Tomosynthesis imaging device, image processing device and image processing program

Abstract

To provide a tomosynthesis imaging device, an image processing device, and an image processing program capable of more reliably executing reconstruction processing for an appropriate range while reducing a burden on an operator in the reconstruction processing for a tomosynthesis image.SOLUTION: A tomosynthesis imaging device includes: a projection image generation unit 21 for generating a projection image F1; a first reconstruction processing unit 31 for executing reconstruction processing for a first reconstruction range L1 of the projection image F1 by a first reconstruction arithmetic method whose arithmetic load is smaller than that of a second reconstruction arithmetic method, and generating a temporary reconstruction image F2; an information amount calculation unit 33 for calculating an information amount J of the temporary reconstruction image F2; a reconstruction range determination unit 35 for determining a range of a cutting height that satisfies a condition of the information amount J being a threshold BL or more as a second reconstruction range L2; and a second reconstruction processing unit 37 for executing reconstruction processing for the second reconstruction range L2 of the projection image F1 by the second reconstruction arithmetic method, and generating a three-dimensional volume image FB.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a tomosynthesis imaging device, an image processing device, and an image processing program that sequentially irradiates X-rays from the X-ray tube while moving an X-ray tube and an X-ray detector in opposite directions to capture multiple projection images, and then performs image processing to reconstruct the multiple projection images to obtain a tomosynthesis image. [Background technology]

[0002] Tomosynthesis imaging devices are devices that use X-rays to acquire tomographic images of a subject. In a tomosynthesis imaging device, the X-ray tube and X-ray detector are positioned facing each other, and while the subject is lying on their back or side, they move synchronously in opposite directions to irradiate X-rays from the X-ray tube and repeatedly acquire projection images. Based on the acquired projection images, image processing is performed to reconstruct a tomographic image (tomosynthesis image) of the subject at an arbitrary cutting position (cutting height), and the image is displayed on a display unit such as a monitor.

[0003] In recent years, iterative reconstruction (IR) and other methods have been used as calculation methods for performing image processing (reconstruction processing) to reconstruct tomographic images from multiple projection images (see, for example, Patent Documents 1 and 2). The iterative reconstruction method is a reconstruction calculation method that requires a relatively large calculation load but can acquire highly accurate tomographic images. When using the iterative reconstruction method, the operator sets values ​​for the body thickness range and the display range to start the reconstruction processing. The body thickness range is the height range in which the subject is estimated to be present. The body thickness range is also the range in which reconstruction processing using the iterative reconstruction method is performed.

[0004] When the calculation begins, pseudo-projection images are generated from the 3D volume image created for the set body thickness range, and a reconstruction calculation is repeated to compare the actually acquired projection images with the pseudo-projection images and correct the 3D volume image, thereby reconstructing a 3D volume image of the subject. Once the 3D volume image is reconstructed, it is sliced ​​at the height of the display range set before the reconstruction calculation, and a tomosynthesis image for the display range is generated. The generated tomosynthesis image is displayed on a monitor or the like, and the operator checks the tomosynthesis image for the display range to make a diagnosis. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-000322 [Patent Document 2] Patent No. 5224057 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the conventional example having such a configuration has the following problems.

[0007] Conventional configurations require the operator to determine an appropriate reconstruction range and manually set the reconstruction range (body thickness range) and display range before performing reconstruction processing. This manual setting of ranges increases the burden on the operator. Furthermore, setting an inappropriate value for the reconstruction range can increase the time required to acquire tomosynthesis images. That is, if the set reconstruction range is too wide, reconstruction calculations are performed for a range wider than necessary, increasing the computational load. Furthermore, if the set reconstruction range is too narrow, calculations for correcting the 3D volume image become inaccurate, resulting in artifacts in the tomosynthesis images. As a result, diagnostic accuracy is reduced, and the process of acquiring tomosynthesis images must be repeated.

[0008] One configuration that reduces the burden on the operator is to automatically set the reconstruction range according to the imaging protocol. That is, appropriate numerical values ​​for the reconstruction range are linked in advance as default values ​​to each imaging protocol, such as "head tomosynthesis imaging" and "abdominal tomosynthesis imaging." Then, when the operator selects the imaging protocol, the reconstruction process is calculated based on the linked default values. This configuration eliminates the need for the operator to manually set the reconstruction range, thereby reducing the burden on the operator.

[0009] However, in a configuration in which a default value is set as the reconstruction range, it is difficult to accurately avoid setting the reconstruction range incorrectly. That is, the default value is set assuming that the subject's body shape and other characteristics are typical. Therefore, depending on the subject's body shape or posture, the region of interest of the subject may not fit within the reconstruction range set by the default value. In this case, after the reconstruction process is completed and a tomosynthesis image is generated, the operator may notice the incorrect setting of the reconstruction range and manually reset the reconstruction range and perform the reconstruction process again. As a result, performing the reconstruction process again, which involves a heavy computational load, increases the time required for image processing.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a tomosynthesis imaging device, an image processing device, and an image processing program that can perform reconstruction processing for an appropriate range more reliably while reducing the burden on the operator in the reconstruction processing of tomosynthesis images. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention has the following configuration. That is, a tomosynthesis imaging apparatus according to a first aspect of the present invention includes an X-ray tube that irradiates an object with X-rays, an X-ray detector that is disposed opposite the X-ray tube and that detects X-rays that have passed through the object, an opposing movement mechanism that moves the X-ray tube and the X-ray detector in opposite directions along the body axis of the object while the X-ray tube and the X-ray detector are opposed to each other with the object in between, an X-ray irradiation control unit that controls the X-ray tube to repeatedly irradiate X-rays while the opposing movement mechanism moves the X-ray tube and the X-ray detector in opposite directions, a projection image generation unit that generates a projection image based on a detection signal output by the X-ray detector for each X-ray irradiation by the X-ray tube, and a first reconstruction processing unit that generates a tentative reconstruction image by performing reconstruction processing on the projection image for a first reconstruction range that is a range of a cutting height using a first reconstruction calculation method. a display range determination unit that determines, from the first reconstruction range, a range of cut heights that satisfies a predetermined condition that the amount of information is appropriate for a reconstructed image to be displayed as a display range; a second reconstruction processing unit that generates a three-dimensional volume image by performing reconstruction processing on the projection image for a preset second reconstruction range using a second reconstruction calculation method; a tomographic image generation unit that cuts the three-dimensional volume image generated for the second reconstruction range for the display range to generate a tomosynthesis image; and a tomographic image display unit that displays the tomosynthesis image generated for the display range, wherein the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

[0012] A tomosynthesis imaging apparatus according to a second aspect of the present invention includes an X-ray tube that irradiates an object with X-rays, an X-ray detector that is disposed opposite the X-ray tube and detects X-rays that have passed through the object, an opposing movement mechanism that moves the X-ray tube and the X-ray detector in opposite directions along the body axis of the object while the X-ray tube and the X-ray detector are opposed to each other with the object in between, an X-ray irradiation control unit that controls the X-ray tube to repeatedly irradiate X-rays while the opposing movement mechanism moves the X-ray tube and the X-ray detector in opposite directions, a projection image generation unit that generates a projection image based on a detection signal output by the X-ray detector for each X-ray irradiation by the X-ray tube, and a projection image generation unit that generates a projection image based on a detection signal output by the X-ray detector for each X-ray irradiation by the X-ray tube using a first reconstruction calculation method. a first reconstruction processing unit that generates a temporary reconstructed image by performing reconstruction processing on the projection image for a first reconstruction range which is equal to or greater than a predetermined value; an information amount calculation unit that calculates the information amount of the temporary reconstructed image for each cutting height; a reconstruction range determination unit that determines, from the first reconstruction range, a range of cutting heights which satisfies a predetermined condition that the information amount is appropriate for a three-dimensional volume image as a second reconstruction range; and a second reconstruction processing unit that generates a three-dimensional volume image by performing reconstruction processing on the projection image for the second reconstruction range using a second reconstruction calculation method, wherein the first reconstruction calculation method is a calculation method having a smaller calculation load than the second reconstruction calculation method.

[0013] A tomosynthesis imaging apparatus according to a third aspect of the present invention includes an X-ray tube that irradiates an object with X-rays, an X-ray detector that is disposed opposite the X-ray tube and detects X-rays that have passed through the object, an opposing movement mechanism that moves the X-ray tube and the X-ray detector in opposite directions along the body axis of the object while the X-ray tube and the X-ray detector are opposed to each other with the object sandwiched therebetween, an X-ray irradiation control unit that controls the X-ray tube to repeatedly irradiate X-rays while the opposing movement mechanism moves the X-ray tube and the X-ray detector in opposing directions, a projection image generation unit that generates a projection image based on a detection signal output by the X-ray detector for each X-ray irradiation by the X-ray tube, a first reconstruction processing unit that generates a temporary reconstructed image by performing reconstruction processing on the projection image for a first reconstruction range that is a range of cutting heights using a first reconstruction calculation method, an information amount calculation unit that calculates an information amount of the temporary reconstructed image for each cutting height, and a reconstruction unit that calculates the information amount from within the first reconstruction range to generate a reconstruction image for display. a reconstruction range determination unit that determines, as a display range, a range of cut heights that satisfies a predetermined first condition that is appropriate for an image; a reconstruction range determination unit that determines, from the first reconstruction range, a range of cut heights that satisfies a predetermined second condition that the amount of information is appropriate for a three-dimensional volume image, as a second reconstruction range; a second reconstruction processing unit that generates a three-dimensional volume image by performing reconstruction processing on the projection image for the second reconstruction range using a second reconstruction calculation method; a tomographic image generation unit that cuts the three-dimensional volume image generated for the second reconstruction range for the display range to generate a tomosynthesis image; and a tomographic image display unit that displays the tomosynthesis image generated for the display range, wherein the first condition and the second condition are set so that the second reconstruction range is wider than the display range, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

[0014] An image processing device according to a fourth aspect of the present invention is an image processing device that performs image processing to generate tomosynthesis images using projection images acquired by repeatedly irradiating X-rays from the X-ray tube while moving an X-ray tube and an X-ray detector that are arranged opposite to each other across a subject in a body axis direction of the subject, and includes a first reconstruction processing unit that generates a temporary reconstructed image by performing reconstruction processing on the projection images for a first reconstruction range that is a range of cut heights using a first reconstruction calculation method, an information amount calculation unit that calculates the information amount of the temporary reconstructed image for each cut height, a display range determination unit that determines, from the first reconstruction range, a range of cut heights that satisfies a predetermined first condition that the information amount is appropriate for a reconstructed image to be displayed, as a display range, and a display range determination unit that determines, from the first reconstruction range, a second reconstruction processing unit that generates a three-dimensional volume image by performing reconstruction processing on the projection image for the second reconstruction range using a second reconstruction calculation method; a tomographic image generation unit that generates the tomosynthesis image by cutting the three-dimensional volume image generated for the second reconstruction range for the display range; and a tomographic image display unit that displays the tomosynthesis image generated for the display range, wherein the first condition and the second condition are set so that the second reconstruction range is wider than the display range, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

[0015] An image processing program according to a fifth aspect of the present invention is an image processing program that causes a computer to execute image processing for generating tomosynthesis images using projection images acquired by repeatedly irradiating X-rays from the X-ray tube while moving an X-ray tube and an X-ray detector that are arranged opposite each other across a subject in the body axis direction of the subject, the image processing program comprising: a first reconstruction processing step of generating a temporary reconstructed image by performing reconstruction processing on the projection images for a first reconstruction range that is a range of cut heights using a first reconstruction calculation method; an information amount calculation step of calculating an information amount of the temporary reconstructed image for each cut height; a display range determination step of determining, from the first reconstruction range, a range of cut heights that satisfies a predetermined first condition that the information amount is appropriate for a reconstructed image to be displayed; and a display range determination step of determining, from the first reconstruction range, The method causes the computer to sequentially execute the following steps: a reconstruction range determination step of determining, as a second reconstruction range, a range of cut heights that satisfies a predetermined second condition that the amount of information is appropriate for a three-dimensional volume image; a second reconstruction processing step of generating a three-dimensional volume image by performing reconstruction processing on the projection image for the second reconstruction range using a second reconstruction calculation method; a tomographic image generation step of cutting the three-dimensional volume image generated for the second reconstruction range for the display range to generate the tomosynthesis image; and a tomographic image display step of displaying the tomosynthesis image generated for the display range, wherein the first condition and the second condition are set so that the second reconstruction range is wider than the display range, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method. [Effects of the Invention]

[0016] According to the tomosynthesis imaging device of the first aspect of the present invention, when generating a tomosynthesis image using projection images, a provisional reconstructed image is generated by first performing reconstruction processing on the projection images for a first reconstruction range using a first reconstruction calculation method with a relatively low computational load. Next, the amount of information in the provisional reconstructed image for an arbitrary cut height is calculated, and the range of cut heights for which the amount of information satisfies a predetermined condition is determined as the display range. Then, a three-dimensional volume image is generated by performing reconstruction processing on the projection images for a predetermined second reconstruction range using a second reconstruction calculation method. Finally, the three-dimensional volume image is cut for the display range to generate a tomosynthesis image, and the generated tomosynthesis image is displayed.

