Image display device, image display method, and program

Abstract

To eliminate the possibility of a WL being unintentionally changed when an image with a reference value allocated to a particular pixel value is displayed on an image display apparatus in which the WL and a WW are adjustable.SOLUTION: The image display apparatus comprises: image acquisition means for acquiring an image of a subject to be displayed; determination means for determining whether or not the image of the subject is a predetermined display type, a reference value of which is allocated to a particular pixel value; setting means for setting a WL and a WW for displaying the image of the subject, and fixing the WL to a predetermined value when the determination means determines that the image of the subject is the predetermined display type; and image conversion means for converting the image of the subject to allow the image of the subject to be displayed with the WL fixed to the predetermined value, or with the set WL and with the set WW.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, in the medical field, doctors make diagnoses by observing images captured by various imaging devices (modalities). Such images usually have gradations that exceed the display capabilities of monitors and the human visual perception. Therefore, image display devices that handle such images generally have a window function that specifies a range (window) of pixel values ​​to be displayed as a display parameter and maps pixel values ​​within that range to display values ​​(display luminance values) on the monitor.

[0003] Patent Document 1 discloses a known window function in which the range of pixel values ​​to be displayed is set using two parameters: a window level (hereinafter referred to as WL), which indicates the pixel value at the center of the range, and a window width (hereinafter referred to as WW), which indicates the width of the range. Image display devices with such a window function are equipped with a manual adjustment function that simultaneously changes WL and WW by, for example, dragging the mouse up, down, left, or right, and an automatic adjustment function that simultaneously calculates and adjusts WL and WW based on the distribution of pixel values ​​in the image. By adjusting WL and WW, this image display device makes it possible to clearly display the area or organ to be observed and perform diagnosis.

[0004] Furthermore, when comparing multiple images, there are cases where images are observed by assigning pixel values ​​to differences or amounts of change between the images. For example, two images to be compared are aligned, and an image (hereinafter referred to as a difference image) that visualizes the difference in pixel values ​​between corresponding pixels (voxels) between the images or an image (hereinafter referred to as a Jacobian map) that visualizes the ratio of local volumes between the images may be observed. In such images that visualize the differences or amounts of change between images, a state in which there is no difference or change between the images (a difference amount in a difference image = 0, or a volume ratio in a Jacobian map = 1) is generally used as a reference, and a value (reference value) indicating the reference is assigned to a specific pixel value. Then, the image is observed from the perspective of the difference from the reference value. For such images in which reference values ​​are assigned to specific pixel values, the WL and WW can usually be adjusted. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-11935 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, for example, a method has been proposed for adjusting at least one of the WL and WW by a single movement or operation of sliding a finger or the like in a specific direction on the screen, as disclosed in Patent Document 1 (see paragraph 0090). This method allows adjustment of the WL and WW through a simple operation, making it possible to easily obtain an image suitable for observation. However, on the other hand, depending on the manner in which the finger is slid, this method may result in a change of the WL even when, for example, only the WW was intended to be adjusted. For example, when displaying an image in which a reference value is assigned to a specific pixel value, such as a difference image, an unintentional change of the WL may hinder proper diagnosis.

[0007] The present invention has been made in consideration of the above situation, and aims to prevent unintentional changes to WL when displaying an image in which a reference value is assigned to a specific pixel value, for example, in an image display device in which WL and WW can be adjusted by a single or identical operation. [Means for solving the problem]

[0008] In order to solve the above problems, an image display device according to one embodiment of the present invention comprises: a display control means for displaying a medical image on a display unit; a switching means for switching between a first mode in which a change in a display value corresponding to a pixel value when the pixel value is a predetermined reference value is restricted and a second mode in which the display value is changeable according to the type of the medical image; Equipped with The first mode is characterized by limiting the change in the display value by at least one of attenuating and applying the instructed input value to the change in the display value, providing a dead zone of a predetermined range corresponding to the reference value for the input value, and limiting the range of the change in the display value. An image display device according to an embodiment of the present invention includes: a display control unit that displays a medical image on a display unit according to a window level and a window width; a switching means for switching between a first mode in which the window width can be changed while restricting changes to the window level, and a second mode in which both the window level and the window width can be changed according to the type of the medical image; Equipped with The first mode is characterized in that the change in the window level is limited by at least one of attenuating and applying an input value instructed for the change in the window level, providing a dead zone of a predetermined range corresponding to a predetermined reference value for the input value, and limiting the range of the change in the window level. Furthermore, a method for controlling an image display device according to an embodiment of the present invention includes the steps of: displaying a medical image on a display unit; a switching step of switching between a first mode that restricts a change in a display value corresponding to a pixel value when the pixel value is a predetermined reference value and a second mode that allows the display value to be changed according to the type of the medical image; Including, The first mode is characterized by limiting the change in the display value by at least one of attenuating and applying the instructed input value to the change in the display value, providing a dead zone of a predetermined range corresponding to the reference value for the input value, and limiting the range of the change in the display value. Furthermore, a method for controlling an image display device according to an embodiment of the present invention includes the steps of: displaying a medical image on a display unit according to a window level and a window width; a switching step of switching between a first mode in which the window width can be changed while restricting changes to the window level, and a second mode in which both the window level and the window width can be changed according to the type of the medical image; Including, The first mode is characterized in that the change in the window level is limited by at least one of attenuating and applying an input value instructed for the change in the window level, providing a dead zone of a predetermined range corresponding to a predetermined reference value for the input value, and limiting the range of the change in the window level. [Effects of the Invention]

[0009] According to the present invention, in an image display device in which WL and WW can be adjusted by a single or identical operation, it is possible to prevent unintentional changes to WL when displaying an image in which a reference value is assigned to a specific pixel value. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing the overall configuration of an image display system including an image display device according to a first embodiment of the present invention. [Figure 2] 5 is a flowchart showing a processing procedure executed by a control unit when an image is displayed in the first embodiment. [Figure 3] 10A and 10B are diagrams illustrating GUIs for setting WL / WW in the "WL adjustment permitted mode" and the "WL adjustment prohibited mode." [Figure 4] 10A and 10B are diagrams illustrating an example of conversion from normal pixel values ​​to display values ​​using a window function. [Figure 5] 10A and 10B are diagrams illustrating examples of a normal image, a difference image, a Jacobian map, and the relationship between the Jacobian map and its histogram; [Figure 6] FIG. 13 is a diagram illustrating an example of an image type designation UI according to the third embodiment. [Figure 7] FIG. 13 is a diagram illustrating an example of a WL / WW parameter selection UI according to the third embodiment. [Figure 8] 13A and 13B are diagrams illustrating an example of conversion from pixel values ​​to display values ​​in the fourth embodiment. [Figure 9] 13A and 13B are diagrams illustrating an example of conversion from pixel values ​​to display values ​​in the fourth embodiment. [Figure 10] 10A and 10B are diagrams illustrating an example of conversion from pixel values ​​to display values ​​during general automatic adjustment of WL / WW. [Figure 11] 13A and 13B are diagrams illustrating an example of conversion from pixel values ​​to display values ​​during automatic adjustment of WL / WW in the fifth embodiment. [Figure 12] 13A and 13B are diagrams illustrating an example of conversion from pixel values ​​to display values ​​during automatic adjustment of WL / WW in a modified example of the fifth embodiment. [Figure 13]FIG. 10 is a diagram showing an example of a mouse cursor in Modification 1 of the first embodiment. [Figure 14] FIG. 10 is a diagram showing another example of the mouse cursor in the first modification of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, exemplary embodiments for carrying out the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of components described in the following embodiments are arbitrary and can be changed depending on the configuration of an apparatus to which the present invention is applied or various conditions. In addition, the same reference numerals are used between drawings to indicate identical or functionally similar elements.

[0012] [First embodiment] An image display device according to a first embodiment of the present invention displays three-dimensional or two-dimensional images. The device has a window function that adjusts the window level (WL) and window width (WW) described above when converting pixel values ​​to display values. The device can appropriately control the WL when displaying an image in which a reference value is assigned (associated) with a specific pixel value, such as a difference image or a Jacobian map. The device also facilitates the setting of display parameters when displaying an image in which a reference value is assigned to a specific pixel value on an image viewer.

[0013] 1 is a diagram showing the overall configuration of an image display system including an image display device according to a first embodiment of the present invention. This image display system includes an image display device 10, a database 22, and a display unit 36. That is, the image display device 10 according to one aspect of the present invention is configured to switch the display format in a predetermined format, which will be described later, and generate a display image to be displayed on the display unit 36. The image display device 10 and the database 22 are connected to each other so as to be able to communicate with each other via communication means 21. In this embodiment, the communication means 21 is configured as a LAN (Local Area Network).

