JP2018114018A - Medical image processing apparatus and radiodiagnostic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medical image processing apparatus and a radiodiagnostic apparatus capable of quickly generating a high-resolution two-dimensional image based on tomosynthetically obtained three-dimensional image data.SOLUTION: A medical image processing apparatus according to the embodiment comprises an image reconstruction unit, a calculation unit, and a generation unit. The image reconstruction unit reconstructs three-dimensional image data from a plurality of projection data sets collected as a projection angle of an X ray from an X-ray tube to a subject is being changed. The calculation unit calculates a resolution in the direction in which the X-ray tube is moved when changing the projection angle with respect to each pixel in a plurality of slices in the three-dimensional image data. The generation unit generates two-dimensional image data by combining the plurality of slices based on the calculated resolution.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a medical image processing apparatus and an X-ray diagnostic apparatus.

  A method (tomosynthesis) is known in which a plurality of projection data is acquired while changing an X-ray irradiation angle from an X-ray tube to a subject, and an image having three-dimensional information is reconstructed from the plurality of projection data. Yes. Hereinafter, an image having three-dimensional information by tomosynthesis is also simply referred to as three-dimensional image data. Of the multiple slices of 3D image data obtained by tomosynthesis, the slice corresponding to the position of the lesion, such as the calcified portion of the mammary gland, is focused (focused) on the lesion, and the lesion has a high resolution. Expressed. On the other hand, in the slice in the vicinity of the slice where the lesion is located, the lesion is out of focus and the lesion is blurred. For example, the doctor can sequentially interpret a plurality of slices of the three-dimensional image data, and can find and observe a lesioned part by paying attention to the focused slice.

Japanese Patent No. 5696305 Special table 2014-534042 gazette Japanese Patent Application Laid-Open No. 2015-066434

  The problem to be solved by the present invention is to provide a medical image processing apparatus and an X-ray diagnostic apparatus capable of quickly generating a high-resolution two-dimensional image based on three-dimensional image data obtained by tomosynthesis.

  The medical image processing apparatus according to the embodiment includes an image reconstruction unit, a calculation unit, and a generation unit. The image reconstruction unit reconstructs three-dimensional image data from a plurality of projection data collected by changing the X-ray irradiation angle from the X-ray tube to the subject. The calculation unit calculates, for each pixel of the plurality of slices in the three-dimensional image data, a resolution in a direction in which the X-ray tube has moved when changing the irradiation angle. The generation unit generates two-dimensional image data by combining the plurality of slices based on the calculated resolution.

FIG. 1 is a block diagram showing an example of the configuration of the X-ray diagnostic apparatus according to the first embodiment. FIG. 2A is a diagram for explaining the collection of projection data according to the first embodiment. FIG. 2B is a diagram for explaining the collection of projection data according to the first embodiment. FIG. 2C is a diagram for explaining the collection of projection data according to the first embodiment. FIG. 3 is a diagram for explaining the reconstruction of 3D image data according to the first embodiment. FIG. 4A is a diagram for describing the two-dimensional image data according to the first embodiment. FIG. 4B is a diagram for describing the two-dimensional image data according to the first embodiment. FIG. 5A is a diagram for describing setting of a region of interest according to the first embodiment. FIG. 5B is a diagram for describing setting of a region of interest according to the first embodiment. FIG. 5C is a diagram for describing setting of a region of interest according to the first embodiment. FIG. 6 is a flowchart for explaining a series of processing steps of the X-ray diagnostic apparatus according to the first embodiment.

  Hereinafter, a medical image processing apparatus according to an embodiment will be described with reference to the drawings. Hereinafter, an X-ray diagnostic apparatus including the medical image processing apparatus according to the embodiment will be described. Hereinafter, a case where the X-ray diagnostic apparatus according to the embodiment is a mammography apparatus will be described as an example.

(First embodiment)
First, an example of the X-ray diagnostic apparatus 1 according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating an example of the configuration of the X-ray diagnostic apparatus 1 according to the first embodiment. As shown in FIG. 1, the X-ray diagnostic apparatus 1 according to the first embodiment includes a base 101 and a stand 102. The stand 102 is erected on the base 101 and supports the imaging table 103, the compression plate 104, the X-ray tube 105, the X-ray diaphragm 106, the X-ray detector 107, and the signal processing circuit 108. To do. Here, the stand 102 supports the imaging table 103, the compression plate 104, the X-ray detector 107, and the signal processing circuit 108 so as to be movable in the vertical direction.

  The imaging table 103 is a table that supports the subject P, and has a support surface on which the subject P is placed. Here, the subject P is, for example, a patient's breast. The compression plate 104 is disposed above the imaging table 103, and is provided so as to be opposed to the imaging table 103 in parallel and to be movable toward and away from the imaging table 103. Note that the compression plate 104 compresses the subject P supported on the imaging table 103 when moving in a direction approaching the imaging table 103. The subject P compressed by the compression plate 104 is thinly spread and the overlap of mammary glands in the subject P is reduced.