[0017] The display range, which is the height range for cutting a three-dimensional volume image to generate a tomosynthesis image, is automatically determined based on the amount of information in the reconstructed provisional image. If the amount of information does not satisfy a predetermined condition, the cutting height is one that is not very necessary for the final reconstructed image to be displayed. Therefore, by determining the display range based on the amount of information, it is possible to reliably avoid including cutting heights that are not very necessary for reconstructing a tomosynthesis image in the display range. Furthermore, because the display range calculation process is performed automatically, the operator does not need to estimate and manually set a display range appropriate for diagnosis. This reduces the burden on the operator and shortens the time required to generate a tomosynthesis image.

[0018] The first reconstruction calculation method used to generate the temporary reconstructed image is a calculation method with a smaller calculation load than the second reconstruction calculation method used in the final reconstruction processing, so that the temporary reconstructed image can be generated quickly and the display range can be determined. Therefore, the display range for generating the tomosynthesis image can be calculated quickly and appropriately, reducing the burden on the operator in the reconstruction processing of the tomosynthesis image and ensuring the generation of a tomosynthesis image with a height range appropriate for diagnosis.

[0019] According to the tomosynthesis imaging device of the second aspect of the present invention, when generating a tomosynthesis image using projection images, a temporary reconstructed image is generated by first performing reconstruction processing on the projection images for a first reconstruction range using a first reconstruction calculation method with a relatively low computational load. Next, the amount of information of the temporary reconstructed image for an arbitrary cutting height is calculated, and the range of cutting heights for which the amount of information satisfies a predetermined condition is determined as a second reconstruction range. Then, a three-dimensional volume image is generated by performing reconstruction processing on the projection images for the second reconstruction range using the second reconstruction calculation method.

[0020] The second reconstruction range, which is the height range for reconstructing a three-dimensional volume image to generate a tomosynthesis image, is automatically determined based on the amount of information in the reconstructed provisional reconstruction image. If the amount of information does not satisfy a predetermined condition, the cut height is one at which there is little need to reconstruct a three-dimensional volume image. Therefore, by determining the second reconstruction range based on the amount of information, it is possible to reliably prevent cut heights at which there is little need to reconstruct a tomosynthesis image from being included in the second reconstruction range. Furthermore, because the calculation process for the second reconstruction range is performed automatically, the operator does not need to estimate and manually set a second reconstruction range appropriate for diagnosis. This reduces the burden on the operator and shortens the time required to generate a tomosynthesis image.

[0021] The first reconstruction calculation method used to generate the temporary reconstruction image is a calculation method with a smaller calculation load than the second reconstruction calculation method used in the final reconstruction processing, so that the temporary reconstruction image can be generated quickly and the second reconstruction range can be determined. Therefore, the second reconstruction range for generating a three-dimensional volume image can be calculated quickly and appropriately, reducing the burden on the operator in the reconstruction processing of the tomosynthesis image and ensuring the generation of a tomosynthesis image with a height range appropriate for diagnosis.

[0022] According to a third aspect of the present invention, when generating a tomosynthesis image using projection images, a provisional reconstructed image is generated by first performing reconstruction processing on the projection images for a first reconstruction range using a first reconstruction calculation method with a relatively low computational load. Next, the amount of information in the provisional reconstructed image for each cut height is calculated, and a range of cut heights for which the amount of information satisfies a predetermined first condition is determined as the display range. Furthermore, a range of cut heights for which the amount of information satisfies a predetermined second condition is determined as the second reconstruction range. The first and second conditions are set so that the second reconstruction range is wider than the display range. A three-dimensional volume image is then generated by performing reconstruction processing on the projection images for the second reconstruction range using the second reconstruction calculation method. Finally, a tomosynthesis image is generated by cutting the three-dimensional volume image for the display range, and the generated tomosynthesis image is displayed.

[0023] In this embodiment, the second reconstruction range and the display range are automatically determined based on the amount of information in the reconstructed provisional reconstruction image. If the amount of information does not satisfy a predetermined condition, the cut height is one at which there is little need to reconstruct a tomosynthesis image. Therefore, by determining the second reconstruction range and the display range based on the amount of information, it is possible to reliably prevent the second reconstruction range and the display range from including a cut height at which there is little need to reconstruct a tomosynthesis image. Furthermore, because the calculation process for the second reconstruction range is performed automatically, the operator does not need to estimate and manually set the second reconstruction range and the display range appropriate for diagnosis. This reduces the burden on the operator and shortens the time required to generate a tomosynthesis image.

[0024] The first reconstruction calculation method used to generate the temporary reconstruction image is a calculation method with a smaller calculation load than the second reconstruction calculation method used in the final reconstruction processing, so that the temporary reconstruction image can be quickly generated and the second reconstruction range and display range can be quickly determined. Therefore, it is possible to reliably generate a tomosynthesis image with a height range appropriate for diagnosis while reducing the burden on the operator in the reconstruction processing of the tomosynthesis image.

[0025] According to the image processing device of the fourth aspect of the present invention, when performing image processing to generate a tomosynthesis image using a projection image, a provisional reconstruction image is generated by first performing reconstruction processing on the projection image for a first reconstruction range using a first reconstruction calculation method with a relatively low computational load. Next, the amount of information in the provisional reconstruction image for each cutting height is calculated, and a range of cutting heights for which the amount of information satisfies a predetermined first condition is determined as the display range. Furthermore, a range of cutting heights for which the amount of information satisfies a predetermined second condition is determined as the second reconstruction range. The first and second conditions are set so that the second reconstruction range is wider than the display range. Then, a three-dimensional volume image is generated by performing reconstruction processing on the projection image for the second reconstruction range using the second reconstruction calculation method. Finally, the three-dimensional volume image is cut for the display range to generate a tomosynthesis image, and the generated tomosynthesis image is displayed. Thus, similar to the tomosynthesis device of the third aspect, the second reconstruction range and the display range are automatically determined based on the amount of information in the provisional reconstruction image. Therefore, the burden on the operator in the reconstruction process of tomosynthesis images can be reduced, and the reconstruction process can be performed more reliably for an appropriate range.

[0026] According to a fifth aspect of the present invention, an image processing program causes a computer to sequentially execute the following steps to perform image processing to generate a tomosynthesis image using a projection image. Specifically, the program first generates a provisional reconstruction image by performing reconstruction processing on the projection image for a first reconstruction range using a first reconstruction calculation method with a relatively low computational load. Next, the program calculates the amount of information in the provisional reconstruction image for each cut height, and determines, as a display range, a range of cut heights for which the amount of information satisfies a predetermined first condition. The program also determines, as a second reconstruction range, a range of cut heights for which the amount of information satisfies a predetermined second condition. The first and second conditions are set so that the second reconstruction range is wider than the display range. Then, the program generates a three-dimensional volume image by performing reconstruction processing on the projection image for the second reconstruction range using the second reconstruction calculation method. Finally, the program cuts the three-dimensional volume image for the display range to generate a tomosynthesis image, and displays the generated tomosynthesis image. Thus, similar to the tomosynthesis device according to the third aspect, the program automatically determines the second reconstruction range and display range based on the amount of information in the provisional reconstruction image. Therefore, the burden on the operator in the reconstruction process of tomosynthesis images can be reduced, and the reconstruction process can be performed more reliably for an appropriate range. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a front view illustrating the overall configuration of a tomosynthesis apparatus according to an embodiment. [Figure 2] 1 is a functional block diagram illustrating an outline of a tomosynthesis apparatus according to an embodiment. [Figure 3] 4 is a flowchart illustrating the operation of the tomosynthesis apparatus according to the embodiment. [Figure 4] 1 is a schematic diagram illustrating the relationship between each step in the operation of a tomosynthesis device according to an embodiment and images generated in each step. [Figure 5] FIG. 10 is a diagram illustrating step S1 according to the embodiment. [Figure 6] FIG. 10 is a diagram illustrating step S3 according to the embodiment. [Figure 7]FIG. 10 is a diagram illustrating step S4 according to the embodiment. [Figure 8] FIG. 10 is a diagram illustrating step S5 according to the embodiment. [Figure 9] FIG. 10 is a diagram illustrating steps S6 and S7 according to the embodiment. [Figure 10] FIG. 2 is a diagram for explaining a first reconstruction range, a second reconstruction range, and a display range in an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0029] <Explanation of overall configuration> As shown in Figures 1 and 2, the tomosynthesis device 1 of the embodiment includes a tabletop 3, an X-ray tube 5, an X-ray detector 7, an X-ray tube moving mechanism 9, a detector moving mechanism 11, an imaging control device 13, and an image processing device 15.

[0030] The patient M is placed on the top board 3 in a horizontal position. The top board 3 is disposed on top of a top board support (not shown) that is configured to be able to move up and down. The X-ray tube 5 irradiates the patient M with X-rays. The X-ray detector 7 detects the X-rays that are irradiated by the X-ray tube 5 and transmitted through the patient M, converts them into an electrical signal, and outputs it as an X-ray detection signal. An example of the X-ray detector 7 is an FPD (Flat Panel Detector). The X-ray tube 5 and the X-ray detector 7 are disposed opposite each other with the top board 3 in between. The X-ray tube 5 and the X-ray detector 7 constitute an imaging system that captures a projection image.

[0031] A collimator 8 is provided below the X-ray tube 5. The collimator 8 limits the X-rays emitted from the X-ray tube 5 to a predetermined shape. An example of a shape that limits the X-rays is a pyramidal cone shape.

[0032] The X-ray tube moving mechanism 9 is connected to the X-ray tube 5 and moves the X-ray tube 5 back and forth along a trajectory parallel to the x direction, and rotates the X-ray tube 5 around an axis in the y direction to change the X-ray irradiation angle of the X-ray tube. In other words, the X-ray tube 5 is configured to be able to move back and forth in the x direction while changing the X-ray irradiation direction by the X-ray tube moving mechanism 9. The x direction corresponds to the longitudinal direction of the tabletop 3 and the body axis direction of the subject M. The y direction corresponds to the lateral direction of the tabletop 3. The detector moving mechanism 11 is connected to the X-ray detector 7 and moves the X-ray detector 7 along a trajectory parallel to the x direction.

[0033] The imaging control device 13 controls the imaging operation of the projection image in the tomosynthesis device 1, and includes a main control unit 16, a movement mechanism control unit 17, an X-ray irradiation control unit 19, a projection image generation unit 21, an imaging operation unit 23, a memory 25, and a monitor 27. The main control unit 16 includes information processing means such as a central processing unit (CPU), and controls each component of the imaging control device 13, such as the X-ray tube 5 and the X-ray detector 7.

[0034] The movement mechanism control unit 17 performs overall control of the X-ray tube movement mechanism 9 and the detector movement mechanism 11. That is, the X-ray tube 5 and the X-ray detector 7 move in opposite directions along trajectories parallel to the x direction, facing each other with the subject M in between, under the control of the movement mechanism control unit 17. The movement mechanism control unit 17 corresponds to the opposing movement mechanism in this embodiment.

