Image processing device, image processing method and program

Abstract

To improve the visibility of a difference image between three-dimensional images.SOLUTION: An image processing device comprises a control unit which generates a slab image in which a pixel value in the axial direction of a display object image is projected to a cross section in a slab that has the prescribed cross section of the three-dimensional display object image and a thickness along the axial direction intersecting the cross section as a slab thickness. The control unit obtains the pixel value of each pixel of the slab image with the combination of the maximum value and the minimum value of the pixel value of each pixel in the axial direction in the slab corresponding to each pixel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image processing device, an image processing method, and a program. [Background technology]

[0002] Patent Document 1 discloses a technology for use in the medical field, which visualizes changes in lesions and the like by presenting to a user a difference image between three-dimensional images obtained by imaging using various modalities. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-33698 Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology disclosed in Patent Document 1 for visualizing changes in lesions and the like, there may be cases where changes contained in a difference image between three-dimensional images are overlooked.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to provide an image processing technique that can improve the visibility of a difference image between three-dimensional images. [Means for solving the problem]

[0006] An image processing device according to one aspect of the present invention includes the following configuration: In a slab including a predetermined cross section of a three-dimensional image and having a thickness along an axial direction intersecting the cross section as a slab thickness, a pixel value obtained by combining the maximum and minimum pixel values ​​of pixels in the slab in the axial direction, The aforementioned Three-dimensional The pixel values ​​in the axial direction of the image are projected onto the cross section. By using the pixel values ​​of the slab image, 1. An image processing device having a control means for generating a slab image, The control means setting a weight using a first distance from the cross section of the pixel giving the maximum value and a second distance from the cross section of the pixel giving the minimum value, and combining the maximum value and the minimum value based on the weight; do. An image processing device according to another aspect of the present invention has the following configuration: The image processing device has a control means for generating a slab image by using, as a pixel value of a slab image projected onto a predetermined cross section of a three-dimensional image, a pixel value obtained by combining maximum and minimum pixel values ​​of pixels in the slab in the axial direction, the pixel value being a pixel value of the slab image projected onto the cross section, the pixel value being determined within the slab, the slab having a thickness along an axial direction intersecting the cross section, The control means compares a first distance from the cross section to the pixel giving the maximum value with a second distance from the cross section to the pixel giving the minimum value, The synthesis process is performed by selecting the maximum value or the minimum value, whichever is closer to the cross section, as the pixel value of the pixel of the slab image. An image processing method according to another aspect of the present invention includes: in a slab including a predetermined cross section of a three-dimensional image, the thickness of the slab being a thickness along an axial direction intersecting the cross section; a pixel value obtained by combining the maximum and minimum pixel values ​​of pixels in the slab in the axial direction, The aforementioned Three-dimensional The pixel values ​​in the axial direction of the image are projected onto the cross section. By using the pixel values ​​of the slab image, An image processing method for an image processing apparatus having a control step of generating a slab image, In the control step, setting a weight using a first distance from the cross section of the pixel giving the maximum value and a second distance from the cross section of the pixel giving the minimum value, and combining the maximum value and the minimum value based on the weight; do. An image processing method according to another aspect of the present invention is an image processing method of an image processing device, comprising a control step of generating a slab image by using pixel values ​​of the axial direction of the three-dimensional image projected onto the cross section, the pixel values ​​being calculated by combining maximum and minimum values ​​of pixel values ​​of pixels in the axial direction within a slab, the slab including a predetermined cross section of a three-dimensional image and having a thickness along an axial direction intersecting the cross section as a slab thickness, and In the control step, a first distance from the cross section to the pixel giving the maximum value is compared with a second distance from the cross section to the pixel giving the minimum value, The synthesis process is performed by selecting the maximum value or the minimum value, whichever is closer to the cross section, as the pixel value of the pixel of the slab image. [Effects of the Invention]

[0007] According to the present invention, it is possible to improve the visibility of a difference image between three-dimensional images. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing the configuration of an image processing system including an image processing apparatus according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the functional configuration of a control unit of the image processing apparatus. [Figure 3] 10 is a flowchart showing an example of a processing procedure of the image processing device. [Figure 4] FIG. 10 is a diagram illustrating a schematic example of a slab image. [Figure 5] FIG. 2 is a diagram for schematically explaining a slab image and pixel values ​​in each slice. [Figure 6] FIG. 10 is a diagram for schematically explaining a differential slab image. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0010] [First embodiment] The image processing device according to this embodiment generates a difference image between two three-dimensional images (three-dimensional medical images) and controls display of the generated difference image on a display unit. The configuration and processing of this embodiment will be described below with reference to FIG.

[0011] 1 is a diagram showing the configuration of an image processing system 10 including an image processing device 100 according to the first embodiment. The image processing system 10 includes, as its functional configuration, the image processing device 100, a network 120, and a data server 130. The image processing device 100 is communicably connected to the data server 130 via the network 120. The network 120 includes, for example, a LAN (Local Area Network) or a WAN (Wide Area Network).

