JP2011056158A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out reconstruction processing that reduces distortion of an object tissue due to motion. <P>SOLUTION: A distortion evaluating section 24 measures a time change of the shape of an object tissue due to motion at a plurality of positions arranged along the moving direction of a scanning surface within a reconstructed image. The distortion evaluating section 24 then evaluates distortion of the reconstructed image by comparing a plurality of time changes acquired from the plurality of positions. A frame interval for forming a reconstructed image is changed in a stepwise fashion and distortion is evaluated for each step. Reconstruction processing is carried out by using an optimal frame interval which gives the smallest distortion among all the frame intervals and a reconstructed image is formed. <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 transmission / reception control unit that controls a probe so as to form a plurality of scanning planes in the three-dimensional space, and a scanning plane interval corresponding to the period of motion from among a plurality of images corresponding to the plurality of scanning planes. A reference image search unit for searching for a plurality of reference images, and dividing each of the plurality of images into a plurality of image groups by using each of the plurality of reference images as a unit of division, and periodically repeating each of the plurality of image groups. Extracting a plurality of images corresponding to each other, an image reconstruction unit that forms a reconstructed image of the target tissue, and a plurality of positions aligned in the direction of movement of the scanning plane in the reconstructed image, Pair with exercise A distortion evaluation unit that measures distortions of the reconstructed image by measuring temporal changes in the morphology of the tissue and comparing multiple temporal changes obtained from the multiple positions so that the distortions are reduced. And adjusting the scanning plane interval.

  In a desirable specific example, the distortion evaluation unit measures a time change of a length in a radial direction of the target tissue in a scanning plane corresponding to each position as a time change of the form of the target tissue. .

  In a preferred embodiment, the distortion evaluation unit evaluates the distortion by comparing a plurality of time changes obtained from the plurality of positions on the same time axis.

  In a preferred embodiment, the distortion evaluation unit evaluates the distortion based on a degree of overlap with respect to a plurality of regions surrounded by each waveform of the plurality of time changes and the time axis.

  In a desirable specific example, the distortion evaluation unit sets a reference line in the target tissue based on a center point in the target tissue, and as a time change of the length in the radial direction, from the reference line to the target tissue boundary. It measures the time change of length.

  In a preferred embodiment, the ultrasonic diagnostic apparatus sequentially performs distortion evaluation on the formed reconstructed image, correction of the scan plane interval, and formation of a reconstructed image based on the corrected scan plane interval. By repeating the search, the scanning plane interval that minimizes the distortion is searched.

  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 measurement of the time change regarding the form of an object structure | tissue. It is a figure for demonstrating the evaluation of the distortion by the distortion evaluation part 24. FIG. It is a flowchart which shows the process which reduces the distortion of a reconstructed 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 22 searches the plurality of tomographic image data stored in the previous memory 14 for a plurality of reference images at frame intervals (image intervals) corresponding to the period of motion related to the target tissue. 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 as a plurality of images by setting each of the plurality of reference images as a unit of division. Reconstruction processing (reconstruction processing) is realized by dividing into groups and extracting a plurality of tomographic image data periodically corresponding to each other from each of the 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 26.

  FIG. 4 is a diagram for explaining the processing by the reconstruction processing unit 20. FIG. 4 shows the correspondence between the data stored in the front memory 14 and the data stored in the rear memory 26. . 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 a plurality of tomographic image data in the order of tomographic images Z1, tomographic images Z2,..., Tomographic images Z60,.

  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 Z <b> 1, the tomographic image Z <b> 15,..., The tomographic image Z <b> 51 are a plurality of reference images searched by the reference image search unit 22. 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. The extracted tomographic image Z1, tomographic image Z15,..., And tomographic image Z51 are stored in the rear memory 26 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 as one data block in the rear memory 26.

  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 26.

  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 26 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 26. 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 number of e data blocks are formed in the rear memory 26.

  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 26.

  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, the data block corresponding to the reference image is shifted from the center of all the data blocks in the rear memory 26.

  Returning to FIG. 1, the three-dimensional image forming unit 28 forms three-dimensional image data that three-dimensionally displays the fetal heart based on a plurality of reconstructed tomographic image data stored in the rear memory 26. The three-dimensional image forming unit 28 forms three-dimensional image data for each time phase based on one data block stored in the post-memory 26. 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 26 shown in FIG. ,..., Three-dimensional image data of time phase T2 is formed based on the tomographic image Z52. Alternatively, the three-dimensional image data of the time phases T1 to Te is formed by forming the three-dimensional image data of each time phase based on each of the total number e of data blocks formed in the post-memory 26 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 28 applies various methods such as a volume rendering method, an integration method, and a projection method to form 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 30, 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.

  As described above, in the present embodiment, a plurality of reference images are searched at frame intervals (image intervals) corresponding to the period of motion related to the target tissue, and based on the searched plurality of reference images, the previous memory 14 is searched. A plurality of tomographic image data stored in is divided into a plurality of image groups to realize reconstruction processing. However, if the frame interval serving as the interval between the plurality of reference images deviates from the period of motion related to the target tissue, for example, the period of the heartbeat of the fetus, the target tissue such as the heart is included in the moving image obtained by reconstruction. It appears to be distorted and exercise. In other words, the period of movement is shifted for each part in the target tissue, and the heart that moves originally in synchronization with each other may appear to move out of synchronization for each part.