[0035] The X-ray irradiation control unit 19 is connected to the X-ray tube 5, and controls the X-ray irradiation time, the tube voltage and tube current applied to the X-ray tube 5, and the like, thereby controlling the dose of X-rays irradiated from the X-ray tube 5 and the timing of X-ray irradiation.

[0036] The projection image generation unit 21 is provided after the X-ray detector 7, and performs various image processing operations to generate a projection image based on the X-ray detection signal output from the X-ray detector 7. The imaging operation unit 23 inputs instructions from the operator regarding imaging operations for projection images, and the main control unit 16 performs overall control in accordance with the instructions input to the operation unit 23 by the operator.

[0037] The memory 25 stores various information such as information on the imaging conditions of the projection image, e.g., tube voltage and tube current, the projection image generated by the projection image generation unit 21, and information on image processing by the projection image generation unit 21. The monitor 27 displays the projection image generated by the projection image generation unit 21 or various information on the imaging of the projection image.

[0038] The image processing device 15 is connected to the imaging control device 13. The image processing device 15 includes a computer that performs various image processing to obtain a tomographic image (tomosynthesis image) using the projection image generated by the projection image generation unit 21. The image processing device 15 includes a main control unit 29, a first reconstruction processing unit 31, an information amount calculation unit 33, a reconstruction range determination unit 35, a display range determination unit 36, a second reconstruction processing unit 37, a tomographic image generation unit 38, an operation unit 39, a storage unit 41, and a display unit 43.

[0039] The main control unit 29 includes an information processing unit such as a central processing unit (CPU), and controls each component in the image processing device 15 in an integrated manner.

[0040] The first reconstruction processing unit 31 is provided in the main control unit 29. The first reconstruction processing unit 31 generates a temporary reconstructed image for a first reconstruction range by applying a first reconstruction calculation method to the projection image generated by the projection image generating unit 21. The first reconstruction range is a range of the cutting height for the subject M, and is a wide area that is large enough to reliably include the region of interest of the subject M.

[0041] The first reconstruction calculation method is a reconstruction calculation method that has a smaller calculation load than the second reconstruction calculation method described below. Examples of the first reconstruction calculation method include filtered back projection (FBP) and shift-and-add. In this embodiment, a temporary reconstructed image is generated from a projection image by using filtered back projection.

[0042] The information amount calculation unit 33 is provided after the first reconstruction processing unit 31, and calculates the information amount in each of the temporary reconstructed images generated by the first reconstruction processing unit 31 to create an information amount map. Examples of information amount include the variance, standard deviation, and entropy of each pixel value in the image. In this embodiment, the variance of pixel values ​​is used as the information amount.

[0043] The reconstruction range determination unit 35 is provided after the information amount calculation unit 33, and determines a second reconstruction range based on the amount of information calculated by the information amount calculation unit 33. The second reconstruction range is a range of cutting heights for which a three-dimensional volume image is to be reconstructed using a second reconstruction calculation method, which will be described later. In this embodiment, the information amount map is referenced, and a range of cutting heights for which the amount of information is equal to or greater than a predetermined threshold is determined as the second reconstruction range.

[0044] The display range determination unit 36 ​​is provided after the reconstruction range determination unit 35. The display range determination unit 36 ​​determines the display range based on the amount of information calculated by the information amount calculation unit 33. The display range is a range of cutting heights within the second reconstruction range in which the three-dimensional volume image is reconstructed, which is the target range for generating a tomographic image (tomosynthesis image) by performing tomographic processing on the three-dimensional volume image.

[0045] The second reconstruction processing unit 37 is provided after the display range determination unit 36. The second reconstruction processing unit 37 uses a second reconstruction calculation method to reconstruct projection images for the second reconstruction range determined by the reconstruction range determination unit 35. By reconstructing the projection images using the second reconstruction calculation method, a three-dimensional volume image of the subject is generated.

[0046] The tomographic image generation unit 38 is provided after the second reconstruction processing unit 37. The tomographic image generation unit 38 performs tomographic processing (slicing) on ​​the three-dimensional volume image generated by the second reconstruction processing unit 37 to generate a tomosynthesis image. The tomographic processing on the three-dimensional volume image is performed for the cut height of the display range determined by the display range determination unit 36.

[0047] The operation unit 39 is used to input instructions from the operator regarding the operation of the image processing device 15, and the main control unit 29 performs overall control in accordance with the instructions input by the surgeon to the operation unit 39. The storage unit 41 stores information related to image processing in the image processing device 15. Examples of information stored in the storage unit 41 include various images such as tomosynthesis images generated by the second reconstruction processing unit 37, programs for executing various image processing steps performed in the main control unit 29, and data on the amount of information calculated by the information amount calculation unit 33. An example of the storage unit 41 is a non-volatile memory.

[0048] The display unit 43 displays information related to image processing in the image processing device 15. Examples of information displayed by the display unit 43 include an information amount map generated by the information amount calculation unit 33, a temporary reconstruction image generated by the first reconstruction processing unit 31, a three-dimensional volume image generated by the second reconstruction processing unit 37, and a tomosynthesis image generated by the tomographic image generation unit 38. Examples of the display unit 43 include a liquid crystal monitor or a high-precision display. The display unit 43 corresponds to the tomographic image display unit in this embodiment.

[0049] <Explanation of operation> Here, an operation for performing tomosynthesis imaging to obtain a tomosynthesis image in the tomosynthesis apparatus 1 according to the present invention will be described. Fig. 3 shows a flowchart of each step in the operation for obtaining a tomosynthesis image in the tomosynthesis apparatus 1.

[0050] First, an overview of the operation for acquiring a tomosynthesis image will be described using FIG. 4. FIG. 4 is a schematic diagram showing the relationship between each step in the operation and the images generated in each step. First, the projection image generation unit 21 generates multiple projection images F1 by intermittently irradiating X-rays from the X-ray tube 5 while moving the imaging system in a counter direction (step S1). Second, the first reconstruction processing unit 31 performs a first reconstruction process on the projection images F1, thereby generating a temporary reconstructed image F2 related to the first reconstruction range (step S2). Third, the information amount calculation unit 33 calculates the information amount for each of the temporary reconstructed images F2 (step S3).

[0051] Fourth, the reconstruction range determination unit 35 determines a second reconstruction range by referring to the amount of information in the temporary reconstructed image F2 (step S4). Fifth, the display range determination unit 36 ​​determines a display range L3 by referring to the amount of information in the temporary reconstructed image F2 (step S5). Sixth, the information on the second reconstruction range is fed back to the projection image F1. That is, the second reconstruction processing unit 37 performs second reconstruction processing on the projection image F1, thereby generating a three-dimensional volume image FB for the second reconstruction range from the projection image F1 (step S6). Finally, the information on the display range is fed back to the three-dimensional volume image FB. That is, the tomographic image generation unit 38 performs tomographic processing on the three-dimensional volume image FB for the cut height of the display range, thereby generating a tomosynthesis image F3 (step S7). Each step will be described in detail below.

[0052] Step S1 (Capturing a projected image) When a command to perform tomosynthesis imaging is input to the tomosynthesis device 1, imaging of projection images begins. The movement mechanism control unit 17 controls the X-ray tube movement mechanism 9 and the detector movement mechanism 11 to synchronously move the X-ray tube 5 and the X-ray detector 7 in opposite directions, as shown in Fig. 5. That is, the X-ray tube 5 moves linearly along a linear trajectory parallel to the x-direction from an initial position P1 indicated by a solid line to an end position P2 indicated by a two-dot chain line, while changing the X-ray irradiation angle as needed so that X-rays are always incident on the subject M.

[0053] At this time, the X-ray detector 7 moves linearly from the initial position indicated by the solid line to the end position indicated by the two-dot chain line along a linear trajectory parallel to the x direction in synchronization with the movement of the X-ray tube 5. Therefore, under the control of the movement mechanism control unit 17, the X-ray tube 5 and the X-ray detector 7 move in opposite directions while facing each other with the subject M sandwiched between them.

[0054] In synchronization with the control of the movement mechanism control unit 17, the X-ray irradiation control unit 19 controls the X-ray tube 5 to repeatedly irradiate X-rays. Every time X-rays are irradiated from the X-ray tube 5, an X-ray detection signal is output from the X-ray detector, and the projection image generation unit 21 generates a projection image based on the X-ray detection signal. Therefore, while the imaging system is moved horizontally once, a series of projection images F1 are acquired, each captured from a different direction relative to the subject M. Data of the series of projection images F1 is transmitted from the projection image generation unit 21 to the main control unit 29 of the image processing device 15.

[0055] Step S2 (first reconstruction process) When the data of the projection image F1 is transmitted to the image processing device 15, the first reconstruction processing is started by the first reconstruction processing unit 31. The first reconstruction processing unit 31 performs reconstruction processing on the projection image F1 using the filtered back projection (FBP) method, which has a relatively low computational load, and generates a series of temporary reconstructed images F2. The FBP method corresponds to the first reconstruction calculation method in this embodiment.

[0056] The provisional reconstructed image F2 is a group of images including tomographic images at various cutting heights included in the first reconstruction range L1. The first reconstruction range L1 is set to a sufficiently wide range so as to reliably include the region of interest for tomosynthesis imaging. The setting conditions for the first reconstruction range L1 may be changed as appropriate as long as the region of interest for tomosynthesis imaging is reliably included.

[0057] In this embodiment, the temporary reconstructed image F2 corresponds to an image group including tomographic images for each cutting height, from a tomographic image F2a for the cutting height Ha to a tomographic image F2b for the cutting height Hb, as shown in FIG.

[0058] The first reconstruction processor 31 performs reconstruction calculations using the FBP method, which has a relatively small computational load, and acquires a temporary reconstructed image F2. Therefore, even when performing reconstruction calculations for the relatively wide first reconstruction range L1, it is possible to avoid an increase in the time required to generate the temporary reconstructed image F2 and reduce the burden on the main controller 29. The data of the temporary reconstructed image F2 generated by the first reconstruction processor 31 is transmitted to the information amount calculator 33.

[0059] Step S3 (calculating the amount of information) When the data of the temporary reconstructed image F2 is transmitted to the information amount calculation unit 33, the information amount calculation unit 33 calculates the information amount of the temporary reconstructed image F2. For each of the series of temporary reconstructed images F2, the information amount calculation unit 33 calculates the variance of pixel values ​​for each pixel included in the image. The calculated value of the variance of pixel values ​​is set as the information amount J of the image. The information amount calculation unit 33 calculates the information amount J of the temporary reconstructed image F2 for each cutting height, thereby generating an information amount map T as shown in FIG. 6.

[0060] The information amount map T is a two-dimensional map showing the relationship between the cutting height and the information amount J of the temporary reconstructed image F2 for the first reconstruction range L1. In this embodiment, as shown in FIG. 6, the information amount map T shows the cutting height on the horizontal axis and the information amount J on the vertical axis. For example, among the series of temporary reconstructed images F2, the information amount J of the tomographic image F2a whose cutting height is the lowest position Ha corresponds to Ea, and the information amount J of the tomographic image F2b whose cutting height is the highest position Hb corresponds to Eb. In this embodiment, the height H0 of the upper surface of the tabletop 3 is used as the reference height, and the specific numerical value of the cutting height is set to zero. The data of the information amount J for each temporary reconstructed image F2 and the data of the information amount map T are transmitted from the information amount calculation unit 33 to the reconstruction range determination unit 35.

[0061] Step S4 (Determining the reconstruction range) When data such as the amount of information J is transmitted to the reconstruction range determination unit 35, the reconstruction range determination unit 35 determines a second reconstruction range based on the amount of information J. The second reconstruction range is a range of cutting heights within the first reconstruction range L1 that is the target of reconstruction processing using the second reconstruction calculation method. In other words, the second reconstruction range is a range of cutting heights within which a three-dimensional volume image is generated.