  The X-ray tube 105 generates X-rays using the high voltage supplied from the high voltage generator 111. The X-ray restrictor 106 is disposed between the X-ray tube 105 and the compression plate 104 and controls the irradiation range of X-rays generated from the X-ray tube 105. Here, the X-ray tube 105 is configured to be movable so that the irradiation angle of the X-rays to the subject P can be changed. The movement of the X-ray tube 105 will be described later.

  The X-ray detector 107 detects X-rays transmitted through the subject P and the imaging table 103 and converts them into electrical signals (transmitted X-ray data). The X-ray detector 107 includes, for example, a CMOS (Complementary Metal Oxide Semiconductor) sensor pixel. For example, the X-ray detector 107 first detects an X-ray pulse emitted from the X-ray tube 105 and generates an electrical signal. Next, the electrical signal generated by the X-ray detector 107 is held by the X-ray detector 107 and read out after irradiation with the X-ray pulse. The signal processing circuit 108 generates projection data from the electrical signal converted by the X-ray detector 107 and stores the projection data in the storage circuit 112.

  As illustrated in FIG. 1, the X-ray diagnostic apparatus 1 includes an input circuit 109, a lift drive circuit 110, a high voltage generator 111, a storage circuit 112, a display 113, and a processing circuit 114.

  The input circuit 109 receives various instructions from an operator who operates the X-ray diagnostic apparatus 1. For example, the input circuit 109 includes a mouse, a keyboard, a button, a trackball, a joystick, a touch panel, and the like.

  The elevation drive circuit 110 is connected to the imaging table 103 and raises / lowers the imaging table 103 in the vertical direction under the control of the processing circuit 114. Further, the elevation drive circuit 110 is connected to the compression plate 104 and raises and lowers the compression plate 104 in the up and down direction (the direction in which the imaging plate 103 contacts and separates) under the control of the processing circuit 114.

  The high voltage generator 111 is connected to the X-ray tube 105 and supplies a high voltage for generating X-rays to the X-ray tube 105 under the control of the processing circuit 114.

  The storage circuit 112 stores various image data generated by the X-ray diagnostic apparatus 1. For example, the storage circuit 112 stores projection data, 3D image data, and 2D image data described later. The storage circuit 112 stores data used when the processing circuit 114 controls the entire processing performed by the X-ray diagnostic apparatus 1. For example, the storage circuit 112 stores a program executed by each circuit shown in FIG.

  The display 113 displays a GUI (Graphical User Interface) for accepting various command input operations from the operator. Further, the display 113 displays an image generated by the X-ray diagnostic apparatus 1. For example, the display 113 displays 3D image data described later for each slice, or displays 2D image data described later.

  The processing circuit 114 controls the overall operation of the X-ray diagnostic apparatus 1 by executing a control function 114a, an image reconstruction function 114b, a calculation function 114c, and a generation function 114d. For example, the processing circuit 114 reads the program corresponding to the control function 114a from the storage circuit 112 and executes it, thereby controlling the projection data collection process. Further, for example, the processing circuit 114 reads out and executes a program corresponding to the generation function 114d from the storage circuit 112, thereby performing logarithmic conversion processing, offset correction, sensitivity on the projection data generated by the signal processing circuit 108. Correction processing such as correction and beam hardening correction is performed to generate corrected projection data, which is stored in the storage circuit 112.

  Further, for example, the processing circuit 114 reads out a program corresponding to the image reconstruction function 114b from the storage circuit 112 and executes it, thereby executing a plurality of projection data (correction) collected by changing the irradiation angle to the subject P. 3D image data by tomosynthesis is reconstructed on the basis of the projection data). Further, for example, the processing circuit 114 reads out and executes a program corresponding to the calculation function 114c and the generation function 114d from the storage circuit 112, thereby generating two-dimensional image data from the three-dimensional image data by tomosynthesis. The reconstruction of the 3D image data and the generation of the 2D image data will be described later.

  The processing circuit 114 reads the program corresponding to the generation function 114d from the storage circuit 112 and executes it, thereby changing the positions of the imaging table 103 and the compression plate 104 in the MLO (Mediolateral-Oblique) direction or the CC. (Cranio-Caudal: head-to-tail) direction and mammography such as MLO image and CC image based on projection data collected by irradiating X-rays with the irradiation angle to the subject P kept constant An image can also be generated.

  Here, in the X-ray diagnostic apparatus 1 shown in FIG. 1, each processing function is stored in the storage circuit 112 in the form of a program executable by a computer. The signal processing circuit 108, the elevation drive circuit 110, and the processing circuit 114 are processors that realize functions corresponding to each program by reading the program from the storage circuit 112 and executing the program. In other words, each circuit that has read each program has a function corresponding to the read program. In FIG. 1, the control function 114a, the image reconstruction function 114b, the calculation function 114c, and the generation function 114d are described as being realized by the single processing circuit 114. However, the processing is performed by combining a plurality of independent processors. The circuit 114 may be configured so that each processor realizes a function by executing a program.

