Image processing device, method for operating image processing device, and work program product

Abstract

The invention provides an image processing device capable of displaying a tomographic image of a specified cross-section in a shorter time than in the prior art, an operation method of the image processing device, and an operation program product. This image processing device is provided with a processor that performs image processing on a plurality of slice images output by a tomographic imaging device and indicating an axial cross-section orthogonal to the body axis of a subject, and in the image processing device, the processor acquires the plurality of slice images and performs image processing on the plurality of slice images. And generates a tomographic image representing the specified cross-section using a function using the pixel values of the plurality of slice images as parameters.

Description

Technical Field

[0001] The technology of the present invention relates to an image processing apparatus, a working method of the image processing apparatus, and a working program. Background Art

[0002] There are known tomography apparatuses such as CT (Computed Tomography) apparatuses and MRI (Magnetic Resonance Imaging) apparatuses that photograph tomographic images of a subject. The tomography apparatus outputs a plurality of slice images representing axial cross-sections orthogonal to the body axis of the subject. Further, the following processing is also performed, that is, an isotropic three-dimensional image in which the three-dimensional resolution is isotropized is generated from the plurality of slice images photographed by the tomography apparatus, and a tomographic image representing an arbitrary cross-section is obtained by cutting out a tomographic image representing an arbitrary cross-section from the isotropic three-dimensional image. A tomographic image representing such a cross-section is called an MPR (Multi Planar Reconstruction) image or the like.

[0003] In the tomography apparatus described in Patent Document 1, three-dimensional preliminary image data (corresponding to a three-dimensional image) is also generated from slice images, and an arbitrary cross-section is specified for the generated three-dimensional preliminary image data to obtain a tomographic image.

[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-143735

[0005] However, the image processing in the process of generating a three-dimensional image from slice images has a large load and takes a long time. Therefore, it takes a long time to display a tomographic image of a specified cross-section. Further, for example, when generating such three-dimensional image data from all slice images within a photographing range set in the body axis direction, the three-dimensional image data is generated after the photographing by the tomographic image photographing apparatus is completed. In this case, it takes even more time. Therefore, it is required to shorten the time from the start of photographing by the tomographic image photographing apparatus to the display of a tomographic image of a specified cross-section. Summary of the Invention

[0006] The technology related to the present invention provides an image processing apparatus, a working method of the image processing apparatus, and a working program that can display a tomographic image of a specified cross-section in a shorter time than before.

[0007] The image processing apparatus according to the technology of the present invention includes a processor that performs image processing on a plurality of slice images output by a tomographic image photographing apparatus and representing axial cross-sections orthogonal to the body axis of the subject. In the image processing apparatus, the processor acquires the plurality of slice images and generates a tomographic image representing a specified cross-section using a function having the pixel values of the plurality of slice images as parameters.

[0008] Preferably, when the tomographic imaging device outputs a plurality of slice images during imaging, the processor uses the plurality of slice images to start the generation process of the tomographic image during imaging.

[0009] The preference function is created according to the imaging conditions of the tomographic imaging device and at least includes the imaging condition of the slice interval of the slice image.

[0010] Preferably, the processor acquires the imaging conditions and creates a function before the tomographic imaging device starts imaging.

[0011] Preferably, when the body axis direction of the subject is set as the Z-axis direction, and the two directions defining the cross-section orthogonal to the body axis direction are set as the X-axis direction and the Y-axis direction, the function includes an isotropic data derivation function that derives isotropic data as the pixel values of pixels whose resolutions are isotropized in the X-axis direction, the Y-axis direction, and the Z-axis direction, and the processor generates a tomographic image based on the isotropic data.

[0012] Preferably, the cross-section of the tomographic image is any one of an axial cross-section, a sagittal cross-section, and a coronal cross-section.

[0013] Preferably, the processor accepts the designation of the slice thickness as the thickness of the tomographic image and performs weighting corresponding to the slice thickness to generate the tomographic image.

[0014] Preferably, when the body axis direction of the subject is set as the Z-axis direction, the width direction of the cross-section orthogonal to the body axis direction is set as the X-axis direction, and the height direction is set as the Y-axis direction, the function includes a pixel value derivation function that derives the pixel values of an inclined cross-section obtained by rotating the axial cross-section of the slice image around the X-axis to be inclined, and the processor uses the pixel value derivation function to generate an inclined image as the tomographic image of the inclined cross-section.

[0015] Preferably, when generating a plurality of inclined images arranged in the Z-axis direction, the heights of the pixels in the Y-axis direction of the plurality of inclined images are the same.

[0016] Preferably, the processor accepts the designation of the slice thickness as the thickness of the inclined image and performs weighting corresponding to the designated slice thickness to generate the inclined image.

[0017] In the working method of the image processing device related to the technology of the present invention, the image processing device includes a processor, and the processor performs image processing on a plurality of slice images output by the tomographic imaging device and representing axial cross-sections orthogonal to the body axis of the subject. In the working method of the image processing device, the processor acquires the plurality of slice images and uses a function taking the pixel values of the plurality of slice images as parameters to generate a tomographic image representing a specified cross-section.

[0018] In the operation program of the image processing apparatus related to the technology of the present invention, the image processing apparatus includes a processor that performs image processing on a plurality of slice images output by a tomographic imaging apparatus and representing axial cross-sections orthogonal to the body axis of a subject. In the operation program of the image processing apparatus, the processor is caused to execute the following processes: acquiring a plurality of slice images; and generating a tomographic image representing a specified cross-section using a function that takes the pixel values of the plurality of slice images as parameters.

[0019] Advantages of the Invention

[0020] According to the technology of the present invention, a tomographic image of a specified cross-section can be displayed in a shorter time compared to the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a diagram showing a CT apparatus.

[0022] Figure 2 It is a diagram showing a schematic structure of a CT apparatus.

[0023] Figure 3 It is a diagram showing the processing of the processor in the first embodiment.

[0024] Figure 4 It is a diagram showing the MPR image generation process using the conventional isotropic three-dimensional image VD_ISO.

[0025] Figure 5 It is a diagram showing the order of the creation process of the MPR image generation function.

[0026] Figure 6 It is a diagram conceptually showing the creation process of the Z coordinate table.

[0027] Figure 7 It is a diagram showing the relationship between the size of the FOV and the isotropic Z coordinate.

[0028] Figure 8 It is a diagram conceptually showing the creation process of the isotropic data extraction function.

[0029] Figure 9 It is a diagram conceptually showing the creation process of the pixel value extraction function for the MPR image of the axial cross-section.

[0030] Figure 10 It is a diagram conceptually showing the creation process of the pixel value extraction function for the MPR image of the sagittal cross-section.

[0031] Figure 11 It is a diagram conceptually showing the creation process of the pixel value extraction function for the MPR image of the coronal cross-section.

[0032] Figure 12It is a flowchart showing the processing sequence of MPR image generation processing.

[0033] Figure 13 It is a diagram showing the processing of the processor of the second embodiment.

[0034] Figure 14 It is a diagram showing the sequence of the creation process of the MPR image generation function.

[0035] Figure 15 It is a diagram conceptually showing the creation process of the coordinate transformation table.

[0036] Figure 16 It is a diagram showing the state of the height inconsistency in the Y-axis direction of the pixels of the tilted image.

[0037] Figure 17 It is a diagram conceptually showing the creation process of the pixel value derivation function of the tilted image.

[0038] Figure 18 It is a diagram conceptually showing the creation process of the weight correction function.

[0039] Figure 19 It is a flowchart showing the processing sequence of the tilted image generation processing.

[0040] Figure 20 It is a diagram showing an example of the image display device functioning as an image processing device.

[0041] Symbol Explanation

[0042] 11 - CT device, 12 - Image DB, 13 - Image display device, 16 - Gantry, 17 - Console, 18 - Rotating gantry, 18A - Opening, 19 - Bed device, 19A - Bed board, 21 - Radiation source, 22 - Detector, 23 - Frame, 24 - Collimator, 26 - High voltage generating device, 27 - Gantry control unit, 31 - Display, 32 - Input device, 33 - Memory, 34 - Communication unit, 36 - Processor, 36A - Control unit, 36B - Image processing unit, 37 - Application program, DT - Tilted image, Fdt - Pixel value derivation function, Fmpr - Pixel value derivation function, GF1 - MPR image generation function, GF2 - Tilted image generation function, H - Subject, Mp, Mp(AX), Mp(SAG), Mp(COR) - MPR images, P, Pt - Pixels, PD - Projection data, PS - Pixel interval, SI - Slice interval, SL - Slice image, SL_ISO - Isotropic slice image, SLP - Point, Sb - Point, Se - Point, VD_ISO - Isotropic three-dimensional image, VOL - Slice volume, w - Weight coefficient, rb, re, qb, qe - Weight coefficients. Detailed Embodiments

[0043] [First Embodiment]

[0044] Figure 1 The CT apparatus 11 shown is an example of a tomographic imaging apparatus related to the technology of the present invention. As is well known, the CT apparatus 11 obtains tomographic images of a subject H, which is an example of a subject to be examined, by taking images using radiation (e.g., X-rays). As an example, the CT apparatus 11 is installed in a radiographic room in a medical facility. The CT apparatus 11 includes a gantry 16 and a console 17. The console 17 functions as an operation terminal and a control device for operating the gantry 16. The console 17 is operated by an operator such as a radiological technologist. Further, the console 17 also functions as an image processing device that generates tomographic images by performing image processing on data output from the gantry 16. The console 17 is an example of the "image processing device" related to the technology of the present invention. Further, the console 17 also functions as an image display device that displays the generated tomographic images.