[0062] To ensure that the cut height of the region of interest is included, the first reconstruction range L1 from which the temporary reconstruction image F2 is generated is set to a relatively wide range. Therefore, the first reconstruction range L1 may include many cut heights that are outside the body thickness of the subject M or cut heights of portions close to the body surface of the subject M. However, there is little need to obtain a final tomosynthesis image for cut heights that are outside the body thickness of the subject M. Therefore, in order to avoid generating tomosynthesis images that are unnecessary for diagnosis, it is preferable that the range of cut heights within the first reconstruction range L1 from which the three-dimensional volume image and tomosynthesis images are generated excludes cut heights that are outside the body thickness of the subject M.

[0063] Therefore, the image processing device 15 according to the present invention excludes the range of cutting heights unnecessary for generating a tomosynthesis image from the first reconstruction range L1 based on the amount of information J (in this embodiment, the variance of pixel values).Then, the range that is not excluded is determined as the second reconstruction range, i.e., the range of cutting heights that is the target for generating a three-dimensional volume image.

[0064] A tomographic image at a cutting height outside the height of the subject M does not show the subject M but shows the background, so the difference in pixel values ​​throughout the tomographic image is small. That is, at cutting heights outside the height of the subject M, the variance of pixel values ​​in the tomographic image tends to be very low. Furthermore, a tomographic image at a cutting height close to the body surface of the subject M shows a lot of fat or skin tissue, which has a small difference in pixel value compared to the background. Therefore, the variance of pixel values ​​also tends to be low at cutting heights close to the body surface of the subject M. On the other hand, a tomographic image at a cutting height corresponding to the inside of the subject M shows bones or organs, which have a large difference in pixel value compared to the background, so the variance of pixel values ​​in the tomographic image tends to be high.

[0065] Therefore, the reconstruction range determination unit 35 selects an area of ​​the first reconstruction range L1 in which the amount of information J satisfies a predetermined condition, and sets this area as the second reconstruction range L2. The second reconstruction range L2 corresponds to the range of cut heights that are the target for generating the three-dimensional volume image FB by performing reconstruction processing on the projection image F1.

[0066] The predetermined condition for selecting the second reconstruction range L2 may be set as appropriate as long as it is a condition that can distinguish between a cutting height for which it is highly necessary to reconstruct the three-dimensional volume image FB and a cutting height for which it is less necessary. In this embodiment, a range of cutting heights for which the amount of information J is equal to or greater than a predetermined threshold value BL is selected as the second reconstruction range L2. The condition that the amount of information J is equal to or greater than the threshold value BL corresponds to the second condition in this embodiment.

[0067] 6 or 7, among the series of temporary reconstructed images F2, the tomographic image for cutting height Hs has the highest amount of information J. When the cutting height is equal to or greater than V1 and equal to or less than V2, the amount of information J in the temporary reconstructed image F2 is equal to or greater than a threshold value BL. The reconstruction range determination unit 35 uses a predetermined algorithm or the like to search for a range of cutting heights in which the amount of information J is equal to or greater than the threshold value BL.

[0068] As a result of the search by the reconstruction range determination unit 35, a range that includes the cutting height Hs at which the amount of information J peaks and has cutting height V1 as its lower limit and cutting height V2 as its upper limit is determined as the reconstruction range L2. In this way, the reconstruction range determination unit 35 automatically determines the second reconstruction range L2 based on the amount of information J in accordance with predetermined conditions. Information on the determined second reconstruction range L2 is transmitted from the reconstruction range determination unit 35 to the second reconstruction processing unit 37. Furthermore, data on the amount of information J and data on the information amount map T are transmitted from the reconstruction range determination unit 35 to the display range determination unit 36.

[0069] Step S5 (Determining the display range) When data such as the amount of information J is transmitted to the display range determination unit 36, the display range determination unit 36 ​​determines the display range L3 based on the amount of information J. The display range L3 is the range of cutting heights that are the target of tomographic processing on the three-dimensional volume image FB within the second reconstruction range L2 in which the three-dimensional volume image FB is generated. In other words, the display range L3 is the range of cutting heights in which tomographic processing is performed on the three-dimensional volume image FB to generate a tomosynthesis image F3.

[0070] As will be described later, an iterative reconstruction method is used as a reconstruction calculation method for reconstructing a three-dimensional volume image FB. In the iterative reconstruction method, the range (second reconstruction range L2) over which the reconstruction calculation is performed must be relatively wide in order to reduce artifacts that occur in the three-dimensional volume image FB. On the other hand, the diagnostic target using tomosynthesis images is not necessarily the entire three-dimensional volume image FB of the subject M, but is generally limited to a portion of the three-dimensional volume image FB. In other words, the range of cut heights required to perform tomographic processing on the three-dimensional volume image FB to obtain a tomosynthesis image F3 is limited to a range with a particularly high amount of information J within the second reconstruction range L2 over which the three-dimensional volume image FB is generated.

[0071] Therefore, in the image processing device 15 according to the present invention, to avoid generating a tomosynthesis image F3 for a cutting height unnecessary for diagnosis, the range of cutting heights unnecessary for generating a tomosynthesis image is excluded from the second reconstruction range L2 based on the amount of information J. Then, the range that has not been excluded is determined as the display range L3, i.e., the range of cutting heights for which the tomosynthesis image F3 is to be generated.

[0072] Specifically, the display range determination unit 36 ​​included in the image processing device 15 selects a region of the first reconstruction range L1 whose information amount J satisfies a predetermined condition, and sets the region as the display range L3. The predetermined condition for selecting the display range L3 may be set as appropriate, as long as it can distinguish between a cutting height for which it is highly necessary to generate and display a tomosynthesis image F3 and a cutting height for which it is less necessary. In this embodiment, the display range L3 is selected as a cutting height range for which the information amount J is equal to or greater than a predetermined threshold value CL. The threshold value CL, which is the selection condition for the display range L3, is set in advance to a value higher than the threshold value BL, which is the selection condition for the second reconstruction range L2. In other words, the display range L3 is narrower than the second reconstruction range L2. The condition that the information amount J is equal to or greater than the threshold value CL corresponds to the first condition in this embodiment. The condition for the information amount J used to determine the display range L3 and the condition for the information amount J used to determine the second reconstruction range L2 are each set so that the second reconstruction range L2 is wider than the display range L3.

[0073] The display range determination unit 36 ​​uses a predetermined algorithm or the like to search for a range of cutting heights where the amount of information J is equal to or greater than the threshold value CL. As shown in Fig. 8, when the cutting height is equal to or greater than N1 and equal to or less than N2 among a series of temporary reconstructed images F2, the amount of information J in the temporary reconstructed image F2 is equal to or greater than the threshold value CL. Therefore, as a result of the search by the display range determination unit 36, a range that includes the cutting height Hs where the amount of information J peaks and has the cutting height N1 as its lower limit and the cutting height N2 as its upper limit is determined as the display range L3.

[0074] In this way, the display range determination unit 36 ​​automatically determines the display range L3 in accordance with predetermined conditions and based on the amount of information J. Information on the determined display range L3 is transmitted from the display range determination unit 36 ​​to the tomographic image generation unit 38.

[0075] The order in which steps S4 and S5 are performed may be reversed, or steps S4 and S5 may be performed in parallel. As an example, when steps S4 and S5 are performed in parallel, data on the information amount J and the information amount map T are transmitted in parallel from the information amount calculation unit 33 to the reconstruction range determination unit 35 and the display range determination unit 36. Then, the reconstruction range determination unit 35 determines a second reconstruction range L2, and the display range determination unit 36 ​​determines a display range L3.

[0076] Step S6 (second reconstruction process) When the data of the second reconstruction range L2 is transmitted to the second reconstruction processing unit 37, the second reconstruction processing is started by the second reconstruction processing unit 37. The second reconstruction processing unit 37 performs reconstruction processing on the series of projection images F1 using an iterative reconstruction method (IR method) to generate a three-dimensional volume image FB. The iterative reconstruction method corresponds to the second reconstruction calculation method in this embodiment.

[0077] In the iterative reconstruction method, a 3D volume image is generated by comparing an actually acquired projection image F1 with a pseudo-projection image generated from a 3D volume image created for a specified height range and repeating calculations to correct the 3D volume image. Generally, when reconstruction is performed using the iterative reconstruction method, the value of the height range for generating the 3D volume image is manually input by the subject.

[0078] On the other hand, in this embodiment, the height range for generating a three-dimensional volume image is automatically determined by the reconstruction range determination unit 35. That is, the second reconstruction processing unit 37 uses the values ​​of the second reconstruction range L2 as the generation range for the three-dimensional volume image and performs reconstruction processing by the iterative reconstruction method. As a result, as shown in Fig. 9, a three-dimensional volume image FB is generated for the height range of the second reconstruction range L2. Data of the generated three-dimensional volume image FB is transmitted from the second reconstruction processing unit 37 to the tomographic image generation unit 38.

[0079] The IR method used in the second reconstruction processing has a larger computational load than the FBP method used in the first reconstruction processing, but is a calculation method that can acquire highly accurate data. In other words, by performing reconstruction calculations using the IR method in the second reconstruction processing, highly accurate data of the three-dimensional volume image FB can be acquired.

[0080] The three-dimensional volume image FB generated by the second reconstruction processing is data whose cut height range is limited to a second reconstruction range L2. The second reconstruction range L2 is the range within the first reconstruction range L1 where the amount of information J is equal to or greater than the threshold value BL. In other words, it is possible to prevent the target range of the calculation processing performed by the second reconstruction processor 37 from extending to a range where the amount of information is low and there is little need for diagnosis. In other words, it is possible to prevent the target range of the reconstruction calculation processing by the IR method from becoming excessively wide. Therefore, even when the IR method, which has a relatively high calculation load, is used as the reconstruction calculation method, it is possible to shorten the time required for the second reconstruction processing.

[0081] Step S7 (generation of tomographic images) When the data of the three-dimensional volume image FB and the display range L3 is transmitted to the tomographic image generation unit 38, the tomographic image generation unit 38 generates a tomosynthesis image F3. That is, as shown in FIG. 9, the tomographic image generation unit 38 performs tomographic processing (slicing) on ​​the cut height range of the display range L3 of the three-dimensional volume image FB generated for the second reconstruction range L2. This tomosynthesis processing generates a tomosynthesis image F3 for the display range L3. The tomosynthesis image F3 is an image group including tomographic images for each cut height, from a tomographic image F3p for the cut height N1 to a tomographic image F3s for the cut height N2.

[0082] The data of the tomosynthesis image F3 generated by the tomographic image generation unit 38 is displayed on the display unit 43. The operator diagnoses the subject M using the tomosynthesis image F3 for the display range L3. The display range L3 is the cut height at which the information amount J of the projection image F1 is equal to or greater than the threshold value CL. Because the threshold value CL is set in advance to a sufficiently high value, the tomosynthesis image L3 is data limited to the range of cut heights that are highly necessary for diagnosis. In other words, by generating the tomosynthesis image L3 limited to the display range L3, the calculation processing time of the tomosynthesis image generation unit 38 can be reduced. Furthermore, since it is possible to prevent the tomosynthesis image L3 from being generated for an excessively wide range, it is possible to prevent tomographic images unnecessary for diagnosis from being included in the tomosynthesis image L3 and thereby hindering the diagnosis.

[0083] Furthermore, the IR method used in the second reconstruction process has a greater computational load than the FBP method used in the first reconstruction process, but is a calculation method that can acquire highly accurate tomographic images with fewer artifacts, etc. In other words, the tomosynthesis image F3, which is the tomographic image used for final diagnosis, is image data generated by the IR method, so the operator can acquire a more accurate tomosynthesis image F3 that is suitable for diagnosis.