[0012] The data server 130 is a picture archiving and communication system (PACS) that stores and manages medical images and information associated with the medical images. The image processing device 100 can acquire medical images stored in the data server 130 via the network 120. The data server 130 receives and stores images captured by a medical imaging device (modality), and transmits the images to each device in response to a request from the device connected to the network 120. The data server 130 also includes a database that can store received images as well as various data associated with the images.

[0013] In the following description, it is assumed that the data server 130 stores a plurality of three-dimensional images (medical images) acquired by imaging a subject in advance under different conditions (different modalities, imaging modes, dates and times, body positions, etc.). In this embodiment, the plurality of three-dimensional images will be described as images captured by an X-ray CT device, but the three-dimensional images may be captured by other modalities. In addition to the X-ray CT device, modalities include, for example, an MRI device, a SPECT device, a PET device, etc., and the image processing device 100 according to this embodiment is applicable to a plurality of three-dimensional images (medical images) acquired by various modalities.

[0014] Furthermore, when the image processing device 100 generates a difference image between two 3D images, the two 3D images to be processed may be any combination of images. For example, they may be images captured at the same time using different modalities or different imaging modes. Furthermore, for follow-up observation, the images may be images of the same subject captured using the same modality in the same position on different dates and times.

[0015] The image processing device 100 is a device that performs image processing according to the embodiment. The image processing device 100 is a device that generates a difference image between two three-dimensional images and displays it on a display unit 150, and functions as a terminal device for image interpretation operated by a user such as a doctor. The image processing device 100 includes a communication IF (Interface) 111 (communication unit), a ROM (Read Only Memory) 112, a RAM (Random Access Memory) 113, a storage unit 114, and a control unit 115. The image processing device 100 is connected to an instruction unit 140 and the display unit 150.

[0016] The communication IF 111 (communication unit) is configured with a LAN card or the like, and realizes communication between an external device (for example, the data server 130) and the image processing device 100. The ROM 112 is configured with a non-volatile memory or the like, and stores various programs. The RAM 113 is configured with a volatile memory or the like, and temporarily stores various pieces of information as data. The storage unit 114 is configured with a HDD (Hard Disk Drive) or the like, and stores various pieces of information as data.

[0017] The instruction unit 140 is configured with a GUI (Graphical User Interface) such as a keyboard, mouse, and touch panel, and inputs instructions from a user (e.g., a doctor) to the image processing device 100. An image to be processed is input to the image processing device 100 in accordance with an instruction from the user who operates the instruction unit 140. Note that the selection of an image does not have to be based on an instruction from the user, and for example, the control unit 115 of the image processing device 100 may be configured to automatically select an image to be processed based on a predetermined rule.

[0018] 2 is a diagram showing the functional configuration of the control unit 115. The control unit 115 is configured with a CPU (Central Processing Unit) and the like, and controls the overall processing in the image processing device 100. The control unit 115 has, as its functional configuration, an input image acquisition unit 101, a difference image acquisition unit 103, and a display control unit 105.

[0019] The input image acquisition unit 101 acquires a reference image and a floating image as images to be processed from the data server 130 via the communication IF 111 (communication unit) and the network 120. In the following description, medical image data that serves as a reference for alignment is referred to as a reference image (hereinafter, reference image), and medical image data that is aligned toward the reference image is referred to as a comparison image (hereinafter, floating image). Then, the difference image acquisition unit 103 generates a difference image between the reference image and the floating image as an image to be processed. The display control unit 105 generates images to be displayed on the display unit 150 and controls the display of the generated images.

[0020] The display unit 150 is configured with any device such as an LCD or CRT, and displays images and various information to the user. Specifically, it displays the reference image and floating image acquired from the image processing device 100. It also displays the difference image generated by the image processing device 100.

[0021] Each of the components of the image processing device 100 described above functions according to a computer program. For example, the control unit 115 (CPU) uses the RAM 113 as a work area to read and execute a computer program stored in the ROM 112 or the storage unit 114, thereby realizing the function of each component. Note that some or all of the functions of the components of the image processing device 100 may be realized using dedicated circuits. Also, some of the functions of the components of the control unit 115 may be realized using a cloud computer.

[0022] For example, a computing device located at a different location from the image processing device 100 may be communicatively connected to the image processing device 100 via the network 120, and the image processing device 100 and the computing device may send and receive data to realize the functions of the components of the image processing device 100 or the control unit 115.

[0023] Next, an example of processing by the image processing device 100 in Fig. 1 will be described with reference to Fig. 3. Fig. 3 is a flowchart showing an example of a processing procedure of the image processing device 100. In this embodiment, processing for obtaining a difference image between two three-dimensional images will be described using an example of a CT image of a subject, but this embodiment can also be applied to images obtained by other modalities.