  The term “processor” used in the above description is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an application specific integrated circuit (ASIC), a programmable logic device (for example, It means circuits such as a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). The processor implements a function by reading and executing a program stored in the storage circuit 112. Instead of storing the program in the storage circuit 112, the program may be directly incorporated in the processor circuit. In this case, the processor realizes the function by reading and executing the program incorporated in the circuit. Note that each processor of the present embodiment is not limited to being configured as a single circuit for each processor, but may be configured as a single processor by combining a plurality of independent circuits to realize the function. Good. Furthermore, a plurality of components in FIG. 1 may be integrated into one processor to realize the function.

  The configuration of the X-ray diagnostic apparatus 1 has been described above. Under such a configuration, the X-ray diagnostic apparatus 1 quickly generates a two-dimensional image with high resolution based on three-dimensional image data obtained by tomosynthesis. Hereinafter, processing performed by the X-ray diagnostic apparatus 1 according to the first embodiment will be described in detail.

  For example, as shown in FIG. 1, after the subject P is arranged so as to be compressed by the imaging table 103 and the compression plate 104, the control function 114 a controls the collection of projection data of the subject P. Here, the control function 114a collects a plurality of projection data used to reconstruct three-dimensional image data by tomosynthesis while changing the X-ray irradiation angle. Hereinafter, the collection of projection data related to tomosynthesis will be described with reference to FIGS. 2A, 2B, and 2C. 2A, 2B, and 2C are diagrams for explaining the collection of projection data according to the first embodiment.

  2A shows the case where the X-ray tube 105 is located at the position X1, FIG. 2B shows the case where the X-ray tube 105 is located at the position X2, and FIG. 2C shows the X-ray tube 105 located at the position X3. Show the case. As shown in FIGS. 2A, 2B, and 2C, the X-ray tube 105 moves in a trajectory including a position X1, a position X2, and a position X3. 2A, 2B, and 2C indicate a part of X-rays emitted from the X-ray tube 105.

  Here, the X-ray irradiation angle is, for example, an angle indicated by a straight line connecting the position of the X-ray tube 105 that irradiates the subject P with X-rays and the position of the subject P. For example, the position of the X-ray tube 105 is the position of the X-ray focal point. The position of the subject P is, for example, the center when the shape of the subject P is regarded as an ellipse. As shown in FIGS. 2A, 2B, and 2C, the X-ray tube 105 moves so as to change the X-ray irradiation angle.

  First, the control function 114a controls X-ray irradiation from the X-ray tube 105 at the position X1 to the subject P as shown in the upper diagram of FIG. 2A. Here, the irradiated X-rays are detected by the X-ray detector 107 after passing through the compression plate 104, the subject P, and the imaging table 103, and the signal processing circuit 108 uses the projection data A1 shown in the lower diagram of FIG. 2A. Generate. Here, the part a, the part b, and the part c in the subject P are respectively projected at positions shown on the projection data A1 in the lower diagram of FIG. 2A.

  Next, as shown in the upper diagram of FIG. 2B, the control function 114a changes the X-ray irradiation angle from the state shown in FIG. 2A to irradiate the subject P with X-rays from the X-ray tube 105 at the position X2. Control. Further, the signal processing circuit 108 generates projection data A2 shown in the lower diagram of FIG. 2B. Here, the part a, the part b, and the part c in the subject P are respectively projected so as to be superimposed on the positions shown on the projection data A2 in the lower diagram of FIG. 2B.

  Further, as shown in the upper diagram of FIG. 2C, the control function 114a changes the X-ray irradiation angle from the state shown in FIG. 2B to control the X-ray irradiation from the X-ray tube 105 at the position X3 to the subject P. To do. Further, the signal processing circuit 108 generates projection data A3 shown in the lower diagram of FIG. 2C. Here, the part a, the part b, and the part c in the subject P are respectively projected at the positions shown on the projection data A3 in the lower diagram of FIG. 2C.

  The control function 114a performs control so that X-rays are emitted from the X-ray tube 105 when the X-ray tube 105 is positioned at the position X1, the position X2, the position X3, or the like while continuously changing the position of the X-ray tube 105. Alternatively, the control function 114a irradiates the X-ray from the X-ray tube 105 stopped at the position X1, the position X2, the position X3, or the like by alternately repeating the movement of the X-ray tube 105 and the X-ray irradiation. You may control.

  As shown in FIGS. 2A, 2B, and 2C, the position of the X-ray tube 105 moves in the X direction. That is, the control function 114a controls the X-ray tube 105 to move in the X direction so as to change the X-ray irradiation angle with respect to the subject P. The trajectory when the X-ray tube 105 moves in the X direction may be an arc as shown in FIGS. 2A, 2B, and 2C, may be a straight line, or may be another trajectory.

  Next, the image reconstruction function 114b reconstructs three-dimensional image data from a plurality of projection data (for example, projection data A1, projection data A2, and projection data A3) collected by changing the irradiation angle. Here, reconstruction of three-dimensional image data by tomosynthesis will be described with reference to FIG. FIG. 3 is a diagram for explaining the reconstruction of 3D image data according to the first embodiment. In the following, a shift addition method will be described as an example of an image reconstruction method.