[0084] <Effects of the configuration of the embodiment> (Item 1) The tomosynthesis apparatus 1 according to the first embodiment includes an X-ray tube 5 that irradiates a subject M with X-rays, an X-ray detector 7 that is disposed opposite the X-ray tube 5 and detects X-rays that have passed through the subject M, a movement mechanism control unit 17 that moves the X-ray tube 5 and the X-ray detector 7 in opposite directions along the body axis of the subject M while the X-ray tube 5 and the X-ray detector 7 are opposed to each other with the subject M in between, an X-ray irradiation control unit 19 that controls the X-ray tube 5 to repeatedly irradiate X-rays while the movement mechanism control unit 17 moves the X-ray tube 5 and the X-ray detector 7 in opposite directions, a projection image generation unit 21 that generates a projection image F1 based on a detection signal output by the X-ray detector 7 for each X-ray irradiation by the X-ray tube 5, and a first reconstruction calculation unit that generates a provisional reconstruction image F2 by performing a reconstruction process on the projection image F1 for a first reconstruction range L1 that is the range of the cutting height using a first reconstruction calculation method. The apparatus includes a processing unit 31, an information amount calculation unit 33 that calculates an information amount J of a temporary reconstructed image F2 for each cutting height, a display range determination unit 36 ​​that determines a range of cutting heights where the information amount J satisfies predetermined conditions for being appropriate as a reconstructed image for display as a display range L3, a second reconstruction processing unit 37 that generates a three-dimensional volume image FB by performing reconstruction processing on a projection image L1 for a predetermined second reconstruction range L2 using a second reconstruction calculation method, a tomographic image generation unit 38 that cuts the three-dimensional volume image FB generated for the second reconstruction range L2 for the display range L3 to generate a tomosynthesis image F3, and a tomographic image display unit 43 that displays the tomosynthesis image F3 generated for the display range L3, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

[0085] In conventional tomosynthesis imaging, the operator manually determines the height range for reconstructing a 3D volume image using an iterative reconstruction method and the height range for generating a tomosynthesis image by slicing the 3D volume image. In conventional configurations where the height ranges of the 3D volume image and the tomosynthesis image are manually set, particularly when the operator is not skilled, situations frequently occur where the set ranges actually fall outside the region of interest for the tomosynthesis imaging or where the set reconstruction range is unnecessarily wide. If the ranges fall outside the region of interest for the tomosynthesis imaging, the operator realizes after the generation of the tomosynthesis image that the manually set ranges were inappropriate. As a result, the operator must regenerate the tomosynthesis image or 3D volume image. Furthermore, the 3D volume image reconstruction process uses a computationally intensive processing method, such as the IR method. Therefore, if reconstruction calculations are performed over an unnecessarily wide range, the time required to acquire a 3D volume image and a tomosynthesis image will be long, and the tomosynthesis image will contain many cross-sectional images at cutting heights that are not necessary for diagnosis. This not only increases the time required for diagnosis, but also raises concerns about a decrease in diagnostic accuracy.

[0086] To address these problems with conventional devices, the tomosynthesis device according to the first aspect performs a process of reconstructing a temporary reconstructed image F2 from the projection images F1, i.e., a provisional reconstruction process, before performing a process of reconstructing a three-dimensional volume image FB from the projection images F1, i.e., a final reconstruction process. The first reconstruction process, which is a provisional reconstruction process, is performed on a sufficiently wide first reconstruction range L1 using a first reconstruction calculation method with a relatively low computational load. The three-dimensional volume image FB is reconstructed by limiting the first reconstruction range L1 to a range with a cut height corresponding to a predetermined second reconstruction range L2. The display range L3 is also calculated using the temporary reconstructed image F2 obtained by the first reconstruction process. Then, a slice process is performed on the three-dimensional volume image limited to a cut height corresponding to the display range L3, thereby generating a tomosynthesis image F3 to be used for final diagnosis.

[0087] The first reconstruction process is performed on a sufficiently wide first reconstruction range L1. That is, the temporary reconstructed image F2 is a group of tomographic images having the sufficiently wide first reconstruction range L1 as a cut height, so it is possible to reliably prevent the cut height that is the region of interest in tomosynthesis imaging from falling outside the first reconstruction range. Therefore, it is possible to reliably include the cut height that is the region of interest in tomosynthesis imaging in the second reconstruction range L2, so it is possible to reliably prevent a situation in which a tomographic image at the cut height that is the region of interest is not included in the tomosynthesis image F3.

[0088] The first reconstruction calculation method used to generate the temporary reconstructed image F2 is a calculation method with a smaller calculation load than the second reconstruction calculation method used in the final process of reconstructing the three-dimensional volume image FB. Therefore, the temporary reconstructed image F2 can be generated quickly. Therefore, the second reconstruction range L2 for generating the three-dimensional volume image FB is calculated quickly and appropriately, so the burden on the operator in the reconstruction process of the three-dimensional volume image FB can be reduced, and the reconstruction process can be performed more reliably for an appropriate range.

[0089] The display range L3 is determined based on the information amount J of the temporary reconstructed image F2. Because the display range L3 is determined based on the information of the temporary reconstructed image F2, which is a tomographic image, it is possible to reliably prevent the display range L3 from deviating from the region of interest in tomosynthesis imaging, and to reliably exclude from the display range L3 a range of cutting heights that are less noticeable.

[0090] Therefore, since the tomosynthesis image F3 is reconstructed for the display range L3, which is a sufficiently limited range that includes the region of interest, it is possible to reliably obtain a highly accurate tomosynthesis image suitable for diagnosis while significantly reducing the time required to generate the tomosynthesis image F3 and to make a diagnosis using the tomosynthesis image F3. Furthermore, since the process of calculating the display range L3 is performed automatically by the main controller 29, the burden on the operator when determining the display range L3 is reduced and the time required to determine the display range L3 can be shortened.

[0091] (Item 2) In the tomosynthesis device described in Item 1, the first reconstruction calculation method is a filtered back projection method, and the second reconstruction calculation method is an iterative reconstruction method. With this configuration, a temporary reconstruction image F2 can be quickly reconstructed using the filtered back projection method, which has a low computational load. This allows the display range determination unit 36 ​​to quickly and accurately determine the display range L3. The second reconstruction processing unit 37 then reconstructs a three-dimensional volume image FB using the iterative reconstruction method. The iterative reconstruction method is a reconstruction calculation method that can reconstruct highly accurate tomographic images with few artifacts, thereby further improving the quality of the three-dimensional volume image FB and the tomosynthesis image.

[0092] (Item 3) In the tomosynthesis device described in Items 1 or 2, the amount of information J is the variance of pixel values ​​in the temporary reconstructed image F2. The variance of pixel values ​​in the reconstructed image is highly relevant to the attention of the image in tomosynthesis imaging. At cut heights with a high variance of pixel values, the differences between pixel values ​​within the image are particularly large, making them highly suitable as a region of interest for tomosynthesis imaging. Therefore, by determining the display range L3 based on the variance of pixel values, the cut height of the region of interest in tomosynthesis imaging is more reliably included in the display range L3. This reliably avoids a situation where the tomosynthesis image F3 does not include a tomographic image of the region of interest, requiring the second reconstruction process to be performed again.

[0093] (Item 4) The tomosynthesis apparatus 1 according to the second embodiment includes an X-ray tube 5 that irradiates X-rays onto a subject M, an X-ray detector 7 that is disposed opposite the X-ray tube 5 and detects X-rays that have passed through the subject M, a movement mechanism control unit 17 that moves the X-ray tube 5 and the X-ray detector 7 in opposite directions along the body axis of the subject M while the X-ray tube 5 and the X-ray detector 7 are opposed to each other with the subject M in between, an X-ray irradiation control unit 19 that controls the X-ray tube 5 to repeatedly irradiate X-rays while the movement mechanism control unit 17 moves the X-ray tube 5 and the X-ray detector 7 in opposite directions, a projection image generation unit 21 that generates a projection image F1 based on a detection signal output by the X-ray detector 7 for each X-ray irradiation by the X-ray tube 5, and a first reconstruction calculation unit that calculates a first reconstruction image F1 within a range of a cutting height using a first reconstruction calculation method. a first reconstruction processing unit 36 ​​that generates a temporary reconstructed image F2 by performing reconstruction processing on the projection image F1 for a desired range of the reconstruction image F1; an information amount calculation unit 33 that calculates an information amount J of the temporary reconstructed image F2 for each cutting height; a reconstruction range determination unit 35 that determines, from the first reconstruction range L1, a range of cutting heights in which the information amount J satisfies a predetermined condition that the range is appropriate for a three-dimensional volume image FB, as a second reconstruction range L2; and a second reconstruction processing unit 37 that generates a three-dimensional volume image FB by performing reconstruction processing on the projection image F1 for the second reconstruction range L2 using a second reconstruction calculation method, wherein the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

[0094] In the tomosynthesis device according to paragraph 4, before performing a process of reconstructing a three-dimensional volume image FB from the projection images F1, i.e., a final reconstruction process, a process of reconstructing a temporary reconstructed image F2 from the projection images F1, i.e., a provisional reconstruction process, is performed. The first reconstruction process, which is a provisional reconstruction process, is performed on a sufficiently wide first reconstruction range L1 using a first reconstruction calculation method with a relatively low computational load. Then, a second reconstruction range L2 is calculated using the temporary reconstructed image F2 obtained in the first reconstruction process, and a three-dimensional volume image FB is reconstructed within a range limited to a cutting height corresponding to the second reconstruction range L2. Then, by performing a slice process on the three-dimensional volume image at an appropriate cutting height, a tomosynthesis image to be used for final diagnosis can be generated.

[0095] The first reconstruction process is performed on a sufficiently wide first reconstruction range L1. That is, the temporary reconstructed image F2 is a group of tomographic images having the sufficiently wide first reconstruction range L1 as a cut height, so it is possible to reliably prevent the cut height that is the region of interest in tomosynthesis imaging from falling outside the first reconstruction range. Therefore, it is possible to reliably include the cut height that is the region of interest in tomosynthesis imaging in the second reconstruction range L2, so it is possible to reliably prevent a situation in which a tomographic image at the cut height that is the region of interest is not included in the tomosynthesis image.

[0096] The first reconstruction calculation method used to generate the temporary reconstructed image F2 is a calculation method with a smaller calculation load than the second reconstruction calculation method used in the final process of reconstructing the three-dimensional volume image FB. Therefore, the temporary reconstructed image F2 can be generated quickly. Therefore, the second reconstruction range L2 for generating the three-dimensional volume image FB is calculated quickly and appropriately, so the burden on the operator in the reconstruction process of the three-dimensional volume image FB can be reduced, and the reconstruction process can be performed more reliably for an appropriate range.

[0097] The second reconstruction range L2 is determined based on the information amount J of the temporary reconstructed image F2. Because the second reconstruction range L2 is determined based on the information of the temporary reconstructed image F2, which is a tomographic image, it is possible to reliably prevent the second reconstruction range L2 from deviating from the region of interest in tomosynthesis imaging, and to reliably exclude from the second reconstruction range L2 a range of cutting heights that are of low interest.

[0098] Therefore, the three-dimensional volume image FB is reconstructed for the second reconstruction range L2, which is a sufficiently limited range that includes the region of interest, so that the time required for the process of reconstructing the three-dimensional volume image FB can be significantly reduced, and highly accurate tomosynthesis images suitable for diagnosis can be reliably obtained. Furthermore, because the process up to the calculation of the second reconstruction range L2 is performed automatically, the burden on the operator when determining the reconstruction range is reduced, and the time required for the reconstruction of the three-dimensional volume image FB can be shortened.

[0099] (Item 5) In the tomosynthesis apparatus described in Item 4, the first reconstruction calculation method is a filtered back projection method, and the second reconstruction calculation method is an iterative reconstruction method. With this configuration, a temporary reconstruction image F2 can be quickly reconstructed using the filtered back projection method, which has a low computational load. Therefore, the reconstruction range determination unit 35 can quickly and accurately determine the second reconstruction range L2. The second reconstruction processing unit 37 then reconstructs a three-dimensional volume image FB using the iterative reconstruction method. The iterative reconstruction method is a reconstruction calculation method that can reconstruct highly accurate tomographic images with few artifacts, and therefore the quality of the three-dimensional volume image FB and the tomosynthesis image can be further improved.

