JP2011062404A - Ultrasonic diagnosis device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reconstruction process with reduced distortion of motion related to a target tissue. <P>SOLUTION: A reference image searching part 26 searches for a plurality of reference images at an interval of a virtual period from data of a plurality of tomographic images stored in a previous memory 14. The virtual period is set by a virtual period setting part 24. A reconstruction processing part 20 carries out a reconstruction process to take each of a plurality of reference images for a unit of division, divide the data of a plurality of tomographic images to a plurality of groups of images, and extract data of a plurality of tomographic images which periodically correspond to each other from each of the plurality of groups of images. A reference image forming part 30 forms a reference image based on a line of images after the reconstruction process. The virtual period setting part 24 corrects the virtual period in accordance with indication from a user who refers to the reference image. Correction of the virtual period and evaluation of distortion using the reference image are repeated to adjust the virtual period for reducing distortion. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus that forms a display image of a target tissue that moves periodically.

  2. Description of the Related Art An ultrasonic diagnostic apparatus that forms a three-dimensional ultrasonic image of a tissue that accompanies motion such as the heart is known. For example, there is a technology that scans an ultrasonic beam in a three-dimensional space, collects echo data from the three-dimensional space, forms a three-dimensional ultrasonic image based on the collected echo data, and displays it in real time. It has been. However, in the case of real-time display, there is a principle restriction that the scan rate, the beam density, and the beam range are in a trade-off relationship with each other.

  Techniques for avoiding the fundamental limitations in real-time display of 3D ultrasound images have also been proposed. For example, Patent Document 1 collects a plurality of tomographic image data over a plurality of time phases at each position on the scanning plane while moving the scanning plane little by little in the three-dimensional space in synchronization with an electrocardiogram signal or the like. A technique (reconstruction processing) is described in which a plurality of collected tomographic image data is rearranged and reconstructed to form three-dimensional image data. Further, Patent Document 2 describes a technique for extracting and reconstructing a plurality of tomographic image data at regular time intervals without using an electrocardiogram signal.

  In the reconstruction process described above, it is desirable that the time interval for rearranging the tomographic image data coincides with the period related to the motion of the target tissue such as the heart. If this time interval deviates from the period related to the movement, the target tissue such as the heart appears to be distorted and moved in the moving image obtained by the reconstruction.

Japanese Patent No. 3537594 JP 2005-74225 A

  In view of the background art described above, the inventor of the present application has repeatedly researched and developed a technique for forming an ultrasonic image by reconstruction processing. In particular, attention was paid to a technique for improving the reliability of ultrasonic images obtained by reconstruction processing.

  The present invention has been made in the course of research and development, and an object of the present invention is to realize a reconstruction process with reduced movement distortion related to a target tissue.

  An ultrasonic diagnostic apparatus suitable for the above object includes a probe that transmits and receives ultrasonic waves to and from a three-dimensional space including a target tissue that moves periodically, and a scanning plane that moves over a plurality of cycles of the movement. A virtual period of motion related to a target tissue from a transmission / reception control unit that controls a probe so as to form a plurality of scanning planes in the three-dimensional space, and an image sequence composed of a plurality of images corresponding to the plurality of scanning planes A reference image search unit that searches for a plurality of reference images at intervals corresponding to each of the plurality of reference images, and the image sequence is divided into a plurality of image groups with each of the plurality of reference images as a division unit. A reconstructing processing unit that rearranges the image sequence to obtain a reconstructed image sequence by extracting the corresponding image, and based on the reconstructed image sequence, the time change of the form of the target tissue accompanying exercise Reference shown A reference image forming unit that forms an image, a virtual cycle setting unit that sets the modified virtual cycle by modifying the virtual cycle in accordance with an instruction from a user who refers to the reference image, and a search based on the modified virtual cycle And a reconstructed image forming unit that forms a reconstructed image of a target tissue based on the reconstructed image sequence obtained by using the plurality of reference images.

  In a preferred specific example, the reference image forming unit forms a tomographic reference image corresponding to a plane intersecting the scanning plane as the reference image.

  In a preferred specific example, the reference image forming unit forms a tomographic reference image in which the expanded portion and the reduced portion of the target tissue are displayed in different display modes.

  In a desirable specific example, the ultrasonic diagnostic apparatus extracts a plurality of images corresponding to the same position from the reconstructed image sequence having different time phases, and calculates a difference value between the extracted images. It is characterized by having.

  In a preferred embodiment, the reference image search unit sets one image corresponding to the maximum mutual difference value as a representative reference image based on the mutual difference value corresponding to each of the plurality of images constituting the image sequence, Starting from the representative reference image as a starting point, from among a plurality of images corresponding to the maximum mutual difference value, the image closest to the position separated by the corrected virtual period is searched one after another, and the plurality of reference images are used. It is characterized by.

  According to the present invention, reconstruction processing with reduced motion distortion related to the target tissue is realized.

1 is a diagram illustrating an overall configuration of an ultrasonic diagnostic apparatus that is preferable in the practice of the present invention. It is a figure for demonstrating the three-dimensional scanning in this embodiment. It is a figure which shows the change of a cross-sectional difference value. It is a figure for demonstrating the process by a reconstruction process part. It is a figure for demonstrating another suitable process by a reconstruction process part. It is a figure for demonstrating the tomographic image of the target tissue formed as a reference image. It is a figure for demonstrating the display mode of the object structure | tissue in a reference image. It is a flowchart for demonstrating the reconstruction process which reduced distortion. It is a figure for demonstrating correction | amendment of the position of a reference | standard image.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 is a diagram showing an overall configuration of an ultrasonic diagnostic apparatus suitable for implementing the present invention. The probe 10 transmits and receives ultrasonic waves in a three-dimensional space including the target tissue. The probe 10 includes a plurality of vibration elements each of which transmits / receives an ultrasonic wave, and transmission of the plurality of vibration elements is controlled by the beam former 12 to form a transmission beam. Further, the plurality of vibration elements receive the ultrasonic waves reflected from the target tissue, and signals obtained thereby are output to the beam former 12, and the beam former 12 forms a reception beam.

  The probe 10 of the present embodiment is a 3D probe that collects echo data three-dimensionally by scanning an ultrasonic beam (a transmission beam and a reception beam) in a three-dimensional space. For example, the ultrasonic beam is scanned three-dimensionally by mechanically moving a scanning surface formed electronically by a plurality of vibration elements (1D array transducers) arranged one-dimensionally. Alternatively, the ultrasonic beam may be scanned three-dimensionally by electronically controlling a plurality of vibration elements (2D array transducers) arranged two-dimensionally.

  The beam former 12 forms an ultrasonic transmission beam by supplying a transmission signal corresponding to each of a plurality of vibration elements included in the probe 10. In addition, the beam former 12 forms an ultrasonic reception beam by performing a phasing addition process or the like on a reception signal obtained from each of a plurality of vibration elements included in the probe 10, and is obtained along the reception beam. Output echo data. In the present embodiment, the target tissue is a periodically moving tissue, such as a fetal heart.

  FIG. 2 is a diagram for explaining three-dimensional scanning in the present embodiment. In FIG. 2, the three-dimensional space including the target tissue is expressed in an XYZ orthogonal coordinate system. In the present embodiment, the scanning surface S is formed so as to be substantially parallel to the XY plane, and a plurality of scanning surfaces S are formed along the Z-axis direction while slowly moving the scanning surface S in the Z-axis direction. It is formed. The scanning plane S moves slowly in the Z-axis direction over a plurality of periods related to periodic movements such as the fetal heart, for example, over a period including about 20 heartbeats in about 8 seconds.

  Returning to FIG. 1, when a plurality of scanning planes are formed along the Z-axis direction over a plurality of periods of the fetal heartbeat, tomographic image data is collected for each scanning plane and corresponds to the plurality of scanning planes. A plurality of tomographic image data is sequentially stored in the previous memory 14.

  The error determination unit 16 determines whether or not the plurality of tomographic image data is good based on the difference amount between the images obtained from the plurality of tomographic image data stored in the previous memory 14. For example, the fetal heart may move greatly in the image due to the movement of the fetus, mother or probe, and a good image may not be obtained. Therefore, the error determination unit 16 determines whether a good image for diagnosis is obtained. In the determination, the error determination unit 16 uses a cross-sectional difference value defined by the following equation.

  X, y, and z in Equation 1 are coordinate values on each axis in the XYZ orthogonal coordinate system of FIG. 2, and p is a pixel value corresponding to each coordinate in the tomographic image data. The difference value between two pieces of tomographic image data adjacent in the Z-axis direction is calculated by Equation (1).

  FIG. 3 is a diagram showing changes in cross-sectional difference values, and the horizontal axis of FIG. 3 shows the position of each tomographic image data. That is, the horizontal axis in FIG. 3 corresponds to the position of each scanning plane and the time at which each scanning plane is obtained, and corresponds to the Z axis in FIG. 2 (the direction of change in position over time). .

  If the fetal heart does not move significantly, the adjacent tomographic image data will be similar to each other, and the difference value obtained from Equation 1 will be relatively small. On the other hand, for example, if there is a movement of the fetus itself, the mother's breathing movement, a large displacement of the probe position, the fetal heart moves greatly in the tomographic image, and the difference value between adjacent tomographic image data is relatively large. Become. Therefore, the error determination unit 16 determines that the heart has greatly shifted in the image when the cross-sectional difference value exceeds a predetermined threshold value.

  Returning to FIG. 1, when the error determination unit 16 determines that the heart has greatly shifted, the control unit 40 controls, for example, the beamformer 12 to stop collecting tomographic image data. Note that the control unit 40 controls each unit in FIG. 1 in a concentrated manner. For example, when the error determination unit 16 determines that an error has occurred, a display or a warning indicating an error is displayed. You may display on the part 30. If the error determination unit 16 does not determine an error, a process to be described later is executed based on a plurality of tomographic image data stored in the previous memory 14.

  The reference image search unit 26 searches the plurality of tomographic image data stored in the previous memory 14 for a plurality of reference images at virtual cycle intervals corresponding to the motion cycle related to the target tissue. The virtual period is set by the virtual period setting unit 24.

  When a plurality of reference images are searched, the reconstruction processing unit 20 sets the plurality of tomographic image data stored in the previous memory 14 to a plurality of image groups by using each of the plurality of reference images as a unit of division. Reconstruction processing (reconstruction processing) is realized by dividing and extracting a plurality of tomographic image data periodically corresponding to each other from each of a plurality of image groups. The reconstruction processing unit 20 reconstructs a plurality of tomographic image data stored in the previous memory 14 and stores it in the rear memory 28.

  FIG. 4 is a diagram for explaining processing by the reconstruction processing unit 20. FIG. 4 shows a correspondence relationship between data stored in the front memory 14 and data stored in the rear memory 28. . In FIG. 4, “tomographic image Zn (n = 1, 2, 3,..., 60)” means tomographic image data at the position of the coordinate Zn on the Z axis (see FIG. 2).

  The previous memory 14 stores a plurality of tomographic image data corresponding to a plurality of scan planes formed one after another along the Z-axis direction. That is, the previous memory 14 stores an image sequence including a plurality of tomographic image data in the order of tomographic images Z1, tomographic images Z2,..., Tomographic images Z60,. ing.

  The reconstruction processing unit 20 divides the plurality of tomographic image data stored in the previous memory 14 into a plurality of image groups by using each of the plurality of reference images as a unit of division. Then, a plurality of tomographic image data periodically corresponding to each other is extracted from each of the plurality of image groups.

  In FIG. 4, the tomographic image Z1, the tomographic image Z15,..., The tomographic image Z51 are a plurality of reference images searched by the reference image search unit 26. The reconstruction processing unit 20 first extracts a tomographic image Z1, a tomographic image Z15,..., A tomographic image Z51, which are reference images, as a plurality of tomographic image data periodically corresponding to each other. Then, the extracted tomographic image Z1, tomographic image Z15,..., Tomographic image Z51 are stored in the rear memory 28 as one data block.

  Next, the reconstruction processing unit 20 extracts a plurality of tomographic images adjacent in the positive direction of the Z-axis direction to each of the plurality of reference images as a plurality of tomographic image data periodically corresponding to each other. That is, the tomographic image Z2, the tomographic image Z16,..., And the tomographic image Z52 are extracted and stored in the rear memory 28 as one data block.

