JP6849440B2 - Medical image processing equipment and X-ray diagnostic equipment - Google Patents

Description

Embodiments of the present invention relate to medical image processing devices and X-ray diagnostic devices.

A method (tomosynthesis) is known in which a plurality of projection data are acquired while changing the irradiation angle of X-rays from an X-ray tube to a subject, and an image having three-dimensional information is reconstructed from the plurality of projection data. There is. Hereinafter, an image having three-dimensional information by tomosynthesis will be 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 part of the mammary gland is in focus with respect to the lesion, and the lesion has a high resolution. Be expressed. On the other hand, in the slice near the slice where the lesion is located, the lesion is out of focus and the lesion is expressed as a halo. For example, a doctor can sequentially interpret a plurality of slices of three-dimensional image data, and can find and observe a lesion portion by paying particular attention to a slice in focus.

Japanese Patent No. 5696305 Japanese Patent Application Laid-Open No. 2014-534042 Japanese Unexamined Patent Publication No. 2015-066344

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

The medical image processing apparatus of the embodiment includes an image reconstruction unit, a calculation unit, and a generation unit. The image reconstructing unit reconstructs three-dimensional image data from a plurality of projected data collected by changing the irradiation angle of X-rays from the X-ray tube to the subject. The calculation unit calculates the resolution in the direction in which the X-ray tube moves when the irradiation angle is changed for each pixel of the plurality of slices in the three-dimensional image data. The generation unit generates two-dimensional image data by synthesizing 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 the three-dimensional image data according to the first embodiment. FIG. 4A is a diagram for explaining the two-dimensional image data according to the first embodiment. FIG. 4B is a diagram for explaining the two-dimensional image data according to the first embodiment. FIG. 5A is a diagram for explaining the setting of the region of interest according to the first embodiment. FIG. 5B is a diagram for explaining the setting of the region of interest according to the first embodiment. FIG. 5C is a diagram for explaining the setting of the region of interest according to the first embodiment. FIG. 6 is a flowchart for explaining a series of processes of the X-ray diagnostic apparatus according to the first embodiment.

Hereinafter, the medical image processing apparatus according to the embodiment will be described with reference to the drawings. In the following, an X-ray diagnostic apparatus including the medical image processing apparatus according to the embodiment will be described. Further, in the following, 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 showing 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 has a base 101 and a stand 102. The stand 102 is erected on the base 101 and supports the photographing 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 photographing 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 photographing 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, the breast of a patient. The compression plate 104 is arranged above the photographing table 103, and is provided so as to face the photographing table 103 in parallel and move in a direction in which the compression plate 104 is brought into contact with and separated from the photographing table 103. When the compression plate 104 moves in a direction approaching the photographing table 103, the compression plate 104 presses the subject P supported on the photographing table 103. The subject P compressed by the compression plate 104 is spread thinly, and the overlap of the mammary glands in the subject P is reduced.

The X-ray tube 105 uses the high voltage supplied from the high voltage generator 111 to generate X-rays. The X-ray diaphragm 106 is arranged 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-ray 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 the X-rays transmitted through the subject P and the imaging table 103 and converts them into an electric signal (transmitted X-ray data). The X-ray detector 107 has, 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 an X-ray tube 105 and generates an electric signal. Next, the electric 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. Then, the signal processing circuit 108 generates projection data from the electric signal converted by the X-ray detector 107 and stores it in the storage circuit 112.

Further, as shown in FIG. 1, the X-ray diagnostic apparatus 1 includes an input circuit 109, an elevating 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 the operator who operates the X-ray diagnostic apparatus 1. For example, the input circuit 109 has a mouse, a keyboard, a button, a trackball, a joystick, a touch panel, and the like, and converts an input operation received from the operator into an electric signal and outputs the input operation to the processing circuit 114.

The elevating drive circuit 110 is connected to the photographing table 103 and raises and lowers the photographing table 103 in the vertical direction under the control of the processing circuit 114. Further, the elevating drive circuit 110 is connected to the compression plate 104, and under the control of the processing circuit 114, the elevating drive circuit 110 is moved up and down in the vertical direction (direction in which the compression plate 104 is brought into contact with the photographing table 103).