[0100] (Item 6) In the tomosynthesis device described in Items 4 or 5, the amount of information J is the variance of pixel values ​​in the temporary reconstructed image F2. The variance of pixel values ​​in the reconstructed image is highly relevant to the attention of the image in tomosynthesis imaging. At a cut height where the variance of pixel values ​​is particularly high, the difference between pixel values ​​within the image is large, making it highly suitable as a region of interest for tomosynthesis imaging. Therefore, by determining the second reconstruction range L2 based on the variance of pixel values, the cut height of the region of interest in tomosynthesis imaging is more reliably included in the second reconstruction range L2. This reliably avoids a situation where the tomographic image of the region of interest is not included in the three-dimensional volume image FB and the second reconstruction process has to be performed again.

[0101] (Item 7) The tomosynthesis apparatus 1 according to the third embodiment includes an X-ray tube 5 that irradiates X-rays onto a subject M, an X-ray detector 7 that is disposed opposite the X-ray tube 5 and detects X-rays that have passed through the subject M, a movement mechanism control unit 17 that moves the X-ray tube 5 and the X-ray detector 7 in opposite directions along the body axis of the subject M while the X-ray tube 5 and the X-ray detector 7 are opposed to each other with the subject M in between, and an X-ray irradiation control unit that controls the X-ray tube 5 to repeatedly irradiate X-rays while the movement mechanism control unit 17 moves the X-ray tube 5 and the X-ray detector 7 in opposite directions. a projection image generating unit 21 that generates a projection image F1 based on a detection signal output by the X-ray detector 7 for each X-ray irradiation from the X-ray tube 5; a first reconstruction processing unit 31 that generates a temporary reconstructed image F2 by performing reconstruction processing on the projection image F1 for a first reconstruction range L1 that is the range of the cutting height using a first reconstruction calculation method; an information amount calculating unit 33 that calculates an information amount J of the temporary reconstructed image F2 for each cutting height; and a unit that calculates, from within the first reconstruction range L1, a unit that calculates an information amount J that is equal to the reconstructed image for display. a reconstruction range determination unit 35 that determines, from the first reconstruction range L1, a range of cut heights that satisfies a predetermined second condition that the amount of information J is appropriate for a three-dimensional volume image FB as a second reconstruction range L2; a second reconstruction processing unit 37 that generates a three-dimensional volume image FB by performing reconstruction processing on the projection image F1 for the second reconstruction range L2 using a second reconstruction calculation method; a tomographic image generation unit 38 that cuts the three-dimensional volume image FB generated for the second reconstruction range L2 for the display range L3 to generate a tomosynthesis image F3; and a tomographic image display unit 43 that displays the tomosynthesis image F3 generated for the display range L3, wherein the first and second conditions are set so that the second reconstruction range L2 is wider than the display range L3, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

[0102] In the tomosynthesis device according to paragraph 7, a process of reconstructing a temporary reconstructed image F2 from the projection images F1, i.e., a provisional reconstruction process, is performed before a process of reconstructing a three-dimensional volume image FB from the projection images F1, i.e., a final reconstruction process. The first reconstruction process, which is a provisional reconstruction process, is performed on a sufficiently wide first reconstruction range L1 using a first reconstruction calculation method with a relatively low computational load. Then, using the temporary reconstructed image F2 obtained in the first reconstruction process, a range of cut heights where the information amount J is higher than a second predetermined value BL is determined as a second reconstruction range L2. Furthermore, a range of cut heights where the information amount J is higher than the first predetermined value CL is determined as a display range L3. Then, a three-dimensional volume image FB is reconstructed within a cut height range corresponding to the second reconstruction range L2. Finally, a cut height of the display range L3 is cut from the three-dimensional volume image to generate a tomosynthesis image F3 to be used for final diagnosis.

[0103] The first reconstruction process is performed on a sufficiently wide first reconstruction range L1. That is, the temporary reconstructed image F2 is a group of tomographic images having the sufficiently wide first reconstruction range L1 as a cut height, so it is possible to reliably prevent the cut height that is the region of interest in tomosynthesis imaging from falling outside the first reconstruction range. Therefore, it is possible to reliably include the cut height that is the region of interest in tomosynthesis imaging in the second reconstruction range L2, so it is possible to reliably prevent a situation in which a tomographic image at the cut height that is the region of interest is not included in the tomosynthesis image F3.

[0104] The first reconstruction calculation method used to generate the temporary reconstructed image F2 is a calculation method with a smaller calculation load than the second reconstruction calculation method used in the final process of reconstructing the three-dimensional volume image FB. Therefore, the temporary reconstructed image F2 can be generated quickly. Therefore, the second reconstruction range L2 for generating the three-dimensional volume image FB is calculated quickly and appropriately, so the burden on the operator in the reconstruction process of the three-dimensional volume image FB can be reduced, and the reconstruction process can be performed more reliably for an appropriate range.

[0105] The second reconstruction range L2 is determined based on the information amount J of the temporary reconstructed image F2. Because the second reconstruction range L2 is determined based on the information of the temporary reconstructed image F2, which is a tomographic image, it is possible to reliably prevent the second reconstruction range L2 from deviating from the region of interest in tomosynthesis imaging, and to reliably exclude from the second reconstruction range L2 a range of cutting heights that are of low interest.

[0106] Therefore, the three-dimensional volume image FB is reconstructed for the second reconstruction range L2, which is a sufficiently limited range that includes the region of interest, so that the time required for the process of reconstructing the three-dimensional volume image FB can be significantly reduced, and a highly accurate tomosynthesis image F3 suitable for diagnosis can be reliably acquired. Furthermore, because the process up to the calculation of the second reconstruction range L2 is performed automatically, the burden on the operator when determining the reconstruction range is reduced, and the time required for the reconstruction of the three-dimensional volume image FB can be shortened.

[0107] The display range L3 is determined based on the information amount J of the temporary reconstructed image F2. Because the display range L3 is determined based on the information of the temporary reconstructed image F2, which is a tomographic image, it is possible to reliably prevent the display range L3 from deviating from the region of interest in tomosynthesis imaging, and to reliably exclude from the display range L3 a range of cutting heights that are less noticeable.

[0108] Therefore, since the tomosynthesis image F3 is generated for the display range L3, which is a sufficiently limited range that includes the region of interest, it is possible to reliably obtain a highly accurate tomosynthesis image suitable for diagnosis while significantly reducing the time required to generate the tomosynthesis image F3 and to make a diagnosis using the tomosynthesis image F3. Furthermore, since the process of calculating the display range L3 is performed automatically by the main controller 29, the burden on the operator when determining the display range L3 is reduced and the time required to determine the display range L3 can be shortened.

[0109] The display range L3 is determined as a range of cutting heights that satisfies the condition that the amount of information J is equal to or greater than a first predetermined value CL. The first predetermined value CL is predetermined to be higher than a second predetermined value BL. That is, the display range L3 is limited to cutting heights where the amount of information J is particularly high, and the tomosynthesis image F3 is generated at a height that is particularly suitable for diagnosis. This prevents the tomosynthesis image F3 from including sectional images at heights unnecessary for diagnosis, allowing the operator to quickly diagnose the subject M using only the tomosynthesis image F3, which is a sectional image that is particularly suitable for diagnosis.

[0110] The second reconstruction range L2 is determined as a range of cut heights that satisfies the condition that the amount of information J of the temporary reconstructed image F2 is equal to or greater than a second predetermined value BL. That is, as shown in Figure 8 or 10, the second reconstruction range L2 for which the second reconstruction calculation method is performed is limited to the same range as the first reconstruction range L1 or a range narrower than the first reconstruction range L1. This makes it possible to avoid reconstructing the three-dimensional volume image FB over an unnecessarily wide range, thereby shortening the time required for the calculation process for reconstructing the three-dimensional volume image FB using the second reconstruction calculation method.

[0111] Furthermore, because the second predetermined value BL is lower than the first predetermined value CL, the second reconstruction range L2 is determined to be wider than the display range L3, as shown in Figure 8 or 10. In the second reconstruction calculation method, which is an iterative reconstruction method for example, if the reconstruction process is performed on an unnecessarily narrow range, the reconstruction calculation may become inaccurate, and artifacts may occur in the three-dimensional volume image FB. By setting the second reconstruction range L2 to be equal to or smaller than the first reconstruction range L1 but wider than the display range L3, it is possible to avoid the second reconstruction range L2 being unnecessarily narrow, thereby preventing artifacts from occurring in the three-dimensional volume image FB.

[0112] (Item 8) In the tomosynthesis device described in Item 7, the first reconstruction calculation method is a filtered back projection method, and the second reconstruction calculation method is an iterative reconstruction method. With this configuration, a temporary reconstruction image F2 can be quickly reconstructed using the filtered back projection method, which has a low computational load. This allows the display range determination unit 36 ​​to quickly and accurately determine the display range L3. The second reconstruction processing unit 37 then reconstructs a three-dimensional volume image FB using the iterative reconstruction method. The iterative reconstruction method is a reconstruction calculation method that can reconstruct highly accurate tomographic images, and therefore the quality of the three-dimensional volume image FB and the tomosynthesis image F3 can be further improved.

[0113] Furthermore, if the height range that is the subject of calculation in the iterative reconstruction method is too narrow, the calculation process that compares the actual projection image with the pseudo projection image and corrects the 3D volume image may be performed inappropriately. Therefore, by making the second reconstruction range L2 that is the subject of the iterative reconstruction method wider than the display range L3, it is possible to avoid situations where artifacts occur in the 3D volume image FB and quality deteriorates.

[0114] (Item 9) In the tomosynthesis device described in Items 7 or 8, the amount of information J is the variance of pixel values ​​in the temporary reconstructed image F2. The variance of pixel values ​​in the reconstructed image is highly relevant to the attention of the image in tomosynthesis imaging. At a cut height with a high variance of pixel values, the difference between pixel values ​​within the image is particularly large, making it highly suitable as a region of interest for tomosynthesis imaging. Therefore, by determining the display range L3 based on the variance of pixel values, the cut height of the region of interest in tomosynthesis imaging is more reliably included in the display range L3. This reliably avoids a situation where the tomosynthesis image F3 does not include a tomographic image of the region of interest, requiring the second reconstruction process to be performed again.

[0115] (Item 10) An image processing device 15 according to this embodiment is an image processing device that performs image processing to generate a tomosynthesis image F3 using projection images F1 acquired by repeatedly irradiating X-rays from the X-ray tube 5 while moving an X-ray tube 5 and an X-ray detector 7, which are arranged opposite to each other across a subject M, in the body axis direction of the subject M, in a direction opposite to each other. The image processing device 15 includes a first reconstruction processing unit 31 that generates a temporary reconstructed image F2 by performing reconstruction processing on the projection images F1 for a first reconstruction range L1, which is a range of cutting heights, using a first reconstruction calculation method; an information amount calculation unit 33 that calculates an information amount J of the temporary reconstructed image F2 for each cutting height; a display range determination unit 36 ​​that determines, from the first reconstruction range L1, a range of cutting heights where the information amount J satisfies a predetermined first condition that the reconstructed image is appropriate for display, as a display range L3; and a display area determination unit 37 that determines, from the first reconstruction range L1, a range of cutting heights where the information amount J satisfies a predetermined first condition that the reconstructed image is appropriate for display. a second reconstruction processing unit 37 that generates a three-dimensional volume image FB by performing reconstruction processing on the projection image F1 for the second reconstruction range L2 using a second reconstruction calculation method; a tomographic image generation unit 38 that cuts the three-dimensional volume image FB generated for the second reconstruction range L2 for a display range L3 to generate a tomosynthesis image F3; and a tomographic image display unit 43 that displays the tomosynthesis image F3 generated for the display range L3, wherein the first and second conditions are set so that the second reconstruction range L2 is wider than the display range L3, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

[0116] According to the image processing device 15 described in paragraph 10, before performing a process of reconstructing a three-dimensional volume image FB from the projection images F1, i.e., a final reconstruction process, a process of reconstructing a temporary reconstructed image F2 from the projection images F1, i.e., a temporary reconstruction process, is performed. The first reconstruction process, which is a temporary reconstruction process, is performed on a sufficiently wide first reconstruction range L1 and is performed using a first reconstruction calculation method with a relatively low computational load. Then, using the temporary reconstructed image F2 obtained in the first reconstruction process, a range of cut heights in which the information amount J satisfies a first condition is determined as a display range L3. Furthermore, a range of cut heights in which the information amount J satisfies a second condition is determined as a second reconstruction range L2. Then, a three-dimensional volume image FB is reconstructed by limiting the cut height range to the second reconstruction range L2. Finally, a tomosynthesis image F3 used for final diagnosis is generated by performing a cut height cut process on the three-dimensional volume image within the display range L3. The first and second conditions are set so that the second reconstruction range L2 is wider than the display range L3, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method. Therefore, similar to the tomosynthesis apparatus 1 according to the embodiment, the burden on the operator in the reconstruction process of the tomosynthesis image F3 can be reduced, and the reconstruction process can be performed more reliably for an appropriate range.