[0045] As Figure 2 shown, the gantry 16 is a main part of the CT apparatus 11 and includes a rotating gantry 18 and a table device 19. In Figure 2 , in addition to the figure of the gantry 16 observed from the front, a figure of the gantry 16 observed from the side is shown within a rectangular dashed line frame. The table device 19 has a table board 19A on which the subject H can be placed in a lying position. The subject H is placed in a posture such that the body axis coincides with the length direction of the table board 19A (the Z-axis direction of the gantry 16). The table board 19A can move in the Z-axis direction. The rotating gantry 18 has an overall ring shape and has a circular opening 18A formed at the center with a diameter larger than the width of the table board 19A. At the time of imaging, the table board 19A on which the subject H is placed moves in the Z-axis direction relative to the rotating gantry 18 and enters the opening 18A. Imaging is performed while moving the table board 19A relative to the rotating gantry 18.

[0046] Inside the rotating gantry 18, a radiation source 21, a detector 22, and a frame 23 are arranged. The radiation source 21 irradiates the subject H with radiation. The detector 22 is a radiation detector that detects radiation that has passed through the subject H. The radiation that has passed through the subject H is attenuated by interaction (such as absorption and scattering of radiation) with structures such as organs and bones in the subject H's body. Each structure has an inherent attenuation coefficient with respect to radiation, and the radiation that has passed through the structure carries intensity information reflecting the attenuation coefficient of the structure. The detector 22 has a detection surface on which pixels are two-dimensionally arranged, and outputs a detection signal corresponding to the intensity information of the radiation for each pixel within the detection surface. Further, the detector 22 has a substantially arc shape according to the curvature of the rotating gantry 18, and the detection surface is also curved.

[0047] Within the rotating gantry 18, the radiation source 21 and the detector 22 are arranged at opposing positions and rotate around the Z-axis while maintaining the opposing posture. The frame 23 has an annular shape and rotatably supports the radiation source 21 and the detector 22. During imaging, the gantry 16 rotates the radiation source 21 and the detector 22 around the subject H on the bed board 19A, and uses the detector 22 to detect the projection data PD at a plurality of positions in the circumferential direction around the Z-axis corresponding to the body axis of the subject H. During imaging, the bed board 19A also moves in the Z-axis direction synchronously with the rotation of the radiation source 21 and the detector 22. Thus, the projection data PD of the radiation at each position around the body axis of the subject H is obtained.

[0048] In the gantry 16, the Y-axis represents the height direction and the X-axis represents the width direction. As an example, in the bed device 19, the subject H is placed in a lying posture with the head side facing the rotating gantry 18. Therefore, during imaging, the subject H enters the rotating gantry 18 from the head side, and the projection data PD is output in the order from the head side to the foot side.

[0049] The DAS (Data Acquisition System) 25 collects the detection signals output by the detector 22, generates the projection data PD at each position around the Z-axis based on the collected detection signals, and outputs the generated projection data PD to the control console 17.

[0050] A collimator 24 (also referred to as a collimator, etc.) that limits the irradiation field of the radiation is arranged in front of the irradiation direction of the radiation source 21. The collimator 24 has an irradiation opening defined by a plurality of shielding plates that shield radiation, and the size of the irradiation opening can be changed by moving the shielding plates. The symbol 26 is a high-voltage generating device that generates the high voltage supplied to the radiation source 21. As an example, the radiation source 21 and the detector 22 are electrically connected to the frame 23 in a slip-ring manner, and power supply and data transmission and reception are performed via the slip ring. Through the connection in the slip-ring manner, the radiation source 21 and the detector 22 can perform imaging in a helical scan mode. The helical scan mode refers to a mode in which imaging is performed while rotating unidirectionally without reversing the rotation direction of the radiation source 21 and the detector 22.

[0051] A gantry control unit 27 is provided on the gantry 16. The gantry control unit 27 controls each part of the gantry 16 according to the instructions from the control console 17, in addition to the rotation of the radiation source 21 and the detector 22 and the movement of the bed board 19A.

[0052] The imaging conditions of the CT apparatus 11 are set by the gantry control unit 27 through operations from the console 17. The imaging conditions include, in addition to the irradiation conditions of the radiation from the radiation source 21, the imaging range, the slice interval, and the like. The irradiation conditions of the radiation include the tube voltage (unit: kV), the tube current (unit: mA), and the radiation irradiation time (unit: msec) applied to the radiation source 21. The product of the tube current and the irradiation time defines the total irradiation dose of the radiation, which is called the mAs value. The irradiation field is adjusted, for example, by changing the size of the irradiation opening of the collimator 24 in the X-Z plane. In addition, when the radiation irradiated by the radiation source 21 is a cone-shaped cone beam, the width of the irradiation field in the Z-axis direction can also be adjusted by adjusting the width of the irradiation opening of the collimator 24 in the Z-axis direction. Moreover, the imaging range in the Z-axis direction of the whole body of the subject H or from the chest to the abdomen is adjusted by changing the moving range of the table 19A.

[0053] Moreover, it is also possible to change the imaging range of the slice image SL (refer to Figure 7 etc.). The slice image SL is a tomographic image representing an axial cross section in the X-Y plane, that is, a plane orthogonal to the body axis of the subject H, and is generated by image reconstruction based on the projection data PD, as described later. The imaging range in the X-Y plane of such a slice image SL is also called the FOV (Field of View). For example, in the axial cross section of the chest of the subject H, it is possible to set a relatively large area that accommodates the entire chest as the FOV, or to set a relatively small area such as a part of the chest as the FOV, etc., to change the size of the FOV. The radiation beam spreads from the focal point of the radiation source 21 toward the detector 22. Therefore, if the distance between the radiation source 21 and the detector 22 in the gantry 18 is set to be constant, by adjusting the height of the table 19A, if the subject H is brought closer to the radiation source 21, the area of the radiation beam passing through the subject H becomes narrower. Since it is possible to image the area of the subject H through which the radiation passes, if the area through which the radiation passes is narrow, the FOV becomes smaller. Conversely, if the subject H is moved away from the radiation source 21, the area of the radiation beam passing through the subject H expands, so the FOV can be expanded. Thus, the size of the FOV is adjusted, for example, by adjusting the height of the table 19A. On the other hand, since the number of pixels of the detector 22 is fixed, if the FOV is reduced, the resolution of the captured slice image SL becomes higher, and if the FOV is expanded, the resolution is reduced. Also, it is possible to adjust the distance that the table 19A advances in the Z-axis direction during one rotation of the radiation source 21 and the detector 22, that is, the moving speed in the Z-axis direction. By adjusting the moving speed in the Z-axis direction, the slice interval of the slice image SL can be adjusted. The FOV and the slice interval are also set as imaging conditions.

[0054] The console 17 includes a display 31, an input device 32, a memory 33, a communication unit 34, and a processor 36. As an example, the console 17 is based on a personal computer or the like and has the same hardware structure as a general computer. The display 31 is, for example, a liquid crystal display or the like, and displays an operation screen, the captured slice image SL, and the like. The input device 32 is a device for an operator to input operation instructions and is composed of a keyboard, a mouse, and the like.

[0055] The memory 33 is a data memory that stores various programs such as a control program for controlling each part of the console 17. Among the various programs, there is an application program 37 for causing the processor 36 to function as a control device and an image processing device of the CT device 11. As the memory 33, for example, an HDD (Hard Disk Drive) and an SSD (Solid State Drive) can be cited. Further, the memory 33 temporarily stores the projection data PD acquired from the gantry 16 and the generated slice image SL. The application program 37 is an example of the "working program" related to the technology of the present invention.

[0056] The communication unit 34 is a communication interface for performing communication between the gantry 16 and external devices such as an external image DB (Data Base) and the console 17. The communication unit 34 is connected to a network (not shown) such as a LAN (Local Area Network) and / or a WAN (Wide Area Network), and performs transmission control in accordance with a communication protocol defined by various wired or wireless communication standards.

[0057] The processor 36 functions as a control unit 36A for controlling each part of the console 17 and an image processing unit 36B for performing various image processes. As an example, the processor 36 is composed of a memory such as a CPU (Central Processing Unit) and a RAM (Random access memory). The CPU functions as the processor 36 by loading various programs including the application program 37 from the memory 33 into the memory and executing the loaded programs. The processor 36 is an example of the "processor" related to the technology of the present invention. Further, the console 17 having the processor 36 that executes image processing is an example of the "image processing device" related to the technology of the present invention.

[0058] The control unit 36A controls the gantry 16 through the gantry control unit 27 according to the instructions of the operator input from the input device 32. The control unit 36A sets the imaging conditions and the like. The image processing unit 36B executes the slice image generation process and the MPR image generation process.