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, three-dimensional image data, and two-dimensional image data, which will be described later. Further, the storage circuit 112 stores data used when the processing circuit 114 controls the entire processing 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 receiving input operations of various commands from the operator. In addition, the display 113 displays an image generated by the X-ray diagnostic apparatus 1. For example, the display 113 displays the three-dimensional image data described later for each slice, or displays the two-dimensional image data described later.

The processing circuit 114 controls the operation of the entire X-ray diagnostic apparatus 1 by executing the control function 114a, the image reconstruction function 114b, the calculation function 114c, and the generation function 114d. For example, the processing circuit 114 controls the projection data collection process by reading the program corresponding to the control function 114a from the storage circuit 112 and executing it. Further, for example, the processing circuit 114 reads the program corresponding to the generation function 114d from the storage circuit 112 and executes it, so that the projection data generated by the signal processing circuit 108 is subjected to logarithmic conversion processing, offset correction, and sensitivity. 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 a program corresponding to the image reconstruction function 114b from the storage circuit 112 and executes it, thereby changing the irradiation angle of the subject P and collecting a plurality of projection data (correction). Based on the completed projection data), the three-dimensional image data by tomosynthesis is reconstructed. Further, for example, the processing circuit 114 generates two-dimensional image data from the three-dimensional image data by tomosynthesis by reading a program corresponding to the calculation function 114c and the generation function 114d from the storage circuit 112 and executing the program. The reconstruction of the three-dimensional image data and the generation of the two-dimensional 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 the position of the imaging table 103 and the compression plate 104 in the MLO (Mediolateral-Oblique) direction or CC. Mammography of MLO images, CC images, etc. based on the projected data collected by irradiating X-rays with the subject P fixed in the (Cranio-Caudal) direction and keeping the irradiation angle on the subject P constant. Images 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 that can be executed by a computer. The signal processing circuit 108, the elevating drive circuit 110, and the processing circuit 114 are processors that realize functions corresponding to each program by reading a program from the storage circuit 112 and executing the program. In other words, each circuit in the state where each program is read has a function corresponding to the read program. Although it has been described in FIG. 1 that the control function 114a, the image reconstruction function 114b, the calculation function 114c, and the generation function 114d are realized by a single processing circuit 114, processing is performed by combining a plurality of independent processors. The circuit 114 may be configured and the function may be realized by each processor executing a program.

The word "processor" used in the above description means, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an integrated circuit for a specific application (ASIC), or a programmable logic device (for example, a programmable logic device). It means a circuit such as a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). The processor realizes the function by reading and executing the 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 circuit of the processor. In this case, the processor realizes the function by reading and executing the program embedded in the circuit. It should be noted that each processor of the present embodiment is not limited to the case where each processor is configured as a single circuit, and a plurality of independent circuits may be combined to form one processor to realize its function. Good. Further, the 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 rapidly generates a high-resolution two-dimensional image based on the three-dimensional image data obtained by tomosynthesis. Hereinafter, the 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 photographing table 103 and the compression plate 104, the control function 114a controls the collection of the projection data of the subject P. Here, the control function 114a collects a plurality of projection data used for reconstructing the 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.

FIG. 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 case where the X-ray tube 105 is located at the position X3. Show the case. As shown in FIGS. 2A, 2B and 2C, the X-ray tube 105 moves in an orbit including position X1, position X2 and position X3. Further, the broken lines in FIGS. 2A, 2B and 2C indicate a part of the 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 for irradiating 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 irradiation angle of X-rays.

First, the control function 114a controls the irradiation of the subject P with X-rays from the X-ray tube 105 at the position X1 as shown in the upper figure 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 displays the projection data A1 shown in the lower figure of FIG. 2A. Generate. Here, the part a, the part b, and the part c in the subject P are projected to the positions shown on the projection data A1 in the lower figure of FIG. 2A, respectively.

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, and irradiates the subject P with the X-ray from the X-ray tube 105 at the position X2. Control. Further, the signal processing circuit 108 generates the projection data A2 shown in the lower figure of FIG. 2B. Here, the part a, the part b, and the part c in the subject P are projected so as to be superimposed on the positions shown on the projection data A2 in the lower figure of FIG. 2B, respectively.

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

The control function 114a controls the X-ray tube 105 to irradiate X-rays when it is located 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 alternately repeats the movement of the X-ray tube 105 and the irradiation of the X-ray so as to irradiate the X-ray from the X-ray tube 105 stopped at the position X1, the position X2, the position X3, or the like. You may control it.