  For example, the image reconstruction function 114b adds the projection data A1, the projection data A2, and the projection data A3 shown in the upper diagram of FIG. 3 so as to match the position where the part a is projected on each projection data. A slice B1 shown in the following figure is generated. In the slice B1, the portion of the projection data A1, the projection data A2, and the projection data A3 onto which the portion a is projected is added in alignment, so that the portion a is clearly expressed.

  Here, each projection data includes a signal indicating the part b and the part c, but the signals of the part b and the part c on the slice B1 are superimposed on the slice B1 because the positions are shifted. Spread and be expressed. Therefore, as shown in the lower diagram of FIG. 3, the slice B1 includes signals of the part a, the part b, and the part c, but only the part a is clearly expressed. That is, the image reconstruction function 114b generates the slice B1 with the XY plane including the part a in the subject P as the reconstruction surface.

  Similarly, the image reconstruction function 114b adds the projection data A1, the projection data A2, and the projection data A3 so as to match the position where the part b is projected on each projection data, and generates a slice B2 (not shown). . That is, the image reconstruction function 114b generates the slice B2 with the XY plane including the part b in the subject P as the reconstruction surface. Further, the image reconstruction function 114b adds the projection data A1, the projection data A2, and the projection data A3 so as to match the position where the portion c is projected on each projection data, and generates a slice B3 (not shown). That is, the image reconstruction function 114b generates a slice B3 with the XY plane including the part c in the subject P as a reconstruction surface.

  As described above, the image reconstruction function 114b uses a plurality of projection data to generate a plurality of slices while shifting the reconstruction plane. Each slice has two-dimensional information on the XY plane, and by generating a plurality of slices whose positions are shifted in the Z direction, the image reconstruction function 114b generates three-dimensional image data having three-dimensional information. Can be reconfigured.

  After the 3D image data is reconstructed, the control function 114a causes the display 113 to display the 3D image data. For example, the control function 114a displays any one of a plurality of slices in the three-dimensional image data, or sequentially displays the plurality of slices. In the slice of the three-dimensional image data displayed in this way, the overlap of information in the Z direction is reduced, and for example, the interpretation of a lesion that becomes difficult to see when the mammary glands overlap is facilitated.

  For example, the control function 114a displays the slice B1 shown in FIG. 3 on the display 113, thereby presenting an XY plane including the part a to an operator (such as a doctor). Here, when the part a is a lesion (for example, calcification of the mammary gland), the operator can easily find the lesion and observe the lesion. Furthermore, the control function 114a enables three-dimensional interpretation by displaying the slice B2 and the slice B3 on the display 113.

  In addition, the control function 114a causes the display 113 to display 2D image data generated from 3D image data. For example, the generation function 114d generates two-dimensional image data from the three-dimensional image data by a method such as a maximum value projection method (MIP: Maximum Intensity Projection) or a minimum value projection method (MinIP: Minimum Intensity Projection). 114 a causes the display 113 to display the generated two-dimensional image data. Note that two-dimensional image data generated by synthesizing slices of three-dimensional image data by tomosynthesis is also referred to as Synthesize 2D or Synthesized 2D. Here, as an example, two-dimensional image data based on MinIP will be described with reference to FIGS. 4A and 4B. 4A and 4B are diagrams for explaining the two-dimensional image data according to the first embodiment.

  The left diagram in FIG. 4A shows three-dimensional image data of “3 pixels” in the X-axis direction, the Y-axis direction, and the Z-axis direction, among the three-dimensional image data reconstructed by the image reconstruction function 114b. Moreover, the middle figure of FIG. 4A shows the pixel value of each pixel for every slice on XY plane in three-dimensional image data. That is, the middle diagram of FIG. 4A shows the pixel value of each pixel on the slice “Z = 1”, the pixel value of each pixel on the slice “Z = 2”, and the slice value “Z = 3”. The pixel value of each pixel is shown.

  The generation function 114d selects the smallest pixel value among the corresponding pixels (pixels having the same X coordinate and Y coordinate) of the plurality of slices, and thereby a two-dimensional image as illustrated in the right diagram of FIG. 4A. Generate data. For example, the pixel value of the center pixel of each slice is “4” in the “Z = 1” slice, “2” in the “Z = 2” slice, and “2” in the “Z = 3” slice. 4 ”, the generation function 114d selects“ 2 ”as the pixel value of the center pixel of the two-dimensional image data.

  Here, when two-dimensional image data is generated by MIP or MinIP shown in FIG. 4A, the two-dimensional image data may be blurred as shown in FIG. 4B. FIG. 4B is two-dimensional image data of the subject P including a calcified site. For example, in the region R1 of the two-dimensional image data shown in FIG. 4B, calcification is expressed so as to spread in the X direction. Similarly, the region R2 of the two-dimensional image data shown in FIG. 4B is buried in noise, and calcification cannot be clearly expressed.