[0059] Figure 3 It shows an outline of the processing of the processor 36 that functions as the image processing unit 36B. The slice image generation process is a process of reconstructing an image based on the projection data PD obtained from the gantry 16 to generate a tomographic image. In the slice image generation process, the reconstructed tomographic image is a tomographic image representing an axial cross-section orthogonal to the body axis (Z-axis) of the subject H. Here, this tomographic image is referred to as a slice image SL. The slice image SL is an example of the "slice image" related to the technology of the present invention. As an example, the reconstruction of the slice image SL based on the projection data PD is performed by the filtered back-projection method.

[0060] In the CT apparatus 11, when imaging is performed, a plurality of slice images SL are sequentially generated. For example, as in this example, when the projection data PD is output from the head side of the subject H, the projection data PD is sequentially output from the head side. Then, the console 17 sequentially executes the reconstruction process of the slice image SL starting from the projection data PD on the head side, and sequentially stores the generated slice images SL in the memory 33. The imaging based on the CT apparatus 11 is ended by generating the slice images SL of all the imaging ranges in the body axis direction (Z-axis direction). A set of slice images SL including a plurality of slice images SL is called a slice volume VOL. The slice volume VOL is composed of a plurality of slice images SL stored in sequence. The slice volume VOL is composed of the slice images SL of a part of the imaging range during imaging, and is composed of the slice images SL of all the imaging ranges after imaging is completed.

[0061] In the MPR image generation process, first, a function creation process for creating an MPR image generation function GF1 for generating an MPR image is executed. The MPR image generation function GF1 is a function that takes the slice image SL as the input image and the MPR image Mp as the output image. The MPR image generation function GF1 is an example of a function that takes the pixel values of a plurality of slice images SL as parameters. The MPR image Mp is a tomographic image representing an arbitrarily specified cross-section of the subject H, and is an example of the "tomographic image representing a specified cross-section" related to the technology of the present invention. In this example, hereinafter, as cross-sections, in addition to the axial cross-section (AX), the sagittal cross-section (SAG) which is the vertical cross-section of the subject H and the coronal cross-section (COR) which is the horizontal cross-section of the subject H are taken as examples for explanation (reference Figures 9 - 11). The X'-axis and Y'-axis with dashes represent the coordinate axes of the cross-section of the MPR image Mp. The X'-Y plane changes according to the direction of the specified cross-section, and thus is sometimes inconsistent with the X-Y plane of the slice image SL.

[0062] As shown in Figure 4 the prior art, the MPR image Mp is generally obtained by the following method, that is, an arbitrary cross-section is specified in the isotropic three-dimensional image VD_ISO, and the specified arbitrary cross-section is cut out. The isotropic three-dimensional image VD_ISO is generated by performing the following processing, that is, an isotropic processing in which the resolutions in the X-axis direction, Y-axis direction, and Z-axis direction are the same according to the slice volume VOL of all the slice images SL including the imaging range.

[0063] As described above, the resolutions in the X-axis direction and Y-axis direction of the slice image SL change according to the FOV. For example, assume that the number of pixels in the X-axis direction and Y-axis direction of the slice image SL is 512×512. If the number of pixels is the same, the larger the FOV, the lower the resolution, and the narrower the FOV, the higher the resolution. For example, if the FOVs of 320 mm and 640 mm are compared, the pixel intervals of the slice image SL become 320 mm / 512 = 0.625 and 640 mm / 512 = 1.25 respectively. The smaller the FOV, the smaller the pixel interval, and thus the higher the resolution.

[0064] On the other hand, the slice interval that defines the resolution in the Z-axis direction is generally longer than the pixel intervals in the X-axis direction and Y-axis direction. Therefore, interpolation processing of the slice image SL is performed in a manner that matches the pixel intervals in the X-axis direction and Y-axis direction. This is the isotropic processing. The isotropic three-dimensional image VD_ISO is a three-dimensional image that makes the three-dimensional resolution isotropic by interpolating the slice image SL based on all the slice images SL in the imaging range, and is composed of three-dimensional isotropic pixels, that is, isotropic voxels. If such an isotropic three-dimensional image VD_ISO is generated, an MPR image Mp of an arbitrary cross-section can be generated. However, the generation of the isotropic three-dimensional image VD_ISO takes time, and it is impossible to generate all the slice images SL in the output imaging range.

[0065] Therefore, the processor 36 according to the technology of the present invention directly generates the MPR image Mp from the slice image SL by using the MPR image generation function GF1 without generating the isotropic three-dimensional image VD_ISO.

[0066] In Figure 3In this case, in order to create the MPR image generation function GF1, the processor 36 acquires the imaging conditions (A) and the tomographic image generation conditions (B). These are set in the CT apparatus 11 before imaging is performed. For example, the processor 36 accepts the specification of the imaging conditions (A) and the tomographic image generation conditions (B) through the operation of the input device 32 by the operator.

[0067] The imaging conditions (A) include A1: slice interval, A2: FOV, and A3: number of pixels (X, Y). In the tomographic image generation conditions (B), there are B1: the direction and position of the section, and B2: slice thickness. The direction and position of the section are the direction and position of the section of the MPR image Mp to be generated. As the direction of the section, in this example, an axial section, a sagittal section, or a coronal section is specified. And regarding the position of the section, for example, in the case of the MPR image Mp(AX) of the axial section, any position in the Z-axis direction is specified. In the case of the MPR image Mp(SAG) of the sagittal section, any positions in the Z-axis direction and the X-axis direction are specified. In the case of the MPR image Mp(COR) of the coronal section, any positions in the Z-axis direction and the Y-axis direction are specified.

[0068] Figure 5 Shows the processing sequence of the creation process (step S1200) of the MPR image generation function GF1. In step S1210, the processor 36 creates a Z coordinate table according to the imaging conditions (A). And in step S1220, the processor 36 creates an isotropic data derivation function using the Z coordinate table. Furthermore, in step S1230, according to the isotropic data derivation function, a pixel value derivation function Fmpr of the MPR image Mp is created.

[0069] Figure 6 Is a diagram conceptually showing the creation process of the Z coordinate table in step S1210. First, use Figure 6 to explain the creation process of the Z coordinate table in step S1210. The Z coordinate table is a table showing the correspondence between the SL position coordinates and the isotropic Z coordinates. The SL position coordinates are the coordinates representing the positions of a plurality of slice images SL in the Z-axis direction, and are derived according to the slice interval included in the imaging conditions (A). In the SL position coordinates, point s is an arbitrary position, and point SLP represents the position where the slice image SL exists. topZ is the position of the slice image SL at the most cephalad position among the slice images SL for which reconstruction is completed, and btmZ is the position of the slice image SL at the most caudal position. That is, it represents the range of the slice images SL that can be used to generate the MPR image Mp. In Figure 6 's example, there are 32 (#0 to #31) slice images SL within the range from topZ to btmZ.

[0070] The isotropic Z coordinate is a Z coordinate with scales attached with resolution settings matching the X-axis direction and the Y-axis direction. That is, the interval of the scales of the isotropic Z coordinate is the same as the pixel intervals in the X-axis direction and the Y-axis direction of the slice image SL. In the isotropic Z coordinate, point z is an arbitrary position of the scale.

[0071] As Figure 7 shown, according to the size of the FOV, the interval of the scales of the isotropic Z coordinate changes. If the case of FOV1 shown in (7A) of Figure 7 is compared with the case of FOV2 smaller than FOV1 shown in (7B) of Figure 7 , the scale interval of FOV2 is shorter. As described above, this is because the smaller the FOV, the higher the resolution, and the shorter the pixel intervals in the X-axis direction and the Y-axis direction.

[0072] In the creation process of the Z coordinate table in step S1210, the processor 36 first creates an isotropic Z coordinate according to the FOV and the number of pixels (X, Y) set as the imaging condition (A). And a table representing the correspondence between the SL position coordinates and each position z of the isotropic coordinates is created as the Z coordinate table. Through this Z coordinate table, when the position of the MPR image Mp is specified in the isotropic Z coordinate, the point s of the corresponding SL position coordinates can be derived. As will be described later, the specification of the position in the Z-axis direction of the MPR image Mp is based on the scale of the isotropic Z coordinate.

[0073] Figure 8 is a diagram conceptually showing the creation process of the isotropic data export function in step S1220. The isotropic data export function is a function for exporting the isotropic slice image SL_ISO at each z position of the isotropic Z coordinate. The isotropic slice image SL_ISO is a slice image obtained by interpolating the isotropic Z coordinate at each z position based on the slice image SL. The isotropic data export function is a function for exporting the pixel value tmp[z][p] of each pixel p of the isotropic slice image SL_ISO as the isotropic data. Here, [z] represents the position on the isotropic Z coordinate, and [p] represents the position in the X-Y plane of the isotropic slice image SL_ISO.

