JP2013005871A - Subject information acquisition apparatus, display control method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for allowing a user to identify image quality in each region of a reconstructed image generated based on an acoustic wave signal.SOLUTION: A subject information acquisition apparatus for acquiring characteristic information in a subject using the acoustic wave signal output from a detection element detecting an acoustic wave propagated in the subject includes: a characteristic information acquisition unit for acquiring the characteristic information in each point of interest in the subject using the acoustic wave signal; an accuracy information generation unit for generating information showing a difference in accuracy between the characteristic information using acoustic wave detection information as a condition relating to the detection of the acoustic sound wave; and a display information generation unit for generating display information capable of identifying a difference in accuracy between the characteristic information using the information showing the characteristic information in the each point of interest and a difference in accuracy, and making a display unit display the display information.

Description

  The present invention relates to a subject information acquisition apparatus, a display control method, and a 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 good image quality in which noise and artifacts are further reduced.

  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、ｐ_０（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 a position, t is time, p (r, t) is a temporal change in sound pressure, p ₀ (r) is an initial sound pressure distribution, and c is a sound speed. δ (t) is a delta function representing the shape of the optical pulse.

ここで、Ω_０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Ｓ_０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 that is typically used in the PAT image reconstruction method will be described below. By analyzing the photoacoustic wave equation of Expression (1) on the frequency space, the inverse problem for obtaining p ₀ (r) can be accurately solved. The result is UBP in time 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（ｒ_０，ｔ）は投影データ、ｄΩ_０は任意の観測点Ｐに対する検出器ｄＳ_０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ｐ_０（ｒ）を得ることができる。 Furthermore, when the formula is easily modified, the following formula (3) is obtained.

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（ｒ_０，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 sound field approximation), the following equation (6) is obtained.

At this time, b (r ₀ , t) becomes the following formula (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 the equation (3). It is known that the initial sound pressure distribution p ₀ (r) is obtained by projection (see Non-Patent Documents 1 and 2).

  However, equation (1), which is a photoacoustic wave equation used to obtain equation (3), is “constant sound velocity”, “measurement from all directions”, “impulse 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. Under such circumstances, a practical measurement apparatus using the PAT technique is an apparatus for detecting an acoustic wave from a specific direction of a subject using a probe (detector) of a limited size. Often composed.

  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.

  The probe is not limited to a flat plate, but can be moved on a flat surface or curved surface where the relative positional relationship with the subject is obvious, such as a surface that is in contact with the subject or parallel to the surface of the subject. In some cases, an acoustic wave may be acquired by arranging. An area where an acoustic wave is received while recording information on the position of an element arranged on the probe on such a surface is referred to as a reception area in this case, and an image using the acoustic wave detected in the entire reception area is used. It can also be reconfigured.

  Here, the reception area is an area occupied by the receiving surface of the probe on which the element is arranged due to movement of the probe, and is an area where the acoustic wave can be received by the element of the probe at different times. is there. The receiving area is not limited to a flat surface depending on the shape of the receiving surface of the probe and the position of the arranged element, and the same can be applied to a curved surface.

  When an acoustic wave is received while moving the probe within the reception area, the position of the element of the probe changes. However, if an acoustic wave detected for each element is regarded as an acoustic wave detected at an element position on the reception area at the time of detection, it can be regarded as an acoustic wave detected at each position on the reception area. That is, it can be treated as an acoustic wave detected by a probe in which an element is arranged on the receiving surface of the receiving area size. In the case of photoacoustic waves, the probe is moved according to the irradiation position and irradiation time of light, and the acoustic wave signals of the entire receiving area are collected by collecting the acoustic wave signals detected at each element position on the receiving area. Can be detected.

  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.

Here, an effective acoustic wave signal corresponding to the directivity of the element of the acoustic wave detector will be described.
An effective acoustic wave signal in this specification is an acoustic wave signal based on an acoustic wave detected at a practical value or more determined by the characteristics and sensitivity of the probe element. In a general ultrasonic probe, an acoustic wave from a sound source that falls within a conical range determined by a directivity angle that is ½ of the sound pressure from the central axis of the element is made effective. Therefore, in the embodiment of the present invention, it will be described as an acoustic wave signal that is effective when an acoustic wave is detected by a sound source within the directivity range of such an element. However, the directivity angle is not necessarily limited to an angle at which the sound pressure is halved. In the description of the present specification, an acoustic wave signal based on detection of an acoustic wave having a sound source in a range determined as effective for each element from the characteristics and sensitivity of each element is regarded as an effective acoustic wave signal. The range determined by the directivity angle will be described as the directivity range of the element.

  When detecting an acoustic wave by moving an acoustic wave detector along a flat plate, the orientation that the probe can take with respect to the subject is limited, so the probe is placed around the entire area to be imaged. Cannot be contacted. As a result, an acoustic wave signal different from the assumption of the photoacoustic wave equation is used because a signal based on the acoustic wave detected at the element position on the receiving area of the probe in a limited orientation with respect to the subject is used. Image reconstruction by group.

  Furthermore, the area to be imaged is an area for image reconstruction, that is, a reconstruction area.In other words, the number of effective acoustic wave signals at each point of the reconstruction area and the condition of the position relative to the detection position However, the conditions are not necessarily the same. That is, there are regions having different conditions regarding the effective acoustic wave signal in the reconstruction region, and regions having different image quality of the reconstructed image are generated due to the difference in the conditions.

  In the display of an ultrasonic image, for example, in Patent Document 2, when the signal intensity for each element of the probe is determined and a map of elements having a signal intensity equal to or greater than a predetermined value or a three-dimensional image is generated, C An example of displaying a mode image is disclosed. However, the intensity of the transmitted / received ultrasonic signal is determined and displayed, and no display capable of identifying regions having different image quality of the reconstructed image of the photoacoustic wave is performed.

US Patent No. 5840023 JP 2007-31980 A

PHYSICAL REVIEW E 71, 016706 (2005)

However, as in the prior art, the acoustic wave used for the reconstruction process at one point in the area to be reconstructed is limited to the acoustic wave detected at the element position on the reception area. Depending on the characteristics of the elements on the reception area, there are positions where an acoustic wave effective for the reconstruction process cannot be detected depending on the relative position from one point that is the target of the reconstruction process. In general, an acoustic wave signal detected by an element of a probe (detector) is handled as an effective acoustic wave signal when a sound source exists in a region that falls within a range based on directivity of each element. Therefore, in image reconstruction,
The detection position information of the acoustic wave signal on the reception area for one point in the reconstruction target area and the acoustic wave signal group effective for each point are extracted.

  For example, when the receiving area is a plane, a circular area determined by the intersection of a directivity angle straight line and a plane parallel to the receiving area from the points in the reconstruction area, centered on the leg of the perpendicular line that extends down to the receiving area. Determined. This area is an effective acoustic wave detection area that is an area where an element for detecting an effective acoustic wave can exist. At a point in the reconstruction area where the effective acoustic wave detection area is located within the reception area, the number of effective acoustic wave signals for each detection position on the reception area increases. However, since points in the reconstruction area that are close to the end of the reception area do not fit in the reception area, the number of effective acoustic signals for each detection position is limited, resulting in a difference in image quality.