[0014] The database 22 stores and manages data such as various images, which will be described later. The image display device 10 acquires images managed in the database 22 via communication means 21, which is exemplified by a LAN. The display unit 36 ​​is realized by a display or the like, and displays various information to the user. The image display device 10 and the display unit 36 ​​are connected by communication means (not shown) or a display cable (not shown). Note that, although the image display device 10, the database 22, and the display unit 36 ​​are shown as being independent from each other in the example here, they may all or partly be integrated into one configuration. Furthermore, the database 22 may be replaced by an imaging device, and the captured image data may be directly visualized by the image display device.

[0015] The image display device 10 has, as its functional configuration, a communication IF (Interface) 31, a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a storage unit 34, an operation unit 35, and a control unit 50. The communication IF 31 is realized by a LAN card or the like, and controls communication between an external device (e.g., a database 22) and the image display device 10. The ROM 32 is realized by a non-volatile memory or the like, and stores various programs and the like. The RAM 33 is realized by a volatile memory or the like, and temporarily stores various types of information. The storage unit 34 is realized by a HDD (Hard Disk Drive) or the like, and stores various types of information. The operation unit 35 is realized by a keyboard, a mouse, or the like, and inputs instructions from the user to the device. The control unit 50 is realized by a CPU (Central Processing Unit) or the like, and controls overall processing in the image display device 10. Although the image display device 10 shown here includes all of the illustrated functional configurations, each of these may be configured independently or partially independently. Also, the operation unit 35 may be integrated with the display unit 36, and all user input to the image display device 10 may be performed in GUI format.

[0016] The control unit 50 has, as its functional configuration, an image acquisition unit 52, an operation content analysis unit 53, a display parameter setting unit 54, an image type determination unit 55, a mode determination unit 56, and a display control unit 57. The function of each unit in the control unit 50 will be explained together with the explanation of the flowcharts in Figures 2 and 3. Figure 2 is a flowchart showing the processing procedure executed by the control unit 50 of the image display device 10 when displaying an image in the first embodiment of the present invention.

[0017] 2 only describes the processing procedure for adjusting the displayed image using the window function when displaying a general image or an image in which a reference value is assigned to a specific pixel value. Although there are many other types of control (processing) performed by the control unit 50 and user inputs related to the control, for ease of understanding, only representative examples will be described here, and other explanations will be omitted. In this embodiment, an image to be displayed is an image with or attached to a header for identifying the image type.

[0018] When the image display process is started, in step S201, the image acquisition unit 52 reads an image designated by the user via the operation unit 35 from the database 22 or the storage unit 34 as an image to be displayed.

[0019] In step S202, the image type determination unit 55 determines the image type of the image to be displayed loaded in step S201. Specifically, the image type determination unit 55 determines whether the image is, for example, a CT image, an MRI image, or a subtraction image. In this embodiment, the image type determination unit 55 analyzes the header of the image to be displayed and acquires information about the image type added to the image in the header. For example, if a subtraction flag is present in the header of the loaded image, the image is determined to be a subtraction image. Note that the information indicating the type of image to be displayed is not limited to the header format and may be in any format that can be read by the image type determination unit 55. For example, if a display position corresponding to the image type is predetermined, the image type determination unit 55 may determine the image type based on the position of the mouse cursor. That is, the image type determination unit 55 can also determine the type of medical image based on the position of a user-movable index on the display unit.

[0020] In step S203, the display parameter setting unit 54 sets the initial values ​​of the display parameters (initial WW and initial WL) when displaying the image to be displayed that was read in step S201. In this embodiment, the display parameters (WL and WW values) recorded in the header of the image to be displayed are obtained and set as the WL and WW when the image is displayed.

[0021] Although it is assumed here that the display parameters are recorded in the header, default display parameters may be set for each image type based on the image type of the image to be displayed determined in step S202. Alternatively, if the display parameters are recorded in the header, those values ​​may be set as the initial values ​​as described above, and if they are not recorded, initial values ​​stored in, for example, the storage unit 34 corresponding to the image type may be read out and set.

[0022] At this time, if the image type is a type of "image in which a reference value is assigned to a specific pixel value," it is desirable to set a pixel value corresponding to that reference value as the initial value of WL. As an example of such a case, if the image type is a difference image, it is desirable for the display parameters to be based on a case in which the difference is zero, so WL=0 is desirable. Below, we will describe the case in which a difference image is loaded as an example of an image generated by assigning this reference value to a specific pixel value.

[0023] In step S204, the mode determination unit 56 determines a display parameter setting mode depending on whether the loaded image to be displayed is a difference image or not. That is, if the image to be displayed is a difference image, the display parameter setting mode is determined to be a "WL adjustment prohibited (disabled) mode" so that adjustment of the WL in future "operations related to window adjustment" is prohibited (disabled). On the other hand, in other cases, the display parameter setting mode is determined to be a "WL adjustment permitted (enabled) mode" so that adjustment of the WL in future "operations related to window adjustment" is permitted. The display control unit 57 causes the display unit 36 ​​to display a GUI for adjusting the display parameters (hereinafter referred to as a WL / WW adjustment UI) depending on the display parameter setting mode determined by the mode determination unit 56.

[0024] 3 shows examples of UIs for adjusting WL / WW, which are displayed on the display unit 36 ​​by the display control unit 57. Here, five forms shown in FIGS. 3(a) to 3(e) are illustrated.

[0025] FIG. 3(a) shows an example of a UI for adjusting WL / WW by dragging the mouse in two dimensions on an image displayed on the display unit 36. In this UI, the UI does not change between a "WL adjustment permission mode" and a "WL adjustment prohibition mode." In this example, the process of prohibiting WL adjustment is executed by the display parameter setting unit 54, for example, in step S208, which will be described later. In this UI, dragging the mouse in the vertical direction is an instruction to change WL, and dragging in the horizontal direction is an instruction to change WW. The mouse can be moved up, down, left, and right simultaneously (diagonally) on the image, and when a diagonal operation is performed, an instruction to change WL and WW is simultaneously acquired. Note that the UI corresponding to mouse dragging operations is not limited to this, and the UI may be changed depending on the mode.

[0026] FIG. 3(b) shows an example in which a GUI resembling a knob is displayed on the display unit 36 ​​and the WL and WW are changed using the GUI. FIG. 3(c) shows an example in which a GUI resembling a trackball is displayed on the display unit 36 ​​and the WL and WW are changed using the GUI. In either case, up-down operation of the GUI commands a change to the WL, and left-right operation commands a change to the WW. When the display parameter setting mode is the "WL adjustment permission mode," the display control unit 57 displays these GUIs on the display unit 36 ​​as being operable in two dimensions. That is, the "knob" and the "trackball" are permitted to be moved up-down, left-right, and a combination of these in diagonal directions. On the other hand, when the display parameter setting mode is the "WL adjustment prohibition mode," the display control unit 57 displays these GUIs on the display unit 36 ​​as being operable only in the left-right direction. That is, in the WL adjustment prohibition mode, the "knob" and the "trackball" are not permitted to be operated up-down or diagonally. This prevents the user from accidentally changing the WL when the differential image is displayed. Note that not allowing the operation is just one example, and it is also possible to allow the operation itself but not have the WL adjustment reflected by the operation.

[0027] 3(d) and 3(e) show examples using a GUI for adjusting WL and WW using independent parts. FIG. 3(d) shows an example in which a GUI is displayed on the display unit 36, displaying slider bars for setting the values ​​of each display parameter and numeric input boxes for directly entering values. FIG. 3(e) shows an example in which a GUI is displayed on the display unit 36, displaying a display parameter to be manipulated using a button and a common dial for changing the value. In these examples using a GUI, the display control unit 57 temporarily disables the WL parts when the display parameter setting mode is in the "WL adjustment prohibited mode." This prevents the user from accidentally changing the WL. Note that the above-described UIs and GUIs are merely examples, and various modifications are possible depending on the allowable display size, display image, etc., and other known UIs may also be used.

[0028] In step S205, the display control unit 57 converts pixel values ​​of the image to be displayed into display values ​​using the display parameters (WL / WW) set in step S203 and step S208 (described later) to generate an image for display. Then, the display control unit 57 controls the display of the generated image for display on the display unit 36. At this time, the above-mentioned GUI and the like are also displayed together with the generated image for display.

[0029] In steps S206 to S208, processing is performed in response to a user operation performed after the image is displayed. In step S206, the operation content analysis unit 53 accepts an operation from the user performed via the operation unit 35. In this embodiment, the operations accepted here include at least operations related to window adjustment using the GUI shown in FIG. 3, as well as other operations. Examples of other operations include display operations other than window adjustment provided in general image display devices, operations to switch images to be displayed, and operations to instruct the end of overall processing.