[0074] In the creation process of the isotropic data export function in step S1220 by the processor 36, first, based on the slice thickness and the Z coordinate table of the isotropic slice image SL_ISO, the range in the SL position coordinates corresponding to each position z is set. This range is defined by the point Sb on the topZ side and the point Se on the btmZ side, and is the selection range for choosing the slice image SL to be used for exporting the pixel value tmp[z][p] of the isotropic slice image SL_ISO. The isotropic slice image SL_ISO is a slice image obtained by interpolating the area where the slice image SL does not exist. Therefore, for the pixel value tmp[z][p] of the isotropic slice image SL_ISO, it is derived by linear interpolation based on the pixel values of multiple nearby slice images SL. The selection range defines the slice image SL to be used for interpolation. The width of this selection range is preset according to the interval of the scale of the isotropic Z coordinate. That is, for one z position, the approximate number of slice images SL to be used for interpolation is preset. In this example, since the number of slice images SL included in the selection range is two (Smin and Smax), two slice images SL are used for interpolation. Of course, the number of slice images SL to be used for interpolation can be arbitrary and can also be set to three or more.

[0075] In Figure 8 the example shown, the processor 36 determines the position of the SL position coordinates corresponding to each position z of the isotropic Z coordinate according to the Z coordinate table. The position corresponding to the z position is set to ztbl[z - topZ]. Centered on this position, in the SL position coordinates, the points that have moved an equal distance to the topZ side and the btmZ side are the point Sb and the point Se respectively. The range of the point Sb and the point Se includes Smin (SLP) on the topZ side and Smax (SLP) on the btmZ side. The annotation SLP in the parentheses indicates that there is a slice image SL at the positions of Smin and Smax respectively. By specifying the point Sb and the point Se, two slice images SL to be used for interpolation are selected.

[0076] Further, in the interpolation process of pixel values, the processor 36 uses an isosceles triangle with the z position as the vertex and the line connecting point Sb and point Se as the base to determine the weights of the pixel values of the respective slice images SL of Smin and Smax. The isosceles triangle represents the distribution of the weights of the pixel values of the slice image SL used. rb is the weight coefficient multiplied by the pixel value of the slice image SL of Smin, and re is the weight coefficient multiplied by the pixel value of the slice image SL of Smax. The maximum value of the weight coefficient is "1". When comparing the weight coefficients of rb and re, rb is larger when closer to the z position in the Z-axis direction. The processor 36 uses the weight coefficients rb and re derived in this way to determine the weights of the pixel values of the respective slice images SL of Smin and Smax, and calculates the pixel value tmp[z][p] of the isotropic slice image SL_ISO.

[0077] Conceptually, the isotropic data derivation function derives the pixel value tmp[z][p] as isotropic data by performing such processing. The pixel value tmp[z][p] is the pixel value of a pixel where, when the body axis direction is set as the Z-axis direction and the two directions defining a cross-section orthogonal to the body axis direction are set as the X-axis direction and the Y-axis direction, the resolution is isotropized in the X-axis direction, Y-axis direction, and Z-axis direction. This is data equivalent to the pixel value of an isotropic voxel in the isotropic three-dimensional image VD_ISO.

[0078] In Figure 8 In the example shown, as an example, the isotropic data derivation function is represented by Equation (1) under the following conditions. As a condition, first, the ranges of x, y, and z of the isotropic slice image SL_ISO are as follows.

[0079] 0 ≤ x < imageWidth

[0080] 0 ≤ y < imageHeight

[0081] topZ ≤ z ≤ btmZ

[0082] Further, in Equation (1), [p] represents the position of the isotropic slice image SL_ISO in the X-Y plane, which is defined by the component [x] in the X-axis direction and the component [y] in the Y-axis direction.

[0083] [Equation 1]

[0084]

[0085] Here, in Equation (1), "vol" refers to the pixel values of the slice image SL included in the slice volume VOL. For example, vol[Smin][p] is the pixel value of each pixel p in the X-Y plane of the slice image SL at Smin in the SL position coordinates. vol[Smax][p] is the pixel value of each pixel p in the X-Y plane of the slice image SL at Smax in the SL position coordinates. The definitions of the other symbols are as follows.

[0086] rb = Smin - Sb

[0087] re = Se - Smax

[0088] Smin = Ceil(Sb)

[0089] Smax = floor(Se)

[0090] Sb = ztbl[z - topZ] - 1

[0091] Se = ztbl[z - topZ] + 1

[0092] For example, assume that the position of the SL position coordinates of ztbl[z - topZ] is "2.3". In this case, in each of the expressions for Sb and Se, Sb becomes "1.3" and Se becomes "3.3". Since the slice image SL is used for interpolation, in order to find the positions (SLP) of the slice images SL near Sb and Se, the "1.3" of Sb is rounded up to find the integer value "2", and thus Smix is determined. On the other hand, the "3.3" of Se is discarded to find the integer value "3", and thus Smax is determined. The respective weight coefficients rb and re of the pixel values of these slice images SL are determined according to the distance from the z position, and thus become rb = 2 - 1.3 = 0.7 and re = 3.3 - 3 = 0.3. The value obtained by adding 70% of the pixel value of Smin and 30% of the pixel value of Smax becomes tmp[z][p] at z = 2.3. Here, to set it to the accurate pixel value, it is necessary to divide by the number of sheets of the slice image SL used for the arithmetic mean of the pixel values of the slice images SL of Smin and Smax. However, as described later, tmp[z][p] is data merged with the pixel value derivation function Fmpr of the MPR image Mp. Therefore, tmp[z][p] is used without dividing by the number of sheets of the slice image SL.

[0093] Also, in this example, the slice thickness, which is the thickness in the Z-axis direction of the isotropic slice image SL_ISO, is "0". Therefore, there is no slice image SL between Smin and Smax. As a result, the second term including Σ in Equation (1) becomes "0". However, when the slice thickness is greater than "0" and there is a slice image SL between Smin and Smax, the second term becomes a value greater than "0". When the slice thickness is greater than "0", the isosceles triangle representing the distribution of the weight coefficients becomes a trapezoidal shape with the length of the thickness of the slice thickness on the upper side. The weight coefficient of the pixel value of the slice image SL specified in the second term has a maximum value of "1".

[0094] Figure 9 is a diagram conceptually showing the creation process of the pixel value derivation function Fmpr of the MPR image Mp in step S1230. Figure 9 The shown pixel value derivation function Fmpr is a function for deriving the pixel value output[p'] of the pixel p' of the MPR image Mp(AX) of the axial cross-section (AX). In the MPR image Mp(AX) of the axial cross-section (AX), the X'-Y' plane represents the cross-section, and the C-axis represents the thickness direction of the slice thickness Slb_Th. In the case of the MPR image Mp(AX) of the axial cross-section (AX), the C-axis corresponds to the isotropic Z coordinate. Labeling the C-axis as C(Z) means that the C-axis corresponds to the isotropic Z coordinate. The position of the MPR image Mp(AX) is specified in the isotropic Z coordinate. Ci is the specified position of the cross-section of the MPR image Mp(AX), and is specified according to the position corresponding to the scale of the isotropic Z coordinate.

[0095] The method for deriving the pixel value of the MPR image Mp(AX) is substantially the same as Figure 8 the method for deriving the pixel value of the isotropic slice image SL_ISO shown. That is, the processor 36 performs linear interpolation based on the pixel value of the isotropic slice image SL_ISO corresponding to the specified position Ci, thereby deriving the pixel value output[p'] of each pixel p' of the MPR image Mp(AX). The trapezoid represented by the dashed line on the C(Z) axis is the same as the isosceles triangle shown as the distribution of the weight coefficients of Figure 8 the isotropic data derivation function. In Figure 9 , the slice thickness Slb_Th is greater than "0", so it becomes a trapezoid. The trapezoid has equal-width distances on the topZ side and the btmZ side centered on the specified position Ci. On the C(Z) axis, the range defined by Cb and Ce corresponds to Figure 8Similarly, Sb and Se shown are the selection ranges of the isotropic slice images SL_ISO used for interpolation. The layer thickness Slb_Th is specified as the tomographic image generation condition (B), and the selection range is set according to the specified layer thickness Slb_Th. qb and qe are the weight coefficients of the pixel values of the isotropic slice images SL_ISO multiplied by Cmin and Cmax.

[0096] The pixel value derivation function Fmpr of the MPR image Mp(AX) conceptually performs such processing to derive the pixel value output[p'].

[0097] In Figure 9 In the example shown, as an example, the pixel value derivation function Fmpr of the MPR image Mp(AX) is represented by Equation (2) under the following conditions. As a condition, first, the ranges of x', y', and cp of the MPR image Mp(AX) are as follows. cp is the position of the isotropic slice image SL_ISO existing within the range corresponding to the layer thickness Slb_Th in the isotropic Z coordinate corresponding to the C(Z) axis.

[0098] 0 ≤ x' < imageWidth

[0099] 0 ≤ y' < imageHeight

[0100] topZ ≤ cp ≤ btmZ

[0101] And, in Equation (2), [p'] represents the position [x'][y'] in the X'-Y' plane of the MPR image Mp(AX).

[0102] [Equation 2]

[0103]

[0104] Here, in Equation (2), "tmp" is the pixel value of the isotropic slice image SL_ISO obtained according to the isotropic data derivation function. For example, tmp[Cmin][p'] is the pixel value of each pixel p' in the X-Y plane of the isotropic slice image SL_ISO of Cmin in the isotropic Z coordinate. tmp[Cmax][p'] is the pixel value of each pixel p' in the X-Y plane of the isotropic slice image SL_ISO of Cmax in the isotropic Z coordinate. The definitions of the other symbols are as follows.