  In addition, even if the number of effective acoustic wave signals is the same from the points in the reconstruction area, artifacts are generated in the biased direction when the detection position of the acoustic wave signal used for reconstruction is in a biased direction. Cheap. Since the image reconstruction processing uses the acoustic wave signal group received by the element at the asymmetrical position, the difference from the assumption of the photoacoustic wave equation becomes large.

  Therefore, in the PAT image reconstruction to which the conventional technique is applied, an artifact is likely to occur when the sound source of the photoacoustic wave is on the normal line of the end portion outside the vicinity of the center of the reception area. A larger artifact is generated in the reconstructed image of the photoacoustic wave sound source in the vicinity of the outer edge of the reception area or on the normal line to the parallel plane further outside the reception area.

  These conditions are different depending on the distance between the receiving surface of the probe and one point on the space where image reconstruction is performed in the subject. That is, the number of points that fall within the range of the directivity angle of the receiving element is reduced from one point on the space close to the receiving area.

  From the above, reconstructed images reconstructed using acoustic wave signal groups detected at positions that do not match the assumptions of the photoacoustic wave equation have regions with different image quality. In the image display, it is difficult to identify this area. It is an object of the present invention to display information that can identify regions of different image quality based on acoustic wave signals used for reconstruction processing that cannot be identified by displaying a reconstructed image.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for enabling a user to identify the image quality for each region of a reconstructed image generated based on an acoustic wave signal. .

  The present invention employs the following configuration. That is, a subject information acquisition device that acquires characteristic information in a subject using an acoustic wave signal output from a detection element that detects an acoustic wave propagated in the subject, the acoustic wave signal being used. Generating information indicating differences in accuracy of the plurality of characteristic information using a characteristic information acquisition unit that acquires characteristic information at each point of interest in the subject and acoustic wave detection information that is a condition relating to the detection of the acoustic wave Display information that can identify the difference in accuracy of the plurality of characteristic information using the accuracy information generation unit that performs, the characteristic information at each point of interest, and the information indicating the difference in accuracy, and displays the display information on the display unit And a display information generation unit for generating the object information.

The present invention also employs the following configuration. That is, a display control method for displaying characteristic information in a subject, using an acoustic wave signal output from a detection element that detects an acoustic wave propagated in the subject, at each point of interest in the subject A step of obtaining characteristic information, a step of generating accuracy information using the acoustic wave detection information that is a condition relating to the detection of the acoustic wave, and a step of generating information indicating a difference in accuracy of the plurality of pieces of characteristic information; A display information generating step for generating display information capable of identifying a difference in accuracy of the plurality of characteristic information using characteristic information and information indicating the difference in accuracy; and a step of displaying the display information. It is a display control method characterized by having.

  ADVANTAGE OF THE INVENTION According to this invention, the technique for enabling a user to identify the image quality for every area | region of the reconstruction image produced | generated based on the acoustic wave signal can be provided.

The figure which shows the functional block of an image information acquisition apparatus. The figure which shows the structure at the time of implement | achieving an information processing part by software. The figure which shows the structural example of the acoustic wave signal measurement part in an Example. The flowchart of an acoustic wave measurement, image quality determination, and a display process. The flowchart of a reconstruction and acoustic wave detection information storage process. The figure which shows the relationship between an attention point and the effective signal detection area | region on a receiving area. The figure which shows an example of an information display.

  Hereinafter, preferred embodiments of an image reconstruction method according to the present invention and an image information acquisition apparatus which is a subject information acquisition apparatus will be described in detail with reference to the accompanying drawings. However, the scope of the invention is not limited to the illustrated examples. In the present invention, an image indicating the characteristic information in the subject is acquired as an image. Therefore, it can be said that the image information acquisition device of the present invention is a subject information acquisition device.

  The image reconstruction method according to the present embodiment is an image reconstruction method in which an initial sound pressure distribution is obtained from detected acoustic waves and a three-dimensional reconstruction image is generated. Moreover, the image information acquisition apparatus which implements the image reconstruction method according to the present embodiment is a photoacoustic wave diagnostic apparatus. The photoacoustic wave diagnostic apparatus generates a three-dimensional reconstructed image based on an acoustic wave signal obtained by detecting an acoustic wave generated by irradiating light. In the present embodiment, a plurality of acoustic wave signal groups having different numbers and positions of acoustic wave signals for each element are extracted from the acoustic wave signals detected by one imaging to generate a plurality of three-dimensional reconstructed images. To do.

  In the present invention, imaging means receiving acoustic waves propagated from within the subject and acquiring characteristic information within the subject. The characteristic information indicates information reflecting object information such as the sound pressure of an acoustic wave, the light energy absorption density derived from the sound pressure, the absorption coefficient, and the concentration of a substance constituting the tissue. The concentration of the substance is, for example, oxygen saturation or oxy / deoxyhemoglobin concentration. Further, the characteristic information may be acquired as numerical data, or may be acquired as image data indicating distribution information (characteristic information distribution) of each position (each attention point) within the subject. That is, the characteristic information may be acquired as image data indicating distribution information reflecting an absorption coefficient distribution, an oxygen saturation distribution, and the like in the subject.

  In addition, in one imaging | photography which acquires the characteristic information in a subject, light irradiation may be performed in multiple times. At that time, acoustic wave detection information such as the number and position of acoustic wave signal groups used for acquiring (reconstructing) the characteristic information of each point in the region for generating the three-dimensional reconstructed image indicating the characteristic information distribution is recorded. . Then, the superiority or inferiority of the image quality of the reconstructed image at each point is determined based on the acoustic wave detection information. Then, the area information based on the determination result is recognized and displayed together with the reconstructed image. In the present invention, the image quality means the accuracy of the acquired characteristic information. “Accuracy of characteristic information” refers to the characteristics of features of an image when image data having characteristics correlated with predetermined characteristics in the subject is generated based on all or part of the acquired characteristic information. The accuracy of the correlation between the quantity and the feature quantity of the feature in the subject is also included.

(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. The photoacoustic wave diagnostic apparatus of the present invention is an object information acquisition system that receives an acoustic wave propagated in a subject and acquires characteristic information in the subject. 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 (subject information acquisition apparatus) 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.

(Acoustic wave detection information)
The acoustic wave signal measurement unit 1100 transmits acoustic wave detection information detected by each element of the 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 ultrasonic waves. The acoustic wave detection information is a reception signal (acoustic wave signal) output from a detection element of an acoustic wave detector that has received an acoustic wave, or a position of an element disposed on the reception surface of the acoustic wave detector 1105. Information on the element, information on the element such as information on sensitivity and directivity is applicable. 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 generates the acoustic wave and the compression when the subject is compressed is also acquired as a condition when acquiring the acoustic wave signal.

  Here, the information regarding the position of the element may be any information as long as it is information that can identify the subject or the positional relationship between the element to be reconstructed for image reconstruction and the element. 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, There is information such as relative position of each. In particular, when the acoustic wave detector is moved, it can be handled as information on the element position on the reception area when the acoustic wave is received while the element on the reception surface of the acoustic wave detector is moving.

  Information acquired for each element is transmitted as information associated with an element identifier of the acoustic wave detector 1105 or position information on the reception area. When the acoustic wave detector does not move, there is a one-to-one correspondence between the element identifier and the position on the reception area. When an acoustic wave is received while the acoustic wave detector is moving, the elements of the acoustic wave detector are received at a plurality of positions, and are therefore associated with each element position on the reception area where the acoustic wave is detected.