[0117] (Item 11) In the image processing device 15 described in Item 10, the first reconstruction calculation method is a filtered back projection method, and the second reconstruction calculation method is an iterative reconstruction method. With this configuration, a temporary reconstruction image F2 can be quickly reconstructed using the filtered back projection method, which has a low computational load. Therefore, the reconstruction range determination unit 35 can quickly and accurately determine the second reconstruction range L2. The second reconstruction processing unit 37 then reconstructs a three-dimensional volume image FB using the iterative reconstruction method. The iterative reconstruction method is a reconstruction calculation method that can reconstruct highly accurate tomographic images, and therefore the quality of the three-dimensional volume image FB and therefore the tomosynthesis image F3 can be further improved.

[0118] (Item 12) In the image processing device 15 described in items 10 or 11, the amount of information J is the variance of pixel values ​​in the temporary reconstructed image F2. The variance of pixel values ​​in the reconstructed image is highly relevant to the attention of the image in tomosynthesis imaging. At a cut height where the variance of pixel values ​​is particularly high, the difference between pixel values ​​within the image is large, making it highly suitable as a region of interest for tomosynthesis imaging. Therefore, by determining the second reconstruction range L2 based on the variance of pixel values, the cut height of the region of interest in tomosynthesis imaging is more reliably included in the second reconstruction range L2. This reliably avoids a situation where the tomosynthesis image F3 does not include a tomographic image of the region of interest, requiring the second reconstruction process to be performed again.

[0119] (Item 13) The image processing program according to this embodiment is an image processing program that causes a computer to execute image processing for generating a tomosynthesis image F3 using projection images F1 acquired by repeatedly irradiating X-rays from the X-ray tube 5 while moving an X-ray tube 5 and an X-ray detector 7, which are arranged opposite to each other across the subject M, in the body axis direction of the subject M, in the image processing program. The image processing program includes a first reconstruction processing step of generating a temporary reconstructed image F2 by performing reconstruction processing on the projection images F1 for a first reconstruction range L1, which is a range of cutting heights, using a first reconstruction calculation method; an information amount calculation step of calculating an information amount J of the temporary reconstructed image F2 for each cutting height; a display range determination step of determining, from the first reconstruction range L1, a range of cutting heights where the information amount J satisfies a predetermined first condition that the display range L3 is appropriate for a reconstructed image to be displayed, and a reconstruction range determination step of determining, as a second reconstruction range L2, from within the range L1, a range of cutting heights that satisfies a predetermined second condition that the amount of information J is appropriate for a three-dimensional volume image FB; a second reconstruction processing step of generating a three-dimensional volume image FB by performing reconstruction processing on the projection image F1 for the second reconstruction range L2 using a second reconstruction calculation method; a tomographic image generation step of generating a tomosynthesis image F3 by cutting the three-dimensional volume image FB generated for the second reconstruction range L2 for a display range L3; and a tomographic image display step of displaying the tomosynthesis image F3 generated for the display range L3, wherein the first and second conditions are set so that the second reconstruction range L2 is wider than the display range L3, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

[0120] According to the image processing program described in paragraph 13, before generating a tomosynthesis image F3 using the projection image F1, a first reconstruction processing step is first performed using a first reconstruction calculation method with a relatively low computational load. In the first reconstruction processing step, a temporary reconstruction image F2 is generated by performing reconstruction processing on the projection image F1 for a first reconstruction range L1. Next, an information amount calculation step is performed to calculate an information amount J for each temporary reconstruction image F2 obtained for the first reconstruction range L1. After that, a display range determination step is performed to determine, as a display range L3, a range of cutting heights where the information amount J satisfies a first condition, and a reconstruction range determination step is performed to determine, as a second reconstruction range L2, a range of cutting heights where the information amount J satisfies a second condition. Then, a second reconstruction processing step is performed to generate a three-dimensional volume image FB by performing reconstruction processing on the projection image F1 for the second reconstruction range L2 using the second reconstruction calculation method. Finally, a tomographic image generating step is executed in which the three-dimensional volume image FB generated for the second reconstruction range L2 is cropped for the display range L3 to generate a tomosynthesis image F3, and a tomographic image display step is executed in which the tomosynthesis image F3 generated for the display range L3 is displayed. The first and second conditions are set so that the second reconstruction range L2 is wider than the display range L3, and the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method. Therefore, similar to the tomosynthesis apparatus 1 according to the embodiment, the burden on the operator in the reconstruction process of the tomosynthesis image F3 can be reduced, and the reconstruction process can be performed more reliably for an appropriate range.

[0121] (Item 14) In the image processing program described in Item 13, the first reconstruction calculation method is the filtered back projection method, and the second reconstruction calculation method is the iterative reconstruction method. With this configuration, a temporary reconstruction image F2 can be quickly reconstructed using the filtered back projection method, which has a low computational load. Therefore, the reconstruction range determination unit 35 can quickly and accurately determine the second reconstruction range L2. Then, the second reconstruction processing unit 37 reconstructs a tomosynthesis image F3 using the iterative reconstruction method. Since the iterative reconstruction method is a reconstruction calculation method that can reconstruct highly accurate tomographic images, the quality of the tomosynthesis image F3 can be further improved.

[0122] (Item 15) In the image processing program described in Item 13 or 14, the amount of information J is the variance of pixel values ​​in the temporary reconstructed image F2. The variance of pixel values ​​in the reconstructed image is highly relevant to the attention of the image in tomosynthesis imaging. At a cut height where the variance of pixel values ​​is particularly high, the difference between pixel values ​​within the image is large, making it highly suitable as a region of interest for tomosynthesis imaging. Therefore, by determining the second reconstruction range L2 based on the variance of pixel values, the cut height of the region of interest in tomosynthesis imaging is more reliably included in the second reconstruction range L2. This reliably avoids a situation where the tomosynthesis image F3 does not include a tomographic image of the region of interest, requiring the second reconstruction process to be performed again.

[0123] <Other embodiments> It should be noted that the embodiments disclosed herein are illustrative in all respects and are not limiting. The scope of the present invention includes the claims and all modifications within the meaning and scope equivalent to the claims. For example, the present invention can be modified as follows:

[0124] (1) In the above-described embodiment, the condition for determining the second reconstruction range L2 is not limited to the condition that the amount of information J is equal to or greater than a predetermined threshold value BL. Another example of a condition for determining the second reconstruction range L2 is that the distance from the peak cutting height Hs is equal to or less than a predetermined value R. As a specific example, the reconstruction range determination unit 35 searches for the cutting height Hs at which the amount of information J peaks according to a predetermined algorithm. Then, the second reconstruction range L2 is determined to be a range whose lower limit is a cutting height V1 that is lower than the cutting height Hs by a predetermined value R and whose upper limit is a cutting height V2 that is higher than the cutting height Hs by a predetermined value R. Similarly, the condition for determining the display range L3 is not limited to the condition that the amount of information J is equal to or greater than a predetermined threshold value CL.

[0125] (2) In the above-described embodiment or modification, the first reconstruction calculation method used in step S2 is not limited to the FBP method as long as it is a calculation method that has a smaller calculation load than the second reconstruction calculation method used in step S5. Furthermore, the second reconstruction calculation method is not limited to the IR method, and any calculation method that has a larger calculation load than the first reconstruction calculation method can be used. Note that, in terms of being able to acquire a highly accurate tomosynthesis image F3, it is preferable that the second reconstruction calculation method be a calculation method that can reconstruct a tomographic image with higher accuracy than the first reconstruction calculation method.

[0126] (3) In the above-described embodiment or modified example, the information amount calculation unit 33 is not limited to a configuration that creates the information amount map T. In other words, as long as it is possible for the reconstruction range determination unit 35 to determine the second reconstruction range L2 or the display range determination unit 36 ​​to determine the display range L3 based on the information amount J, the information amount calculation unit 33 may be configured not to create the information amount map T.

[0127] (4) In the above-described embodiment and modified example, the second reconstruction range L2 and the display range L3 are automatically determined using the amount of information J. However, the present invention is not limited to this. In other words, only one of the second reconstruction range L2 and the display range L3 may be automatically calculated using the amount of information J.

[0128] As one modified example, in which only the second reconstruction range L2 is automatically determined using the amount of information J, the main control unit 29 is provided with only the reconstruction range determination unit 35 out of the reconstruction range determination unit 35 and the display range determination unit 36. Then, in step S4 according to the modified example, as in the embodiment, the reconstruction range determination unit 35 determines, as the second reconstruction range L2, a range of cutting heights in which the amount of information J of the temporary reconstructed image F2 is equal to or greater than the threshold value BL. That is, in step S6, a three-dimensional volume image FB is generated using information on the second reconstruction range L2 automatically determined by the reconstruction range determination unit 35.

[0129] Meanwhile, in step S5 according to this modified example, the operator manually inputs information about the display range L3 using the operation unit 39 or the like. By inputting the information about the display range L3, the display range L3 of the tomosynthesis image F3 is determined. The operator may use any appropriate method to identify an appropriate value for the display range L3. One example is a method of estimating the display range L3 from the relationship between the height at which the subject M is placed and the position of the region of interest. In step S7, the information about the display range L3 determined manually is used to slice the three-dimensional volume image FB to generate the tomosynthesis image F3.

[0130] The tomosynthesis apparatus 1 according to one modification includes a first reconstruction processing unit 31, an information amount calculation unit 33, and a reconstruction range determination unit 35, and thus can automatically determine the second reconstruction range L2 based on the information amount J of the temporary reconstructed image F2. This eliminates the need to manually input information about the second reconstruction range L2, which corresponds to the reconstruction range of the three-dimensional volume image FB, as in the conventional method. This reduces the time required to generate the three-dimensional volume image FB and the tomosynthesis image F3 using the iterative reconstruction method, and also prevents the range of the cutting height for generating the three-dimensional volume image FB from becoming an inappropriate value due to an operator's setting error.

[0131] As another modified example, in which only the display range L3 is automatically determined using the amount of information J, the main control unit 29 includes only the display range determination unit 36 ​​out of the reconstruction range determination unit 35 and the display range determination unit 36. In step S5 according to this modified example, similar to the embodiment, the display range determination unit 36 ​​determines the range of the cutting height at which the amount of information J of the temporary reconstructed image F2 is equal to or greater than the threshold value CL as the display range L3. That is, in step S7, the three-dimensional volume image FB is sliced ​​using information about the display range L3 automatically determined by the display range determination unit 36 ​​to generate a tomosynthesis image F3.

[0132] Meanwhile, in step S4 according to this other modified example, the operator manually inputs information about the second reconstruction range L2 using the operation unit 39 or the like. By inputting the information about the second reconstruction range L2, the second reconstruction range L2, which is the range of cut heights for generating the three-dimensional volume image FB, is determined. The method for specifying the value of the second reconstruction range L2 can be changed as appropriate. As an example, the body thickness of the subject M can be measured or estimated, and the value of the second reconstruction range L2 can be determined according to the height of the body thickness of the subject M. In step S6, the reconstruction range determination unit 35 performs reconstruction processing by an iterative reconstruction method using the information about the second reconstruction range L2 determined manually, thereby generating the three-dimensional volume image FB.