  The blur shown in FIG. 4B is caused by the blur included in each slice of the three-dimensional image data of tomosynthesis. For example, in the slice B1 reconstructed with the XY plane including the part a as a reconstruction plane, the part b, the part c, and the like are opened and expressed. Similarly, the slice B2 reconstructed with the XY plane including the part b as the reconstruction plane is represented by the part a, the part c, etc., and the slice B3 reconstructed with the XY plane including the part c as the reconstruction plane. Is expressed with the part a, the part b, and the like.

  Here, for example, when only the part a is a calcified portion, the slice B1 in focus on the calcified portion does not produce a blur, but the slice B2 and the slice B3 have a calcified portion. Expressed. That is, in the slice B2 and the slice B3, a blur (flow line) in the same direction as the direction in which the X-ray tube 105 moves when changing the irradiation angle is generated, and the blur is applied to the two-dimensional image data by MinIP. Remains.

  Therefore, in order to reduce the blur in the X direction in the two-dimensional image data and generate the two-dimensional image data without impairing the resolution obtained by tomosynthesis, the calculation function 114c is provided for each of a plurality of slices in the three-dimensional image data. The resolution in the X direction is calculated for the pixel, and the generation function 114d generates two-dimensional image data by synthesizing a plurality of slices based on the calculated resolution. Hereinafter, this point will be described in detail.

  First, the calculation function 114c extends the direction (X direction) in which the X-ray tube 105 moves when the irradiation angle is changed for each pixel of a plurality of slices in the three-dimensional image data reconstructed by the image reconstruction function 114b. Set the direction area. In other words, the calculation function 114c sets a long region in the blur direction (X direction) for each pixel of the plurality of slices. Hereinafter, a region set for each pixel of a plurality of slices is also referred to as a region of interest.

  For example, as shown in FIG. 5A, the calculation function 114c sets a rectangular region of interest T1 having the X direction as a longitudinal direction. FIG. 5A is a diagram for describing setting of a region of interest according to the first embodiment. FIG. 5A represents a slice B4 that does not include any blur in the X direction among a plurality of slices in the three-dimensional image data. Moreover, the six white spots shown in FIG. 5A indicate, for example, calcified portions of the mammary gland. That is, the slice B4 is a slice focused on the calcified portion of the mammary gland.

  The region of interest T1 in FIG. 5A is a region of interest set for a pixel located at the center of the region of interest T1, for example. The calculation function 114c similarly sets a region of interest that is long in the X direction for each pixel of the slice B4 illustrated in FIG. 5A. For example, the calculation function 114c sets the region of interest T1 illustrated in FIG. 5A while translating one pixel at a time in the X direction or the Y direction.

  Furthermore, the calculation function 114c sets a region of interest that is long in the X direction for each of a plurality of slices in the three-dimensional image data. For example, as illustrated in FIG. 5B, the calculation function 114 c generates a rectangular region of interest T <b> 2 having the X direction as the longitudinal direction for the pixel of the slice B <b> 5 including the blur in the X direction among the plurality of slices in the three-dimensional image data. Set. FIG. 5B is a diagram for describing setting of a region of interest according to the first embodiment. In FIG. 5B, the six calcification parts are expressed in the X direction. That is, the slice B5 is a slice out of focus with respect to the calcified portion of the mammary gland.

  Further, for example, as illustrated in FIG. 5C, the calculation function 114 c performs X-direction on a pixel of the slice B6 that is disposed in the X-direction so that six calcified portions cannot be recognized among a plurality of slices in the three-dimensional image data. A rectangular region of interest T3 is set with a longitudinal direction of. FIG. 5C is a diagram for describing setting of a region of interest according to the first embodiment. That is, the slice B6 is a slice whose focus is greatly deviated from the calcified portion of the mammary gland.

  Next, the calculation function 114c calculates the resolution in the region of interest set for each pixel of the plurality of slices as the resolution in the direction (X direction) moved when the X-ray tube 105 changes the irradiation angle. For example, the calculation function 114c calculates the resolution in the region of interest T1 illustrated in FIG. 5A as the resolution in the X direction for the pixel located at the center of the region of interest T1.

  For example, the calculation function 114c first obtains a Fourier transform of the autocorrelation function of the image in the region of interest T1 in FIG. 5A. For example, the calculation function 114c performs a Fourier transform on the image in the region of interest T1, squares and adds the real part and the imaginary part output as a result of the Fourier transform, and thereby adds the image of the image in the region of interest T1. Find the Fourier transform of the autocorrelation function. Then, the calculation function 114c calculates “a value corresponding to a high frequency” among the results of Fourier-transforming the autocorrelation function of the image in the region of interest T1 as the resolution in the region of interest T1. Here, as the “value corresponding to the high frequency”, for example, an amplitude value of an autocorrelation function with respect to a preset frequency value or a square thereof can be used. Further, for example, the amplitude value of the autocorrelation function or the square thereof may be integrated for a region having a frequency higher than a preset frequency threshold value, and this may be set as a “value corresponding to a high frequency”. Moreover, you may use what normalized these values suitably. That is, various values can be used as long as the high frequency component of the autocorrelation function is evaluated. Similarly, the calculation function 114c calculates the resolution in the region of interest set for each pixel of the slice B4 shown in FIG. 5A.