Further, 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 shape, a linear shape, or another trajectory as shown in FIGS. 2A, 2B, and 2C.

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, the reconstruction of the three-dimensional image data by tomosynthesis will be described with reference to FIG. FIG. 3 is a diagram for explaining the reconstruction of the three-dimensional image data according to the first embodiment. In the following, the shift addition method will be described as an example of the 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 figure of FIG. 3 so as to align the positions where the portion a is projected on the projection data, and adds the projection data A1 and the projection data A3. The slice B1 shown in the figure below is generated. In the slice B1, the portion of the projection data A1, the projection data A2, and the projection data A3 on which the portion a is projected is aligned and added, so that the portion a is clearly expressed.

Here, the individual projection data also includes a signal indicating the part b or the part c, but since the slice B1 is overlapped with the positions shifted, the signal of the part b or the part c is displayed on the slice B1. It is diffused and expressed in a blurred manner. Therefore, as shown in the lower part of FIG. 3, although the slice B1 contains the signals of the part a, the part b, and the part c, only the part a is clearly expressed. That is, the image reconstruction function 114b generates the slice B1 with the XY plane including the site a in the subject P as the reconstruction plane.

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

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

After the three-dimensional image data is reconstructed, the control function 114a causes the display 113 to display the three-dimensional image data. For example, the control function 114a displays any one of the plurality of slices in the three-dimensional image data, or displays the plurality of slices in sequence. The slices of the three-dimensional image data displayed in this way reduce the overlap of information in the Z direction, and facilitate the interpretation of lesions that are difficult to see when the mammary glands overlap, for example.

For example, the control function 114a presents the XY plane including the portion a to the operator (doctor or the like) by displaying the slice B1 shown in FIG. 3 on the display 113. Here, when the site a is a lesion (for example, calcification of the mammary gland), the operator can easily find the lesion and observe the lesion. Further, the control function 114a enables three-dimensional image interpretation by displaying the slice B2 and the slice B3 on the display 113.

Further, the control function 114a causes the display 113 to display the two-dimensional image data generated from the three-dimensional image data. For example, the generation function 114d generates two-dimensional image data from 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), and has a control function. The 114a causes the generated two-dimensional image data to be displayed on the display 113. The two-dimensional image data generated by synthesizing each slice of the three-dimensional image data by tomosynthesis is also described as Synthesize2D or Synthesized2D. Here, as an example, the two-dimensional image data by 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 figure of FIG. 4A shows the 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. Further, the middle figure of FIG. 4A shows the pixel value of each pixel for each slice on the XY plane in the three-dimensional image data. That is, the middle figure of FIG. 4A shows the pixel value of each pixel on the slice of "Z = 1", the pixel value of each pixel on the slice of "Z = 2", and the pixel value of each pixel on the slice of "Z = 3". The pixel value of each pixel is shown.

The generation function 114d selects the smallest pixel value among the corresponding pixels (pixels in which the X and Y coordinates match) of a plurality of slices, thereby forming a two-dimensional image as shown in the right figure of FIG. 4A. Generate data. For example, the pixel value of the pixel in the center of each slice is "4" in the slice "Z = 1", "2" in the slice "Z = 2", and "2" in the slice "Z = 3". Since it is "4", the generation function 114d selects "2" as the pixel value of the central pixel of the two-dimensional image data.

Here, when the two-dimensional image data is generated by the MIP or the MinIP shown in FIG. 4A, the two-dimensional image data may be blurred as shown in FIG. 4B. Note that FIG. 4B is two-dimensional image data of the subject P including the calcified site. For example, in the area R1 of the two-dimensional image data shown in FIG. 4B, calcification is expressed so as to blur 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 halo shown in FIG. 4B is due to the halo contained in each slice of the three-dimensional image data of tomosynthesis. For example, the portion b, the portion c, and the like are expressed in the slice B1 reconstructed with the XY plane including the portion a as the reconstruction plane. Similarly, the slice B2 in which the XY plane including the part b is reconstructed as the reconstructed surface is represented by the part a and the part c being blurred, and the slice B3 in which the XY plane including the part c is reconstructed as the reconstructed surface is expressed. The part a, the part b, and the like are expressed in a blurred manner.