[0024] (S1010: Acquire input image) In step S1010, when the user issues an instruction to acquire two images (a first image and a second image) via the instruction unit 140, the input image acquisition unit 101 acquires a reference image and a floating image as the multiple images (image data) designated by the user from the data server 130. Then, the acquired reference image and floating image are output to the difference image acquisition unit 103 and the display control unit 105.

[0025] (S1020: Obtaining the difference image) In step S1020, the difference image acquisition unit 103 generates a difference image between the reference image and the floating image acquired in step S1010. First, the difference image acquisition unit 103 performs deformation registration of one of the two images (reference image, floating image) acquired from the input image acquisition unit 101 (reference image) toward the other (floating image). For deformation registration, known deformation registration processes such as the FFD (Free-Form Deformation) method or the LDDMM (Large Deformation Diffeomorphic Metric Mapping) method can be applied. In both cases, deformation registration maintains the structure of the target area in the medical image data.

[0026] The difference image acquisition unit 103 can calculate the pixel position on the floating image corresponding to each pixel on the reference image through the deformation registration process (acquire deformation information (deformation information) indicating the corresponding pixel positions between images). The pixel positions of the pixels in the floating image corresponding to each pixel constituting the reference image are defined as corresponding pixel position information.

[0027] The difference image acquisition unit 103 can acquire a difference image by subtracting the pixel value of a position on the floating image corresponding to the pixel value at each position on the reference image from the pixel value at that position based on the deformation information between the reference image and the floating image.

[0028] Note that if a difference image is stored in advance in the data server 130, the process of generating a difference image based on deformation information obtained by deformation alignment may be skipped, and the difference image stored in the data server 130 may be read and acquired. Furthermore, the image processing device 100 does not necessarily have to have a function of generating a difference image, and the difference image acquisition unit 103 may be configured to acquire a difference image stored in the data server 130. In this case, the process of the input image acquisition unit 101 performed in step 1010 is not necessarily required. That is, if the purpose is to observe only the difference image, it is not necessary to input either the reference image or the floating image. Furthermore, if the purpose is to observe the difference image in comparison with the reference image, it is not necessary to input the floating image.

[0029] (S1030: Generation of display image and display control) In step S1030, the display control unit 105 acquires three-dimensional images to be displayed (reference image, floating image, difference image) from the input image acquisition unit 101 and the difference image acquisition unit 103, and performs control to display the acquired images to be displayed on the display unit 150. The display control unit 105 also generates an image to be displayed on the display unit 150 based on the images acquired from the input image acquisition unit 101 and the difference image acquisition unit 103, and performs control to display the generated image on the display unit 150. The three-dimensional images to be displayed include a difference image that indicates the difference between a reference image (reference image) that serves as a reference for alignment and a comparison image (floating image) that is aligned toward the reference image.

[0030] Here, the display control unit 105 has the functions of a general medical image viewer, and has the function of acquiring (cutting out) a slice image (cross section of interest), which is an arbitrary two-dimensional tomographic image in a reference image or a floating image, in response to a user instruction via the instruction unit 140, and displaying the acquired slice image on the display unit 150 (slice display function).

[0031] The display control unit 105 also has a function of acquiring (cutting out) a slice image (difference slice image) of the difference image corresponding to the target cross section of the reference image (at the same cross section position as the target cross section) from the difference image, and displaying the acquired difference slice image on the display unit 150.

[0032] At this time, a linked display mode may be provided in which the cross section of interest of the reference image and the corresponding cross section (difference slice image) of the difference image are displayed side by side on the display unit 150. Note that the cross section of interest can be specified by any cross section in response to a user's instruction via the instruction unit 140, and may be, for example, an axial cross section, a coronal cross section, a sagittal cross section in an X-ray CT image, or any other cross section.

[0033] The display control unit 105 also has a function (slab display function) for generating slab images (described later) for each of the reference image, floating image, and difference image in response to a user instruction and displaying them (slab display) on the display unit 150. In a linked display mode in which the cross section of interest of the reference image and the cross section of interest of the difference image are displayed side by side on the display unit 150, the display control unit 105 performs display control so that when displaying the cross section of interest of the reference image in a slab, the corresponding cross section of the difference image is displayed with the same slab thickness. When displaying a slab image of a slab including a cross section of interest extracted from a base image (reference image), the display control unit 105 performs display control so that the slab image of a slab including a cross section corresponding to the cross section of the difference image corresponding to the cross section of interest is displayed with the same slab thickness.

[0034] Here, a slab image is an image generated by setting a "slab" with a predetermined thickness (slab thickness) on a cross section of interest in image space and projecting pixels in the slab onto the cross section of interest. In other words, a slab image is an image in which the pixel values ​​of each pixel at corresponding positions in images of several slices before and after the cross section of interest are aggregated (projected) onto the cross section of interest.