[0030] When an operation related to window adjustment is accepted in step S206, the operation content analysis unit 53 acquires information related to window adjustment from the operation. Specifically, depending on the type of GUI exemplified above, the amount of change in WL and WW (value to be added to the current setting value) or the specified values ​​of WL and WW are acquired as information related to window adjustment. The acquired information is sent to the display parameter setting unit 54.

[0031] In step S207, the operation content analysis unit 53 invokes processing according to the operation content. For example, if an operation related to window adjustment is received, the process proceeds to step S208. If an operation related to displaying a new file is received, the process returns to step S201 again, and a new image to be displayed is read. If an instruction to end the process is received, the entire process ends. Furthermore, if an instruction for another display operation is received, the process returns to step S205. In step S205, the display control unit 57 generates a display image from the image to be displayed after reflecting the various operation contents, and causes the display unit 36 ​​to display this. In this way, by responding to instructions for other display operations, basic functions as an image display device, such as slice switching, zooming in / out, and translation, are realized.

[0032] In step S208, the display parameter setting unit 54 updates the setting values ​​of WL and WW based on the information related to window adjustment acquired in step S206. As described above, for example, if the values ​​of WL and WW themselves are acquired as information related to window adjustment, those values ​​are used as new setting values ​​for WL and WW. On the other hand, if a change amount for WL or WW is acquired as information related to window adjustment, those values ​​are added to the current setting values ​​of WL and WW, and the new setting values ​​are used. At this time, if the display parameter setting mode is "WL adjustment prohibited mode" and a GUI that allows WL manipulation, such as a UI that adjusts WL / WW by dragging the mouse in two dimensions, is used, WL manipulation is suppressed in this step. In other words, even if a change amount for WL is specified, the current setting value of WL is not changed. Then, only the setting value of WW is updated, and the process proceeds to step S205.

[0033] Fig. 4 shows an example of the result of adjusting WL and WW of a difference image, for example. Fig. 4 is a diagram explaining a mapping function for allocating pixel values ​​of a difference image, which is an image to be displayed, to pixel values ​​(display values) of a display image, where the horizontal axis represents the pixel values ​​of the difference image, which is an image to be displayed, and the vertical axis represents the pixel values ​​(display values) of the display image. In Fig. 4(a), which shows the initial state when an image is displayed, a pixel value of 0, which is the reference value of the difference image, is allocated to the median value of 127 of the display values. In other words, WL=0 is set. In the case of a general UI in which WL adjustment is enabled, the displayed image can be freely transitioned to the states shown in Figs. 4(b) to 4(d) by adjusting WW and WL.

[0034] If only the WW is adjusted to be wider, the window range (the range of pixel values ​​to be displayed) will change from -256 to +256 to, for example, -400 to +400, as shown in FIG. 4(b). However, because the WL is not adjusted, the pixel value 0 will continue to be assigned to the median display value of 127. In contrast, if only the WL is adjusted, the window range will change from -256 to +256 to, for example, -156 to +356, as shown in FIG. 4(c). In other words, the width of the pixel values ​​to be displayed remains unchanged. However, because the WL is adjusted, the pixel value 100 will be assigned to the median display value of 127. If both the WW and WL shown in FIGS. 4(b) and 4(c) are adjusted simultaneously, the window range will change to -300 to +500, and the pixel value 100 will be assigned to the median display value of 127, as shown in FIG. 4(d).

[0035] However, when the image to be displayed is a difference image, observation is performed based on the assumption that there is no difference. Therefore, for example, the value (reference value) must always be expressed as a specific display value. In this example, the pixel value 0, which is the reference value, must always be assigned to the median display value of 127. That is, as described above, when observing a difference image, it is preferable to maintain the display value of this reference value even when the display parameters are changed, so WL adjustment is an unnecessary function. By prohibiting or disabling WL adjustment through mode selection in step S204, it is possible to prevent the transition to Figures 4(c) and 4(d) when displaying a difference image. As a result, the user can avoid unintentional changes to the WL due to operational error or unavoidable circumstances when adjusting the WW.

[0036] In this embodiment, a difference image has been described as an example of an image in which a reference value is assigned to a specific pixel value. However, this type of image is not limited to a difference image, and various other images in which a reference value is assigned to a specific pixel value in a similar manner are applicable. For example, the prohibition of changing the WL described above is also effective when displaying a Jacobian map in which the pixel value is the expansion / contraction ratio of each pixel (voxel) when two types of images are aligned with each other. Because the reference value of a Jacobian map is 1 (no volume change), when displaying a Jacobian map, it is desirable to fix the WL to a pixel value (usually 1) corresponding to "no volume change" in the map and allow only the WW to be manipulated. The same can be said for displaying a displacement field image in which the pixel value is the movement amount of each pixel (voxel) before and after deformation when two types of images are aligned with each other. That is, because the reference value of a displacement field image is 0 (no displacement), when displaying a displacement field image, it is desirable to fix the WL to a pixel value (usually 0) corresponding to "no displacement" in the image and allow only the WW to be manipulated. In this way, by always displaying a fixed WL in areas where there are no differences or changes, differences and changes can be effectively visualized. As described above, images in which reference values ​​that are the subject of this invention are assigned to specific pixel values ​​include images generated by converting differences and changes between multiple images into pixel values. Furthermore, the prohibition on changing the WL described above is also effective for images other than those that visualize the difference or amount of change between multiple images, as long as a reference value is assigned to a specific pixel value. For example, it may be an image that visualizes the spatial differentiation of an arbitrary image. In this case, a derivative of 0 becomes the reference value. It may also be an image that visualizes the results of comparing each pixel of an image that visualizes the distribution of some metric value (concentration or density) with a specified value (e.g., a standard value or norm value) of that metric value. In this case, if the comparison is made as a difference, the reference value is 0, and if the comparison is made as a ratio, the reference value is 1.

[0037] In actual processing, the mode determination unit 56 may store a list of image types for which WL changes are prohibited in advance and refer to the list for header information of the image to be displayed. If the image type of the image to be displayed belongs to the list, the mode determination unit 56 sets the mode to "WL adjustment prohibited mode," and otherwise to "WL adjustment permitted mode." For each image type for which WL changes are prohibited, a reference value for each image type may be stored in the list, and the WL may be set to the reference value corresponding to the image type of the image to be displayed. Furthermore, the reference value does not necessarily have to be defined. For an image type for which a reference value is not defined, the WL stored in the image header or the current WL may be used as the reference value.

[0038] Furthermore, this embodiment has been described on the assumption that a method of writing header information such as image type within an image file, such as DICOM, is used. That is, the image type of a medical image is determined based on the supplementary information exemplified in the header information, and the mode is switched based on this determination result. However, various header information may be stored in a file independent of the image file, and the header information may be referenced when the image file itself is loaded. That is, in this embodiment, the difference image, which is the image to be displayed, may be a typical JPEG image. Furthermore, the supplementary information indicating the image type is not limited to the format of header information, and may be attached to the image using various known linking formats.

[0039] Furthermore, in the present embodiment, the description is given on the assumption that the images to be displayed are three-dimensional images such as MRI or CT images. However, the images to be displayed in the present invention are not limited to these, and images of different dimensions, such as two-dimensional plain X-ray images and 4DCT images including time-series information, may also be displayed. Furthermore, in the present embodiment, the description is given on the assumption that the display control unit 57 uses a window function for grayscale images on the display unit 36, but a window function for color images may also be used.

[0040] Furthermore, in this embodiment, a difference image having a difference value between images as a pixel value has been exemplified, but images expressing the difference between images using other values ​​may also be targeted. For example, a difference image having an absolute value of the difference as a pixel value may be used as the image to be displayed. In this case, the reference value of the image to be displayed is 0 (unchanged pixels), but since the image to be displayed does not have negative values, it is desirable to set 0 at the bottom of the window rather than WL (the center of the window). It is also desirable to fix the bottom of the window and make only WW adjustable. In this way, control of the display parameters of an image generated by assigning a reference value to a specific pixel value is not limited to fixing WL to the center position of the window.