  Therefore, in this embodiment, the distortion evaluation unit 24 evaluates the distortion of the reconstructed image, and the frame interval for extracting the reference image is adjusted so that the distortion is reduced. The distortion evaluation unit 24 measures temporal changes in the shape of the target tissue accompanying the motion at a plurality of positions arranged in the reconstructed image obtained by the reconstructing process along the moving direction of the scanning plane, The distortion of the reconstructed image is evaluated by comparing a plurality of time changes obtained from the positions.

  FIG. 6 is a diagram for explaining the measurement of the time change related to the form of the target tissue. FIG. 6I shows a plurality of tomographic images Sr included in the reconstructed image. 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. The plurality of tomographic images Sr are, for example, a tomographic image Z1, a tomographic image Z15,..., A tomographic image Z51 stored in the post-memory 26 shown in FIG. As described above, the reconstructed image (three-dimensional image data) (for example, time phase T1) is formed.

  First, an evaluation reference plane R is set for a reconstructed image composed of a plurality of tomographic images Sr. The evaluation reference plane R is preferably a plane that is parallel to the YZ plane and includes a central portion of the target tissue. For example, the user may specify the position of the evaluation reference plane R in the display image while viewing the reconstructed display image, or the distortion evaluation unit 24 may perform the target tissue in the reconstructed image by binarization processing or the like. The evaluation reference plane R may be set so as to identify the portion and pass through the center of gravity of the target tissue portion.

  FIG. 6 (II) shows a tomographic image of the target tissue on the evaluation reference plane R. That is, the boundary B of the target tissue is shown in the evaluation reference plane R. In this evaluation reference plane R, the center point P of the target tissue is set. For example, the user may specify the position of the center point P in the display image while viewing the display image of the evaluation reference plane R including the target tissue, or the distortion evaluation unit 24 may perform the target tissue by binarization processing or the like. May be identified, and the center point P may be set at the barycentric position of the region surrounded by the boundary B. When the center point P is set, the distortion evaluation unit 24 sets a reference line K that passes through the center point P and is parallel to the Z axis. Note that the reference line K may be set by the user.

  When the reference line K is set, the length (radius) from the reference line K to the boundary B of the target tissue is measured at a plurality of positions arranged at equal intervals along the reference line K, for example. That is, the length of each of the line segments L1 to L4 shown in FIG. 6 (II) is measured. The position of the boundary B of the target tissue (coordinate values in the YZ plane) is specified by extracting the target tissue using, for example, binarization processing and identifying the target tissue and other tissues. The 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.

  The distortion evaluation part 24 measures the time change of each length of line segment L1-L4 over several time phases. For example, for the reconstructed image of time phases T1 to Te formed based on each of the total number e of data blocks formed in the post-memory 26 shown in FIG. The length of each of the line segments L1 to L4 shown is measured. And the distortion evaluation part 24 evaluates the distortion of a reconstructed image by comparing the time change of the length of line segment L1-L4.

  FIG. 7 is a diagram for explaining the evaluation of distortion by the distortion evaluation unit 24. FIG. 7A shows a specific example when the distortion is large, and FIG. 7B shows a specific example when the distortion is small.

  The change with time of the lengths of the line segments L1 to L4 when the distortion is large is shown in (A1). In (A1), the horizontal axis is the time axis and the vertical axis is the length of each line segment. As shown in (A1), the distortion evaluation unit 24 measures the temporal changes in the lengths of the line segments L1 to L4 on the same time axis. If the time change of the length of line segment L1-L4 is measured, the variation | change_quantity of several time change will be normalized. The distortion evaluation unit 24 extracts, for example, peak values for each time-varying waveform, and enlarges / reduces each waveform in the length axis direction so that the peak values of a plurality of waveforms are aligned to the same value. Thereby, as shown to (A2), the height (size of a length-axis direction) of each waveform of line segment L1-L4 is arrange | equalized.

  And the distortion evaluation part 24 evaluates distortion based on the extent of the overlap regarding the several area | region enclosed by each waveform and time axis of normalized line segment L1-L4. The distortion evaluation unit 24 identifies a region surrounded by each waveform and the time axis, and extracts a region part of a logical product (AND) of a plurality of regions related to the plurality of waveforms. Thereby, as shown to (A3), the area | region part where all the four area | regions corresponding to line segment L1-L4 overlap is extracted. The distortion evaluation unit 24 calculates the area S of the extracted region portion as in (A3), and evaluates that the smaller the calculated area S, the greater the distortion. For example, based on the area S, the distortion value D (= 1 / S) is calculated.