[0035] Figure 4 is a diagram for explaining a slab image, and the cross section of interest is S z0 (z=z0 section), and the section of interest Sz0 n slices in the +Z direction (S z1 , S z2 ···S zn-1 , S zn ) is set, and the cross section of interest S z0 n slices in the -Z direction (S z-1 , S z-2 ···S z-(n-1) , S z-n ) is set. As shown in Figure 4, the cross section of interest S z0 When considering n slices before and after the slab, the slab thickness is z0 This gives 1+2n slices, which is a combination of n slices (=2n) before and after the slice of interest.

[0036] FIG. 5 is a diagram for explaining the pixel values ​​in the slab image and each slice. z0 (z=z0 section), and the section of interest S z0 Two slices in the +Z direction (S z1 , S z2 ) is set, and the cross section of interest S z0 Two slices in the -Z direction (S z-1 , S z-2 ) is set.

[0037] In Figure 5, P0 is the cross section of interest S z0 P0(x, y) indicates the pixel value at coordinates (x, y, z0). Slice S in the +Z direction z1 In this case, the cross section S z0 The pixel value at the position corresponding to pixel P0 in the slice S is denoted as P1(x, y). z2 In this case, the cross section S z0 The pixel value at the position corresponding to pixel P0 in the slice S is denoted as P2(x, y). z-1 In this case, the cross section S z0 The pixel value at the position corresponding to pixel P0 in -1 Let (x, y) be the slice S. z-2 In this case, the cross section S z0 The pixel value at the position corresponding to pixel P0 in -2 It is shown as (x, y).

[0038] As shown in Figure 5, when a slice of interest and two slices (=2 x 2) before and after the slice of interest are specified, the slab has a slab thickness of 5 slices. Each pixel value of the slab image can be obtained by aggregating (projecting) the pixel values ​​of each pixel at the corresponding position in multiple slice images onto the slice of interest. For example, in the example of Figure 5, each pixel value of the slab image is calculated based on the slice of interest S. z0 Each pixel (P -2 , P -1 , P0, P1, P2) pixel values ​​on the cross section S z0 It can be obtained by aggregating (projecting) it into

[0039] The slab thickness can be arbitrarily set by the user via the instruction unit 140. As shown in FIGS. 4 and 5, the cross section of interest S z0 Setting at the center of the slab is just one example, and it may also be set at the top end of the slab (e.g., the end of the slab in the +Z direction in Figures 4 and 5) or the bottom end (e.g., the end of the slab in the -Z direction in Figures 4 and 5).

[0040] The display control unit 105 generates a slab image by projecting pixel values ​​in the axial direction of the image to be displayed onto a slab that includes a predetermined cross section (cross section of interest) of the three-dimensional image to be displayed and has a thickness along an axial direction intersecting the cross section (for example, the Z axis in the examples of FIGS. 4 and 5) as the slab thickness. The display control unit 105 can generate slab images of reference images or floating images using various image processing methods. For example, the display control unit 105 can use methods such as calculating the average value, calculating the median value, obtaining the maximum value, or obtaining the minimum value of pixel values ​​as aggregating (projecting) each pixel value at a corresponding position in multiple slice images.

[0041] A method of acquiring each pixel value of a slab image by obtaining the maximum value of each pixel value of multiple slice images is called maximum intensity projection (MIP). Similarly, a method of acquiring each pixel value of a slab image by obtaining the minimum value of each pixel value of multiple slice images is called minimum intensity projection (MIP). The display control unit 105 can generate a slab image using maximum intensity projection (MIP) or minimum intensity projection (MIP). The display control unit 105 can also create a slab image using other calculation methods.

[0042] (Slab image generation) The display control unit 105 generates a slab image of the difference image (difference slab image) by the following process. That is, the display control unit 105 generates a difference slab image Slab by the calculation process of the following equation (1). Z=Z0 Generate (x, y).

[0043] Here, when generating a difference image between a reference image and a floating image as the image to be processed, the difference image acquisition unit 103 generates determination information for determining the image type of the image to be displayed. Then, when generating a slab image, the display control unit 105 determines the image type of the image to be displayed (reference image, floating image, difference image) based on the presence or absence of determination information. When there is no determination information, the display control unit 105 determines that the image type of the image to be displayed is a reference image or a floating image, and generates a slab image by the process described above. On the other hand, when there is determination information, the display control unit 105 determines that the image type of the image to be displayed is a difference image, and generates a difference slab image Slab by the calculation process of the following equation (1): Z=Z0 Generate (x, y).

[0044]

number

[0045] In the calculation process of equation (1), the display control unit 105 calculates the pixel value of each pixel on the differential slab image. sub represents the difference image. Also, I sub (x, y, z') represents the pixel value at coordinates (x, y, z') on the differential image. Z=Z0 indicates that a subtraction slab image is generated using the z=z0 cross section as the cross section of interest. Also, n is a parameter that defines the slab thickness.