  The calculation function 114c calculates the resolution in the region of interest set for each pixel for each of a plurality of slices in the three-dimensional image data such as the slice B5 shown in FIG. 5B and the slice B6 shown in FIG. 5C. The calculation function 114c may use the above-described value corresponding to the high frequency as the resolution, or may use the value based on the value corresponding to the high frequency (for example, a value obtained by multiplying the value corresponding to the high frequency by a coefficient) as the resolution. Good.

  Here, when the resolution in the region of interest T1 in FIG. 5A is compared with the resolution in the region of interest T2 in FIG. 5B and the resolution in the region of interest T3 in FIG. 5C, the resolution in the region of interest T1 is the largest. . That is, the region of interest T1 includes a signal (sharp signal) expressed without blurring, and the autocorrelation function based on the image in the region of interest T1 also has a sharp shape. When a sharp autocorrelation function is Fourier transformed, a value (resolution) corresponding to a high frequency is a large value. On the other hand, the region of interest T2 includes a lost signal, and the autocorrelation function based on the image in the region of interest T2 has a gentle shape. When such an autocorrelation function is Fourier transformed, it corresponds to a high frequency. The value (resolution) to be performed is a small value. In a region of interest where the signal is so bright that the calcified portion cannot be recognized, such as the region of interest T3, image noise becomes the main signal in the region of interest, and the resolution is the smallest value.

  Here, the calculation function 114c can quickly calculate the resolution of each pixel by calculating the resolution within the region of interest that is long in the blur direction. That is, in the three-dimensional image data by tomosynthesis, the direction of blurring generated in the slice is the moving direction (X direction) of the X-ray tube 105, for example, the direction orthogonal to the moving direction of the X-ray tube 105 (Y direction). Since it is difficult for blurring to occur, the necessity for calculating the resolution in the Y direction is small. Accordingly, the calculation function 114c calculates the resolution within the region of interest that is long in the blur direction (X direction), thereby omitting part or all of the Y direction resolution calculation processing and reducing the calculation amount. The resolution can be calculated.

  Next, the generation function 114d generates two-dimensional image data by combining a plurality of slices in the three-dimensional image data based on the resolution calculated by the calculation function 114c. For example, the generation function 114d performs weighting according to the resolution on the pixel values of the pixels of the plurality of slices, and adds the weighted pixel values between the corresponding pixels of the plurality of slices to generate the two-dimensional image data Is generated. Here, the corresponding pixels of the plurality of slices are, for example, pixels having the same X coordinate and Y coordinate in each slice. For example, the central pixel of the region of interest T1 in FIG. 5A, the central pixel of the region of interest T2 in FIG. 5B, and the central pixel of the region of interest T3 in FIG. 5C are corresponding pixels.

  The pixel value of the central pixel of the region of interest T1 is “10”, the pixel value of the central pixel of the region of interest T2 is “8”, and the pixel value of the central pixel of the region of interest T3 is “2”. The resolution calculated for the region of interest T1 is “0.85”, the resolution calculated for the region of interest T2 is “0.10”, and the resolution calculated for the region of interest T3 is “0.05”. Taking a case as an example, processing by the generation function 114d will be described.

  First, the generation function 114d calculates a weighted pixel value by multiplying the pixel value of the center pixel of the region of interest by using the calculated resolution as a coefficient. For example, the generation function 114d calculates the weighted pixel value “8.5” by multiplying the region of interest T1 by the pixel value “10” and the resolution “0.85”. The generation function 114d multiplies the region of interest T2 by the pixel value “8” and the resolution “0.10” to calculate a weighted pixel value “0.8”. In addition, the generation function 114d calculates the weighted pixel value “0.1” by multiplying the region of interest T3 by the pixel value “2” and the resolution “0.05”.

  Next, the generation function 114d adds the weighted pixel values between corresponding pixels, and divides by the total value of the coefficients (resolution). For example, the generation function 114d performs the weighted pixel value “8.5” of the region of interest T1, the weighted pixel value “0.8” of the region of interest T2, and the weighted pixel value “0.1” of the region of interest T3. Are combined to calculate “9.4”. Next, the generation function 114d divides the total value “9.4” of the weighted pixel value by the total value “1.0” of the resolution, and the pixel value “9.4” of the pixel of the two-dimensional image data. Is calculated. The pixel value “9.4” of the pixel of the calculated two-dimensional image data is the pixel value of the region of interest T1 calculated with a higher resolution than the pixel value of the region of interest T2 or the region of interest T3 calculated with a low resolution. A close value.

  Further, the generation function 114d performs a process of adding pixel values between corresponding pixels of a plurality of slices with a weight corresponding to the resolution while shifting the X coordinate and the Y coordinate in each slice, thereby obtaining the two-dimensional image data. Generate. By adding the pixel values with weights according to the resolution, the generation function 114d changes the pixel value of each pixel of the two-dimensional image data to the pixel value of the high-resolution region of interest from the pixel value of the low-resolution region of interest. It can be a close value. That is, the generation function 114d generates two-dimensional image data in which a focused portion is emphasized in each slice and blur is reduced.