[0105] qb = Cmin - Cb

[0106] re = Ce - Cmax

[0107] Cmin = Ceil(Cb)

[0108] Cmax = floor(Ce)

[0109] Cb = Ci - ΔT / 2 - 1

[0110] Ce = Ci + ΔT / 2 + 1

[0111] ΔT = Slb_Th / PS

[0112] qb and qe correspond to rb and re of the isotropic data derivation function, and are weight coefficients for pixel values multiplied by Cmin and Cmax. Similar to rb and re, qb and qe are obtained according to the distribution of weights represented by a trapezoid. ΔT is the value obtained by dividing the slice thickness Slb_Th in millimeters by the pixel interval PS, and is the thickness corresponding to the slice thickness Slb_Th that matches the scale unit of the isotropic Z coordinate.

[0113] The pixel value derivation function Fmpr includes tmp in Equation (2) and incorporates the isotropic data derivation function. After creating the isotropic data derivation function, the processor 36 creates the pixel value derivation function Fmpr according to the slice thickness Slb_Th specified as the tomographic image generation condition (B).

[0114] Figure 10 is a diagram conceptually showing the creation process of the pixel value derivation function Fmpr that derives the pixel value output[p'] of the pixel p' of the MPR image Mp(SAG) of the sagittal section (SAG). It is basically the same as Figure 9 the example of the axial section (AX) shown. Hereinafter, the description will be centered on the differences. In the MPR image Mp(SAG), the X'-Y' plane represents the section, and the C axis represents the thickness direction of the slice thickness Slb_Th. In the case of the MPR image Mp(SAG) of the sagittal section (SAG), the C axis corresponds to the isotropic X coordinate. The position of the MPR image Mp(SAG) is specified on the C(X) axis corresponding to the isotropic X coordinate. Ci is the specified position of the section of the MPR image Mp(SAG), and is specified according to the position corresponding to the scale of the isotropic X coordinate.

[0115] Furthermore, the processor 36 obtains the selection range defined by Cb and Ce on the C(X) axis according to the specified position Ci and the slice thickness Slb_Th. The weight coefficients for multiplying the pixel values of the isotropic slice image SL_ISO are obtained according to the trapezoidal weight distribution defined by Cb, Ce, and the specified position Ci.

[0116] In the case of the MPR image Mp(SAG) in the sagittal section (SAG), unlike the case of the axial section (AX), the isotropic Z coordinate has a different direction from the slice thickness Slb_Th. Therefore, the ranges of topZ and btmZ are defined in the width direction (Y'-axis direction) of the X'-Y' plane.

[0117] In Figure 10 In the example shown, as an example, the pixel value derivation function Fmpr of the MPR image Mp(SAG) is represented by Equation (3) under the following conditions. As a condition, first, the ranges of x', y', and cp of the MPR image Mp(SAG) are as follows. Here, cp is the pixel position of the isotropic slice image SL_ISO that exists within the range corresponding to the slice thickness Slb_Th in the isotropic X coordinate corresponding to the C(X) axis.

[0118] 0 ≤ cp < imageWidth

[0119] 0 ≤ x’ < imageHeight

[0120] topZ ≤ y’ ≤ btmZ

[0121] Moreover, in Equation (3), [p’] represents the position [x’][y’] in the X’-Y’ plane of the MPR image Mp(SAG).

[0122] [Equation 3]

[0123]

[0124] In Equation (3), it also includes "tmp" which is the output value of the isotropic data derivation function, and the isotropic data derivation function is incorporated. The definitions of the symbols in Equation (3) are as follows, which are the same as those in Equation (2). ΔT is the thickness corresponding to the slice thickness Slb_Th that matches the scale unit of the isotropic X coordinate.

[0125] qb = Cmin - Cb

[0126] re = Ce - Cmax

[0127] Cmin = Ceil(Cb)

[0128] Cmax = floor(Ce)

[0129] Cb = Ci - ΔT / 2 - 1

[0130] Ce = Ci + ΔT / 2 + 1

[0131] ΔT = Slb_Th / PS

[0132] Figure 11FIG. 0 conceptually shows a creation process of a pixel value derivation function Fmpr that derives a pixel value output[p'] of a pixel p' of an MPR image Mp(COR) of a coronal section (COR). Basically the same as the example of the sagittal section (SAG) shown in Figure 10 is presented. Hereinafter, the description will be centered on the differences. In the MPR image Mp(COR), the X'-Y' plane represents the section, and the C-axis represents the thickness direction of the slice thickness Slb_Th. In the case of the MPR image Mp(COR) of the coronal section (COR), the C-axis corresponds to the isotropic Y coordinate. The position of the MPR image Mp(COR) is specified on the C(Y) axis corresponding to the isotropic Y coordinate. Ci is the specified position of the section of the MPR image Mp(COR), and is specified according to the position corresponding to the scale of the isotropic Y coordinate.

[0133] And, the processor 36, similarly to the case of the sagittal section (SAG), obtains a selection range defined by Cb and Ce on the C(Y) axis according to the specified position Ci and the slice thickness Slb_Th. The weight coefficient for multiplying the pixel value of the isotropic slice image SL_ISO is obtained according to the weight distribution of the trapezoid defined by Cb, Ce, and the specified position Ci.

[0134] In the case of the MPR image Mp(COR) of the coronal section (COR), similarly to the sagittal section (SAG), since the isotropic Z coordinate is different from the direction of the slice thickness Slb_Th, the ranges of topZ and btmZ are defined in the width direction (Y'-axis direction) of the X'-Y' plane.

[0135] In Figure 11 the example shown, as an example, the pixel value derivation function Fmpr of the MPR image Mp(COR) is represented by Equation (4) under the following conditions. Equation (4) is the same as Equation (3) of the sagittal section (SAG). By making efforts in the way of taking the X'-axis and Y'-axis of the section of the MPR image Mp(COR), Equation (3) of the sagittal section (SAG) and Equation (4) of the coronal section are unified. The conditions are different from the case of the sagittal section (SAG). As conditions, first, the ranges of x', y', and cp of the MPR image Mp(COR) are as follows. Here, cp is the pixel position of the isotropic slice image SL_ISO that exists within the range corresponding to the slice thickness Slb_Th in the isotropic Y coordinate corresponding to the C(Y) axis.

[0136] 0 ≤ x' < imageWidth

[0137] 0 ≤ cp < imageHeight

[0138] topZ ≤ y' ≤ btmZ

[0139] Further, in Equation (4), [p'] represents the position [x'][y'] in the X'-Y' plane of the MPR image Mp(COR).

[0140] [Equation 4]

[0141]

[0142] In Equation (4), it also includes "tmp" which is the output value of the isotropic data derivation function, and the isotropic data derivation function is incorporated. The definitions of the symbols in Equation (4) are as follows, the same as in Equation (3). ΔT is the thickness corresponding to the slice thickness Slb_Th that matches the scale unit of the isotropic Y coordinate.

[0143] qb = Cmin - Cb

[0144] re = Ce - Cmax

[0145] Cmin = Ceil(Cb)

[0146] Cmax = floor(Ce)

[0147] Cb = Ci - ΔT / 2 - 1

[0148] Ce = Ci + ΔT / 2 + 1

[0149] ΔT = Slb_Th / PS

[0150] Regarding the operation based on the above structure, it will be described using Figure 12 the flowchart showing the processing sequence of the MPR image generation process as shown. When shooting is performed by the CT device 11, the processor 36 of the console 17 waits for the acquisition of the imaging conditions (A) and the tomographic image generation conditions (B) in step S1100. As Figure 2 explained, the imaging conditions (A) include the slice interval, FOV, and the number of pixels (X, Y). The tomographic image generation conditions (B) include the direction and position of the section of the MPR image Mp and the slice thickness Slb_Th.

[0151] In step S1100, when the imaging conditions (A) and the tomographic image generation conditions (B) are acquired (Yes in step S1100), the processor 36 proceeds to step S1200.

[0152] In step S1200, the processor 36 acquires the imaging conditions (A) and the tomographic image generation conditions (B) before the CT device 11 starts shooting, and creates the MPR image generation function GF1. The processor 36 creates, according to the imaging conditions (A) and the tomographic image generation conditions (B), in accordance with Figure 5Create the MPR image generation function GF1 in the order shown. More specifically, the MPR image generation function GF1 includes Figure 6 the Z - coordinate table shown, Figure 8 the isotropic data export function shown, and Figures 9 - 11 the pixel value export function Fmpr shown. In step S1200, the processor 36 creates these. The imaging condition (A) of the CT apparatus 11 includes at least the slice interval, and the processor 36 creates the MPR image generation function GF1 according to the imaging condition (A).

[0153] And, if shooting starts in step S1300, the processor 36 sequentially acquires the projection data PD from the head side of the subject H, and starts generating the slice images SL based on the acquired projection data PD.