[0041] In this embodiment, the WL adjustment prohibition mode prohibits WL adjustment in display processing even if an operation related to window adjustment is performed. For example, when using the UI shown in FIG. 3(a), the current WL setting is not changed even if a WL change amount is specified. However, for example, in this mode, the width of the dead band in the WL change instruction (input value) may be made larger than the dead band width in the normal mode, and WL change instructions within this dead band may be considered zero. Alternatively, for example, the instruction may be converted to a smaller value using an exponential conversion, and the instruction value may be reduced before being received. In other words, WL adjustment may be limited in this mode. Furthermore, an allowable range of WL values ​​may be defined based on a reference value, and WL changes may be permitted within this allowable range even in the WL adjustment prohibition mode. For example, a range of ±a (i.e., -a to a) centered on the reference value 0 may be predefined as the allowable WL range. In this case, a may be set to, for example, 1 or 2. In the WL adjustment prohibition mode, the display parameter setting unit 54 sets the WL value in accordance with the WL change instruction so that the WL value always falls within the WL allowable range. That is, if the WL value changed based on the WL change instruction exceeds the upper limit of the allowable range, the WL value is corrected to the upper limit, and if the WL value is below the lower limit, the WL value is corrected to the lower limit.

[0042] Furthermore, with regard to the display processing in the image display device 10 described in the first embodiment, at least some of the units included in the control unit 50 may be implemented as independent devices. Alternatively, they may be implemented as software that realizes the functions of each unit. Furthermore, at least some of the functions implemented by the control unit 50 may be implemented by cloud computing. That is, the image display device 10 may be connected to a computing device located in a different location via the communication means 21, and data may be transmitted and received, causing the computing device to execute the above-mentioned processing.

[0043] As described above, an image display device according to one aspect of the present invention includes an image acquisition unit (image acquisition means) 52, an image type determination unit (determination means) 55, a display parameter setting unit (setting means) 54, and a display control unit (display control means) 57. The image acquisition unit 52 acquires an image to be displayed from the database 22 or the like, and the image type determination unit 55 determines whether the acquired image to be displayed is of a predetermined image type, such as the illustrated difference image. The display parameter setting unit 54 sets the WL and WW when displaying the image to be displayed, and if the image type determination unit 55 determines that the image type of the image to be displayed is the predetermined image type, fixes the WL to a predetermined value, such as 0. The display control unit 57 displays the image to be displayed on the display unit (display means) 36 with the WL fixed to the predetermined value or the set WL and the set WW. A control method for controlling the image display device also includes a step of causing each of the above-mentioned means to execute the respective processes.

[0044] As described above, in the image display device according to one aspect of the present invention, the display control unit 57 (display control means) displays medical images on the display unit 36 ​​according to the WL and WW. The image display device has two display modes: a first mode, which is a "WL adjustment prohibited (disabled) mode" for images such as the difference image, and a second mode, which is a "WL adjustment permitted (enabled) mode" for normal images. In the first mode, changing the WL is prohibited, while the WW is changeable. In contrast, in the second mode, the WL and WW are changeable. At least one of the image type discrimination unit 55 and the display parameter setting unit 54 serves as a switching means in this embodiment, switching the display mode between the first mode and the second mode according to the type of medical image when displaying the medical image. More specifically, when the medical image is a difference image or the like, the switching means switches the display mode to the first mode. Furthermore, when the medical image is an image for which WL is not necessarily fixed to a predetermined value, such as an image that is the basis of a difference image, the switching means switches the display format to the second mode.

[0045] Furthermore, when the medical image is limited to a difference image, the image display device according to one aspect of the present invention may be configured to include an image acquisition unit (acquisition means) 52 and a display control unit (display control means) 57. In this case, the acquisition means acquires a difference image showing the difference between a first image and a second image obtained by capturing images of the subject at different times. The display control means displays this difference image on the display unit, but prohibits changes to display values ​​in the difference image that correspond to a difference value of 0. This allows the user to easily adjust the WL and observe an appropriate difference image without being distracted by unintentional misadjustment of the WL.

[0046] In the above-described embodiment, when setting WL and WW, the display parameter setting unit 54 has a mode in which both WL and WW can be set with a single operation, such as the mouse drag mode illustrated in FIG. 3( a). For example, in the case of the drag mode, WL and WW are changed by a user drag operation (drag), and at least one of WL and WW is changed depending on the drag direction. In such a mode, if the image type determination unit 55 determines that the image to be displayed is, for example, a differential image, the display parameter setting unit 54 fixes WL to a predetermined value, such as 0. Note that modes in which WL should be fixed to a predetermined value include setting modes (such as GUI setting methods) in which the user may unintentionally reset WL. In addition to modes in which both WL and WW can be set with a single operation, such modes also include modes in which WL and WW can be set with similar operations.

[0047] In a mode in which both the WL and WW can be set with a single operation, the display parameter setting unit 54 may provide a predetermined dead zone for the input value for setting the WL, as described above. That is, in the WL adjustment prohibition mode described above, the display control unit 57 provides a predetermined dead zone for changes to the WL by the user, thereby substantially prohibiting changes to the WL. In this case, even if a value within this predetermined range is input, the WL is fixed to a predetermined value. Specifically, in the UI of FIG. 3( a), even if the mouse cursor used for input is moved vertically to a certain extent, the input value corresponding to that movement is not reflected. Alternatively, the input value is reduced by subtracting or reducing the amount of movement before being reflected in the actual WL setting. The display parameter setting unit 54 accepts changes to the WW with the WL fixed. That is, when accepting mode changes via the UI, the display control unit 57 may prohibit changes to the WL by disabling the interface that accepts changes to the WL. Alternatively, the UI itself that instructs users to change the WL may be hidden, thereby substantially prohibiting changes to the WL.

[0048] The predetermined image types for which the present invention fixes the WL include image types generated by converting the difference or change between images into pixel values. A specific example of the predetermined image type, as illustrated in this embodiment, is a difference image generated by converting the difference between multiple images of an object into pixel values. Other predetermined image types include a Jacobian map generated from the scaling ratio during object deformation, or a displacement field image generated from the movement amount of each pixel before and after object deformation. Additionally, the predetermined image types include any image type in which a reference value is assigned to a specific pixel value. The image type determination unit 55 determines whether the image to be displayed is of one of these predetermined image types based on information attached to the image to be displayed, exemplified as a header.

[0049] The image display device may also be configured to include an image acquisition unit 52, a display control unit 57, and a display parameter setting unit 54. In this case, the image acquisition unit 52 acquires an image to be displayed, and the display control unit 57 displays the image to be displayed on the display unit 36 ​​at a predetermined WL and a predetermined WW. The display parameter setting unit 54 has a mode in which the predetermined WL and the predetermined WW can be reset together with a single operation, and can also reset the predetermined WL and the predetermined WW individually. Furthermore, when the image to be displayed is an image type such as a difference image in which a reference value is assigned to a specific pixel value, the display parameter setting unit 54 acts as a control unit to limit the setting of the WL in the above-mentioned mode.

[0050] In this case, the control means can limit the setting by providing a dead band of the above-mentioned predetermined range for the input value for setting the WL, or the control means can accept the input value for setting the WL after reducing it.

[0051] As described above, the image display device according to this embodiment has the advantage that, when displaying an image in which a reference value is assigned to a specific pixel value, the WL can be fixed to a predetermined value, preventing the user from accidentally changing it. This allows the user to easily adjust the WL and view an appropriate image without worrying about being distracted by an unintentional misadjustment of the WL.

[0052] <Modification 1 of the First Embodiment> In the process of step S204 in the first embodiment described above, when using the UI of FIG. 3(a) for adjusting the WL / WW by dragging the mouse, the design of the UI may be changed to indicate whether the mode is a "WL adjustment permitted mode" or a "WL adjustment prohibited mode." For example, the design of the mouse cursor may be changed depending on the mode. FIG. 13 is an example of a UI for WL / WW adjustment displayed on the display unit 36 ​​by the display control unit 57. Here, two forms are shown in FIGS. 13(a) and 13(b).

[0053] 13(a) and (b) show examples of mouse cursors displayed on the image displayed on the display unit 36 ​​when a "window adjustment operation" is being performed (during mouse dragging) when using the UI of FIG. 3(a). The mouse cursor shown in FIG. 13(a) uses a color scheme to notify the user that up-down dragging and left-right dragging are associated with WL / WW adjustment, respectively. That is, in the "WL adjustment permitted mode" shown in the upper row, the mouse cursor 1310 has a white and black color scheme on the top and bottom, indicating that WL adjustment is possible by dragging up and down. Also, the gray area extending to the right indicates that WW adjustment is possible by dragging left and right. On the other hand, in the "WL adjustment prohibited mode" shown in the lower row, the mouse cursor 1320 has the same color scheme on the top and bottom, indicating that WL will not change even when dragged up and down.