Here, for example, when only the portion a is a calcified portion, the slice B1 in which the calcified portion is in focus does not have a blur, but the slice B2 and the slice B3 have a blurred portion. Be expressed. That is, the slice B2 and the slice B3 have a halo (flow line) in the same direction as the X-ray tube 105 moves when the irradiation angle is changed, and the two-dimensional image data by MinIP is affected by the halo. Remain.

Therefore, in order to reduce the blurring 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 used for each of the plurality of slices in the three-dimensional image data. The resolution in the X direction is calculated for the pixels, and the generation function 114d generates two-dimensional image data by synthesizing a plurality of slices based on the calculated resolution. This point will be described in detail below.

First, the calculation function 114c lengthens 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 area to be the direction. 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. In the following, the area set for each pixel of the plurality of slices is also described as the area of interest.

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

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

Further, the calculation function 114c sets a long region of interest in the X direction for each of the plurality of slices in the three-dimensional image data. For example, as shown in FIG. 5B, the calculation function 114c sets a rectangular region of interest T2 having the X direction as the longitudinal direction for the pixels of the slice B5 including the blur in the X direction among the plurality of slices in the three-dimensional image data. Set. Note that FIG. 5B is a diagram for explaining the setting of the region of interest according to the first embodiment. In FIG. 5B, the six calcified portions are represented by a halo in the X direction. That is, slice B5 is a slice that is out of focus with respect to the calcified portion of the mammary gland.

Further, for example, as shown in FIG. 5C, the calculation function 114c has the X direction for the pixels of the slice B6 that are blurred in the X direction so that the six calcified portions cannot be recognized among the plurality of slices in the three-dimensional image data. A rectangular region of interest T3 with Note that FIG. 5C is a diagram for explaining the setting of the region of interest according to the first embodiment. That is, slice B6 is a slice that is significantly out of focus with respect to 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) that the X-ray tube 105 moves when changing the irradiation angle. For example, the calculation function 114c calculates the resolution in the region of interest T1 shown 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 the Fourier transform of the autocorrelation function of the image in the region of interest T1 in FIG. 5A. As an example, the calculation function 114c Fourier transforms the image in the region of interest T1 and squares and adds the real part and the imaginary part output as a result of the Fourier transform to add the image in the region of interest T1. Find the Fourier transform of the autocorrelation function. Then, the calculation function 114c calculates the "value corresponding to the 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, the amplitude value of the autocorrelation function with respect to the preset frequency value or the square thereof can be used. Further, for example, the amplitude value of the autocorrelation function or the square thereof can be integrated for a region having a frequency higher than a preset frequency threshold value, and this can be set as a “value corresponding to a high frequency”. Moreover, you may use the thing which standardized these values as appropriate. That is, various values can be used as long as they evaluate the high frequency component of the autocorrelation function. Similarly, the calculation function 114c calculates the resolution within the set area of interest for each pixel of the slice B4 shown in FIG. 5A.

Further, the calculation function 114c calculates the resolution in the region of interest set for each pixel for each of the 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-mentioned value corresponding to the high frequency as the resolution as it is, or may use a 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, the resolution in the region of interest T2 in FIG. 5B, and the resolution in the region of interest T3 in FIG. 5C are compared, the resolution in the region of interest T1 becomes the largest. .. That is, the signal (sharp signal) expressed without blurring is included in the region of interest T1, and the autocorrelation function based on the image in the region of interest T1 also has a sharp shape. Then, when the sharp autocorrelation function is Fourier transformed, the value (resolution) corresponding to the high frequency becomes a large value. On the other hand, a blurred signal is included in the region of interest T2, 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 used is a small value. Further, in the region of interest such as the region of interest T3 where the signal is blurred so that the calcified portion cannot be recognized, 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 long in the halo direction. That is, in the three-dimensional image data by tomosynthesis, the direction of the blurring that occurs in the slice is the moving direction of the X-ray tube 105 (X direction), and for example, the direction orthogonal to the moving direction of the X-ray tube 105 (Y direction). Since blurring is unlikely to occur, there is little need to calculate the resolution in the Y direction. Therefore, the calculation function 114c reduces the amount of calculation by calculating the resolution in the region of interest long in the blurring direction (X direction), omitting a part or all of the resolution calculation process in the Y direction, and is quick. The resolution can be calculated.