[0046] FIG. 6 is a diagram for explaining a differential slab image. subz0 (z=z0 section), and the section of interest I subz0 n slices in the +Z direction (I subz1 , I subz2 I subzn-1 , I subzn ) is set, and the cross section I subz0 n slices in the -Z direction (I subz-1 , I subz-2 I subz-(n-1) , I subz-n ) is set.

[0047] In the calculation process of equation (1), max represents the maximum value function, and min represents the minimum value function, which indicate that the maximum and minimum pixel values ​​of each pixel within the search range (projection range) are obtained.

[0048] However, the maximum value function max has a constraint that the maximum value must be greater than or equal to 0. In other words, if the maximum value is less than or equal to 0, the maximum value is set to 0. Similarly, the minimum value function min has a constraint that the minimum value must be less than or equal to 0. In other words, if the minimum value is greater than or equal to 0, the minimum value is set to 0. This process is equivalent to the process of finding the maximum positive value and the minimum negative value.

[0049] The display control unit 105 calculates the pixel values ​​of the differential slab image based on the maximum and minimum pixel values ​​thus obtained. That is, the display control unit 105 obtains the pixel value of each pixel of the slab image (difference slab image) by combining the maximum and minimum pixel values ​​of each pixel in the axial direction (direction of the slab thickness) within the slab corresponding to each pixel.

[0050] In the first embodiment, the synthesis of the maximum and minimum pixel values ​​may include, in addition to the sum (addition) of the maximum and minimum pixel values ​​as described in equation (1), calculations such as the average of the maximum and minimum pixel values, or a weighted sum using the weighted maximum and minimum pixel values.

[0051] For example, as shown in Figure 6, subz0 When n slices (n slices set in the +Z direction and n slices set in the -Z direction) in front and behind the slab are used as a slab, the display control unit 105 calculates the pixel value of each pixel of the slab image (difference slab image) by calculating the maximum and minimum pixel values ​​of each pixel in the axial direction (direction of the slab thickness) within the slab corresponding to each pixel.

[0052] More specifically, in the calculation process of equation (1), the display control unit 105 sets z0-n≦z'≦z0+n as the search range, centered on the z=z0 cross section. Then, assuming that multiple slices within the search range (projection range) are slabs, the display control unit 105 acquires the maximum and minimum pixel values ​​of each pixel in the axial direction (direction of the slab thickness) within the slab at a position corresponding to each pixel in the difference slab image. The display control unit 105 then calculates the pixel value of each pixel in the difference slab image by performing a calculation using the acquired maximum and minimum pixel values. The display control unit 105 combines the maximum and minimum values ​​by adding them together to acquire the pixel value of each pixel in the slab image.

[0053] The display control unit 105 can also modify the calculation process of equation (1) to generate the average value of the maximum and minimum values ​​of the acquired pixel values ​​as the pixel value of the difference slab image.

[0054] (weighted sum of maximum and minimum values) Furthermore, the display control unit 105 calculates the difference slab image Slab by the calculation process of the following equation (2): Z=Z0 It is also possible to generate (x, y) as the pixel value of the differential slab image. That is, the display control unit 105 can generate a value obtained by combining the maximum and minimum values ​​of the acquired pixel values ​​[0] using the following equation (2).

[0055]

number

[0056] The calculation process of equation (2) corresponds to the weighted sum of the maximum and minimum values ​​described in equation (1). The display control unit 105 calculates the pixel value of each pixel of the slab image by calculating the weighted sum using weights for the maximum and minimum values. In the calculation process of equation (2), I sub represents the difference image. Also, I sub (x, y, z) represents the pixel value at coordinates (x, y, z) on the difference image. Z=Z0 indicates that a subtraction slab image is generated using the z=z0 cross section as the cross section of interest. Also, n is a parameter that defines the slab thickness, and indicates that a subtraction slab image is generated using n slices before and after the cross section of interest (i.e., the z=z0 cross section).

[0057] The display control unit 105 sets a weight using a first distance from the cross section (cross section of interest) of the pixel that gives the maximum value and a second distance from the cross section (cross section of interest) of the pixel that gives the minimum value. The display control unit 105 sets the weight so that the weight increases as the first distance or the second distance approaches the cross section (cross section of interest), and decreases as the first distance or the second distance moves away from the cross section (cross section of interest).

[0058] In the calculation process of equation (2), the weights (w_max and w_min) used in the weighted sum can be calculated as follows. That is, the weights are determined based on the relationship between a first distance (hereinafter referred to as d_max) from the cross section of interest of a pixel that gives the maximum value in the maximum function and a second distance (hereinafter referred to as d_min) from the cross section of interest of a pixel that gives the minimum value in the minimum function. The display control unit 105 sets the weights of the weighted sum, for example, so that the weight of a pixel closer to the cross section of interest is larger and the weight of a pixel farther from the cross section of interest is smaller. The weights are set so that the closer the first distance (d_max) or the second distance (d_min) is to the cross section of interest (the closer it is to 0), the larger the weights are. The farther the first distance (d_max) or the second distance (d_min) is from the cross section of interest, the smaller the weights are set.

[0059] Equation (3) is a formula for calculating the weight of the maximum value, and equation (4) is a formula for calculating the weight of the minimum value.

[0060] w_max= 2*d_min / (d_max+d_min)···(3) w_min= 2*d_max / (d_max+d_min)···(4) Note that the weights may be set by any method as long as the weights are set in accordance with the above constraints. For example, this can be achieved by preparing in advance a table of weights corresponding to combinations of distances (d_max, d_min). The display control unit 105 can acquire a first distance (d_max) from the cross section of interest of a pixel that gives the maximum value in the maximum value function and a second distance (d_min) from the cross section of interest of a pixel that gives the minimum value in the minimum value function, and acquire a weight corresponding to the combination of the acquired distances (d_max, d_min) by referring to the table. The display control unit 105 sets the weights by referring to a table that stores in advance weights corresponding to combinations of the first distance and the second distance.

[0061] Note that the method of calculating the weighted sum of the maximum and minimum values ​​by the calculation process of Equation (2) is merely one example of a method of combining the maximum and minimum values ​​based on the distance from the cross section of interest. For example, a first distance (d_max) from the cross section of interest of a pixel that gives the maximum value in the maximum function and a second distance (d_min) from the cross section of interest of a pixel that gives the minimum value in the minimum function may be compared, and the value closer to the cross section of interest (maximum or minimum) may be selected as the pixel value of the difference slab image.

[0062] When combining the maximum and minimum pixel values ​​weighted based on the distance from the cross section of interest, if either the maximum or minimum value is 0, that value is interpreted as not existing, and the other value is used.

[0063] Because the difference image has both positive and negative values ​​that are important, the above-described process can be used to calculate the maximum and minimum values ​​within the slab and combine them to generate a slab image suitable for the difference image. If each pixel value of the slab image is calculated based solely on the pixel values ​​(maximum pixel values) obtained by maximum intensity projection, the characteristics of the pixel values ​​(negative values) that can be obtained by minimum intensity projection will not be reflected in the pixel values ​​of the slab image. Furthermore, if each pixel value of the slab image is calculated based solely on the pixel values ​​(minimum pixel values) obtained by minimum intensity projection, the characteristics of the pixel values ​​(positive values) that can be obtained by maximum intensity projection will not be reflected in the pixel values ​​of the slab image.

[0064] According to this embodiment, the visibility of the difference image between three-dimensional images can be improved by image processing using pixel values ​​(maximum pixel values) obtained by maximum intensity projection and pixel values ​​(minimum pixel values) obtained by minimum intensity projection.

[0065] As described above, the display control unit 105 can change the generation method of the slab image based on the image type of the image to be displayed. Note that the generation method of the slab image does not necessarily have to be automatically selected based on the image type, and the user may specify the generation method via the UI of the instruction unit 140.

[0066] In the process of step S1030, the display control unit 105 may store the generated subtraction slab image in the storage unit 114 of the image processing device 100 or in the data server 130 via the network 120. This allows the subtraction slab image to be displayed in any other medical image viewer. In this case, the image display in step S1030 does not necessarily have to be performed.

[0067] According to this embodiment, the visibility of the difference image between three-dimensional images can be improved by generating a slab image suitable for the difference image.

[0068] <Second embodiment> In the first embodiment, a configuration for displaying a differential image on a display unit was described. In this embodiment, a configuration for displaying a superimposed image in which the differential value of the differential image is superimposed as color information on a reference image as an image that makes it easier to grasp the information of the differential image on a display unit 150 is described.

[0069] The configuration of the image processing system 10 according to this embodiment is the same as that of the first embodiment. However, in the second embodiment, the processing performed by the display control unit 105 is partially different from that of the first embodiment. In the following explanation, only the configuration of the different parts will be explained.

[0070] The flowchart showing the overall processing procedure performed by the image processing device 100 in this embodiment is the same as that in the first embodiment. However, since part of the processing performed by the display control unit 105 in S1030 is different, only the differences from the first embodiment will be described.

[0071] (S1030: Generation of display image and display control) In step S1030, similarly to the first embodiment, the display control unit 105 acquires three-dimensional images to be displayed (reference image, floating image, difference image) from the input image acquisition unit 101 and the difference image acquisition unit 103, and performs control to display the acquired images to be displayed on the display unit 150. Furthermore, the display control unit 105 generates an image to be displayed on the display unit 150 based on the images acquired from the input image acquisition unit 101 and the difference image acquisition unit 103, and performs control to display the generated image on the display unit 150. In this embodiment, the display control unit 105 further generates a superimposed image by superimposing the difference image on the reference image, and performs control to display the generated image on the display unit 150.

[0072] Here, the superimposed image is an image obtained by superimposing a difference image, in which each pixel is colored based on the maximum pixel value and the minimum pixel value, on a reference image. When the superimposed image is displayed in slices (i.e., when a slice image obtained by cutting out a cross section of a portion of the superimposed image is displayed), the display control unit 105 sets a first color (e.g., blue) to pixels in the corresponding difference image of the reference image whose difference value is positive, and sets a second color (e.g., red) to pixels in the corresponding difference image of the reference image whose difference value is negative. Then, the display control unit 105 controls the display unit 150 to display an image obtained by superimposing a color with a transparency corresponding to the magnitude of the absolute value of the difference value (the greater the absolute value of the difference value, the more opaque it becomes).

[0073] On the other hand, when the superimposed image is to be displayed as a slab (i.e., when a slab image of the superimposed image is displayed), the display control unit 105 generates a slab image of the reference image in the cross section of interest, and also generates an MIP slab image and a MinIP slab image of the difference image in the corresponding cross section. Here, the MIP slab image is a slab image based on pixel values ​​acquired by the maximum intensity projection method described above, and the MinIP slab image is a slab image based on pixel values ​​acquired by the minimum intensity projection method.

[0074] In the second embodiment, the combination of the maximum and minimum pixel values ​​may include, in addition to the combination described in the first embodiment, a process of setting different display colors for the maximum and minimum pixel values ​​and obtaining a mixed color of the display color set for the maximum pixel value and the display color set for the minimum pixel value.

[0075] The display control unit 105 sets a first color (e.g., blue) as the display color of each pixel in the MIP slab image, and a second color (e.g., red) as the display color of each pixel in the MinIP slab image. The display control unit 105 can also change the shade of the display color depending on the magnitude of the pixel value (absolute value) of each pixel. The display control unit 105 then determines a mixed color (e.g., purple) of the first color (blue) and the second color (red) based on the pixel values ​​of corresponding pixels at corresponding pixel positions between the MIP slab image and the MinIP slab image. The display control unit 105 generates a superimposed image in which the mixed color of the first color (blue) and the second color (red) is superimposed on the slab image of the reference image, and controls the display unit 150 to display the superimposed image.

[0076] According to this embodiment, it is possible to improve visibility by visualizing the pixel values ​​of each pixel of the slab image as a mixture of different colors (first color, second color) set to the maximum pixel value and the minimum pixel value, respectively.

[0077] (Other embodiments) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0078] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0079] 101: Input image acquisition unit, 103: Difference image acquisition unit, 105: Display control unit

Claims

1. An image processing device having a control means for generating a slab image by projecting pixel values ​​of the three-dimensional image in the axial direction onto the cross section, the pixel values ​​being calculated by combining maximum and minimum values ​​of pixel values ​​of pixels in the slab in the axial direction, the pixel values ​​being calculated by combining maximum and minimum values ​​of pixel values ​​of pixels in the slab in the axial direction, the pixel values ​​being calculated by projecting pixel values ​​of the three-dimensional image in the axial direction onto the cross section, The control means sets weights using a first distance from the cross section of a pixel that gives the maximum value and a second distance from the cross section of a pixel that gives the minimum value, and combines the maximum value and the minimum value based on the weights.

2. 2. The image processing apparatus according to claim 1, wherein said control means obtains the pixel value of the pixel of said slab image by combining said maximum value and said minimum value by adding said maximum value and said minimum value together.

3. 2. The image processing device according to claim 1, wherein the control means sets the weight so that it increases as the first distance or the second distance approaches 0, and so that it decreases as the first distance or the second distance increases.

4. 4. The image processing device according to claim 1, wherein the control means sets the weight by referring to a table that stores in advance weights corresponding to combinations of the first distance and the second distance.

5. 5. The image processing apparatus according to claim 1, wherein the control means determines the pixel value of the pixel of the slab image by calculating a weighted sum of the maximum value and the minimum value using the weights.

6. An image processing device having a control means for generating a slab image by using, in a slab containing a predetermined cross section of a three-dimensional image and having a thickness along an axial direction intersecting said cross section as a slab thickness, pixel values ​​obtained by a synthesis process of maximum and minimum pixel values ​​of pixels in said slab in said axial direction as pixel values ​​of the slab image projected onto said cross section, the control means compares a first distance from the cross section to the pixel giving the maximum value with a second distance from the cross section to the pixel giving the minimum value, an image processing device that performs, as the synthesis process, a process of selecting one of the maximum value and the minimum value, whichever is closer to the cross section, as the pixel value of the pixel of the slab image.