[0054] 13(b) uses arrows and text to notify the user that up-down dragging and left-right dragging are associated with WL / WW adjustment, respectively. That is, in the "WL adjustment permitted mode" shown in the upper row, the mouse cursor 1330 indicates that both the up-down and left-right arrows are available for WL / WW adjustment by displaying them without being grayed out. On the other hand, in the "WL adjustment prohibited mode" shown in the lower row, the mouse cursor 1340 indicates that the up-down arrow representing WL adjustment will not change the WL even if dragged up or down.

[0055] In step S205, the display control unit 57 sets the display unit 36 ​​to switch the mouse cursor to the above-mentioned GUI during dragging. The display unit 36 ​​switches between the normal mouse cursor and the above-mentioned mouse cursor in accordance with the user's drag start / end operations. After the user actually drags, the display unit 36 ​​performs the processes of steps S206 to S208, for example, as in FIG. 3(a), and controls whether or not WL adjustment is possible.

[0056] Note that the design of the mouse cursor is not limited to that shown in FIG. 13 , and various designs may be used, for example, as the mouse cursor 1320 indicating the "WL adjustment prohibited mode" as shown in FIG. 14 . As described above, according to the image display device of this embodiment, the display control unit 57 displays information on the display unit 36 ​​that enables the user to identify whether the mode has been switched to the "WL adjustment permitted mode" or the "WL adjustment prohibited mode." This allows the user to easily read whether the mode is the "WL adjustment permitted mode" or the "WL adjustment prohibited mode" from the mouse cursor being dragged. Note that, although the illustrated example in which the current display style is modified is preferable as the display style, the display style is not limited to this as long as the user can identify the mode.

[0057] [Second embodiment] The first embodiment describes a case where the type of an image can be determined by a header attached to the image, etc. In contrast, the image display device according to the second embodiment can automatically identify whether an image is a differential image or not, and fix the WL as necessary, even if there is no header indicating that the image is a differential image.

[0058] The image display device of this embodiment has the same device configuration as the image display system shown in Fig. 1, so a description of the device configuration will be omitted here. The processing procedure according to this embodiment is the same as the image display processing procedure in the first embodiment shown as a flowchart in Fig. 2. However, only the processing performed by the image type discrimination unit 55 in step S202 differs from the first embodiment. Below, only step S202 in this embodiment will be described, and descriptions of the other steps will be omitted.

[0059] In step S202, the image type determination unit 55 determines the image type of the image to be displayed that was read in step S201. First, the image type determination unit 55 determines whether or not information indicating the image type is included in the header of the image to be displayed. If the information is included, the image type determination unit 55 reads the header information as in the first embodiment and determines the image type based on the information. On the other hand, if the information is not included, the image type determination unit 55 determines the image type based on the pixel value information in the image. Note that the image type may always be determined based on the pixel value information in the image, regardless of whether or not header information is included.

[0060] In this embodiment, the image type discrimination unit 55 generates, for example, a histogram of the pixel values ​​of the image as pixel value information, and discriminates the image type based on the characteristics of the histogram. That is, in this embodiment, the image type of the medical image is determined based on the distribution of pixel values ​​of the medical image, and the mode is switched according to this determination result. Here, the main purpose of discriminating the image type is to obtain information for determining the display parameter setting mode in step S204. Therefore, it is most important to determine whether the image to be displayed is an image in which a reference value is assigned to a specific pixel value.

[0061] Whether or not the image to be displayed is a differential image can be determined, for example, by determining whether or not the image satisfies any of the following conditions: That is, one of the following conditions is determined, and the determination is made based on the result. Condition 1) The maximum peak of pixel values ​​is 0 (or close to 0), and the distribution on the left and right sides of the maximum peak pixel value is highly symmetric (the degree of agreement is above a threshold). Condition 2) The degree of agreement with the histogram of the average difference image is high (above a threshold). Condition 3) The image is identified as a differential image by an inference model trained on the histograms of the normal image and the differential image.

[0062] FIG. 5 shows examples of a normal CT image (FIG. 5(a)), a normal MRI image (FIG. 5(b)), a difference image (FIG. 5(c)), and a Jacobian map (FIG. 5(d)), along with their histograms. Many CT images and MRI images have a peak pixel value at or near 0, and the histograms on the left and right are usually asymmetric. On the other hand, a difference image has a peak at 0 and is nearly symmetric on the left and right. The control unit 50 in this embodiment distinguishes between difference images and other images based on these characteristics.

[0063] Note that even when an image other than a difference image is displayed as an image in which a reference value is assigned to a specific pixel value, the image type can be similarly identified from the pixel value information in the image. For example, as shown in FIG. 5(d), the histogram of a Jacobian map is approximately symmetrical with a peak at 1. Furthermore, the histogram of a displacement field image has a distribution similar to that of a difference image. Therefore, it may be difficult to distinguish a difference image from a displacement field image using a histogram. However, as long as it can be determined that the image has a reference value of 0, it is possible to transition to a mode in which WL is fixed to 0, and this is not a problem. That is, it is sufficient to determine whether the image is an "image in which a reference value is assigned to pixel value 0," an "image in which a reference value is assigned to pixel value 1," or an "image in which a reference value is not assigned to a specific pixel value" (the image type). In this case, in step S203, if the image type is an "image in which a reference value is assigned to pixel value 0," the display parameter setting unit 54 sets the initial value of WL to 0. If the image type is an "image in which a reference value is assigned to pixel value 1," the display parameter setting unit 54 sets the initial value of WL to 1. Furthermore, in step S204, the mode determination unit 56 determines the display parameter setting mode to be the "WL adjustment prohibited mode" if the image type is "an image in which a reference value is assigned to a pixel value of 0" or "an image in which a reference value is assigned to a pixel value of 1." In addition, in other cases, the mode determination unit 56 determines the display parameter setting mode to be the "WL adjustment permitted mode."

[0064] <Modification 1 of the Second Embodiment> In the second embodiment described above, a histogram of the image to be displayed is generated and used to determine the image type. However, the image type may be determined by directly analyzing the image without using a histogram. In this modification, for example, if the image to be displayed satisfies any of the following conditions, the image is determined to be a difference image. That is, one of the following conditions is determined, and the determination is made based on the result. Condition 1) High agreement with the statistical information of the average difference image. Condition 2) When the image is identified as a differential image by a model that has learned the tendencies of differential images through machine learning. In such a case, the image to be displayed is determined to be a difference image, and the processing from step S203 onward in the flowchart shown in FIG. 2 is executed.

[0065] <Modification 2 of the Second Embodiment> As described above, in the second embodiment and its modified examples, the image to be displayed is analyzed using a histogram or the like to determine its image type, and after the determination result is obtained, the processes from step S203 onward are executed. However, this embodiment is not limited to this. For example, it is also possible to omit the image type determination process in step S202.

[0066] Specifically, the image analysis performed in the second embodiment or the like may be executed in step S204. That is, without determining the image type, the mode determination unit 56 may directly determine whether to set the "WL adjustment prohibited mode" or the "WL adjustment permitted mode" based on the analysis results of the histogram of the image to be displayed. For example, if it is determined that the histogram has a high symmetry between the left and right distributions around the peak position (the symmetry exceeds a predetermined standard), the mode may be set to the "WL adjustment prohibited mode," and otherwise the mode may be set to the "WL adjustment permitted mode." Alternatively, the histograms of images to be set to the "WL adjustment prohibited mode" and images to be set to the "WL adjustment permitted mode" may be machine-learned in advance, so that the mode to be set for the image to be displayed may be automatically determined.

[0067] When the "WL adjustment prohibited mode" is set based on the result of the above-mentioned determination, the WL value may be set from the peak position of the histogram. By doing so, for example, the peak position can be set directly as the WL value. Also, if the peak position is within a predetermined distance from 0, WL may be set to 0, and if it is within a predetermined distance from 1, WL may be set to 1. In this case, the predetermined distance corresponds to an arbitrary range of pixel values, such as a range corresponding to pixel values ​​of 2 to 3 pixels from the pixel value of the peak position. Alternatively, the WL stored in the image header may be used as a reference value. This makes it possible to estimate the image type even if the image type is unknown, and to appropriately control the WL according to the image type.

[0068] As described above, in this embodiment, the image type determination unit 55 determines whether the image to be displayed is a predetermined image type, such as a differential image, based on the distribution of pixel values ​​of the image. If the image is determined to be a predetermined image type and the WL is changed by a setting mode that may cause the user to unintentionally reset the WL even though the WL should not be changed, the WL is fixed to a predetermined value.

[0069] As described above, according to the image display device of this embodiment, when an image in which a reference value is assigned to a specific pixel value is displayed, the WL can be fixed to a predetermined value even if the image does not have header information that identifies the image type. Furthermore, since it is possible to prevent the user from accidentally changing the WL, the user can easily adjust the WL and observe an appropriate image without being distracted by an unintentional misadjustment of the WL.