  Alternatively, the generation function 114d may be a case where two-dimensional image data is generated by synthesizing pixels having the highest resolution among corresponding pixels of a plurality of slices. For example, the generation function 114d calculates a weighted pixel value by setting the coefficient for the pixel having the highest resolution among the corresponding pixels of the plurality of slices to “1” and the coefficient for the other pixels as “0”. The calculated weighted pixel value is set as the pixel value of the two-dimensional image data. In such a case, the generation function 114d can generate two-dimensional image data in which the focused portions in each slice are connected.

  The generation function 114d stores the two-dimensional image data generated from the three-dimensional image data in the storage circuit 112. In addition, the control function 114 a reads the two-dimensional image data from the storage circuit 112 and displays it on the display 113.

  In the X-ray diagnostic apparatus 1, it is possible to switch the mode for generating 2D image data from 3D image data by tomosynthesis. For example, the X-ray diagnostic apparatus 1 calculates the resolution in the direction (X direction) moved when the X-ray tube 105 changes the irradiation angle, and synthesizes a plurality of slices based on the calculated resolution. It is possible to switch between a mode for generating two-dimensional image data, a mode for generating two-dimensional image data by MinIP, and a mode for generating two-dimensional image data by MIP.

  Next, an example of a processing procedure performed by the X-ray diagnostic apparatus 1 will be described with reference to FIG. FIG. 6 is a flowchart for explaining a series of processing flow of the X-ray diagnostic apparatus 1 according to the first embodiment. Step S101 is a step corresponding to the control function 114a. Step S102 is a step corresponding to the image reconstruction function 114b. Step S103 is a step corresponding to the calculation function 114c. Step S104 is a step corresponding to the generation function 114d.

  First, the processing circuit 114 collects a plurality of projection data while changing the X-ray irradiation angle with respect to the subject P disposed between the imaging table 103 and the compression plate 104 (step S101). Next, the processing circuit 114 reconstructs three-dimensional image data by tomosynthesis from a plurality of projection data (step S102).

  Next, the processing circuit 114 moves the X-ray tube 105 when each X-ray tube 105 changes the X-ray irradiation angle to the subject P for each pixel of the plurality of slices in the three-dimensional image data (which occurs in the plurality of slices). Resolution) is calculated (step S103). Then, the processing circuit 114 synthesizes a plurality of slices in the three-dimensional image data based on the calculated resolution, and generates two-dimensional image data (step S104).

  As described above, according to the first embodiment, the image reconstruction function 114b is obtained from a plurality of pieces of projection data collected by changing the X-ray irradiation angle from the X-ray tube 105 to the subject P. Reconstruct dimensional image data. The calculation function 114c calculates the resolution in the direction in which the X-ray tube 105 has moved when the irradiation angle is changed for each pixel of the plurality of slices in the three-dimensional image data. The generation function 114d generates two-dimensional image data by combining a plurality of slices based on the calculated resolution. Therefore, the X-ray diagnostic apparatus 1 according to the first embodiment can quickly generate two-dimensional image data with high resolution based on three-dimensional image data obtained by tomosynthesis. For example, the X-ray diagnostic apparatus 1 according to the first embodiment generates two-dimensional image data based on the resolution in each slice, and thus obtains two-dimensional image data with higher resolution than in the case of using MIP or MinIP. be able to.

  In addition, according to the first embodiment, the calculation function 114c includes the direction in which the X-ray tube 105 moves when changing the irradiation angle when calculating the resolution in each pixel of the plurality of slices of the three-dimensional image data. By providing anisotropy with the direction orthogonal to this, the resolution can be calculated quickly. Therefore, the X-ray diagnostic apparatus 1 according to the first embodiment can quickly generate two-dimensional image data.

  According to the first embodiment, the generation function 114d generates 2D image data from 3D image data. Therefore, the X-ray diagnostic apparatus 1 according to the first embodiment generates 3D image data and 2D image data in one imaging, and reduces the exposure amount of the subject P by reducing the number of imaging. can do.

(Second Embodiment)
The first embodiment has been described so far, but may be implemented in various different forms other than the above-described embodiment.

  In the above-described embodiment, a case has been described in which the calculation function 114c sets a rectangular region of interest whose longitudinal direction is the blur direction for each pixel of a plurality of slices in the three-dimensional image data. However, the embodiment is not limited to this. For example, the calculation function 114c may select an area of an arbitrary shape, such as an elliptical area whose longitudinal direction is the long direction (major axis direction) as the area of interest. Can be set.

  Further, in the above-described embodiment, the case where the calculation function 114c calculates the resolution for each pixel for each pixel of the plurality of slices in the three-dimensional image data has been described. However, the embodiment is not limited to this. For example, the calculation function 114c sets a region of interest for each predetermined number of pixel groups (for example, “2 × 2” four pixels), The resolution is calculated as the resolution of each pixel included in the pixel group. In other words, when calculating the resolution for each pixel, the calculation function 114c may calculate the resolution for each pixel or may calculate the resolution for each of a plurality of pixels.