  On the other hand, the time change of the length of line segment L1-L4 in case distortion is small is shown by (B1). Compared to (A1), in (B1), the four time-change waveforms are almost aligned on the time axis. When the waveform shown in (B1) is normalized so that the peak values are aligned as in the case of (A2), the waveform shown in (B2) is obtained. Then, a region portion where all the four regions related to the four waveforms shown in (B2) overlap is extracted and becomes a region portion shown in (B3). The distortion evaluation unit 24 calculates a distortion value D (= 1 / S) based on the area S of the region portion shown in (B3).

  Note that a logical sum (OR) region of the four regions corresponding to the line segments L1 to L4 may be extracted, and it may be evaluated that the larger the area, the greater the distortion.

  Line segments L1 to L4 are the lengths in the radial direction at a plurality of positions (parts) related to the target tissue in the reconstructed image (see FIG. 6). Therefore, the movement of the target tissue at the position corresponding to each line segment is reflected in the time change of the line segments L1 to L4. When the waveforms of the time changes of the line segments L1 to L4 are greatly deviated from each other on the time axis as shown in FIG. 7A, the period of motion at a plurality of positions of the target tissue is deviated, and reconstruction In the moving image of the image, the target tissue appears to distort and move as a whole. On the other hand, when the time-change waveforms of the line segments L1 to L4 are substantially aligned on the time axis as shown in FIG. 7B, the motion cycles at the plurality of positions of the target tissue are aligned. In the moving image of the reconstructed image, the target tissue appears to move in synchronism as a whole.

  In this embodiment, the frame interval used for searching for a plurality of reference images is changed in stages, and a reconstructed image is formed for each changed frame interval. The distortion of the reconstructed image is reduced by evaluating the distortion and adjusting the frame interval so that the distortion is reduced.

  FIG. 8 is a flowchart showing a process for reducing the distortion of the reconstructed image. 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 frame interval for extracting a plurality of reference images is set (S802). For example, the frame interval is set to a preset initial value. Then, based on the set frame interval, as described with reference to FIGS. 4 and 5, the reconstruction process is executed to form a reconstructed image (S803).

  When the reconstructed image is formed, as described with reference to FIG. 6, line segments L1 to L4 corresponding to a plurality of positions related to the target tissue in the reconstructed image are set, and each of the line segments L1 to L4 is set. Is measured over time (S804). Then, as described with reference to FIG. 7, the temporal changes in the lengths of the line segments L1 to L4 are compared to evaluate distortion (S805). In this distortion evaluation, when it is determined that the distortion is small, the frame interval at that time is set as the optimum frame interval. In the first distortion evaluation after the start of this flowchart, the first frame interval is set as the optimum frame interval.

  Next, the end of the evaluation is determined (S806). The evaluation of distortion is performed at each stage by changing the frame interval in stages. For example, an upper limit value and a lower limit value related to the frame interval are provided in advance, and the frame interval is changed stepwise between the upper limit value and the lower limit value. If the change of the frame interval is not completed, the process returns from S806 to S802, the frame interval is changed, and the processes from S803 to S805 are executed.

  On the other hand, when the evaluation for all the frame intervals is completed, the process proceeds from S806 to S807, and the reconstruction process is performed at the optimum frame interval determined to have the smallest distortion among all the frame intervals to form a reconstructed image. Is done. Then, the reconstructed image is displayed on the display unit 30 (S808). In this way, reconstruction processing with reduced motion distortion related to the target tissue is realized.

  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 reference image search unit, 24 distortion evaluation unit, 28 three-dimensional image formation unit.

Claims (6)

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 a scan plane interval corresponding to the period of motion from a plurality of images corresponding to the plurality of scan planes;
By dividing each of the plurality of reference images into a plurality of images by dividing each of the plurality of reference images into a plurality of image groups, and extracting a plurality of images periodically corresponding to each other from each of the plurality of image groups, An image reconstruction unit for forming a reconstructed image of the target tissue;
At a plurality of positions arranged in the reconstructed image along the moving direction of the scanning plane, time changes in the form of the target tissue accompanying the movement are measured, and a plurality of time changes obtained from the plurality of positions are compared. A distortion evaluation unit that evaluates the distortion of the reconstructed image,
Have
Adjusting the scan plane spacing so as to reduce the distortion;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The distortion evaluation unit measures the time change of the length in the radial direction of the target tissue in the scanning plane corresponding to each position as the time change of the shape of the target tissue.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The distortion evaluation unit evaluates the distortion by aligning and comparing a plurality of time changes obtained from the plurality of positions on the same time axis.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 3.
The distortion evaluation unit evaluates the distortion based on the degree of overlap related to a plurality of regions surrounded by each waveform of the plurality of time changes and the time axis.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 2 to 4,
The distortion evaluation unit sets a reference line in the target tissue based on a center point in the target tissue, and a time change in length from the reference line to the target tissue boundary as a time change in length in the radial direction Measuring
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 5,
The scanning that minimizes the distortion by sequentially repeating the evaluation of the distortion regarding the formed reconstructed image, the correction of the scan plane interval, and the formation of the reconstructed image based on the corrected scan plane interval. Search for surface spacing,
An ultrasonic diagnostic apparatus.

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