[0070] [Third embodiment] As described above, the image display device according to the present invention may read images to be displayed from the database 22 or the storage unit 34, or may acquire the images to be displayed directly from an imaging device. In this case, the images to be read may be images captured by various devices or images derived therefrom, and some images may not contain appropriate header information, and the image type may not be automatically determined. The image display device according to the third embodiment is capable of fixing the WL by the user's explicit or implicit designation of the image type.

[0071] The image display device of this embodiment has the same device configuration as the image display system shown in Fig. 1, so a description of the device configuration will be omitted here. The processing procedure according to this embodiment is the same as the image display processing procedure in the first embodiment shown as a flowchart in Fig. 2. However, in this embodiment, the processing performed by the image type discrimination unit 55 in step S202 in the first embodiment is different. Below, only step S202 and the processing associated therewith in this embodiment will be described, and a description of the other steps will be omitted.

[0072] In this embodiment, in step S202, the operation content analysis unit 53 acquires an operation to specify an image type or an operation to select a preset value of a display condition (e.g., WL / WW) input to the control unit 50 from the operation unit 35. Then, processing associated with the acquired operation is performed. In this embodiment, the user directly performs the input operation of step S202 based on an image specified by the image display device 10 and read from the database 22, etc. Alternatively, the image read in step S201 may first be temporarily displayed on the display unit 36, and the user may refer to this to perform the above input operation in step S206. In this case, the display conditions such as WL / WW are set to predetermined values, but may also be values ​​specified in advance by the user. The user refers to the displayed image, etc., and performs either an operation to specify an image type or an operation to select a preset value of WL / WW via the operation unit 35.

[0073] 6 and 7 are examples of GUIs that the display control unit 57 displays on the display unit 36 ​​and that the user operates via the operation unit 35. FIG. 6 is an example of an image type designation GUI, illustrating a GUI using radio buttons. This GUI allows the user to explicitly designate an image type by selecting (e.g., by clicking with the mouse) an option (radio button) associated with the desired image type. On the other hand, FIG. 7 is an example of a GUI for setting preset values ​​for display conditions (WL / WW), illustrating a GUI using a pull-down menu. This GUI allows the user to select appropriate display parameters according to the observation site and image type by selecting (e.g., by clicking with the mouse) an option (pull-down item) associated with the desired preset value. Note that when display parameters are selected using the GUI illustrated in FIG. 7, the image type is implicitly designated at the same time, allowing the operation content analysis unit 53 to acquire information for estimating the image type.

[0074] That is, when the user selects a desired display parameter (hereinafter referred to as a preset value) from the WL / WW preset list shown in Fig. 7, the operation content analysis unit 53 can determine whether the selected preset is, for example, a preset for a difference image. For example, if a preset including a preset value of WL=0 is selected, the preset can be determined to be for a difference image. However, since there may be cases where it is desired to set the WL of a normal image to 0, it is desirable to use other determination methods as well, as shown below, so that it is possible to specify the image type, etc., in parallel.

[0075] In the preset list illustrated in FIG. 7, each preset name and WL / WW preset value are defined as a pair. The operation content analysis unit 53 may determine whether the preset value is for a difference image based on the preset name. For example, if the preset name contains the character string "difference," it can be determined that the selected preset is for a difference image. Alternatively, each preset may have a flag indicating whether it is for a difference image, and when the flag is true, it can be determined that the selected preset is for a difference image.

[0076] In step S203, the operation content analysis unit 53 acquires the image type and display parameters based on the operation content. The control unit 50 executes the processes from step S203 onward using the image type specified by the user. As a result, in the process of step S204, an appropriate display parameter setting mode ("WL adjustment permitted mode" or "WL adjustment prohibited mode") is set according to the image type specified by the user.

[0077] That is, in this embodiment, the image type and display parameters that were read from the header in the first embodiment are acquired in response to a user operation. Therefore, the display parameters initially set in step S203 and the setting mode of the display parameters determined in step S204 are set and determined in response to the acquired image type and preset values. In step S205, the display control unit 57 displays an image generated using these display parameters on the display unit 36. If an operation specifying the image type is acquired in step S206, the operation content analysis unit 53 invokes processing appropriate to the operation in step S207. That is, in addition to the branching in the first embodiment, if an operation specifying the image type is accepted, the process proceeds to step S203. Then, the process from step S203 onward is executed. The UI operated by the user may be any other UI as long as it allows the image type to be identified or inferred.

[0078] Furthermore, a configuration may be provided in which a UI allows a user to instruct switching between the "WL adjustment prohibited mode" and the "WL adjustment permitted mode" without specifying the image type. For example, as an example of a UI in which a user directly instructs switching between modes, a configuration may be adopted in which the "WL adjustment prohibited mode" is set only while a specific key (e.g., the "Shift key" or the "Ctrl key") is pressed, and the "WL adjustment permitted mode" is set otherwise. Alternatively, in the above-described configuration in which the mode is set based on the image type, etc., a configuration may be further adopted in which the mode is inverted only while a specific key is pressed. That is, when the "WL adjustment prohibited mode" is set based on the image type, etc., the configuration may be such that the mode is changed to the "WL adjustment permitted mode" only while a specific key is pressed. Similarly, when the "WL adjustment permitted mode" is set based on the image type, etc., the configuration may be such that the mode is changed to the "WL adjustment prohibited mode" only while a specific key is pressed.

[0079] As another example of a UI in which the user directly instructs mode switching, when using a UI that adjusts WL / WW by dragging the mouse, the mode may be determined and switched based on the direction of the initial mouse movement during the drag operation. That is, if the mouse is first moved horizontally after starting the drag, the mode may be set to "WL adjustment prohibited mode," while in other cases (such as when the mouse is first moved vertically or diagonally), the mode may be set to "WL adjustment permitted mode." Note that if the mouse is first moved vertically, the mode may be set to "WW adjustment prohibited mode," which allows only WL adjustment. Note that because manual operation often makes it difficult to accurately determine whether the vertical or horizontal direction is correct immediately after dragging, the mode may be determined based on the direction of mouse movement when the amount of mouse movement exceeds a predetermined threshold. Furthermore, the above switching process may be performed only if the image type of the image to be displayed corresponds to "an image in which a reference value is not assigned to a specific pixel value." In this case, if the image type of the image to be displayed is a general image that does not correspond to "an image in which a reference value is not assigned to a specific pixel value," the mode may be set to "WL adjustment permitted mode" regardless of the "direction of the initial mouse movement" without performing the switching process.

[0080] As described above, in this embodiment, the image type discrimination unit 55 determines whether the image to be displayed is a predetermined image type, such as a difference image, based on the image type specified by the user. If the image type is determined to be a predetermined image type and the WW is changed by a setting mode in which the user may unintentionally reset the WL even though the WL should not be changed, the WL is fixed to a predetermined value. That is, as described above, in an image display device according to one aspect of the present invention, the display control unit 57 (display control means) displays medical images on the display unit 36 ​​according to the WL and WW. The image display device also has two display modes: a first mode, which is a "WL adjustment prohibited (disabled) mode" for images such as difference images, and a second mode, which is a "WL adjustment permitted (enabled) mode" for normal images. In the first mode, changing the WL is prohibited, while the WW is changeable. In contrast, in the second mode, the WL and WW are changeable. At least one of the image type discrimination unit 55 and the display parameter setting unit 54 serves as a switching unit in this embodiment, which switches the display style between the first mode and the second mode in response to various user operations when displaying a medical image. More specifically, if the medical image is a difference image, as exemplified above, the switching unit switches the display style to the first mode. Also, if the medical image is an image for which the WL is not necessarily fixed to a predetermined value, such as an image that is the source of the difference image, the switching unit switches the display style to the second mode.

[0081] For example, when input regarding the display mode is made on the operation unit 35 using a keyboard or the like, in the example described above, a mode switching instruction is issued when a specific key on the keyboard is pressed as a user operation. In this case, the display style is switched to the first mode. Alternatively, when input regarding the display mode is made by dragging the mouse or the like, in the example described above, the user operation for changing WL and WW is dragging. The display style is switched depending on the drag direction when the dragging is started. In this case, the display style is switched to the first mode.

[0082] Furthermore, the image display device according to this embodiment may include a display control unit (display control means) 57 and a change means including, for example, an operation content analysis unit 53 and a display parameter setting unit 54. In this case, the change means fixes the WL while changing the WW in response to a user's operation to instruct changes to the WL and WW of a medical image. Note that while only the mode in which the WL is fixed is described here, an effect similar to that of a fixed WL may be obtained by reducing the amount of change in the WL relative to the amount of change in the WW. For example, in the above-described change means, the ratio of the change in the WL in response to an instruction to change the WL is made smaller than the ratio of the change in the WW in response to an instruction to change the WW. This changes the reference value, but also makes it possible to roughly grasp changes in the overall trend.