  In the above-described embodiment, the case where the calculation function 114c sets a long region in the blur direction has been described. However, the embodiment is not limited to this. For example, the calculation function 114c may be a case in which a square or circular region of interest is set for each pixel of a plurality of slices, and the weight is changed for each direction in the set region of interest to calculate the resolution. . For example, the calculation function 114c first divides a square region of interest into coordinates in a direction (Y direction) orthogonal to the blur direction, and for each divided region, an autocorrelation function of an image in the region. And the resolution is calculated based on the high frequency component of the Fourier transform of the autocorrelation function. Then, the calculation function 114c calculates the resolution in the square region of interest as the resolution in the blur direction (X direction) by averaging the resolutions calculated for each coordinate in the Y direction.

  Moreover, although X-ray diagnostic apparatus which has the processing circuit 114 was demonstrated in embodiment mentioned above, embodiment is not limited to this. For example, a function corresponding to the image reconstruction function 114b, the calculation function 114c, and the generation function 114d may be realized in the processing circuit included in the medical image processing apparatus. For example, the processing circuit included in the medical image processing apparatus first acquires a plurality of projection data acquired by changing the irradiation angle of the X-rays from the X-ray tube to the subject, and acquires the plurality of acquired projections. 3D image data is reconstructed from the data. Then, the processing circuit calculates the resolution in the direction in which the X-ray tube moves when changing the irradiation angle for each pixel of the plurality of slices in the three-dimensional image data, and synthesizes the plurality of slices based on the calculated resolution. Thus, two-dimensional image data is generated.

  Each component of each device according to the first and second embodiments is functionally conceptual and does not necessarily need to be physically configured as illustrated. That is, the specific form of distribution / integration of each device is not limited to the one shown in the figure, and all or a part of the distribution / integration may be functionally or physically distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured. Further, all or a part of each processing function performed in each device may be realized by a CPU and a program that is analyzed and executed by the CPU, or may be realized as hardware by wired logic.

  The control methods described in the first and second embodiments can be realized by executing a control program prepared in advance on a computer such as a personal computer or a workstation. This control program can be distributed via a network such as the Internet. The control program can also be executed by being recorded on a computer-readable recording medium such as a hard disk, a flexible disk (FD), a CD-ROM, an MO, and a DVD and being read from the recording medium by the computer.

  According to at least one embodiment described above, it is possible to quickly generate a two-dimensional image with high resolution based on three-dimensional image data obtained by tomosynthesis.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

1 X-ray Diagnostic Device 114 Processing Circuit 114a Control Function 114b Image Reconstruction Function 114c Calculation Function 114d Generation Function

Claims (7)

An image reconstruction unit for reconstructing three-dimensional image data from a plurality of projection data collected by changing the irradiation angle of the X-rays from the X-ray tube to the subject;
For each pixel of the plurality of slices in the three-dimensional image data, a calculation unit that calculates the resolution in the direction in which the X-ray tube has moved when changing the irradiation angle;
A generating unit that generates two-dimensional image data by combining the plurality of slices based on the calculated resolution;
A medical image processing apparatus comprising:   The calculation unit sets, for each pixel of the plurality of slices, an area whose longitudinal direction is a direction in which the X-ray tube moves when changing the irradiation angle, and sets the resolution in the set area to the X The medical image processing apparatus according to claim 1, wherein the medical image processing apparatus calculates a resolution in a direction in which the ray tube has moved when changing the irradiation angle.   The calculation unit obtains a Fourier transform of an autocorrelation function of an image in the region, and calculates a resolution in the region based on a value corresponding to a high frequency in the Fourier transform of the autocorrelation function. The medical image processing apparatus described in 1.   The calculation unit obtains a Fourier transform of an autocorrelation function of an image in the region by performing a Fourier transform on the image in the region and squaring and adding the output real part and imaginary part. The medical image processing apparatus described in 1.   The generation unit weights the pixel values of the pixels of the plurality of slices according to the resolution, adds the weighted pixel values between corresponding pixels of the plurality of slices, and The medical image processing apparatus according to any one of claims 1 to 4, which generates image data.   The medical unit according to any one of claims 1 to 4, wherein the generation unit generates the two-dimensional image data by combining pixels having the highest resolution among corresponding pixels of the plurality of slices. Image processing device. An X-ray tube movable to change the irradiation angle of the X-ray to the subject;
A control unit for controlling the collection of a plurality of projection data with the irradiation angle changed;
An image reconstruction unit for reconstructing three-dimensional image data from the plurality of projection data;
For each pixel of the plurality of slices in the three-dimensional image data, a calculation unit that calculates the resolution in the direction in which the X-ray tube has moved when changing the irradiation angle;
A generating unit that generates two-dimensional image data by combining the plurality of slices based on the calculated resolution;
An X-ray diagnostic apparatus comprising: