Image processing apparatus, image processing method, and image processing program

Abstract

To provide an image processing device, image processing method and image processing program which can obtain a difference image in which a contrast agent is clearly imaged and an artifact component is suppressed.SOLUTION: A processor of an image processing device acquires a first low energy image and a first high energy image captured in such a state that a grid for removing a scattered ray is inserted to a space between a radiation source and a radiation detector and the radiation source is arranged at a first position at which the incident direction of the radiation becomes the normal direction with respect to the grid, acquires a second low energy image and a second high energy image captured in such a state that the grid is retracted from the space between the radiation source and the radiation detector and the radiation source is arranged at a second position, estimates the thickness of a subject from the first low energy image and the first high energy image, and generates a difference image showing a difference between the second high energy image and the second low energy image from the second low energy image and the second high energy image on the basis of the thickness.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present disclosure relates to an image processing apparatus, an image processing method, and an image processing program.

Background Art

[0002] In contrast imaging, radiation with different energies is radiated to a subject injected with a contrast agent to capture a low-energy image and a high-energy image, and a difference image showing the difference between the high-energy image and the low-energy image is generated, thereby generating a radiation image in which the contrast agent is emphasized. This technology is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when imaging is performed without using a grid, there is a problem that artifact components remain.

[0005] The present disclosure has been made in consideration of the above circumstances, and an object thereof is to provide an image processing apparatus, an image processing method, and an image processing program capable of obtaining a difference image in which a contrast agent is clearly shown and artifact components are suppressed.

Means for Solving the Problems

[0006] To achieve the above object, an image processing apparatus according to a first aspect of the present disclosure is an image processing apparatus that processes a radiation image captured by a radiation imaging apparatus that performs imaging to irradiate a subject in a state where a contrast agent is injected with radiation of a first energy from a radiation source and acquire a low-energy image with a radiation detector, and imaging to irradiate the subject in a state where the contrast agent is injected with radiation of a second energy higher than the first energy from the radiation source and acquire a high-energy image with the radiation detector. The image processing apparatus includes at least one processor. The processor acquires a first low-energy image and a first high-energy image captured by the radiation imaging apparatus in a state where a grid for removing scattered radiation is inserted between the radiation source and the radiation detector and the radiation source is disposed at a first position where the incident direction of the radiation with respect to the grid is the normal direction, acquires a second low-energy image and a second high-energy image captured by the radiation imaging apparatus in a state where the grid is retracted from between the radiation source and the radiation detector and the radiation source is disposed at a second position different from the first position, estimates the thickness of the subject from the first low-energy image and the first high-energy image, and generates a difference image indicating the difference between the second high-energy image and the second low-energy image from the second low-energy image and the second high-energy image based on the estimated thickness.

[0007] An image processing apparatus according to a second aspect of the present disclosure is the image processing apparatus according to the first aspect, wherein the processor removes an artifact component from each of the second high-energy image and the second low-energy image, and generates a difference image from the second low-energy image and the second high-energy image from which the artifact component has been removed.

[0008] An image processing apparatus according to a third aspect of the present disclosure is the image processing apparatus according to the first aspect, wherein the processor generates a difference image from the second low-energy image and the second high-energy image, and removes an artifact component from the difference image.

[0009] The image processing apparatus according to the fourth aspect of the present disclosure is the image processing apparatus according to any one of the first to third aspects, wherein the processor estimates the thickness from a difference image showing the difference between the first high-energy image and the first low-energy image.

[0010] The image processing apparatus according to the fifth aspect of the present disclosure is the image processing apparatus according to any one of the first to fourth aspects, wherein the processor identifies the position in the depth direction of an object of interest stained with a contrast agent from a difference image showing the difference between the first high-energy image and the first low-energy image and a difference image showing the difference between the second high-energy image and the second low-energy image.

[0011] The image processing apparatus according to the sixth aspect of the present disclosure is the image processing apparatus according to any one of the first to fifth aspects, wherein the artifact component is a component caused by the oblique incidence of radiation.

[0012] The image processing apparatus according to the seventh aspect of the present disclosure is the image processing apparatus according to any one of the first to fifth aspects, wherein the artifact component is a scattered ray component caused by scattered rays.

[0013] In addition, in order to achieve the above object, an image processing method according to an eighth aspect of the present disclosure is an image processing method in which a computer executes image processing of a radiation image captured by a radiation imaging apparatus that performs imaging to irradiate a subject in a state where a contrast agent is injected with radiation of a first energy from a radiation source and acquire a low-energy image with a radiation detector, and imaging to irradiate the subject in a state where the contrast agent is injected with radiation of a second energy higher than the first energy from the radiation source and acquire a high-energy image with the radiation detector, a grid for removing scattered radiation is inserted between the radiation source and the radiation detector, and a first low-energy image and a first high-energy image captured by the radiation imaging apparatus in a state where the radiation source is arranged at a first position where the incident direction of the radiation with respect to the grid is the normal direction are acquired, the grid is retracted from between the radiation source and the radiation detector, and a second low-energy image and a second high-energy image captured by the radiation imaging apparatus in a state where the radiation source is arranged at a second position different from the first position are acquired, the thickness of the subject is estimated from the first low-energy image and the first high-energy image, and a computer executes a process of generating a difference image showing the difference between the second high-energy image and the second low-energy image from the second low-energy image and the second high-energy image based on the estimated thickness.