[0083] As described above, according to the image processing device of this embodiment, when an image in which a reference value is assigned to a specific pixel value is displayed, the WL can be fixed to a predetermined value in accordance with the image type specified explicitly or implicitly by the user. Furthermore, since it is possible to prevent the user from accidentally changing it, the user can easily adjust the WL and observe an appropriate image without being distracted by an unintentional misadjustment of the WL.

[0084] [Fourth embodiment] In addition to the configurations shown in the first to third embodiments, the image display device according to the fourth embodiment converts pixel values ​​into display values ​​so that the user can more easily and intuitively recognize difference information. That is, in this embodiment, the display control unit 57 nonlinearly converts pixel values ​​of the image to be displayed into display values ​​and displays them.

[0085] The image display device of this embodiment has the same device configuration as the image display system shown in Fig. 1, so a description of the device configuration will be omitted here. The processing procedure according to this embodiment is the same as the image display processing procedure in the first embodiment shown as a flowchart in Fig. 2. However, this embodiment differs from the first embodiment and the like in that, when converting pixel values ​​to display values ​​in step S205, the conversion formula is switched depending on the image type. Below, only the processing performed in step S205 in this embodiment will be described, and descriptions of the other steps will be omitted.

[0086] In this embodiment, in step S205, the display control unit 57 changes the processing content for converting pixel values ​​to display values, which is performed when the image is displayed, depending on the image type of the image to be displayed obtained in step S202. For example, if the image type is a differential image, the pixel values ​​are converted to display values ​​using a Sigmoid conversion formula. On the other hand, if the image type is another image, the pixel values ​​are converted to display values ​​using a Linear conversion formula, which is used in a normal window function. Furthermore, if the image type is determined to be a Jacobian map in step S202, the pixel values ​​are converted to display values ​​using a Log conversion formula. The display image, which has been converted to display values, is displayed on the display unit 36 ​​by the display control unit 57.

[0087] Figure 8 illustrates the difference in the conversion from pixel values ​​to display values ​​when the conversion formula for the difference image is changed from linear to sigmoid. In the conventional linear conversion shown in Figure 8(a), when the difference is small, the display value is close to the median, making it difficult for the user to recognize the presence or absence of a difference from the difference image. On the other hand, by changing the conversion formula to sigmoid conversion shown in Figure 8(b), the display value deviates significantly from the median even when the difference is small. For example, if the display value differs from the display value 127 by a difference dl near the pixel value 0 (median) in Figure 8(a), changing to sigmoid conversion expands the difference to the difference ds in Figure 8(b). This allows the user to easily recognize the presence or absence of a difference from the difference image.

[0088] FIG. 9 illustrates the difference in the conversion from pixel values ​​to display values ​​when the conversion formula in a Jacobian map is changed from linear to logarithmic. In FIG. 9(a), which shows conventional linear conversion, the pixel values ​​of a pixel enlarged twice and a pixel reduced to half are asymmetrical around a median value of 1.0. Therefore, even if the scaling ratio is the same, the reduced side is not sufficiently dark when converted to display values, making it difficult for users to intuitively grasp the degree of deformation from the Jacobian map. On the other hand, by changing the conversion formula to logarithmic conversion (see FIG. 9(b)), when the scaling ratio is the same, the values ​​become symmetrical around a median value of 0.0, making it easier for users to grasp the degree of enlargement or reduction from the brightness or darkness of the Jacobian map.

[0089] Note that, while the above-described embodiment has been described assuming a specific combination of image types and conversion formulas, the image types and conversion formulas are not limited to those exemplified here, and other image types and conversion formulas may be employed. Furthermore, while one conversion formula is assigned to each type of difference in the above-described embodiment, multiple conversion formulas may be assigned to the same type of difference image. Furthermore, in addition to automatically assigning a conversion formula based on the type of difference, the conversion formula may also be switched by user specification.

[0090] As described above, according to the image display device of this embodiment, when an image in which a reference value is assigned to a specific pixel value is displayed, the image can be displayed in a manner that emphasizes slight differences and changes due to the same degree of enlargement or reduction, etc. Therefore, when the images to be displayed are images in which the differences or changes between multiple images are present, the images can be converted into images that allow the differences or changes between the images to be easily or intuitively recognized, and then displayed.

[0091] [Fifth embodiment] In an image display device, it is also possible to automatically adjust the display parameters of the window function. In an image display device according to a fifth embodiment, when automatically adjusting the display parameters of the window function, the WL is maintained when an image in which a reference value is assigned to a specific pixel value, such as a difference image, is displayed. That is, in this embodiment, when an image in which a reference value is assigned to a specific pixel value is displayed, the display parameter setting unit 54 automatically adjusts the WW based on the distribution of pixel values ​​of the image to be displayed, while keeping the WL fixed.

[0092] The image display device of this embodiment has the same device configuration as the image display system shown in Fig. 1, so a description of the device configuration will be omitted here. The processing procedure according to this embodiment is the same as the image display processing procedure in the first embodiment shown as a flowchart in Fig. 2. However, this embodiment differs from the other embodiments described above in that an operation to instruct automatic adjustment of display parameters is acquired in step S206 in the first embodiment, and automatic adjustment of display parameters is performed in step S208. The processing of steps S206 to S208 in this embodiment will be described below, and a description of the other steps will be omitted.

[0093] A common method for automatically adjusting the display parameters of a window function is to assign the maximum and minimum pixel values ​​of the image to be displayed (or a portion thereof) to the maximum and minimum values ​​of the window, respectively. This prevents the so-called overexposure and underexposure of the image. In addition to this method, other known automatic adjustment methods set display parameters based on distribution information (such as the average value and variance) of pixel values ​​of the image to be displayed. However, when the display parameters are automatically adjusted using the above-described common method for an image with a diverse distribution of pixel values, such as a difference image, it may not be possible to maintain the WL at a predetermined reference value.

[0094] Here, with reference to Fig. 10, a case where display parameters are automatically adjusted for an actual difference image using the general method described above, in which the maximum and minimum pixel values ​​of the image to be displayed are assigned to the maximum and minimum values ​​of a window, will be described. Fig. 10(a) shows the relationship between the histogram of the difference image and the display parameters before the automatic adjustment. Fig. 10(b) shows the relationship between the histogram of the difference image and the display parameters after the display parameters have been automatically adjusted using the general method described above. As can be seen from Fig. 10(b), since WL is basically set to the intermediate value between the maximum and minimum pixel values, the value of WL after the automatic adjustment will be set to a value different from the reference value of 0.

[0095] In contrast, in the automatic setting of display parameters in this embodiment, the value of WL is fixed at WL=0, and the following adjustment of WW is performed. In this embodiment, in step S206, the operation content analysis unit 53 accepts an operation from the user performed via the operation unit 35. In this embodiment, in addition to at least the same operations as in the first embodiment, an operation to instruct automatic adjustment of display parameters is accepted. Note that this automatic adjustment may be performed automatically, regardless of whether or not there is a user operation. Alternatively, the display parameter setting unit 54 may determine the automatic adjustment in accordance with header information such as the image type, or the user may specify the automatic adjustment in accordance with the header information.

[0096] In step S207, the operation content analysis unit 53 invokes processing suited to the operation content. That is, in addition to the branching in the first embodiment, if an operation instructing automatic adjustment of the display parameters is received, the flow proceeds to step S208. In step S208, the display parameter setting unit 54 automatically sets WL / WW using a method suited to the current display parameter setting mode. In the "WL adjustment prohibited mode," the display parameter setting unit 54 sets WL and WW as display parameters as follows: That is, WL is set to a reference value (0 in the case of a difference image), and WW is set to twice the larger value of "maximum pixel value - WL" and "WL - minimum pixel value." This fixes WL to the reference value, and sets the smallest window that includes the pixel values ​​of all pixels of the image to be displayed within the window range. On the other hand, in the "WL adjustment permitted mode," the display parameter setting unit 54 sets the display parameters using a conventional automatic adjustment method.

[0097] FIG. 11 is a diagram illustrating an example in which display parameters of an actual difference image are automatically adjusted in this embodiment. FIG. 11(a) shows a histogram of pixel values ​​of the difference image before the automatic adjustment and the display parameters. FIG. 11(b) shows a histogram of pixel values ​​of the difference image after the automatic adjustment and the display parameters. In the example shown here, since "WL-minimum pixel value" is larger than "maximum pixel value-WL" and "WL-minimum pixel value," WW is set to twice the "WL-minimum pixel value." WL is also fixed at WL=0. When the display parameters are automatically adjusted using the method shown in FIG. 11(b), the display parameters are set so that WL=0 is maintained, the pixel values ​​of all pixels in the image to be displayed fall within the window, and whiteout and blackout are avoided.