[0133] The tomosynthesis apparatus 1 according to this modification includes a first reconstruction processing unit 31, an information amount calculation unit 33, and a display range determination unit 36, and thus can automatically determine the display range L3 based on the information amount J of the provisional reconstructed image F2. Therefore, it is not necessary to manually input information about the display range L3, which corresponds to the range within which the tomosynthesis image F3 is generated and displayed, as in the conventional method. Furthermore, it is not necessary to determine an appropriate value for the display range L3 by performing a process such as measuring the body thickness of the subject M. Therefore, it is possible to shorten the time required for the process of generating a three-dimensional volume image FB and a tomosynthesis image F3 using the iterative reconstruction method, and to prevent the range of the cutting height within which the tomosynthesis image F3 is generated from becoming an inappropriate value due to an operator's setting error.

[0134] (5) In the above-described embodiment and modified examples, the reconstruction range determination unit 35 or the display range determination unit 36 ​​is configured to search for a range in which the value of the information amount J satisfies a predetermined condition. However, this is not limiting. That is, a range in which the slope of the information amount J in the graph of the information amount map T satisfies a predetermined condition may be searched for. As an example, the reconstruction range determination unit 35 determines the upper or lower limit of the cutting height at which the absolute value of the slope of the information amount J in the graph of the information amount map T rises sharply from a value close to zero, and determines the range of cutting heights corresponding to the upper and lower limits as the second reconstruction range L2. Alternatively, the display range determination unit 36 ​​can determine the upper or lower limit of the cutting height at which the slope of the information amount J in the graph of the information amount map T rises sharply from a predetermined value, and determine the range of cutting heights corresponding to the upper and lower limits as the display range L3.

[0135] The second reconstruction range L2 often corresponds to the range where the subject M is placed, and the absolute value of the gradient of the amount of information J increases particularly at the boundary between the range where the subject M is placed and other ranges. The display region L3 often corresponds to the height of the region of interest, and the absolute value of the gradient of the amount of information J also increases at the boundary between the range of the region of interest and other ranges. Therefore, by performing calculation processing based on the gradient of the amount of information J, the second reconstruction range L2 or the display region L3 can be appropriately determined. [Explanation of symbols]

[0136] 1. Tomosynthesis device 3. Top plate 5...X-ray tube 7...X-ray detector 8...Collimator 9...X-ray tube movement mechanism 11...Detector moving mechanism 13...Shooting control device 15...Image processing device 17...Movement mechanism control unit 19...X-ray irradiation control unit 21...Projection image generation unit 29...Main control unit 31 ... first reconstruction processing unit 33…Information amount calculation unit 35...Reconstruction range determination unit 36 ... Display range determination unit 37 ... second reconstruction processing unit 38 ... Tomographic image generation unit 39...Operation unit 41...Storage section 43...Display section L1 ... First reconstruction range L2 ... Second reconstruction range L3...Display range F1...Projected image F2 ... Provisional reconstructed image FB: 3D volume image F3...Tomosynthesis image

Claims

1. an X-ray tube that irradiates an object with X-rays; an X-ray detector disposed opposite the X-ray tube and configured to detect X-rays transmitted through the subject; an opposing movement mechanism that moves the X-ray tube and the X-ray detector in opposite directions to each other along the body axis of the subject while the X-ray tube and the X-ray detector are opposed to each other across the subject; an X-ray irradiation control unit that controls the X-ray tube to repeatedly irradiate X-rays while the X-ray tube and the X-ray detector are moved in opposite directions by the opposing movement mechanism; a projection image generating unit that generates a projection image based on a detection signal output by the X-ray detector for each X-ray irradiation by the X-ray tube; a first reconstruction processing unit that generates a provisional reconstructed image by performing reconstruction processing on the projection image for a first reconstruction range that is a range of the cutting height using a first reconstruction calculation method; an information amount calculation unit that calculates an information amount of the temporary reconstructed image for each cutting height; a display range determination unit that determines, from the first reconstruction range, a range of cutting heights that satisfies a predetermined condition that the amount of information is appropriate for a reconstructed image to be displayed, as a display range; a second reconstruction processing unit that generates a three-dimensional volume image by performing reconstruction processing on the projection images for a second reconstruction range set in advance using a second reconstruction calculation method; a tomographic image generating unit that generates a tomosynthesis image by cutting the three-dimensional volume image generated for the second reconstruction range with respect to the display range; a tomographic image display unit that displays the tomosynthesis image generated for the display range; Equipped with A tomosynthesis apparatus, wherein the first reconstruction calculation method is a calculation method that has a smaller calculation load than the second reconstruction calculation method.

2. 2. The tomosynthesis device according to claim 1, the first reconstruction calculation method is a filtered back projection method, A tomosynthesis apparatus, wherein the second reconstruction calculation method is an iterative reconstruction method.

3. 3. The tomosynthesis apparatus according to claim 1, A tomosynthesis apparatus, wherein the amount of information is the variance of pixel values ​​in the provisionally reconstructed image.

4. an X-ray tube that irradiates an object with X-rays; an X-ray detector disposed opposite the X-ray tube and configured to detect X-rays transmitted through the subject; an opposing movement mechanism that moves the X-ray tube and the X-ray detector in opposite directions to each other along the body axis of the subject while the X-ray tube and the X-ray detector are opposed to each other across the subject; an X-ray irradiation control unit that controls the X-ray tube to repeatedly irradiate X-rays while the X-ray tube and the X-ray detector are moved in opposite directions by the opposing movement mechanism; a projection image generating unit that generates a projection image based on a detection signal output by the X-ray detector for each X-ray irradiation by the X-ray tube; a first reconstruction processing unit that generates a provisional reconstructed image by performing reconstruction processing on the projection image for a first reconstruction range that is a range of the cutting height using a first reconstruction calculation method; an information amount calculation unit that calculates an information amount of the temporary reconstructed image for each cutting height; a reconstruction range determination unit that determines, from the first reconstruction range, a range of cutting heights that satisfies a predetermined condition that the amount of information is appropriate for a three-dimensional volume image, as a second reconstruction range; a second reconstruction processing unit that generates a three-dimensional volume image by performing reconstruction processing on the projection images for the second reconstruction range using a second reconstruction calculation method; Equipped with A tomosynthesis apparatus, wherein the first reconstruction calculation method is a calculation method that has a smaller calculation load than the second reconstruction calculation method.

5. 5. The tomosynthesis device according to claim 4, the first reconstruction calculation method is a filtered back projection method, A tomosynthesis apparatus, wherein the second reconstruction calculation method is an iterative reconstruction method.

6. The tomosynthesis apparatus according to claim 4 or 5, A tomosynthesis apparatus, wherein the amount of information is the variance of pixel values ​​in the provisionally reconstructed image.

7. an X-ray tube that irradiates an object with X-rays; an X-ray detector disposed opposite the X-ray tube and configured to detect X-rays transmitted through the subject; an opposing movement mechanism that moves the X-ray tube and the X-ray detector in opposite directions to each other along the body axis of the subject while the X-ray tube and the X-ray detector are opposed to each other across the subject; an X-ray irradiation control unit that controls the X-ray tube to repeatedly irradiate X-rays while the X-ray tube and the X-ray detector are moved in opposite directions by the opposing movement mechanism; a projection image generating unit that generates a projection image based on a detection signal output by the X-ray detector for each X-ray irradiation by the X-ray tube; a first reconstruction processing unit that generates a provisional reconstructed image by performing reconstruction processing on the projection image for a first reconstruction range that is a range of the cutting height using a first reconstruction calculation method; an information amount calculation unit that calculates an information amount of the temporary reconstructed image for each cutting height; a display range determination unit that determines, from the first reconstruction range, a range of cutting heights that satisfies a predetermined first condition that the amount of information is appropriate for a reconstructed image for display, as a display range; a reconstruction range determination unit that determines, from the first reconstruction range, a range of cutting heights that satisfies a predetermined second condition that the amount of information is appropriate for a three-dimensional volume image, as a second reconstruction range; a second reconstruction processing unit that generates a three-dimensional volume image by performing reconstruction processing on the projection images for the second reconstruction range using a second reconstruction calculation method; a tomographic image generating unit that generates a tomosynthesis image by cutting the three-dimensional volume image generated for the second reconstruction range with respect to the display range; a tomographic image display unit that displays the tomosynthesis image generated for the display range; Equipped with the first condition and the second condition are set so that the second reconstruction range is wider than the display range; A tomosynthesis apparatus, wherein the first reconstruction calculation method is a calculation method that has a smaller calculation load than the second reconstruction calculation method.

8. 8. The tomosynthesis device according to claim 7, the first reconstruction calculation method is a filtered back projection method, A tomosynthesis apparatus, wherein the second reconstruction calculation method is an iterative reconstruction method.

9. The tomosynthesis apparatus according to claim 7 or 8, A tomosynthesis apparatus, wherein the amount of information is the variance of pixel values ​​in the provisionally reconstructed image.

10. An image processing device that performs image processing to generate a tomosynthesis image using projection images acquired by repeatedly irradiating X-rays from the X-ray tube while moving an X-ray tube and an X-ray detector that are arranged opposite to each other across a subject in a body axis direction of the subject, the image processing device comprising: a first reconstruction processing unit that generates a provisional reconstructed image by performing reconstruction processing on the projection image for a first reconstruction range that is a range of the cutting height using a first reconstruction calculation method; an information amount calculation unit that calculates an information amount of the temporary reconstructed image for each cutting height; a display range determination unit that determines, from the first reconstruction range, a range of cutting heights that satisfies a predetermined first condition that the amount of information is appropriate for a reconstructed image for display, as a display range; a reconstruction range determination unit that determines, from the first reconstruction range, a range of cutting heights that satisfies a predetermined second condition that the amount of information is appropriate for a three-dimensional volume image, as a second reconstruction range; a second reconstruction processing unit that generates a three-dimensional volume image by performing reconstruction processing on the projection images for the second reconstruction range using a second reconstruction calculation method; a tomographic image generating unit that generates the tomosynthesis image by cutting the three-dimensional volume image generated for the second reconstruction range with respect to the display range; a tomographic image display unit that displays the tomosynthesis image generated for the display range; Equipped with the first condition and the second condition are set so that the second reconstruction range is wider than the display range; An image processing device, wherein the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

11. 11. The image processing device according to claim 10, the first reconstruction calculation method is a filtered back projection method, The image processing device wherein the second reconstruction calculation method is an iterative reconstruction method.

12. 12. The image processing device according to claim 10, The image processing device, wherein the amount of information is the variance of pixel values ​​in the provisionally reconstructed image.

13. An image processing program that causes a computer to execute image processing for generating a tomosynthesis image using projection images acquired by repeatedly irradiating X-rays from an X-ray tube and an X-ray detector that are arranged opposite to each other across a subject while moving the X-ray tube and the X-ray detector in opposite directions along the body axis of the subject, the program comprising: a first reconstruction processing step of generating a provisional reconstructed image by performing reconstruction processing on the projection image for a first reconstruction range, which is a range of the cutting height, using a first reconstruction calculation method; an information amount calculation step of calculating an information amount of the temporary reconstructed image for each cutting height; a display range determination step of determining, from the first reconstruction range, a range of cutting heights that satisfies a predetermined first condition that the amount of information is appropriate for a reconstructed image for display, as a display range; a reconstruction range determination step of determining, from the first reconstruction range, a range of cutting heights that satisfies a predetermined second condition that the amount of information is appropriate for a three-dimensional volume image, as a second reconstruction range; a second reconstruction processing step of generating a three-dimensional volume image by performing reconstruction processing on the projection images for the second reconstruction range using a second reconstruction calculation method; a tomographic image generating step of generating the tomosynthesis image by cutting the three-dimensional volume image generated for the second reconstruction range with respect to the display range; a tomographic image display step of displaying the tomosynthesis image generated for the display range; and causing the computer to execute the above steps in sequence. the first condition and the second condition are set so that the second reconstruction range is wider than the display range; An image processing program in which the first reconstruction calculation method is a calculation method with a smaller calculation load than the second reconstruction calculation method.

14. 14. The image processing program according to claim 13, the first reconstruction calculation method is a filtered back projection method, The image processing program, wherein the second reconstruction calculation method is an iterative reconstruction method.

15. 15. The image processing program according to claim 13, An image processing program in which the amount of information is the variance of pixel values ​​in the provisionally reconstructed image.

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