[0154] In step S1400, the processor 36 waits for the acquisition of the required slice images SL corresponding to the tomographic image generation condition (B). If the specified position Ci of the MPR image Mp is on the head side of the subject H, the required slice images SL can be acquired relatively quickly. When the required slice images SL are acquired in step S1400, the processor 36 proceeds to step S1500.

[0155] In step S1500, the processor 36 uses the created MPR image generation function GF1, takes the slice images SL as input, and generates the MPR image Mp under the specified conditions. Thus, when the CT apparatus 11 outputs a plurality of slice images SL during shooting, the processor 36 starts the generation process of the MPR image Mp during shooting.

[0156] And, in step S1600, the processor 36 displays the MPR image Mp on the display 31.

[0157] Thus, the console 17 having the processor 36 is an example of an image processing apparatus having a processor, and the processor performs image processing on a plurality of slice images SL output by the CT apparatus 11 (an example of a tomographic image photographing apparatus) and representing axial cross - sections (AX) orthogonal to the body axis of the subject H (an example of a subject). The processor 36 acquires a plurality of slice images SL, and uses the MPR image generation function GF1, which is an example of a function taking the pixel values of the plurality of slice images SL as parameters, to generate the MPR image Mp, which is an example of a tomographic image representing a specified cross - section.

[0158] Therefore, compared with generating an isotropic three - dimensional image VD_ISO in which the three - dimensional resolution of all slice images SL within the imaging range is isotropized (refer to Figure 4), as compared with the conventional method of cutting out tomographic images representing a specified cross-section from the generated isotropic three-dimensional image VD_ISO, it is possible to obtain tomographic images similar to the MPR image Mp representing the specified cross-section in a short time. That is, since a function such as the MPR image generation function GF1 that directly inputs the slice image SL and outputs a tomographic image similar to the MPR image Mp is used, it is possible to obtain a tomographic image representing the specified cross-section without going through the process of generating an isotropic three-dimensional image. Therefore, it is possible to shorten the acquisition time from the start of imaging to the acquisition of tomographic images in the tomographic imaging apparatus as compared with the prior art.

[0159] And, as Figure 12 shown in steps S1400 and S1500, when the CT apparatus 11 outputs a plurality of slice images SL during imaging, the processor 36 according to the technology of the present invention starts the generation process of tomographic images taking the MPR image Mp as an example during imaging using the plurality of slice images SL. As described above, since the generation process of tomographic images starts during imaging, it is possible to further shorten the acquisition time of tomographic images. Here, "during imaging" means from the start of imaging of a specified imaging range in the body axis direction of the subject to the end of imaging of the entire imaging range. In the above example, for example, when the whole body of the subject H is the imaging range, it means from the start of imaging of the head of the subject H to before the end of the entire imaging range up to the feet. And, as shown in step S1400, as an example, the processor 36 can start the generation of the MPR image Mp without waiting for the end of imaging at the moment when the slice image SL required for generating the MPR image Mp at the specified position Ci is output.

[0160] And, a function taking the MPR image generation function GF1 as an example is created according to the imaging conditions of the CT apparatus 11 and the imaging conditions including the slice interval of the slice image SL. Therefore, the processor 36 can create an appropriate function corresponding to the imaging conditions including the slice interval.

[0161] And, before the tomographic imaging apparatus starts imaging, the processor 36 acquires the imaging conditions and creates a function such as the MPR image generation function GF1. Therefore, as compared with creating a function by acquiring the imaging conditions after the start of imaging, it is possible to obtain tomographic images of a specified cross-section similar to the MPR image Mp in a shorter time. In addition, instead of creating a function each time imaging is performed, for example, a plurality of functions corresponding to different slice intervals may be prepared in advance, and a function may be selected according to the slice interval set as the imaging condition.

[0162] Further, the MPR image generation function includes an isotropic data derivation function that derives isotropic data as pixel values of pixels whose resolutions are isotropized in the X-axis direction, Y-axis direction, and Z-axis direction, and the processor generates a tomographic image similar to the MPR image Mp based on the isotropic data. Therefore, an MPR image Mp equivalent to the MPR image cropped from the isotropic three-dimensional image VD_ISO can be obtained. Such an MPR image Mp is useful because it is frequently used.

[0163] Further, in the above example, the cross-section of the MPR image Mp, which is an example of a tomographic image, is any one of an axial cross-section (AX), a sagittal cross-section (SAG), and a coronal cross-section (COR). These cross-sections are frequently used and thus useful. In addition, compared with generating other cross-sections, the creation of the MPR image generation function GF1 is simple. Further, as the cross-section of the MPR image Mp, in addition to the cross-sections in the above example, it can also be a cross-section in any other direction such as an inclined cross-section. In this case, a function corresponding to the cross-section in any other direction is created.

[0164] Further, the processor 36 accepts the specification of the slice thickness as the thickness of the MPR image Mp, which is an example of a tomographic image, and performs weighting corresponding to the slice thickness to generate the MPR image Mp. Since weighting corresponding to the slice thickness is performed, a tomographic image that accurately reflects the information of the subject H can be obtained as compared with the case where no weighting is performed.

[0165] [Second Embodiment]

[0166] Figures 13 - 19 The second embodiment shown is an example of generating an inclined image DT as a tomographic image representing a specified cross-section using an inclined image generation function GF2 that takes the pixel values of the slice image SL as parameters. The inclined image DT refers to a tomographic image representing an inclined cross-section obtained by rotating the axial cross-section of the slice image SL about the X-axis when the body axis direction is set as the Z-axis direction, the width direction of the cross-section orthogonal to the body axis direction is set as the X-axis direction, and the height direction is set as the Y-axis direction.

[0167] Conventionally, gantry tilt photography in which the gantry 18 is physically tilted for imaging has been known. By tilting the gantry 18, the irradiation direction of the radiation is also tilted with respect to the body axis, so that the radiation passes through the subject H obliquely. Thereby, a slice image SL tilted with respect to the body axis of the subject H is obtained. Since the orientation of the cross-section of the slice image SL obtained by gantry tilt photography is tilted, it is called an inclined image. However, the mechanism for rotating the gantry 18 is complex and has a huge structure, so the cost is very high.

[0168] Therefore, in the second embodiment, based on the slice image SL representing a cross-section orthogonal to the body axis, an inclined image DT is generated through image processing. The processor 36 creates an inclined image generation function GF2 for generating the inclined image DT according to the imaging condition (A) and the tomographic image generation condition (B). The imaging condition (A) includes A1: slice interval, A2: FOV, and A3: number of pixels (X, Y) as in the first embodiment. The tomographic image generation condition (B) includes B2: slice thickness and B3: inclination angle.

[0169] Figure 14 The processing sequence representing the creation process (step S2200) of the inclined image generation function GF2 is shown. In step S2210, the processor 36 creates a coordinate transformation table. And in step S2220, the processor 36 creates a pixel value derivation function Fdt for the inclined image DT, and in step S2230, the processor 36 creates a pixel value derivation function Fdt for the inclined image DT.

[0170] Figure 15 It is a diagram conceptually showing the creation process of the coordinate transformation table in step S2210. As Figure 15 shown in (15A) of Figure 15 the coordinate transformation table is a table that transforms the position of the pixel P of the slice image SL into the position of the pixel Pt of the inclined image DT. In

[0171] more specifically, as Figure 15 shown in (15A) of

[0172] [Equation 5]

[0173]

[0174] Here, y and z are the coordinates in the Y-Z plane of the pixel P of the slice image SL.

[0175] And y' and z' are the coordinates in the Y-Z plane of the pixel Pt of the inclined image DT.

[0176] The processor 36 generates an inclined image DT representing an inclined cross-section by performing such a coordinate transformation using Equation (5), where the inclined cross-section is obtained by tilting the slice image SL of the axial cross-section as Figure 15 shown in (15B) of Figure 15The cross-section is tilted by rotating the tilt angle ω about the X-axis as shown in (15C).

[0177] However, as Figure 15 shown in (15A), in the plurality of tilted images DT arranged in the Z-axis direction, coordinate transformation is performed in such a manner that the height in the Y-axis direction of the pixel Pt is made consistent. For example, when tilting a plurality of slice images SL about the tilt center CTR, as Figure 16 shown, the pixels P arranged in the Z-axis direction in the slice image SL become pixels Pt arranged in a direction that is tilted with a rising right shoulder with respect to the Z-axis in the tilted image DT. Also, in the gantry tilt photography in which the gantry 18 is tilted, the gantry 18 moves in the Z-axis direction in a tilted posture, and the detector 22 has a width. Therefore, the height of the pixel Pt in the Y-axis direction changes in a stepped manner corresponding to the width of the detector 22. Thus, if the height of the pixel Pt changes in the Y-axis direction, it may not be preferable in terms of visual recognition and the like. Therefore, in the tilted image DT related to the technology of the present invention, the height of the pixel Pt in the Y-axis direction is made consistent. As an example, the height of the pixel Pt in the Y-axis direction is constant.