7. The image processing device according to claim 1 , further comprising a display unit that displays the slab image.

8. The image processing device according to claim 7 , wherein the three-dimensional image includes a display target image to be displayed on the display unit.

9. The image processing device according to claim 8 , wherein the control means controls the display of the display target image on the display unit.

10. The image processing device according to claim 8 , wherein the control means includes a display control section that controls display of the display target image on the display section.

11. 7. The image processing device according to claim 1, further comprising an instruction unit that receives a designation of the three-dimensional image to be processed.

12. The image processing device according to claim 11 , wherein the instruction unit is configured to accept at least one instruction from among a designation of the predetermined cross section, a designation of the slab thickness, and a designation of a method for generating the slab image.

13. 13. The image processing apparatus according to claim 11, wherein the control means receives input of a reference image and a comparison image designated by the instruction unit as the three-dimensional image to be processed.

14. 13. The image processing apparatus according to claim 11, wherein the control means comprises an input image acquisition section to which a reference image and a comparison image designated by the instruction section as the three-dimensional images to be processed are input.

15. 15. The image processing device according to claim 13, wherein the control means comprises a difference image generating section that generates a difference image between the reference image and the comparison image.

16. The image processing device according to claim 15 , wherein the difference image generating section performs a process of aligning the comparison image with the reference image, using the reference image as a reference.

17. The image processing device according to claim 15 or 16, wherein the three-dimensional image includes at least one of the reference image, the comparison image, and the difference image.

18. 18. The image processing apparatus according to claim 15, wherein the control means generates the slab image based on the difference image.

19. An image processing device described in any one of claims 15 to 18, wherein the control means controls display so that when displaying a slab image of a slab including a cross section of interest extracted from the reference image, the slab image of a slab including a corresponding cross section of the difference image corresponding to the cross section of interest is displayed with the same slab thickness.

20. 20. The image processing device according to claim 15, wherein the control means generates a superimposed image by superimposing the difference image, in which pixels are colored based on the maximum pixel value and the minimum pixel value, on the reference image.

21. the control means sets a first color as a display color for the pixel value of the maximum value, and a second color as a display color for the pixel value of the minimum value; The image processing apparatus according to claim 20 , wherein a superimposed image is generated by superimposing a mixture of the first color and the second color on the slab image of the reference image.

22. The image processing device according to any one of claims 1 to 21, wherein the control means generates a slab image by projecting pixel values ​​of the image to be displayed in a predetermined cross section of the three-dimensional image to be displayed onto the cross section within a slab having a thickness along an axial direction intersecting the cross section as a slab thickness.

23. 23. The image processing apparatus according to claim 22, wherein said control means determines the pixel value of a pixel of said slab image by combining the maximum and minimum pixel values ​​of pixels in said slab in said axial direction corresponding to said pixel.

24. An image processing method of an image processing device, comprising a control step of generating a slab image by projecting pixel values ​​of the three-dimensional image in the axial direction onto the cross section, the pixel value being calculated by combining a maximum value and a minimum value of pixel values ​​of pixels in the axial direction within the slab, the slab including a predetermined cross section of the three-dimensional image and having a thickness along an axial direction intersecting the cross section as a slab thickness, the pixel value being calculated by combining a maximum value and a minimum value of pixel values ​​of pixels in the axial direction within the slab, the pixel value being calculated by projecting pixel values ​​of the three-dimensional image in the axial direction onto the cross section, In the control step, a weight is set using a first distance from the cross section of the pixel giving the maximum value and a second distance from the cross section of the pixel giving the minimum value, and the maximum value and the minimum value are combined based on the weight.

25. An image processing method for an image processing device, comprising a control step of generating a slab image by using pixel values ​​obtained by combining the maximum and minimum pixel values ​​of pixels in the axial direction of the three-dimensional image projected onto the cross section, the pixel values ​​being calculated in a slab that includes a predetermined cross section of a three-dimensional image and has a thickness along an axial direction intersecting the cross section as a slab thickness, the pixel values ​​being calculated in the axial direction of the three-dimensional image as pixel values ​​of the slab image projected onto the cross section, In the control step, a first distance from the cross section to the pixel giving the maximum value is compared with a second distance from the cross section to the pixel giving the minimum value, an image processing method in which the synthesis process selects one of the maximum value and the minimum value, whichever is closer to the cross section, as the pixel value of the pixel of the slab image;

26. The image processing method of claim 24 or 25, wherein the control step generates a slab image in which pixel values ​​in the axial direction of the three-dimensional image to be displayed are projected onto a cross section of the slab, the slab having a thickness along an axial direction intersecting the cross section as a slab thickness.

27. 27. The image processing method according to claim 26, wherein said control step determines the pixel value of a pixel of said slab image by combining the maximum and minimum pixel values ​​of pixels in said slab in said axial direction corresponding to said pixel.

28. A program for causing a computer to execute the steps of the image processing method according to any one of claims 24 to 27.

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