals corresponding to two or more light irradiations performed in a first period from the plurality of electrical signals;
Obtaining first image data of the object based on the first two or more electrical signals;
From the plurality of electrical signals, the combination of electrical signals differs from the first two or more electrical signals, and corresponds to two or more light irradiations performed in a second period different from the first period. Select a second two or more electrical signals to
Obtaining second image data of the object based on the second two or more electrical signals;
Based on the first image data and the second image data, the positional information after the positional deviation of the first image data and the second image data is obtained,
A photoacoustic apparatus, wherein a plurality of positional deviation amounts corresponding to the plurality of times of light irradiation are acquired based on positional information after positional deviation of the first image data and the second image data. The image data acquisition unit
Based on the plurality of positional deviation amounts, obtain positional information after positional deviation of the receiving unit corresponding to the multiple times of light irradiation,
10. The photoacoustic apparatus according to claim 9, wherein third image data is acquired based on the plurality of electrical signals and position information after the receiving unit is displaced. The image data acquisition unit
Based on the plurality of electrical signals, obtain a plurality of image data of the object corresponding to the plurality of times of light irradiation,
Based on the plurality of positional deviation amounts, obtain positional information after positional deviation of the plurality of image data,
The third image data is obtained by combining the plurality of image data arranged at positions corresponding to position information after positional deviation of the plurality of image data. Photoacoustic device. The image data acquisition unit
First light irradiation and second light corresponding to the first image data and the second image data based on the positional information after the positional deviation of the first image data and the second image data. Obtaining a first misregistration amount and a second misregistration amount corresponding to the irradiation;
The plurality of misregistration amounts corresponding to the plurality of times of light irradiation are obtained by performing interpolation processing on the first misregistration amount and the second misregistration amount. 11. The photoacoustic apparatus according to any one of 11 above. An object holding unit for holding the object so as to suppress displacement of the object in a specific direction;
The said image data acquisition part does not acquire the positional offset amount to the said specific direction of the said 1st image data and the said 2nd image data, The any one of Claim 9 to 12 characterized by the above-mentioned. Photoacoustic device. The photoacoustic apparatus according to claim 13, wherein the image data acquisition unit acquires a displacement amount of the first image data and the second image data in a direction other than the specific direction. . 15. The image data acquisition unit according to claim 9, wherein the image data acquisition unit acquires a displacement amount of at least one of translation, rotation, and deformation of the first image data and the second image data. The photoacoustic apparatus of any one of Claims. The said image data acquisition part selects said 1st 2 or more electrical signal based on the image quality of said 1st image data, The any one of Claim 9 to 15 characterized by the above-mentioned. Photoacoustic device. The light according to any one of claims 9 to 16, wherein the image data acquisition unit selects the first two or more electrical signals based on image quality of the plurality of image data. Acoustic device. The image data acquisition unit selects, from the plurality of image data, the first two or more electrical signals corresponding to two or more continuous light irradiations performed in the first period. The photoacoustic apparatus according to any one of claims 9 to 17, wherein: The photoacoustic apparatus according to any one of claims 1 to 18, further comprising a drive unit that moves the receiving unit during a period in which the light irradiation is performed a plurality of times. The image data acquisition unit acquires the first image data and the second image data so that the first image data and the second image data overlap each other. The photoacoustic apparatus according to any one of 1 to 19.

Images