[0178] As Figure 15 shown in (15A), the slice interval SI of the slice image SL is the same as the interval in the direction orthogonal to the two tilt axes of the tilted image DT. The interval in the Z-axis direction of the two tilt axes is wider than the slice interval SI by 1 / cosω times. Also, the pixel interval PS between two adjacent pixels P in the Y-axis direction of the slice image SL is the same as the pixel interval PS between two pixels Pt in the tilted image DT in the direction adjacent to the tilt axis. The coordinate transformation table is set to satisfy such conditions. As already described in the first embodiment, the pixel interval PS is obtained based on the FOV and the number of pixels (X, Y) set as the imaging condition (A).

[0179] Figure 17 is a diagram conceptually showing the creation process of the pixel value derivation function Fdt in step S2220. The pixel value of the pixel Pt in the tilted image DT is obtained by linear interpolation based on the distance d, which is the distance from the pixel values of the pixels P near the four points arranged so as to surround the pixel Pt. If the distance between each of the four pixels P and the pixel Pt is set as d, and the weight coefficient of the pixel values of the four points is set as w, then as shown in the graph representing the relationship between d and w, the smaller the d, the larger the weight coefficient w. That is, the closer the distance to the pixel Pt, the greater the weight of the pixel value of the pixel P. The pixel value derivation function Fdt is created based on such conditions.

[0180] When the slice thickness Slb_Th of the tilted image DT is "0", the generation of the tilted image DT can be completed by only performing coordinate transformation and linear interpolation of the pixel values based on the function Fdt derived from the pixel values. However, when the slice thickness Slb_Th is greater than "0", weighting corresponding to the slice thickness Slb_Th is performed to generate the tilted image DT, and a tilted image DT that more accurately reflects the information of the subject H can be obtained.

[0181] Step S2230 is a process for creating a weight correction function for performing weighting corresponding to the slice thickness Slb_Th. Figure 18 It is a diagram conceptually showing the process of creating the weight correction function in step S2230. In Figure 18 the pixel Pt_i is the pixel Pt that is the object of weight correction corresponding to the slice thickness Slb_Th. Figure 18 The method of weight correction shown is the same as the Figures 9 - 11 weighting process shown in the first embodiment. That is, using the pixel values of a plurality of pixels Pt arranged in the thickness direction of the slice thickness Slb_Th, each pixel value is multiplied by a weight coefficient corresponding to the distance from the correction target pixel Pt_i, thereby correcting the pixel value of the correction target pixel Pt_i. The range defined by Pt_b and Pt_e is the selection range of the pixels Pt used for correction, and is set according to the slice thickness Slb_Th. The pixel Pt_min and the pixel Pt_max are the pixels Pt arranged at both ends within the selection range. qb and qe are the weight coefficients for setting the weights of the pixel Pt_min and the pixel Pt_max. In step S2230, the processor 36 creates such a weight correction function according to the slice thickness Slb_Th.

[0182] Regarding the operation based on the above structure, it will be described using the Figure 19 flowchart showing the processing sequence of the tilted image generation process shown. When shooting is performed by the CT apparatus 11, the processor 36 of the console 17 waits for the acquisition of the imaging conditions (A) and the tomographic image generation conditions (B) in step S2100. As Figure 13 explained, the imaging conditions (A) include the slice interval, FOV, and the number of pixels (X, Y). The tomographic image generation conditions (B) include the slice thickness Slb_Th and the tilt angle ω.

[0183] In step S2100, when the imaging conditions (A) and the tomographic image generation conditions (B) are acquired (yes in step S2100), the processor 36 transfers to step S2200.

[0184] In step S2200, the processor 36 creates the tilted image generation function GF2. The processor 36 creates the tilted image generation function GF2 according to the imaging conditions (A) and the tomographic image generation conditions (B), in accordance with Figure 13Create the oblique image generation function GF2 in the order shown. More specifically, the oblique image generation function GF2 includes Figure 15 the coordinate transformation table shown, Figure 17 the pixel value derivation function Fdt based on four-point interpolation shown, and Figure 18 the weight correction function shown. In step S2200, the processor 36 creates these. Thus, the processor 36 creates the oblique image generation function GF2 according to the imaging condition (A) of the CT device 11 including the slice interval SI.

[0185] Moreover, if shooting starts in step S2300, the processor 36 sequentially acquires the projection data PD from the head side of the subject H, and starts generating the slice image SL based on the acquired projection data PD.

[0186] In step S2400, the processor 36 waits for the acquisition of the required slice image SL corresponding to the tomographic image generation condition (B). If the specified position of the oblique image DT is the head side of the subject H, the required slice image SL can be acquired relatively quickly. When the required slice image SL is acquired in step S2400, the processor 36 transfers to step S2500.

[0187] In step S2500, the processor 36 uses the created oblique image generation function GF2, takes the slice image SL as input, and generates the oblique image DT corresponding to the specified conditions such as the oblique angle ω. Thus, when the CT device 11 outputs a plurality of slice images SL during shooting, the processor 36 starts the generation process of the oblique image DT during shooting.

[0188] Moreover, in step S2600, the processor 36 displays the oblique image DT on the display 31.

[0189] Thus, the processor 36 generates the oblique image DT representing the oblique section using the oblique image generation function GF2 including the pixel value derivation function Fdt, and the oblique section is the section obtained by tilting the axial section of the slice image SL by rotating it around the X axis. By using the oblique image generation function GF2, the oblique image DT can be obtained at low cost compared with the case of performing gantry tilt imaging.

[0190] Moreover, when the processor 36 generates a plurality of oblique images DT arranged in the Z-axis direction, the heights of the pixels Pt of the plurality of oblique images DT in the Y-axis direction are the same. Therefore, as an example, compared with Figure 16 the case where the heights of the pixels Pt in the Y-axis direction are inconsistent as shown, the visual recognition of the oblique image DT is good.

[0191] The processor 36 receives the specification of the slice thickness Slb_Th as the thickness of the inclined image DT, and performs weighting corresponding to the specified slice thickness Slb_Th to generate the inclined image DT. As described above, by performing the weighting, an inclined image DT that accurately reflects the information of the subject H can be obtained.

[0192] In addition, the processor 36 can execute the MPR image generation process shown in the first embodiment in addition to the inclined image generation process.

[0193] Moreover, as shown in the above embodiments, the "function" related to the technology of the present invention can be in the form of table data or in the form of an arithmetic expression.

[0194] [Third Embodiment]

[0195] In the above embodiments, as an example of the image processing apparatus that performs the MPR image generation process and the inclined image generation process, the console 17 has been described as an example, but as Figure 20 shown, an image display device 13 different from the console 17 can function as the image processing apparatus. In this case, for example, the slice images SL output by the CT device 11 are temporarily stored in the image DB 12. The image DB 12 is, for example, a PACS (Picture Archiving and Communication System). The image DB 12 stores the slice images SL of the subject H output from the CT device 11, and transmits the slice images SL stored according to the request from the image display device 13 to the image display device 13 that is the request source. The image display device 13 has the same processor as the processor 36, and performs image processing such as the MPR image generation process and the inclined image generation process based on the transmitted slice images SL. As an example, the image display device 13 is arranged in each medical department in a medical facility and is used by doctors in the medical department.

[0196] In this case, the tomographic image generation condition (B) is specified by the doctor in the medical department. And the image display device 13 obtains the imaging condition (A) set in the CT device 11 from the CT device 11 through the console 17. In the image display device 13, based on these imaging conditions (A) and the tomographic image generation condition (B), image processing such as the MPR image generation process and the inclined image generation process is executed.

[0197] In the above-described embodiment, an example of performing image processing such as MPR image generation processing based on the slice image SL output during the imaging process of the CT apparatus 11 is shown. However, image processing such as MPR image generation processing may also be performed after the imaging is completed. In this case, the process of generating the isotropic three-dimensional image VD_ISO is not required, and thus the effect of being able to execute MPR image generation processing or inclined image generation processing in a short time can be obtained.

[0198] In the above-described embodiment, the CT apparatus 11 is taken as an example of the tomographic imaging apparatus. However, it may also be an MRI apparatus. And, as the radiation, it is not limited to X-rays, and may also be γ-rays.

[0199] Moreover, in the above-described embodiment, as the hardware configuration of the processor 36 of the console 17 or the processor of the image display apparatus 13, various processors (Processer) shown below can be used. As the various processors, in addition to the general-purpose processor, i.e., the CPU, which executes software (program) and functions as various processing units, it also includes PLDs (Programmable Logic Devices) such as FPGAs (Field-Programmable Gate Arrays) that can change the circuit configuration after manufacturing, and processors with a circuit configuration specifically designed to execute specific processing, i.e., application-specific circuits, such as ASICs (Application Specific Integrated Circuits).

[0200] Moreover, the above-described various processing can be executed by one of these various processors, or can also be executed by a combination of two or more processors of the same type or different types (for example, a combination of multiple FPGAs and a CPU and an FPGA, etc.). Also, multiple processing units can be constituted by one processor. As an example of constituting multiple processing units by one processor, there is a method of using a processor that realizes the functions of the entire system including multiple processing units with one IC (Integrated Circuit) chip, such as a system on chip (SOC).

[0201] Thus, the various processing units are configured as a hardware configuration using one or more of the above-described various processors.

[0202] Furthermore, as the hardware configuration of these various processors, more specifically, a circuit (Circuitry) combined with circuit elements such as semiconductor elements can be used.