  As the acoustic wave detection information, an acoustic wave signal may be transmitted, or information on the acoustic wave signal after correction such as element sensitivity correction and gain correction may be transmitted. In the photoacoustic wave diagnostic apparatus, the present invention can be implemented even by a method of irradiating light multiple times in one imaging process and transmitting an average of the obtained acoustic wave signals as an acoustic wave signal. .

  The acoustic wave detection information includes information that does not hinder the implementation of the present invention even as a static constant according to the configuration of the embodiment. Such information may be stored in advance in the main memory 102 of the information processing unit 1000 or the magnetic disk 103 (both of which are shown in FIG. 2) and used when executing the image reconstruction process. On the other hand, 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 detection information.

  For example, consider a case where information regarding the position of an element on the reception surface of the acoustic wave detector 1105 is transmitted. In this case, after the element identifier and the position information of the acoustic wave detector are transmitted from the acoustic wave signal measuring unit 1100 to the information processing unit 1000, the acoustic wave detector and the element stored in the information processing unit 1000 in advance are stored. It is also possible to implement the present invention with reference to relative position information.

(Information Processing Department)
The information processing unit 1000 performs a three-dimensional image reconstruction process using the acoustic wave detection information obtained from the acoustic wave signal measurement unit 1100. Further, the generated three-dimensional reconstructed image and acoustic wave detection information are generated, and determination result information and area information in the present invention are generated. Furthermore, display information is generated using these. Then, by displaying the reconstructed image based on the display information in such a way that the determination result can be recognized, a display that can identify regions having different image quality is performed. That is, a display that can identify the difference in accuracy of the acquired characteristic information (including the degree of correlation between the feature of the subject and the feature on the image) is performed.

Next, functional blocks of the information processing unit 1000 will be described.
In FIG. 1, the information processing unit 1000 includes an acoustic wave information acquisition unit 1001, a reconstruction processing unit 1002, an image quality determination unit 1003, an area information generation unit 1004, a display information generation unit 1005, and a display unit 1006.

The acoustic wave information acquisition unit 1001 acquires the acoustic wave detection information transmitted from the acoustic wave signal measurement unit 1100 and transmits the acoustic wave detection information to the reconstruction processing unit 1002.
In this embodiment, a procedure for performing image reconstruction using acoustic wave detection information transmitted from the acoustic wave signal measurement unit 1100 will be described. However, the embodiment of the present invention can be implemented without limiting the means by which the acoustic wave information acquisition unit 1001 acquires acoustic wave detection information. The acoustic wave signal measurement unit 1100 is not necessarily required, and for example, acoustic wave detection information equivalent to data transmitted by the acoustic wave signal measurement unit 1100 may be acquired from the server device via a network. It is also possible to read out from a storage device or storage medium in the acoustic wave information acquisition unit 1001 and implement.

The reconstruction processing unit 1002 performs three-dimensional image reconstruction using only the selected acoustic wave signal resulting from the acoustic wave from the attention point for each attention point in the region to be image reconstructed, and obtains characteristic information. The three-dimensional image shown is generated. Then, a three-dimensional reconstructed image (volume data) based on the acoustic wave detection information is generated from the characteristic information for each target point. That is, in the present invention, the reconstruction processing unit functions as a characteristic information acquisition unit.
Here, as long as the image reconstruction process of the reconstruction processing 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.

  In the case of a photoacoustic wave diagnostic apparatus, a value indicating a light absorption coefficient distribution in a subject is calculated as characteristic information, and a reconstructed three-dimensional image is generated. Since the degree of light absorption varies within the subject depending on the wavelength of 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 signal measuring unit 1100 as acoustic wave detection information, or information stored in advance on the magnetic disk 103 is used. Also good. Furthermore, it is possible to specify by an operation instruction from the input unit 106 (FIG. 2) according to an operator instruction. Examples of information used in the reconstruction process include selection of an algorithm for the reconstruction process, information corresponding to parameters of the reconstruction process such as the number of voxels output in the reconstruction process, and the pitch.

The generated reconstructed image is sent from the reconstruction processing unit 1002 to the display information generating unit 1005. Further, it is also sent to the image quality determination unit 1003 as necessary.
Also, the reconstruction processing unit 1002 generates acoustic wave detection information used for the reconstruction process.

The acoustic wave detection information is recorded by associating the acoustic wave detection information used in the reconstruction process with each point in the reconstruction area. The acoustic wave detection information can include any information as long as the acoustic wave detection information affects the image quality of the reconstructed image generated by the reconstruction process. For example, the number of acoustic wave signals used at each point where reconstruction processing is performed, the reception position, the number of acoustic wave signals received within the directivity range of the elements of the acoustic wave detector, the reception conditions of acoustic wave signals, etc. It is done. Any information that can be used by the image quality determination unit 1003 to determine reconstructed image quality (that is, the degree of superiority or inferiority of the characteristic information accuracy) can be included in the acoustic wave detection information. Furthermore, in the case of a photoacoustic wave, the wavelength of the light that generated the acoustic wave, illumination conditions, and the like can be included.

  As an example of a method of recording acoustic wave detection information, there is a method of recording as information associated with voxels in volume data output by reconstruction processing. The acoustic wave detection information may be recorded in association with information on the size and shape of the volume data and position information of each voxel in the volume data.

  The generated acoustic wave detection information is sent from the reconstruction processing unit 1002 to the image quality determination unit 1003.

  The image quality determination unit 1003 determines the image quality of the reconstructed image generated by the reconstruction processing unit 1002. In the present invention, the image quality determination unit 1003 is a characteristic information accuracy determination unit. The image quality determination in the present invention refers to characteristic information (reconstruction) in a subject generated by the reconstruction processing unit 1002 based on an acoustic wave signal. This is to determine the accuracy of the image. If the volume data is output by the reconstruction process, the accuracy of the characteristic information is determined by determining the quality of the voxel value and the level of validity. Therefore, when displaying a reconstructed image, it is determination of image quality. However, when the quality of the voxel value, which is the calculated value of the reconstruction process, is determined, this is synonymous with determining the quality of the characteristic information indicated by the voxel value and the level of validity according to the purpose. In the present embodiment, including these, the determination of the accuracy of the characteristic information will be described as the determination of the image quality.

  Here, even if the acoustic wave detection region is a three-dimensional region, if the reconstruction process is performed only on a region on an arbitrary plane, the validity of the pixel value on the two-dimensional reconstruction image is determined. Will do. In the present embodiment, the description is for a three-dimensional area, but the embodiment of the present invention can also be implemented in a two-dimensional area.

  The image quality determination unit 1003 determines the image quality based on the acoustic wave detection information of each point in the reconstruction area recorded by the reconstruction processing unit 1002. However, a determination method that refers to the reconstructed image may be performed as necessary.

  As an image quality determination method based on acoustic wave detection information, there is a determination method based on the number of acoustic wave signals used in reconstruction processing. In the reconstruction processing algorithm, a larger number of acoustic wave signals reduces artifacts and improves image quality. Further, at each point in the reconstruction area, it is possible to determine the maximum number of acoustic wave signals in consideration of the directivity of the element as an area having a good image quality. Furthermore, each point in the reconstruction area is selected based on the directivity of the element, and an acoustic wave signal that is available in the reception area is selected and used by selecting an acoustic wave signal in a symmetric position on the reception area. Artifacts can be suppressed. In the reconstruction area, an area occupied by such points can be determined as an area with good image quality.

  As an example of a determination method that refers to a reconstructed image, there is a method that uses a pixel value in the reconstructed image or a feature amount extracted from the reconstructed image for determination. As an example of the feature amount of the reconstructed image used for the image quality determination, a distribution of pixel values or a feature of a shape with a pixel value equal to or greater than a predetermined threshold can be used. In addition, the degree of correlation with each point of the adjacent cross-sectional image can be used at each point on each cross-sectional image when the three-dimensional reconstructed image is divided into cross-sectional images. When the image quality determination unit 1003 performs a determination method that refers to the reconstructed image, both the acoustic wave detection information and the reconstructed image are sent from the reconstruction processing unit 1002 to the image quality determination unit 1003.

  The determination result of the image quality determination unit 1003 is sent to the region information generation unit 1004 as determination result information associated with each point in the reconstructed image.

  As an example of the determination result information, there are a method of recording the quality of the image quality of each point in the reconstructed image as a binary value, and a method of recording stepwise with a weighted numerical value. It can also be implemented by indicating the image quality of each point with information such as a mathematical expression indicating the shape and size information of the reconstructed image and the distribution of determination results in the reconstructed image. The determination result information may be information that can be used by the region information generation unit 1004 to generate region information that can identify a difference in image quality in the reconstructed image.

  The area information generation unit 1004 generates area information based on the determination result information sent from the image quality determination unit 1003. The area information is information for identifying areas with different image quality in the reconstructed image. In other words, the region information is accuracy information indicating the difference in accuracy of the characteristic information (including the degree of correlation between the feature of the subject and the feature on the image), and the region information generation unit can be said to be an accuracy information generation unit. . The area information generation unit 1004 refers to the determination result included in the determination result information, and divides the area for each area having the same image quality in the reconstructed image.

The area information may be information in any format as long as it can identify areas with different image quality in the reconstructed image, but is information associated with the image quality level. For example, position information or a mathematical expression indicating a boundary between regions having different image quality may be used. In this case, information regarding the boundary and information indicating the image quality level of the area delimited by the boundary are included.
When the reconstructed image is volume data, it may be information in which identifiers of voxel groups having the same image quality are grouped and associated with the image quality level. Further, it may be information indicating the level of image quality of an area separated from information specifying voxels near the boundary.

  The generated region information is sent from the region information generation unit 1004 to the display information generation unit 1005.

  The display information generating unit 1005 can identify the difference in image quality determined by the image quality determining unit 1003 based on the reconstructed image sent from the reconstruction processing unit 1002 and the region information sent from the region information generating unit 1004. Is generated. For example, a display image that shows only the distribution of a region with good image quality in the volume data of the reconstructed image may be generated separately from the display information of the reconstructed image and used as display information for identifying whether the image quality is good or bad.

  In addition, when displaying display information based on the reconstructed image, the display information is displayed by color-coding regions with different image quality based on the region information, changing the transparency, or superimposing the boundary line on the image indicating the characteristic information distribution. Can also be generated. Furthermore, there are also methods for generating, as display information, coordinates and mathematical formulas indicating boundaries and shapes of regions in the image based on the reconstructed image, annotations that promote region identification, character strings, and cross-sectional images.

  Here, any display information can be implemented as long as the display information based on the reconstructed image generated by the display information generation unit 1005 is display information 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 a photoacoustic wave diagnostic apparatus that performs image reconstruction based on photoacoustic waves, three-dimensional image information based on the absorption coefficient distribution value in the subject according to the wavelength of irradiation light can be obtained. By comparing the wavelength dependence specific to the substances (glucose, collagen, oxidized / reduced hemoglobin, etc.) constituting the living tissue with these values, the concentration distribution of the substances constituting the living body can be imaged. Furthermore, statistical information of each value can be displayed as a numerical value, a graph, a histogram, or the like. The display information generated by the display information generation unit 1005 includes generation of such information.

  The generated display information is sent from the facial expression information generation unit 1005 to the display unit 1006.

  The display unit 1006 is a graphic card for displaying the generated display information, and an information display device such as a liquid crystal display or a CRT display, and displays the display information sent from the display information generation unit 1005. The display unit may be included in the functional block of the acoustic wave measuring unit, or the display information may be transmitted and displayed on an external information display device.

  In the description of the image information apparatus that performs 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 can be implemented as one image information acquisition apparatus including the acoustic wave signal measurement unit 1100 and the information processing unit 1000. For example, a general ultrasonic diagnostic apparatus can be implemented with an apparatus configuration such as a modality having functions corresponding to the acoustic wave signal measuring unit 1100 and the information processing unit 1000 of the present invention.

  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, for example, a CRT display or a liquid crystal monitor, and displays an image based on data from the display memory 104.

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 types of data between the information processing unit 1000 and the outside, and includes an IEEE 1394, USB, 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.

(Acoustic wave signal measurement unit)
FIG. 3 is a diagram illustrating 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, light having a wavelength that is 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 (acoustic wave signal) of the photoacoustic wave obtained by the acoustic wave detector 1105, and converts the analog signal into 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 control of a light source such as a laser include control of the timing, waveform, intensity, etc. of laser irradiation. 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 light 1103 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 generated. The generated photoacoustic wave 1109 propagates through the subject and is emitted outside the subject. 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, press the subject with a plate such as a flat plate 1110, and detect the photoacoustic wave 1109 of the compressed subject. You may detect over a flat plate.

  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. Further, between the acoustic wave detector 1105 and the subject, an acoustic impedance matching agent such as gel or water (not shown) for suppressing reflection of acoustic waves may be used.

  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.

Here, in the method of moving the acoustic wave detector, the acoustic wave signal detected by the element at each position on the reception area can be regarded as the acoustic wave signal detected by the acoustic wave detector having the element arranged at that position. Any moving method may be used. For example, when the surface on which the acoustic wave detector elements are arranged is a rectangle, depending on the moving direction of the acoustic wave detector, the vertical or horizontal size of the surface on which the acoustic wave detector elements are arranged After moving the acoustic wave detector without a gap, it can be carried out by a method in which the acoustic wave is detected by stopping at each position.
By treating this acoustic wave signal group as an acoustic wave signal for each position of the element on the receiving area, it can be regarded as an acoustic wave detector having the same element pitch and the size of a moving element multiplied by a number. Can do.

  Note that the amount of movement of the acoustic wave detector is not necessarily the same size as the size of the surface on which the elements of the acoustic wave detector are arranged. In addition, even if the surface on which the element is arranged has another shape, the movement amount may be such that the area before the movement of the surface on which the element is arranged and the area after the movement contact or overlap each other. Further, the acoustic wave detector can be moved even if there is a gap in the reception area. For example, the representative value of the acoustic wave signal at each position on the reception area that received the acoustic wave is extracted or determined by a method such as calculating an average value, and finally the acoustic wave at each position on the reception area is determined. The acoustic wave detector may be moved so that the detection information is aligned. In this case, the acoustic wave signals may be aligned at each position corresponding to the element pitch when the acoustic wave detector is regarded as having a reception surface having a reception area size.

  Further, the acoustic wave detector may be moved such that the acoustic wave detection is continued while the acoustic wave detector is moved without being stationary. A method of extracting a representative signal from an acoustic wave signal group detected for each position and element position of the acoustic wave detector or taking an average value in a reception area corresponding to the moving range of the acoustic wave detector Thus, an acoustic wave signal at each position on the reception area is determined. By adjusting the speed and moving range of the acoustic wave detector, it can be regarded as an acoustic wave detector in which elements are arranged at an arbitrary pitch in a receiving area of an arbitrary size. Further, scanning control becomes easy and the scanning time can be shortened. Note that the apparent element pitch of the acoustic wave detector, that is, the pitch of the element position for detecting the acoustic wave in the reception area, is an arbitrary pitch different from the pitch of the element arranged on the acoustic wave detector. You can also

  When imaging is performed with the photoacoustic wave diagnostic apparatus having the configuration of the acoustic wave signal measurement unit 1100 in the present invention, an imaging region is instructed by the user via the input unit 106. Then, an acoustic wave signal necessary for the imaging area is acquired. The imaging area is an acquisition area of characteristic information that can acquire characteristic information in the subject, which is determined by the specifications of each apparatus, and is a three-dimensional area that is designated for each target imaging.

Any method may be used for inputting the imaging region as long as the acoustic wave signal measuring unit 1100 can identify the target imaging region. The coordinates of the vertices of the rectangular parallelepiped and mathematical formulas may be input within a range that can be photographed within the apparatus. The user designates a rectangular area on the camera image that captures the subject, projects the area onto the subject, and measures the depth direction of the subject to determine the three-dimensional area specified as the imaging area. A method etc. can also be implemented. In this case, a rectangular parallelepiped serving as an imaging region can be specified by photographing the subject through a transparent flat plate and measuring the thickness of the subject from the flat plate. In general, a rectangular parallelepiped region is used as volume data as three-dimensional data, but the imaging region is not necessarily a rectangular parallelepiped.

  In the implementation of the present invention, basically, in order to display the information of the three-dimensional area, it is assumed that the imaging area corresponds to the reconstruction area as it is, and the acoustic wave receiving area, that is, the acoustic wave detector is scanned. The scanning area for acquiring the acoustic wave is determined. However, based on the acquired acoustic wave detection information, it is also possible to set a reconstructed area of a different area and implement it on a reconstructed image of a different area. Furthermore, the area where the image quality determination process and the area information generation process of the present invention are performed on the reconstructed image can also be performed on different areas in the reconstructed image.

  When displaying a three-dimensional image on a display that performs two-dimensional display, after the display information generation unit performs some region limitation or image processing, the image is displayed on the display unit. Therefore, it is possible to display an image and image information for an area different from each of the imaging area, the reconstruction area, the reconstructed image, the image quality determination, and the area information.

(Implementation procedure)
Next, a specific display control method processing procedure executed by the information processing unit, which is the subject information acquisition apparatus of the present invention, will be described using the flowcharts of FIGS. 4 and 5. In the following embodiment, an acoustic wave is measured by the acoustic wave signal measurement unit 1100. A display control method for generating a reconstructed image based on an acoustic wave measured by the information processing unit 1000 and determining image quality, generating region information and display information, and displaying a cross-sectional image and a boundary line in the reconstructed image. An example will be described.

(Acoustic wave measurement)
FIG. 4A is a flowchart illustrating a procedure in which the acoustic wave signal measurement unit 1100 according to the present invention measures an acoustic wave and acquires an acoustic wave signal and acoustic wave detection information. In this embodiment, an example in which acoustic waves and acoustic wave detection information are acquired by the photoacoustic wave measurement apparatus shown in FIG. 3 will be described. However, the application of the present invention is not limited to the photoacoustic wave measuring apparatus. Any device can be applied as long as it can acquire an acoustic wave and generate an acoustic wave signal and acoustic wave detection information in order to generate information based on the acoustic wave.

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.
In step S <b> 402, the photoacoustic wave emitted from the subject 1107 is detected by the acoustic wave detector 1105. If a photoacoustic wave is detected, it will progress to S403.
In step S <b> 403, the control unit 1102 generates acoustic wave detection information including parameters at the time of imaging, an acoustic wave signal detected for each element of the acoustic wave detector 1105, and the like.

  Here, the acoustic wave detection information may include any information as long as it is information related to acoustic 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 detection information. Furthermore, the information etc. which match the acoustic wave signal with respect to the subject to the received acoustic wave signal can be included.

  The generated acoustic wave detection information is transmitted to the information processing unit 1000, and the acoustic wave detection information acquisition procedure in the present embodiment is completed.

(Reconstruction and storage of acoustic wave detection information)
In FIG. 5, the acoustic wave information acquisition unit 1001 acquires the acoustic wave detection information in the information processing unit 1000, and the reconstruction processing unit 1002 records the acoustic wave detection information used for the reconstruction processing while recording the acoustic wave detection information. 5 is a flowchart showing a procedure for generating a reconstructed image based on the image.

The flowchart of FIG. 5 starts when the acoustic wave information acquisition unit 1001 of the information processing unit 1000 acquires acoustic wave detection information.
In step S501, the acoustic wave information acquisition unit 1001 stores the acoustic wave detection information acquired from the acoustic wave signal measurement unit 1100 in the main memory 102 or a storage device such as the magnetic disk 103, and can be used by the reconstruction processing unit 1002. Like that. Then, acoustic wave detection information or information regarding the stored address is transmitted to the reconstruction processing unit 1002.

  In step S <b> 502, the reconstruction processing unit 1002 extracts one point on the unextracted space in the reconstruction area that is an area for executing the reconstruction process inside the subject as a point of interest. Here, the reconstruction area can also reconstruct an area different from the imaging area when the acoustic wave signal measurement unit 1100 acquires the acoustic wave. An area smaller than the imaging area may be used as the reconstruction area. Alternatively, since the acquired acoustic wave signal includes an acoustic wave having a sound source in a region other than the imaging region, the display method of the present invention can be implemented even if a region larger than the imaging region is used as a reconstruction region. it can.

  In step S503, the reconstruction processing unit 1002 calculates an effective acoustic wave detection area that is an area in which an effective acoustic wave on the reception area with respect to the point of interest can be detected. The effective acoustic wave detection area is an area determined based on the positional relationship between the point of interest and the reception area and the characteristics of the element (for example, the directivity angle) relating to the detection of an effective acoustic wave signal. An example of the effective acoustic wave detection region is shown in an effective acoustic wave detection region 604 in FIG.

In step S504, the reconstruction processing unit 1002 extracts an effective acoustic wave signal group used for the reconstruction process for the point of interest inside the subject extracted in step S503. The extracted effective acoustic wave detection information group is extracted from the acoustic wave signal group detected in the effective acoustic wave detection area calculated in step S503.
Here, the number of acoustic wave signal groups extracted for each point of interest is not necessarily the same. For example, an acoustic wave signal group detected by all elements of the acoustic wave detector may be used, or an acoustic wave signal group detected by some elements may be extracted.

  The number of acoustic wave signals that can be effectively used at each point of interest varies depending on the relative positional relationship between the point of interest and the element when receiving the acoustic wave signal and the range of directivity of the element. An acoustic wave signal received by an element at a position where the point of interest does not fall within the directivity range can be acquired only with an acoustic wave signal whose sensitivity has been significantly reduced even if the acoustic wave signal is the same. Therefore, it cannot be treated as an acoustic wave signal effective for reconstruction processing, and the number of effective acoustic wave signals for each point of interest may be different. For example, the attention point (voxel) 602 and the attention point (voxel) 605 of FIG. 6 are equal to each other in the effective signal detection regions 604 and 606 even if the distance from the attention point (voxel) 605 is equal to the perpendicular line 603 lowered from the attention point to the reception region. As described above, the areas overlapping on the reception area 601 are different. Therefore, since the number of elements that can detect an effective acoustic wave signal included in a circle having a predetermined radius centered on the intersection of the perpendicular and the reception area is different, the number of effective acoustic wave signals for each target point is different.

In addition, the element group in the reception area that receives the acoustic wave signal exists in a limited area, and the acoustic wave signal group that is detected at a position that is not necessarily symmetric exists in the relative position to the point of interest. . This symmetry is, for example, when there is a pair of acoustic wave signals in a point-symmetrical position around the foot of the perpendicular line 603 dropped from the point of interest 602 on the reception area 601 and the acoustic wave signal at the symmetrical position. It is considered. When image reconstruction in the subject area is performed in a reception area in a limited orientation, it is out of the process of the photoacoustic wave equation, but there is no symmetry in the acoustic signal received on the same reception area. Further, the reconstructed image becomes more biased and the artifact increases. Therefore, even if the number of acoustic wave signals is the same, there is a difference in image quality between a region reconstructed with a group of acoustic waves having no symmetry and a region reconstructed with a group of acoustic waves with symmetry. As a result, the higher the ratio of those having other detection elements at symmetrical positions, the better the image quality.

Therefore, in the process of step S504, the reconstruction processing unit 1002 may further select and reconstruct symmetrical acoustic wave detection information from effective acoustic wave signals in order to reduce the difference in image quality. is there.
In some cases, effective acoustic wave signals are limited under conditions specific to the apparatus. Even in the case of a subject at a position where imaging can be performed, an effective acoustic wave signal group may be limited if the factors affecting the acoustic wave characteristics of the inner wall and parts of the apparatus can be grasped.
Further, in order to shorten the processing time required for image reconstruction, the number of acoustic wave signals used for reconstruction processing may be reduced.

  In step S505, the reconstruction processing unit 1002 performs a reconstruction process using the acoustic wave detection information group extracted in step S504. It is assumed that the reconstruction processing algorithm executed by the reconstruction processing unit 1002 is stored in the main memory 102, the magnetic disk 103, or the like. Also, it is assumed that parameters relating to selection of a reconstruction algorithm and reconstruction processing are set in advance by the user via the input unit 106 and stored in the main memory 102 or the magnetic disk 103 or the like.

  Here, as a processing procedure of the reconstruction processing unit 1002, it has been described that effective acoustic wave detection information is first extracted in step S504, and then reconstruction processing is performed in step S505. However, if the reconstruction processing algorithm and parameters are determined in advance, the acoustic wave detection information group necessary for step S505 can be extracted as effective acoustic wave detection information in step S504.

  In step S506, the reconstruction processing unit 1002 stores the value calculated in the reconstruction process as a reconstructed image for each point of interest. When a three-dimensional reconstructed image is calculated as volume data, the calculated value is stored as a voxel value.

  Here, in the present embodiment, the calculated value of the reconstruction process has been described as a reconstructed image. However, the information calculated by the reconstruction process stored as voxel values in the volume data is not necessarily in the range of values that can be directly displayed in the gradation of the display device, like image data such as a general bitmap. It does not have to be a value. Information calculated in the reconstruction process is stored as a value distributed in the voxel space, and in the display process, an appropriate window process is performed according to the specifications of the display device, and a display image is displayed. The reconstructed image is also included including the calculated value obtained by.

  In step S507, the reconstruction processing unit 1002 stores acoustic wave detection information for each point of interest. The stored acoustic wave detection information may be any method as long as it is a storage method associated with each voxel as long as it is a point of interest and volume data.

  Here, in the acoustic wave detection information, the acoustic wave detection information acquired by the acoustic wave signal measuring unit 1100 is an acoustic wave signal associated with the detection position information of the acoustic wave, for example, the characteristics of the element of the acoustic wave detector. And information on acoustic wave acquisition conditions such as acoustic characteristics of the measuring device. Furthermore, in the case of a photoacoustic wave, it is also possible to include information relating to the condition that caused the photoacoustic wave to be generated, and further information relating to the control of the acoustic wave detector and light irradiation.

  In step S508, the reconstruction processing unit 1002 determines whether there is an unprocessed attention point among the attention points in the reconstruction area. If there is an unprocessed attention point, the processing from step S502 to step S507 is repeatedly executed.

  If there is no unprocessed point of interest in step S508, the reconstruction processing unit 1002 executes processing necessary for the completion of the reconstruction processing, such as closing the recording information file. Thereafter, the acoustic wave detection information is transmitted to the image quality determination unit 1003, and the reconstruction process in the embodiment of the present invention is terminated.

(Image quality judgment and area information generation)
FIG. 4B is a flowchart showing a procedure for determining image quality and generating region information based on the determination result in the embodiment of the present invention. Hereinafter, the determination process of the present embodiment will be described with reference to the flowchart of FIG.

Step S801 is started when the image quality determination unit 1003 acquires the acoustic wave detection information of the image quality determination unit 1003 after the reconstruction process according to the embodiment of the present invention ends.
In step S801, the image quality determination unit 1003 determines image quality based on the information regarding the acoustic wave detection information sent from the reconstruction processing unit 1002 and the image quality determination setting information set in advance by the user. The image quality determination setting information may be information that designates setting information that can specify the image quality determination method, the standard for determining the image quality of the reconstructed image, or the stage. In particular, when the acoustic wave detection information is designated as a parameter, any information can be set.

  As an example of the determination method, effective signal groups detected within the range of directivity of the elements are prepared from the position information of each voxel of the volume data of the three-dimensional reconstructed image and the characteristics and position information of the detection element of the acoustic wave. There is a method of determining the image quality based on whether or not it is a voxel. From the number of acoustic wave signals that fall within the directivity range for each voxel and the positional relationship between each voxel and the reception area, the maximum number of acoustic wave signals that can be detected in the directivity range on the reception area is calculated. If the number of acoustic wave signals used in the reconstruction process for each voxel is the maximum number, it is regarded as a region with good image quality. In this embodiment, an example of display based on the determination result of the image quality by this determination method is shown. A determination method is designated in the image quality determination setting information in the case of this determination method.

  Further, the threshold information and the identification information of the determination method are set as the image quality determination setting information for the number of effective acoustic wave signals used for calculating each voxel value of the volume data constituting the reconstructed image, and the image quality determination unit 1003 Based on the above, it is possible to implement a method for determining whether the image quality is good or bad.

  Furthermore, in the case where the artifact bias occurring in the pixels in the reconstructed image is a problem, the determination may be made based on whether or not the acoustic wave signal used for calculating each voxel value is an acoustic wave signal group at a symmetrical position. .

  Here, from the characteristics of the elements of a general acoustic wave detector, as the position is farther from the reception area, the element positions that can be detected in the directivity range increase, and the number of effective acoustic wave detection signals tends to increase. is there. Even if the number of effective acoustic wave signals that can be detected is the maximum number, there is a difference in image quality depending on the relative position of the reconstruction area to the reception area. Therefore, you may use together with said determination method by making each attention point in a reconstruction area | region and the distance from a receiving area into a threshold value.

  In addition, the three-dimensional reconstructed image described in step S801 corresponds to an imaging region when the acoustic wave is measured by the acoustic wave signal measurement unit 1100. Similar to the distance between the reception area and each attention point in the reconstruction area, it may be applied to image quality determination of each attention point in the reconstruction area in consideration of the acoustic characteristics of the imaging area.

  The determination results of these determination methods may be provided with stages as well as pass / fail determinations, and in the case of a determination method combining a plurality of criteria, a method of enumerating a plurality of determination results may be used.

  The input of the image quality determination setting information in the embodiment of the present invention is assumed to be stored in the main memory 102 or the magnetic disk 103 by the user via the input unit 106.

  The image quality determination unit 1003 transmits information obtained by adding information related to the determination method of image quality determination to the region information generation unit 1004 as determination result information, as necessary. The information regarding the position of each determination result included in the determination result information can be implemented as information listing position information regarding individual voxels. Alternatively, when the display area is sufficiently accurate with respect to the target display image, any of the information converted into information approximate to a mathematical expression including an area with good image quality may be used. In the present embodiment, the region information that approximates the boundary surface of the region of the voxel group with good image quality in which the number of effective acoustic wave detection information at each point of interest is aligned, and information such as an ID that identifies the determination method are the determination result information. To do.

  Here, the region information in the present embodiment will be described. The attention point with good image quality in this embodiment is an attention point that maximizes the number of effective acoustic wave signals that can be detected in the reception area, such as the attention point 605 corresponding to the effective signal detection area 606 in FIG. is there. Therefore, the area with good image quality in this embodiment is an area occupied by a point group consisting of attention points equivalent to the attention point 605 with good image quality. Such a point cloud exists in an image reconstruction area having a shape like a large truncated pyramid on the reception area side. For this reason, the boundary surface for the quality of image quality can be approximated by an expression indicating the surface of the truncated pyramid.

  In step S <b> 802, the region information generation unit 1004 generates region information as accuracy information indicating a difference in accuracy of characteristic information based on the determination result information transmitted from the image quality determination unit 1003. The area information generated in this step indicates the difference in accuracy of the characteristic information by dividing the area of the reconstructed image based on the determination result information. However, as the area information, any information may be used as long as the information can identify the difference in accuracy of the characteristic information when displaying information based on the reconstructed image generated by the reconstruction processing unit 1002.

  As an example of the area information, for example, an area in the reconstructed image can be indicated by information of a point cloud or a polyhedron vertex. In the case of volume data, voxel position information indicating the vertexes of a point cloud or polyhedron corresponds. Further, it may be information such as a mathematical expression that divides an area in the reconstructed image, information obtained by grouping position information of voxels, or regularity of position information. Since these pieces of information are values calculated based on the determination result information, the area information and the contents of the determination result information can be associated with each other. For example, the determination result at each point of a specific area obtained by dividing the reconstructed image based on the area information can be referred to.

  Furthermore, the region information does not necessarily have to be exactly the same as the determination result information. If it is not always necessary to faithfully reflect the determination result of each voxel in the reconstructed image, the accuracy of the region information may be rough. For example, when the resolution of the reconstructed image is high and the resolution of the display image is low, the degree of user identification does not change, but the display speed is reduced, so that area information with coarse accuracy may be required. .

  As an example of a method for generating region information with coarse accuracy, there is the following method. That is, based on the determination result information and display setting information, a method that targets only representative points corresponding to the resolution necessary for display, a boundary line that approximates the boundary of the region divided based on the determination result, Alternatively, the method is based on information such as a mathematical expression related to the boundary surface. In addition, it is good also as area | region information as it is, without making it approximate at the time of area | region information generation, and the information of the boundary surface of the area | region divided | segmented included in determination result information.

Here, in the implementation of the present invention, even if the entity of the region information uses the information generated in another step as it is, it is treated as the region information. That is, the present invention relates to a region for generating display information based on a region obtained by dividing a region in a reconstructed image based on a determination result of an image quality determination unit even if there is no step of clearly generating region information when implementing the present invention. If it is information, it can be said that it is area information of the present invention.

  In the present embodiment, the determination result information and an expression indicating a boundary surface approximated to the boundary of a voxel group with good image quality are used as region information.

  The region information generation unit 1004 transmits the generated region information to the display information generation unit 1005, and ends the image quality determination process in this embodiment.

(Display information generation and display procedure)
FIG. 4C is a flowchart illustrating a display procedure in which the display information generation unit 1005 generates display information and the display unit 1006 displays in the present embodiment. The process starts when the display information generation unit 1005 acquires area information.

  In step S901, the display information generation unit 1005 displays based on the reconstructed image generated by the reconstruction processing unit 1002, the determination result information generated by the image determination unit 1003, and the region information generated by the region information generation unit 1004. Generate image information.

  As an example of the display image information, there is a method of superimposing and displaying the boundary lines of regions divided according to the quality of image quality on the reconstructed image when the reconstructed image is displayed by MPR (Multi Planner Reconstruction). An example of display on the display unit in the information display method of the present invention by this method will be described with reference to FIG.

FIG. 7 is a diagram showing an example of a window for displaying three sections of a three-dimensional reconstructed image displayed on the display unit, using the display information of the present invention as an example of display. A display window 701 is a display window generated by an OS that executes display processing. Axial image display area 702
Coronal image display area 703 and Sagittal image display area 704 are examples of display areas on the display window 701 for displaying the Axial, Coronal, and Sagittal sections of the reconstructed image, respectively. An Axial image 705, a Coronal image 706, and a Sagittal image 707 represented as hatched areas are examples of image display of the Axial, Coronal, and Sagittal sections of the reconstructed image of the subject, respectively.

  A boundary line 708 represented by a dotted line is an example of a boundary line display that is displayed on the basis of the display information in the embodiment of the present invention and that can identify whether the image quality is good or bad. The boundary line is calculated for each cross-sectional image displayed at the time of generating the display information by intersecting with the boundary surface of the region information (an expression representing the surface of the quadrangular pyramid) according to the position of the cross-sectional image. In the present embodiment, a region 709 with good image quality can be identified as a region surrounded by the boundary line 708 on the display image.

In addition, since the display position and display direction of each image in the three cross-sectional views and the position in the reconstructed image for determining the cross-sectional image can be arbitrarily changed, the display is not necessarily the same as the position and orientation in FIG. There is no problem in the implementation of the present invention.
There is also a method of generating display information so that a cross-sectional image is displayed by changing the color, density, and transparency of each region instead of the boundary line or boundary surface based on the same region information.

When a display image is generated by volume rendering, the region determined by the region information can be reflected in the value of each voxel projected on the volume rendering display image so that the region can be identified. As an example, there is a method of differentiating the transparency of voxel values in areas with good image quality and voxel values in areas with poor image quality, or by changing the color information and density to different values to reflect the effects of area differences. Can be implemented.

  Furthermore, regions having different image quality can be generated as identifiable display information by a method other than superimposed display with a three-dimensional image. For example, the display information may be a display information that displays a boundary line or a boundary surface of an area in accordance with the quality of the image quality in the reconstructed image. It is also possible to display the coordinates and point group information of the vertices of a plane or a polygon for each of the areas with good image quality, bad areas, or areas with stepwise differences in the reconstructed image. Message or text information based on the image quality determination result for a specific coordinate point or region in the reconstructed image may be generated as display information that can identify the difference in accuracy of the characteristic information.

  The display information generation unit 1005 transmits the generated display information to the display unit 1006.

  In step S902, the display unit 1006 performs display based on the display information. When the display information generation unit generates an image like a bitmap, it is displayed on the display as it is. In the case of compressed or encoded image data such as JPEG, it may be displayed after being decompressed and combined.

With the above procedure, the display procedure of the present embodiment shown in FIG.
As described above, the information display device or the information display method of the present invention that performs the procedure described above can display information that can identify regions of different image quality in the reconstructed image.

  In this embodiment, in the acoustic wave detection information acquisition procedure of the acoustic wave signal measurement unit 1100, the acoustic wave detection information is transmitted to the information processing unit 1000. However, the acoustic wave detection information may be transmitted to another device such as a server capable of recording, or the acoustic wave signal measurement unit 1100 may record the storage unit.

  Further, in the present embodiment, the information processing unit 1000 has been described as the process in which the acoustic wave information acquisition unit 1001 acquires the acoustic wave detection information transmitted from the acoustic wave signal measurement unit 1100 after measurement by the acoustic wave signal measurement unit. However, even if the acoustic wave information acquisition unit 1001 acquires acoustic wave information from a device such as a server other than the acoustic wave signal measurement unit or a stored file, the embodiments after the reconstruction processing of the present invention are implemented. can do.

  Furthermore, in the present embodiment, the reconstructed image generated by the reconstruction processing unit 1002 and the acoustic wave detection information are described as examples sent to the image quality determination unit 1003. However, the reconstructed image and the acoustic wave detection information are stored in the storage device, the image quality determination method is designated before the display procedure of the present embodiment, and the process after the image quality determination process is performed. Also good. In this case, since the reconstruction process is completed, there is also an effect that display information to which various image quality determination methods are applied can be displayed in a short processing time in the implementation of the present invention.

In addition, in this embodiment, a method of storing the determination result information generated by the image quality determination unit 1003 and the region information generated by the region information generation unit 1004 in a storage device can be implemented. A procedure for performing the subsequent procedure after the region information generation unit 1004 acquires the determination result information stored in advance, or a procedure for the display information generation unit 1005 to generate display information by acquiring the region information stored in advance. Even so, it can be similarly implemented. According to the present invention, the processing time until displaying display information that can identify regions having different image quality is further shortened. In addition, there is an effect that it is possible to implement even software having a simple configuration such as software having only necessary function blocks of the information processing unit 1000.
<Other embodiments>
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 the computer of the system or apparatus (or CPU, MPU, etc.) reads the program. To be executed.

1000: Information processing unit, 1001: Acoustic wave information acquisition unit, 1002: Reconstruction processing unit, 1003: Image quality determination unit, 1004: Area information generation unit, 1005: Display information generation unit, 1100: Acoustic wave signal measurement unit

Claims (17)

A subject information acquisition apparatus that acquires characteristic information in a subject using an acoustic wave signal output from a detection element that detects an acoustic wave propagated in the subject,
Using the acoustic wave signal, a characteristic information acquisition unit that acquires characteristic information at each point of interest in the subject;
An accuracy information generating unit that generates information indicating a difference in accuracy of the plurality of characteristic information using acoustic wave detection information that is a condition relating to the detection of the acoustic wave;
A display information generating unit that generates display information capable of identifying the difference in accuracy of the plurality of characteristic information using the characteristic information at each attention point and the information indicating the difference in accuracy, and displays the display information on the display unit;
A subject information acquisition apparatus characterized by comprising: A determination unit that determines the accuracy of the characteristic information using the acoustic wave detection information;
The subject information acquisition apparatus according to claim 1, wherein the accuracy information generation unit generates information indicating a difference in accuracy of the characteristic information using a determination result in the determination unit. The characteristic information acquisition unit extracts an acoustic wave signal group caused by an acoustic wave from an attention point inside the subject for each attention point, and obtains characteristic information at each attention point using the acoustic wave signal group. The object information acquiring apparatus according to claim 1, wherein the object information acquiring apparatus is an object information acquiring apparatus. The display information generation unit is configured to divide the characteristic information distribution composed of the plurality of characteristic information into a plurality of regions based on the information indicating the difference in accuracy, and thereby display the difference in accuracy of the plurality of characteristic information The object information acquiring apparatus according to claim 1, wherein information is generated. The subject information acquisition apparatus according to claim 4, wherein the display information generation unit generates the display information such that boundary lines of the plurality of regions are superimposed and displayed on the characteristic information distribution. The object information acquisition apparatus according to claim 1, wherein the acoustic wave detection information includes information regarding a position of the detection element. The object information acquiring apparatus according to claim 6, wherein the acoustic wave detection information further includes information on sensitivity and directivity of the detection element. The characteristic information acquisition unit calculates, based on the acoustic wave detection information, an effective acoustic wave detection area that is an area where an effective acoustic wave can be detected for each target point, and is included in the effective acoustic wave detection area The object information acquiring apparatus according to claim 3, wherein the acoustic wave signal group is extracted using information on a position of a detection element to be detected. A display control method for displaying characteristic information in a subject,
Obtaining characteristic information at each point of interest in the subject using an acoustic wave signal output from the detection element that has detected the acoustic wave propagated in the subject;
An accuracy information generating step for generating information indicating a difference in accuracy of the plurality of characteristic information using acoustic wave detection information which is a condition relating to the detection of the acoustic wave;
A display information generating step for generating display information capable of identifying a difference in accuracy of the plurality of characteristic information using the characteristic information at each of the attention points and the information indicating the difference in accuracy;
Displaying the display information;
A display control method comprising: A determination step of determining the accuracy of the characteristic information using the acoustic wave detection information;
The display control method according to claim 9, wherein in the accuracy information generation step, information indicating a difference in accuracy of the characteristic information is generated using a determination result in the determination step. In the obtaining step, an acoustic wave signal group caused by an acoustic wave from an attention point inside the subject is extracted for each attention point, and characteristic information at each attention point is obtained using the acoustic wave signal group. The display control method according to claim 9 or 10. In the display information generation step, a display capable of identifying the difference in accuracy of the plurality of characteristic information by dividing the characteristic information distribution including the plurality of characteristic information into a plurality of regions based on the information indicating the difference in accuracy. 12. The display control method according to claim 9, wherein information is generated. 13. The display control method according to claim 12, wherein in the display information generation step, the display information is generated such that boundary lines of the plurality of regions are superimposed and displayed on the characteristic information distribution. The display control method according to claim 9, wherein the acoustic wave detection information includes information related to a position of the detection element. The display control method according to claim 14, wherein the acoustic wave detection information further includes information on sensitivity and directivity of the detection element. In the obtaining step, an effective acoustic wave detection area, which is an area where an effective acoustic wave can be detected, is calculated for each target point based on the acoustic wave detection information, and is included in the effective acoustic wave detection area. The display control method according to claim 11, wherein the acoustic wave signal group is extracted using information on a position of a detection element.   The program for making a computer perform each step of the display control method of any one of Claims 9 thru | or 16.

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