Next, the generation function 114d synthesizes a plurality of slices in the three-dimensional image data based on the resolution calculated by the calculation function 114c to generate the two-dimensional image data. For example, the generation function 114d weights the pixel values of each pixel of a plurality of slices according to the resolution, adds the weighted pixel values among the corresponding pixels of the plurality of slices, and adds two-dimensional image data. To generate. Here, the corresponding pixels of the plurality of slices are, for example, pixels in which the X coordinate and the Y coordinate match in each slice. For example, the pixel at the center of the region of interest T1 in FIG. 5A, the pixel at the center of the region of interest T2 in FIG. 5B, and the pixel at the center 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". The processing by the generation function 114d will be described by taking a certain case as an example.

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

Next, the generation function 114d adds up the weighted pixel values between the corresponding pixels and divides by the total value of the coefficients (resolutions). For example, the generation function 114d has a weighted pixel value “8.5” in the region of interest T1, a weighted pixel value “0.8” in the region T2 of interest, and a weighted pixel value “0.1” in the region T3 of interest. And are added up to calculate "9.4". Next, in the generation function 114d, the total value of the resolution is "1.0", and the total value of the weighted pixel values is divided by "9.4" to obtain the pixel value "9.4" of the pixels 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 interest region T1 calculated with a higher resolution than the pixel values of the interest region T2 and the interest region T3 calculated with a lower resolution. It will be a close value.

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

Alternatively, the generation function 114d may be a case where two-dimensional image data is generated by synthesizing the pixel having the highest resolution among the corresponding pixels of the plurality of slices. For example, the generation function 114d calculates the 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 to "0". The calculated weighted pixel value is used 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 joined together.

The generation function 114d stores the two-dimensional image data generated from the three-dimensional image data in the storage circuit 112. Further, the control function 114a 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 the two-dimensional image data from the three-dimensional image data by tomosynthesis. For example, the X-ray diagnostic apparatus 1 calculates the resolution of the direction (X direction) in which the X-ray tube 105 moves when the irradiation angle is changed, and synthesizes a plurality of slices based on the calculated resolution. It is possible to switch between a mode for generating 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 the processing procedure by the X-ray diagnostic apparatus 1 will be described with reference to FIG. FIG. 6 is a flowchart for explaining a series of processes 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 arranged between the photographing table 103 and the compression plate 104 (step S101). Next, the processing circuit 114 reconstructs the three-dimensional image data by tomosynthesis from the plurality of projection data (step S102).

Next, the processing circuit 114 moves the direction in which the 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 (a beam generated in the plurality of slices). Calculate the resolution (in the direction of the X-ray) (step S103). Then, the processing circuit 114 synthesizes a plurality of slices in the three-dimensional image data based on the calculated resolution to generate the two-dimensional image data (step S104).

As described above, according to the first embodiment, the image reconstruction function 114b is 3 from a plurality of projection data collected by changing the irradiation angle of X-rays from the X-ray tube 105 to the subject P. Reconstruct the 3D image data. The calculation function 114c calculates the resolution in the 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. The generation function 114d generates two-dimensional image data by synthesizing a plurality of slices based on the calculated resolution. Therefore, the X-ray diagnostic apparatus 1 according to the first embodiment can quickly generate high-resolution two-dimensional image data based on the three-dimensional image data obtained by tomosynthesis. For example, since the X-ray diagnostic apparatus 1 according to the first embodiment generates two-dimensional image data based on the resolution of each slice, it obtains two-dimensional image data having a higher resolution than the case of using MIP or MinIP. be able to.

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

Further, according to the first embodiment, the generation function 114d generates two-dimensional image data from the three-dimensional image data. Therefore, the X-ray diagnostic apparatus 1 according to the first embodiment generates three-dimensional image data and two-dimensional image data in one imaging, and reduces the number of imagings to reduce the exposure dose of the subject P. can do.

(Second embodiment)
By the way, although the first embodiment has been described so far, it may be implemented in various different forms other than the above-described embodiment.

In the above-described embodiment, the case where the calculation function 114c sets a rectangular region of interest with the halo direction as the longitudinal direction 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, and for example, the calculation function 114c has an arbitrary shape region such as an elliptical region having a halo direction as a longitudinal direction (semi-major axis direction) as a region of interest. Can be set.

Further, in the above-described embodiment, the case where the calculation function 114c calculates the resolution 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, and for example, the calculation function 114c sets an area of interest for each of a predetermined number of pixel groups (for example, 4 pixels of “2 × 2”), and the area of interest is within the area of interest. The resolution is calculated as the resolution of each pixel included in the pixel group. That is, 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.

Further, in the above-described embodiment, the case where the calculation function 114c sets a long region in the halo direction has been described. However, the embodiment is not limited to this. For example, the calculation function 114c may be a case where a square or circular area of interest is set for each pixel of a plurality of slices, and the weighting is changed for each direction in the set area of interest to calculate the resolution. .. As an example, the calculation function 114c first divides a square area of interest into coordinates in a direction orthogonal to the blurring direction (Y direction), and then divides each divided area into autocorrelation functions of images in the area. The Fourier transform of is obtained, 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 area of interest of the square as the resolution in the blurring direction (X direction) by averaging the resolutions calculated for each coordinate in the Y direction.

Further, in the above-described embodiment, the X-ray diagnostic apparatus having the processing circuit 114 has been described, but the embodiment is not limited to this. For example, in the processing circuit of the medical image processing apparatus, the functions corresponding to the image reconstruction function 114b, the calculation function 114c, and the generation function 114d may be realized. As an example, the processing circuit of the medical image processing apparatus first acquires a plurality of projection data collected by changing the irradiation angle of X-rays from an X-ray tube to a subject, and then acquires a plurality of acquired projections. Reconstruct 3D image data from the data. Then, the processing circuit calculates the resolution in the direction in which the X-ray tube moves when the X-ray tube changes 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. By doing so, two-dimensional image data is generated.

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

Further, the control method described in the first to 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. Further, this control program can also be executed by being recorded on a computer-readable recording medium such as a hard disk, flexible disk (FD), CD-ROM, MO, or DVD, and being read from the recording medium by the computer.

According to at least one embodiment described above, a two-dimensional image having high resolution can be rapidly generated based on the three-dimensional image data by tomosynthesis.

Although some embodiments of the present invention have been described, these embodiments are presented as examples 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 gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope 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 that reconstructs three-dimensional image data from a plurality of projection data collected by changing the irradiation angle of X-rays from an X-ray tube to a subject.
Set the area for each pixel of the plurality of slices in the three-dimensional image data, a calculation unit resolution in the set area, the X-ray tube is calculated as the direction of the resolution moved when changing the irradiation angle ,
A generator that generates two-dimensional image data by synthesizing the plurality of slices based on the calculated resolution, and a generator.
A medical image processing device. The calculation unit sets a region in which the direction in which the X-ray tube moves when changing the irradiation angle is the longitudinal direction for each pixel of the plurality of slices, and sets the resolution within the set region to the X. The medical image processing apparatus according to claim 1, which is calculated as a resolution in the direction in which the X-ray tube moves when the irradiation angle is changed. The calculation unit obtains the Fourier transform of the autocorrelation function of the image in the area, based on the value corresponding to the frequency of the Fourier transform of the autocorrelation function to calculate the resolution in the area, according to claim 1 Or the medical image processing apparatus according to 2. The calculation unit obtains the Fourier transform of the autocorrelation function of the image in the region by performing a Fourier transform on the image in the region, squares the output real part and the imaginary part, and adds them. The medical image processing apparatus according to. 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 the corresponding pixels of the plurality of slices, and performs the two-dimensional. The medical image processing apparatus according to any one of claims 1 to 4, which generates image data. The medical use according to any one of claims 1 to 4, wherein the generation unit generates the two-dimensional image data by synthesizing the pixel having the highest resolution among the corresponding pixels of the plurality of slices. Image processing device. An X-ray tube that can be moved to change the X-ray irradiation angle for the subject,
A control unit that controls the collection of a plurality of projection data with different irradiation angles,
An image reconstruction unit that reconstructs three-dimensional image data from the plurality of projection data,
Set the area for each pixel of the plurality of slices in the three-dimensional image data, a calculation unit resolution in the set area, the X-ray tube is calculated as the direction of the resolution moved when changing the irradiation angle ,
A generator that generates two-dimensional image data by synthesizing the plurality of slices based on the calculated resolution, and a generator.
X-ray diagnostic apparatus.

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