  Furthermore, the reconstruction processing unit 20 extracts a plurality of tomographic images adjacent to each of the tomographic image Z2, the tomographic image Z16,. In this way, data blocks of a plurality of tomographic images periodically corresponding to each other from each of the plurality of reference images are sequentially extracted and stored in the rear memory 28.

  In the reconstruction process described above, there may be a tomographic image that is not used for the reconstruction process among a plurality of tomographic images stored in the previous memory 14. For example, the tomographic images (Z11 to Z14) between the tomographic image Z10 and the tomographic image Z15 in the previous memory 14 may not be used for the reconstruction process.

  Thus, a plurality of data blocks are formed in the rear memory 28 by the above-described reconstruction process. For example, the tomographic image Z1, the tomographic image Z15,..., And the tomographic image Z51 become one data block, and the tomographic image Z2, the tomographic image Z16,. In the example shown in FIG. 4, the data block corresponding to the reference image is the head of the plurality of data blocks. However, a plurality of data blocks may be formed around the data block corresponding to the reference image.

  FIG. 5 is a diagram for explaining another suitable process by the reconstruction processing unit 20. Like FIG. 4, FIG. 5 shows data stored in the front memory 14 and stored in the rear memory 28. Correspondences between data are shown.

  Also in the example illustrated in FIG. 5, the reconstruction processing unit 20 divides a plurality of tomographic image data stored in the previous memory 14 into a plurality of image groups by using each of the plurality of reference images as a unit of division. . At that time, when the number of data blocks is e, e / 2 tomographic images in the negative direction of the Z-axis and e / 2 sheets in the positive direction of the Z-axis from each reference image around the position of each reference image. A tomographic image is defined as one image group.

  For example, in the previous memory 14 shown in FIG. 5, e / 2 tomographic images Z14, tomographic images Z13,... In the negative direction of the Z axis centered on the tomographic image Z15 that is the reference image, and the Z axis The e / 2 tomographic images Z16, tomographic images Z17,... In the positive direction form an image group including e tomographic images centered on the tomographic image Z15. Similarly, an image group composed of e tomographic images centered on the tomographic image Z32 that is the reference image is formed, and an image group composed of e sheet tomographic images centered on the tomographic image Z51 that is the reference image. The

  Also in the example shown in FIG. 5, a plurality of tomographic image data periodically corresponding to each other is extracted from each of the plurality of image groups. That is, the reconstruction processing unit 20 first extracts a tomographic image at the smallest position on the Z axis from each of the image groups to form one data block, and then the second smallest on the Z axis. A tomographic image at a position is extracted to form one data block. By continuing this extraction process from the smallest position to the largest position on the Z axis, a total of e data blocks are formed in the rear memory 28.

  FIG. 5 shows three data blocks out of the total number e. That is, a data block composed of a tomographic image Z14, a tomographic image 31,..., A tomographic image 50 each preceding the reference image, and a tomographic image Z15, a tomographic image 32,. , A data block composed of a tomographic image 51, and a data block composed of a tomographic image Z16, a tomographic image 33,.

  As described above, in the example of FIG. 5, data blocks of a plurality of tomographic images periodically corresponding to each other around each of the plurality of reference images are sequentially extracted and stored in the rear memory 28.

  In the example shown in FIG. 5, e / 2 tomographic images in the negative direction of the Z axis and e / 2 tomographic images in the positive direction of the Z axis are centered on the position of each reference image. Although one image group is provided, one image group may be formed by shifting the position of each reference image from the center. That is, one image group may be formed by adding different numbers of tomographic images before and after each reference image. In this case, in the rear memory 28, the data block corresponding to the reference image is shifted from the center of all the data blocks.

  Returning to FIG. 1, the reference image forming unit 30 forms a reference image showing a temporal change in the form of the target tissue accompanying exercise based on the image sequence after the reconstruction process stored in the post-memory 28. The reference image forming unit 30 forms a tomographic image of the target tissue as a reference image on a plane orthogonal to the scanning plane, and further displays the expanded portion and the reduced portion of the target tissue in the tomographic images in different display modes. .

  FIG. 6 is a diagram for explaining a tomographic image of a target tissue formed as a reference image. FIG. 6I shows a plurality of tomographic images Sr included in the image sequence after the reconstruction process. The XYZ coordinate system in FIG. 6I corresponds to the XYZ coordinate system in FIG. 2 before reconstruction processing. A plurality of tomographic images Sr shown in FIG. 6 corresponding to each other periodically are extracted from the plurality of tomographic images corresponding to the plurality of scanning planes S shown in FIG. These tomographic images Sr are, for example, a tomographic image Z1, a tomographic image Z15,..., A tomographic image Z51 stored in the rear memory 28 shown in FIG. For example, it becomes a reconstructed image of time phase T1).

  The reference image forming unit 30 sets the plane R1 or the plane R2 for the reconstructed image composed of the plurality of tomographic images Sr. The plane R1 is a plane parallel to the YZ plane and is orthogonal to the tomographic image Sr (scanning plane). The plane R2 is a plane parallel to the ZX plane and is orthogonal to the tomographic image Sr (scanning plane). The plane R1 and the plane R2 are desirably set so as to include the central portion of the target tissue. For example, the user may specify the position of the plane R1 or the plane R2 in the display image while viewing the reconstructed display image, or the reference image forming unit 30 may perform a binarization process or the like in the reconstructed image. The target tissue portion may be identified, and the plane R1 or the plane R2 may be set so as to pass through the center of gravity of the target tissue portion.

  When the plane R1 or the plane R2 is set, the reference image forming unit 30 forms a tomographic image 50 of the target tissue by the plane R1 or the plane R2, as shown in FIG. 6 (II). Further, the reference image forming unit 30 displays the expanded site and the reduced site of the target tissue in the tomographic image 50 in different display modes.

  FIG. 7 is a diagram for explaining a display mode of the target tissue in the reference image. The reference image forming unit 30 displays the expanded portion and the reduced portion of the target tissue in different display modes in the tomographic image 50 of the target tissue. The reference image forming unit 30 forms a tomographic image 50 of the target tissue on the plane R1 (or plane R2) over a plurality of time phases. Then, for each time phase, for example, a target organization is extracted using a binarization process and the target organization and other organizations are identified. By the way, if the target tissue is the heart, the echo value in the heart (heart chamber) is smaller than that in other tissues. Therefore, a portion with a small echo value is extracted by binarization processing, and the heart is extracted from the other tissue. The inside (heart chamber) can be identified. Of course, in addition to the binarization process, a known noise removal process or labeling process may be used to improve the extraction accuracy.

  When the tomographic image 50 of the target tissue is extracted for each time phase over a plurality of time phases, the reference image forming unit 30 identifies the expanded portion and the reduced portion from the change of the tomographic image 50 between the time phases. For example, when an image portion corresponding to another tissue in the time phase T1 changes to an image portion corresponding to the target tissue in the next time phase T2, the image portion is set as an expansion site. Further, when the image portion corresponding to the target tissue in the time phase T1 changes to an image portion corresponding to another tissue in the next time phase T2, the image portion is set as a reduced portion.

  7A and 7B show examples of display modes. In the tomographic image 50 of the target tissue, the reference image forming unit 30 displays the expanded portion in a cold color system such as blue or green, and displays the reduced portion in a warm color system such as red or yellow.

  For example, as shown in FIG. 7A, when the tomographic image 50 indicated by the solid line changes from the state before the one-phase phase indicated by the broken line, the region 54 surrounded by the broken line and the solid line is determined as the expansion part, The region 54 is expressed in a cool color system. In addition, a region 52 surrounded by a broken line and a solid line is determined as a reduced portion, and the region 52 is expressed in a warm color system. The state shown in FIG. 7A includes a region 54 corresponding to the expanded region and a region 52 corresponding to the reduced region, and the target tissue (for example, the heart) is partially enlarged and partially reduced. It corresponds to a moving image.

  On the other hand, in the state shown in FIG. 7B, the region 54 surrounded by the broken line and the solid line is determined to be an expanded region, and the target tissue (for example, the heart) is enlarged uniformly as a whole. This corresponds to a moving image with a small amount (preferably completely without distortion).

  Note that the extended portion may be a warm color system and the reduced portion may be a cold color system, or other colors may be used. Further, different fill patterns may be used instead of identification by color.

  Returning to FIG. 1, when a reference image is formed in the reference image forming unit 30, the reference image is displayed on the display unit 36. The user (examiner) of the ultrasonic diagnostic apparatus in FIG. 1 looks at the reference image displayed on the display unit 36 and evaluates the distortion of the moving image related to the target tissue such as the heart. When the distortion is large (for example, in the case of the image in FIG. 7A), the user corrects the virtual period using the operation device 22.

  The virtual cycle setting unit 24 corrects the virtual cycle in accordance with an instruction from the user. Then, the reference image search unit 26 searches for a plurality of reference images based on the corrected virtual period, and the reconstruction processing unit 20 executes a reconstruction process based on the plurality of reference images. Based on the reconstructed image sequence obtained in this way, the reference image forming unit 30 forms a reference image, and the user looks at the reference image and evaluates the distortion. Then, the correction of the virtual period and the evaluation of the distortion are repeatedly performed, and the virtual period is adjusted so that the distortion is reduced.

  The image evaluation unit 32 calculates an evaluation value that serves as an index when the user evaluates distortion. The image evaluation unit 32 extracts a plurality of images corresponding to the same position of the target tissue from image sequences with different time phases stored in the post-memory 28, and calculates a difference value between the extracted images. The image evaluation unit 32 calculates, for example, an inter-volume difference value of the following equation as the difference value.

  In Equation 2, x, y, and z are coordinate values on each axis in the XYZ orthogonal coordinate system of FIG. 6I, and p is a pixel value corresponding to each coordinate in the tomographic image data. Further, v is a volume number (time phase), and the coordinate Z / 2 is the center position in the Z-axis direction, for example, the center position of the target tissue. The difference value between the two tomographic image data at the center position in the Z-axis direction obtained from the reconstructed images of the volume v and the volume (v−1) is calculated by Equation (2).

  The difference value calculated by the image evaluation unit 32 is displayed on the display unit 36 together with the reference image formed in the reference image forming unit 30, for example. For example, a bar having a length corresponding to the difference value is displayed next to the tomographic image 50 displayed as shown in FIGS. Of course, the magnitude of the difference value may be displayed as a numerical value.

  When the virtual period is corrected according to an instruction from the user and a virtual period for reducing distortion is set, the 3D image forming unit 34 stores a plurality of tomographic image data after reconstruction stored in the rear memory 28 ( Based on the reconstructed image sequence), three-dimensional image data that three-dimensionally displays a target tissue such as a fetal heart is formed.

  The three-dimensional image forming unit 34 forms three-dimensional image data for each time phase based on one data block stored in the post-memory 28. For example, three-dimensional image data of time phase T1 is formed based on the tomographic image Z1, tomographic image Z15,..., Tomographic image Z51 stored in the post-memory 28 shown in FIG. ,..., Three-dimensional image data of time phase T2 is formed based on the tomographic image Z52. Alternatively, three-dimensional image data of time phases T1 to Te is formed by forming three-dimensional image data of each time phase based on each of the total number e of data blocks formed in the post-memory 28 shown in FIG. Is formed. In the reconstruction process described with reference to FIG. 5, the three-dimensional image data corresponding to the reference image serving as a temporal reference for a periodic motion such as a heartbeat is a three-dimensional image from time phases T1 to Te. Placed in the center of the data. That is, it becomes possible to arrange the three-dimensional image data based on the reference image that is considered to have the most coincident temporal relationship with each other at the center of the time phases T1 to Te.

  The three-dimensional image forming unit 34 applies various methods such as a volume rendering method, an integration method, and a projection method, and forms three-dimensional image data over a plurality of time phases for each time phase. Thus, an image corresponding to the three-dimensional image data formed over a plurality of time phases is displayed on the display unit 36, and a pseudo real-time three-dimensional moving image is displayed. For example, an image corresponding to three-dimensional image data from the time phase T1 to the final time phase Te may be repeatedly displayed and loop reproduction may be executed.

  FIG. 8 is a flowchart for explaining a reconstruction process with reduced distortion. With respect to the portion (configuration) illustrated in FIG. 1, the process of each step illustrated in FIG.

  First, as described with reference to FIG. 2, a plurality of scanning planes are formed along the Z-axis direction over a plurality of periods related to the motion of the target tissue, and tomographic image data is collected for each scanning plane. It is stored in the previous memory 14 (S801). Note that the error determination unit 16 may determine whether or not the plurality of tomographic image data is good based on the difference amount between the images obtained from the plurality of tomographic image data stored in the previous memory 14.

  Next, a virtual cycle for extracting a plurality of reference images is set (S802). For example, the virtual period is set to a preset initial value. Then, as described with reference to FIGS. 4 and 5 based on the set virtual period, the reconstruction process is executed, and the reconstructed image sequence is stored in the post-memory 28 (S803).

  When the reconstruction process is executed, the reference image forming unit 30 forms a reference image as shown in FIG. 7 (S804), and the user views the reference image and evaluates the distortion (S805). When it is determined that the distortion is large (NG), the user corrects the virtual period using the operation device 22, and the virtual period setting unit 24 sets the corrected virtual period (S802). Then, the processing from S802 to S804 is executed again, and the user evaluates the distortion by looking at the reference image (S805).

  When the processes from S802 to S805 are repeatedly executed and it is determined in S805 that the distortion is small (OK), the reference image search unit 26 corrects the position of the reference image (S806).

  FIG. 9 is a diagram for explaining the correction of the position of the reference image. In correcting the position of the reference image, the reference image search unit 26 calculates a mutual difference value defined by the following equation based on the image sequence stored in the previous memory 14.

  X, y, and z in Equation 3 are coordinate values on each axis in the XYZ orthogonal coordinate system of FIG. 2, and p is a pixel value corresponding to each coordinate in the tomographic image data. In Equation 3, one pixel value is multiplied by the difference between two pixel values between two tomographic image data adjacent in the Z-axis direction. As a result, the mutual difference value is relatively large when the heart expands compared to when the heart contracts, and it is possible to identify expansion and contraction that are difficult to identify with a simple difference value by the mutual difference value. .

  For example, in a certain tomographic image data z, it is assumed that the pixel p (x, y, z) is a myocardium in the vicinity of the inner wall of the heart, and the pixel value is set to p (x, y, z) = 100. When the heart expands and the heart chamber becomes larger, the pixel p (x, y, z + 1) becomes the heart chamber pixel in the tomographic image data z + 1 obtained following the tomographic image data z. Since the pixel value of the heart chamber is smaller than that of the myocardium, the pixel value is set to p (x, y, z + 1) = 10. In this example, the absolute value of the right side of Equation 3 is calculated to be 100 × (100−10) = 9000. When the heart expands, many pixels that change from the myocardium to the heart chamber are generated around the inner wall of the heart, so that the mutual difference value of Equation 3 becomes relatively large.

  On the other hand, when the heart contracts, a phenomenon opposite to the above example occurs. That is, since the heart contracts and the heart chamber becomes smaller, the pixel p (x, y, z) = 10 corresponding to the heart chamber changes from the pixel p (x, y, z + 1) = 100 corresponding to the heart muscle. . In this example, when the absolute value of the right side of Equation 3 is calculated, it becomes | 10 × (10−100) | = 900, which is smaller than the value 9000 in the case of expansion. Therefore, expansion and contraction can be identified by the mutual difference value.

  Each of FIGS. 9A to 9C illustrates a change in the mutual difference value calculated by the reference image search unit 26. That is, in FIG. 9, the horizontal axis indicates the position of each tomographic image data (position and time of each scanning plane), and corresponds to the Z axis of FIG. 2 (position change direction with time). Yes. When the mutual difference value is calculated at each position (z) on the Z axis using Equation 3, the mutual difference value becomes a relatively large value when the heart expands.

  In searching for a reference image, the reference image search unit 26 first searches a representative reference image (representative reference image) from a plurality of tomographic images. As shown in FIG. 9A, the reference image search unit 26 sets, for example, tomographic image data corresponding to a position where the mutual difference value is maximum as a representative reference image (representative reference cross section). Then, the reference image search unit 26 uses the representative reference image as a starting point, and the virtual period set by the virtual period setting unit 24 (FIG. 1) from among a plurality of tomographic images corresponding to the maximum mutual difference value, that is, The tomographic images closest to the positions separated by the virtual period determined to reduce the distortion are sequentially searched.

  First, as shown in FIG. 9A, a tomographic image closest to a position separated from the representative reference image by a virtual period (VHR) in the positive and negative directions in the Z-axis direction is searched for as a reference image. Next, as shown in FIG. 9B, the reference image search unit 26 searches for the tomographic image closest to the position separated from the searched reference image by the virtual period (VHR) to be a new reference image. . In FIG. 9B, broken arrows indicate the positions of a plurality of reference images (reference cross sections).

  The reference image search unit 26 searches for a plurality of reference images one after another using the representative reference image as a starting point. Thus, a plurality of reference images are searched from a plurality of tomographic images corresponding to the maximum mutual difference values as shown in FIG. 9C. In FIG. 9C, broken-line arrows indicate the positions of a plurality of reference images (reference cross sections). By correcting the position of the reference image in this way, an appropriate reference image is searched according to the fluctuation of the cycle even when a fetal heart or the like whose heart cycle is unstable is targeted for diagnosis.

  Returning to FIG. 8, when the position of the reference image is corrected, the reconstruction process is executed based on the corrected reference images as described with reference to FIGS. 4 and 5 (S807). The original image forming unit 34 forms a reconstructed image based on the reconstructed image sequence, and the reconstructed image is displayed on the display unit 36 (S808). In this way, a reconstructed image is displayed with reduced distortion, preferably with complete distortion removed.

  As mentioned above, although preferred embodiment of this invention was described, embodiment mentioned above is only a mere illustration in all the points, and does not limit the scope of the present invention. The present invention includes various modifications without departing from the essence thereof.

  10 probe, 12 beamformer, 16 error determination unit, 20 reconstruction processing unit, 22 operation device, 24 virtual cycle setting unit, 26 reference image search unit, 30 reference image forming unit, 32 image evaluation unit.

Claims (5)

A probe for transmitting and receiving ultrasonic waves to and from a three-dimensional space including a target tissue that moves periodically;
A transmission / reception control unit that controls the probe so as to form a plurality of scanning planes in the three-dimensional space while moving the scanning planes over a plurality of cycles of the movement;
A reference image search unit that searches a plurality of reference images at intervals corresponding to a virtual period of motion related to a target tissue from an image sequence composed of a plurality of images corresponding to the plurality of scanning planes;
The image sequence is rearranged by dividing the image sequence into a plurality of image groups using each of the plurality of reference images as a division unit, and extracting images periodically corresponding to each other from each of the plurality of image groups. A reconstruction processing unit for obtaining a reconstructed image sequence;
Based on the reconstructed image sequence, a reference image forming unit that forms a reference image showing a temporal change in the form of the target tissue accompanying exercise,
A virtual cycle setting unit that sets the corrected virtual cycle by correcting the virtual cycle according to an instruction from a user who refers to the reference image;
A reconstructed image forming unit that forms a reconstructed image of a target tissue based on the reconstructed image sequence obtained using the plurality of reference images searched based on the modified virtual period;
Having
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The reference image forming unit forms a tomographic reference image corresponding to a plane intersecting the scanning plane as the reference image;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The reference image forming unit forms a tomographic reference image showing the expanded portion and the reduced portion of the target tissue in different display modes;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 3,
An image evaluation unit that extracts a plurality of images corresponding to the same position from the reconstructed image sequence at different time phases and calculates a difference value between the extracted images,
An ultrasonic diagnostic apparatus. In the ultrasonic diagnostic apparatus according to any one of claims 1 to 4,
The reference image search unit sets one image corresponding to the maximum mutual difference value as a representative reference image based on a mutual difference value corresponding to each of a plurality of images constituting the image sequence, and the representative reference image is As a starting point, from among a plurality of images corresponding to the maximum mutual difference value, sequentially search for the image closest to the position separated by the modified virtual period, the plurality of reference images,
An ultrasonic diagnostic apparatus.

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