[0098] In the process of step S208 above, the WW calculated in the "WL adjustment prohibited mode" may be calculated using the "minimum value" of "maximum pixel value - WL" and "WL - minimum pixel value" rather than the "maximum value" of these two. This will result in pixels that do not fit within the window, making it impossible to avoid overexposure and underexposure. However, on the other hand, in this case, priority is given to utilizing the gradation expression capabilities of the display device.

[0099] The above-described process of setting display parameters using the maximum and minimum pixel values ​​of the image to be displayed is an example of the process performed by the display parameter setting unit 54 in step S208, and other methods may be used to automatically set display parameters. For example, a method of setting display parameters by analyzing the distribution of pixel values ​​of the image to be displayed may also be used. For example, in the "WL adjustment permitted mode," the average (or most frequent) pixel value may be set as the WL, and the WW may be set based on the variance of the pixel values ​​(e.g., the WW may be set within a 3σ range). On the other hand, in the "WL adjustment prohibited mode," the WL may be set to a reference value of the image to be displayed. The WW may then be set based on the variance of the pixel values ​​of the image to be displayed, as in the "WL adjustment permitted mode." Alternatively, the variance may be calculated when the reference value is regarded as the average value, and the WW may be set based on the calculated variance (e.g., the WW may be set within a 3σ range). As described above, automatic setting of display parameters that is not affected by outliers can be achieved.

[0100] <Modification 1 of the Fifth Embodiment> In the fifth embodiment described above, the automatic adjustment of the display parameters sets the WW so that the range (left side) with pixel values ​​smaller than the WL and the range (right side) with pixel values ​​larger than the WL have equal widths. However, instead of using a straight line passing through the current WL in this way, it is also possible to adjust the WW separately on the larger and smaller pixel value sides from the current WL, thereby eliminating waste in gradation expression while fixing the WL to a predetermined value.

[0101] In this modified example, unlike the fifth embodiment, brightness adjustment (conversion from pixel values ​​to display values) is performed on the difference image, dividing it into larger and smaller pixel values ​​from the current WL. Specifically, the display parameters for the larger and smaller pixel values ​​from WL are adjusted under the following conditions, for example: That is, on the side smaller than WL (display value 127), conventional pixel value adjustment is performed within a display value range of 0 to 126 based on WL and the minimum pixel value. On the other hand, on the side larger than WL, conventional pixel value adjustment is performed within a display value range of 128 to 255 based on WL and the maximum pixel value.

[0102] FIG. 12 is a diagram illustrating an example in which display parameters of an actual difference image are automatically adjusted in this modified example. Automatic adjustment of display parameters is performed on the difference image of FIG. 12(a), which shows the pixel values ​​and histogram before automatic adjustment, similar to FIG. 11. As shown in FIG. 12(b), the slope of the line representing the conversion formula changes between the side where the pixel values ​​are greater than WL and the side where they are less than WL. According to this method, while maintaining WL=0, all pixel values ​​are subject to display, thereby avoiding the above-mentioned blown-out highlights and crushed shadows. Furthermore, all pixel values ​​correspond to display values, eliminating the situation where pixel values ​​remain outside the window range, thereby avoiding wasteful gradation expression.

[0103] As described above, according to the image display device of this embodiment, when displaying an image in which a reference value is assigned to a specific pixel value, it is possible to automatically adjust the display parameters while maintaining, for example, a predetermined WL in the differential image. In the above-described embodiment, the display means displays the image to be displayed at a fixed or set window level and a set window width. However, the image display device according to the present invention is not limited to this embodiment, and may simply generate a display image by converting pixel values ​​of the image to be displayed using a process equivalent to the above-described window function, and store the generated image. In other words, the display control means may function as image conversion means for converting the image to be displayed so that the image to be displayed is displayed at a fixed or set window level and a set window width.

[0104] (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.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0105] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-described embodiments. The present invention also includes inventions that have been modified within the scope of the gist of the present invention, and inventions equivalent to the present invention. Furthermore, the above-described embodiments and modifications can be combined as appropriate within the scope of the gist of the present invention. [Explanation of symbols]

[0106] 10 Image display device 21 Communication means (LAN) 22 Databases 31 Communication Interface 32 ROM 33 RAM 34 Storage section 35 Control section 36 Display section 50 control section 52 Image acquisition unit 53 Operation content analysis section 54 Display parameter setting section 55 Image type discrimination unit 56 Mode determination section 57 Display control unit

Claims

1. a display control means for displaying a medical image on a display unit; a switching means for switching between a first mode in which a change in a display value corresponding to a pixel value when the pixel value is a predetermined reference value is restricted and a second mode in which the display value is changeable according to the type of the medical image; Equipped with The first mode is an image display device characterized in that it limits the change of the display value by at least one of weakening and applying the instructed input value to the change of the display value, providing a dead zone of a predetermined range corresponding to the reference value for the input value, and limiting the range of the change of the display value.

2. a display control means for displaying a medical image on a display unit according to the window level and the window width; a switching means for switching between a first mode in which the window width can be changed while restricting changes to the window level, and a second mode in which both the window level and the window width can be changed according to the type of the medical image; Equipped with The image display device is characterized in that the first mode limits the change of the window level by at least one of attenuating and applying an input value instructed for the change of the window level, providing a dead zone of a predetermined range corresponding to a predetermined reference value for the input value, and limiting the range of the change of the window level.

3. 2. The image display device according to claim 1, wherein the switching means switches to the first mode when the medical image is a difference image.

4. 4. The image display device according to claim 3, wherein the switching means switches to the second mode when the medical image is an image that is the source of the difference image.

5. the display control means converts pixel values ​​of the differential image into the display values ​​nonlinearly; 5. The image display device according to claim 3, wherein the display control means uses the display value to display the difference image on the display unit.

6. 3. The image display device according to claim 2, wherein the switching means switches to the first mode when the medical image is a difference image.

7. 7. The image display device according to claim 6, wherein the switching means switches to the second mode when the medical image is an image that is the source of the difference image.

8. the display control means converts pixel values ​​of the differential image nonlinearly into display values ​​to be displayed on the display unit; 8. The image display device according to claim 6, wherein the display control means uses the display value to display the difference image on the display unit.

9. 9. The image display device according to claim 1, wherein the switching means determines the type of the medical image based on the position of an index on the display unit that can be moved by a user, and switches between the first mode and the second mode.

10. 10. The image display device according to claim 1, wherein the switching means determines the type of the medical image based on supplementary information of the medical image, and switches between the first mode and the second mode.

11. 10. The image display device according to claim 1, wherein the switching means determines the type of the medical image based on a distribution of pixel values ​​of the medical image, and switches between the first mode and the second mode.

12. 9. The image display device according to claim 1, wherein the switching means switches to the first mode when the image is generated by converting differences or changes between a plurality of images into the pixel values.

13. The image display device according to claim 1 , wherein the switching means switches to the first mode when the type of the medical image is at least one of a difference image, a Jacobian map, and a displacement field image.

14. displaying the medical image on a display unit; a switching step of switching between a first mode that restricts a change in a display value corresponding to a pixel value when the pixel value is a predetermined reference value and a second mode that allows the display value to be changed according to the type of the medical image; Including, The control method for an image display device is characterized in that the first mode limits the change of the display value by at least one of weakening and applying the instructed input value to the change of the display value, providing a dead zone of a predetermined range corresponding to the reference value for the input value, and limiting the range of the change of the display value.

15. displaying a medical image on a display unit according to the window level and the window width; a switching step of switching between a first mode in which the window width can be changed while restricting changes to the window level and a second mode in which both the window level and the window width can be changed according to the type of the medical image; Including, The control method for an image display device, characterized in that the first mode limits the change of the window level by at least one of attenuating and applying an input value instructed for the change of the window level, providing a dead zone of a predetermined range corresponding to a predetermined reference value for the input value, and limiting the range of the change of the window level.

16. 15. The method for controlling an image display device according to claim 14, wherein the switching step switches to the first mode when the image is generated by converting differences or changes between a plurality of images into the pixel values.

17. 17. The method for controlling an image display device according to claim 14, wherein the switching step switches to the first mode when the type of the medical image is at least one of a difference image, a Jacobian map, and a displacement field image.

18. A program for causing a computer to execute the control method for an image display device according to any one of claims 14 to 17.

Images