[0203] In addition, the technology of the present invention relates to a storage medium (such as a USB memory or a DVD (Digital Versatile Disc)-ROM (Read Only Memory)) that can be read by a computer that non-temporarily stores a working program, in addition to the working programs of the CT device 11 or the image display device 13.

[0204] The description content and the illustrated content shown above are detailed descriptions of parts related to the technology of the present invention and are merely examples of the technology of the present invention. For example, the descriptions related to the above structure, function, action, and effect are descriptions related to an example of the structure, function, action, and effect of the parts related to the technology of the present invention. Therefore, within the scope of not departing from the gist of the technology of the present invention, the description content and the illustrated content shown above can be processed as follows: deleting unnecessary parts, adding new elements, or making replacements. In addition, in order to avoid complication and make it easier to understand the parts related to the technology of the present invention, in the description content and the illustrated content shown above, descriptions related to common technical knowledge and the like that do not require special explanation are omitted on the basis of being able to implement the technology of the present invention.

[0205] The following technical content described in the attached notes can be understood from the above content.

[0206] [Appended Note Item 1]

[0207] An image processing device includes a processor that performs image processing on a plurality of slice images output by a tomographic imaging device and representing axial cross-sections orthogonal to the body axis of a subject. In the image processing device, the processor performs the following processing:

[0208] Acquire a plurality of slice images; and

[0209] Generate a tomographic image representing a specified cross-section using a function with the pixel values of the plurality of slice images as parameters.

[0210] [Appended Note Item 2]

[0211] According to the image processing device described in Appended Note Item 1, wherein

[0212] When the tomographic imaging device outputs a plurality of slice images during imaging,

[0213] The processor uses the plurality of slice images to start the generation process of the tomographic image during imaging.

[0214] [Appended Note Item 3]

[0215] According to the image processing device described in Appended Note Item 1 or 2, wherein

[0216] The function is created based on the imaging conditions of the tomographic imaging device and at least includes the imaging condition of the slice interval of the slice images.

[0217] [Supplementary Note Item 4]

[0218] The image processing device according to Supplementary Note Item 2 or 3, wherein

[0219] Before the tomographic imaging device starts imaging, the processor acquires the imaging conditions and creates a function.

[0220] [Supplementary Note Item 5]

[0221] The image processing device according to any one of Supplementary Note Items 1 to 4, wherein

[0222] When the body axis direction of the subject is set as the Z-axis direction, and the two directions defining a cross-section orthogonal to the body axis direction are set as the X-axis direction and the Y-axis direction,

[0223] The function includes an isotropic data derivation function that derives isotropic data as the pixel values of pixels whose resolutions are isotropized in the X-axis direction, Y-axis direction, and Z-axis direction,

[0224] The processor generates tomographic images based on the isotropic data.

[0225] [Supplementary Note Item 6]

[0226] The image processing device according to Supplementary Note Item 5, wherein

[0227] The cross-section of the tomographic image is any one of an axial cross-section, a sagittal cross-section, and a coronal cross-section.

[0228] [Supplementary Note Item 7]

[0229] The image processing device according to Supplementary Note Item 5 or 6, wherein

[0230] The processor accepts the specification of the slice thickness as the thickness of the tomographic image and performs weighting corresponding to the slice thickness to generate the tomographic image.

[0231] [Supplementary Note Item 8]

[0232] The image processing device according to any one of Supplementary Note Items 1 to 7, wherein

[0233] When the body axis direction of the subject is set as the Z-axis direction, the width direction of the cross-section orthogonal to the body axis direction is set as the X-axis direction, and the height direction is set as the Y-axis direction,

[0234] The function includes a pixel value derivation function that derives the pixel values of an inclined cross-section obtained by rotating the axial cross-section of the slice image around the X-axis to make it inclined,

[0235] The processor uses a pixel value derivation function to generate an inclined image that is a tomographic image of an inclined section.

[0236] [Supplementary Note Item 9]

[0237] The image processing apparatus according to Supplementary Note Item 8, wherein

[0238] When generating a plurality of inclined images arranged in the Z-axis direction,

[0239] the heights of the pixels of the plurality of inclined images in the Y-axis direction are the same.

[0240] [Supplementary Note Item 10]

[0241] The image processing apparatus according to Supplementary Note Item 7 or 8, wherein

[0242] The processor accepts the designation of the slice thickness as the thickness of the inclined image and performs weighting corresponding to the designated slice thickness to generate the inclined image.

[0243] [Supplementary Note Item 11]

[0244] A working method of an image processing apparatus, the image processing apparatus including a processor that performs image processing on a plurality of slice images output by a tomographic image photographing apparatus and representing axial sections orthogonal to the body axis of a subject. In the working method of the image processing apparatus, the processor performs the following processing:

[0245] Obtain a plurality of slice images; and

[0246] Use a function with the pixel values of the plurality of slice images as parameters to generate a tomographic image representing a specified section.

[0247] [Supplementary Note Item 12]

[0248] A working program of an image processing apparatus, the image processing apparatus including a processor that performs image processing on a plurality of slice images output by a tomographic image photographing apparatus and representing axial sections orthogonal to the body axis of a subject. In the working program of the image processing apparatus, the processor is caused to execute the following processing:

[0249] Obtain a plurality of slice images; and

[0250] Use a function with the pixel values of the plurality of slice images as parameters to generate a tomographic image representing a specified section.

[0251] In this specification, "A and / or B" has the same meaning as "at least one of A and B". That is, "A and / or B" means that it can be only A, only B, or a combination of A and B. Also, in this specification, when connecting three or more matters with "and / or", the same way of thinking as in "A and / or B" shall also be applied.

[0252] All documents, patent applications, and technical standards described in this specification are incorporated by reference into this specification to the same extent as if each document, patent application, and technical standard were specifically and separately described.

Claims

1. An image processing apparatus includes a processor that performs image processing on a plurality of slice images output by a tomographic imaging device and representing axial cross-sections orthogonal to the body axis of a subject. In the image processing apparatus, the processor performs the following processing: Obtain the plurality of slice images; and Generate a tomographic image representing a specified cross-section using a function taking the pixel values of the plurality of slice images as parameters.

2. The image processing apparatus according to claim 1, wherein when the tomographic imaging device outputs the plurality of slice images during imaging, the processor uses the plurality of slice images to start the generation process of the tomographic image during the imaging.

3. The image processing apparatus according to claim 1, wherein the function is created based on the imaging conditions of the tomographic imaging device and at least includes the imaging condition of the slice interval of the slice images.

4. The image processing apparatus according to claim 3, wherein the processor obtains the imaging conditions and creates the function before the tomographic imaging device starts imaging.

5. The image processing apparatus according to claim 1, wherein when the body axis direction of the subject is set as the Z-axis direction, and two directions defining a cross-section orthogonal to the body axis direction are set as the X-axis direction and the Y-axis direction, the function includes an isotropic data derivation function that derives isotropic data as pixel values of pixels whose resolutions are isotropized in the X-axis direction, Y-axis direction, and Z-axis direction, and the processor generates the tomographic image based on the isotropic data.

6. The image processing apparatus according to claim 5, wherein the cross-section of the tomographic image is any one of an axial cross-section, a sagittal cross-section, and a coronal cross-section.

7. The image processing apparatus according to claim 5, wherein the processor accepts the designation of a slice thickness as the thickness of the tomographic image and performs weighting corresponding to the slice thickness to generate the tomographic image.

8. The image processing apparatus according to claim 1, wherein when the body axis direction of the subject is set as the Z-axis direction, the width direction of a cross-section orthogonal to the body axis direction is set as the X-axis direction, and the height direction is set as the Y-axis direction, the function includes a pixel value derivation function that derives the pixel values of an inclined cross-section obtained by rotating the axial cross-section of the slice image about the X-axis to be inclined, and the processor uses the pixel value derivation function to generate an inclined image as the tomographic image of the inclined cross-section.

9. The image processing apparatus according to claim 8, wherein when generating a plurality of inclined images arranged along the Z-axis direction, the heights of the pixels in the Y-axis direction of the plurality of inclined images are the same.

10. The image processing apparatus according to claim 8, wherein the processor accepts the designation of a slice thickness as the thickness of the inclined image and performs weighting corresponding to the designated slice thickness to generate the inclined image.

11. A working method of an image processing apparatus, the image processing apparatus including a processor that performs image processing on a plurality of slice images output by a tomographic imaging apparatus and representing axial cross-sections orthogonal to the body axis of a subject. In the working method of the image processing apparatus, the processor performs the following processing: Obtain the plurality of slice images; and Generate a tomographic image representing a specified cross-section using a function that takes the pixel values of the plurality of slice images as parameters.

12. A working program product of an image processing apparatus, the image processing apparatus including a processor that performs image processing on a plurality of slice images output by a tomographic imaging apparatus and representing axial cross-sections orthogonal to the body axis of a subject. The working program product of the image processing apparatus causes the processor to execute the following processing: Obtain the plurality of slice images; and Generate a tomographic image representing a specified cross-section using a function that takes the pixel values of the plurality of slice images as parameters.

Images