[0014] Also, in order to achieve the above object, an image processing program according to a ninth aspect of the present disclosure causes a computer to execute image processing of a radiation image captured by a radiation image capturing apparatus that performs imaging to irradiate a subject in a state where a contrast agent is injected with radiation of a first energy from a radiation source and acquire a low-energy image with a radiation detector, and imaging to irradiate the subject in a state where the contrast agent is injected with radiation of a second energy higher than the first energy from the radiation source and acquire a high-energy image with the radiation detector, obtains a first low-energy image and a first high-energy image captured by the radiation image capturing apparatus in a state where a grid for removing scattered radiation is inserted between the radiation source and the radiation detector and the radiation source is disposed at a first position where the incident direction of the radiation with respect to the grid is the normal direction, obtains a second low-energy image and a second high-energy image captured by the radiation image capturing apparatus in a state where the grid is retracted from between the radiation source and the radiation detector and the radiation source is disposed at a second position different from the first position, estimates the thickness of the subject from the first low-energy image and the first high-energy image, and causes the computer to execute a process of generating a difference image showing the difference between the second high-energy image and the second low-energy image from the second low-energy image and the second high-energy image based on the estimated thickness.

Advantages of the Invention

[0015] According to the present disclosure, it is possible to obtain a difference image in which the contrast agent is clearly shown and the artifact component is suppressed.

Brief Description of the Drawings

[0016]

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Best Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present embodiments do not limit the present invention.

[0018] First, an example of the overall configuration of the radiation image imaging system according to the present embodiment will be described. FIG. 1 shows a configuration diagram representing an example of the overall configuration of the radiation image imaging system 1 according to the present embodiment. As shown in FIG. 1, the radiation image imaging system 1 according to the present embodiment includes a mammography apparatus 10 and a console 12. The mammography apparatus 10 according to the present embodiment is an example of the radiation image imaging apparatus of the present disclosure. Further, the console 12 according to the present embodiment is an example of the image processing apparatus of the present disclosure.

[0019] First, the mammography apparatus 10 according to the present embodiment will be described. FIG. 2 shows a side view representing an example of the appearance of the mammography apparatus 10 according to the present embodiment. Note that FIG. 2 shows an example of the appearance when the mammography apparatus 10 is viewed from the right side of the subject.

[0020] The mammography apparatus 10 according to the present embodiment is an apparatus that irradiates radiation R (for example, X-rays) onto the breast of a subject and captures a radiation image of the breast with the breast as the subject. Note that the mammography apparatus 10 may be an apparatus that captures an image of the breast of a subject not only in a state where the subject is standing (standing state) but also in a state where the subject is sitting on a chair (including a wheelchair) or the like (sitting state).

[0021] The operation unit 26 is provided, for example, as a plurality of switches on the imaging table 30 of the mammography apparatus 10 or the like. Note that the operation unit 26 may be provided as a touch panel type switch, or may be provided as a foot switch that is operated by a user such as a doctor and a technician with their feet.

[0022] As shown in FIG. 2, the mammography apparatus 10 of the present embodiment includes a control unit 20, a storage unit 22, and an I / F (Interface) unit 24, the details of which will be described later, inside the imaging table 30.

[0023] Also, as shown in FIG. 2, a radiation detector 28 is disposed inside the imaging table 30. In the mammography apparatus 10 of the present embodiment, when performing imaging, the breast of the subject is positioned by the user on the imaging surface 30A of the imaging table 30. The radiation detector 28 detects the radiation R that has passed through the breast of the subject and the imaging table 30, generates a radiation image based on the detected radiation R, and outputs image data representing the generated radiation image. The type of the radiation detector 28 of the present embodiment is not particularly limited. For example, it may be an indirect conversion type radiation detector that converts radiation R into light and then converts the converted light into electric charge, or a direct conversion type radiation detector that directly converts radiation R into electric charge.

[0024] Also, a grid 27 for removing scattered radiation is provided between the radiation source 37R and the radiation detector 28. As shown in FIG. 3, the grid 27 of the present embodiment is movable between a position where it is inserted between the radiation source 37R and the radiation detector 28 (hereinafter referred to as the "insertion position") and a position where it is retracted from between the radiation source 37R and the radiation detector 28 (hereinafter referred to as the "retracted position") by a grid moving unit 31 (see FIG. 5). As an example, in the mammography apparatus 10 of the present embodiment, as shown in FIG. 3, the grid 27 is moved from the insertion position to the retracted position by sliding it in the direction of the compression unit 36.

[0025] As shown in FIG. 3, at the insertion position, specifically, a grid 27 is disposed substantially parallel to the radiation detector 28 between the imaging surface 30A of the imaging table 30 and the radiation detector 28, and the normal to the detection surface 28A of the radiation detector 28 and the normal to the grid 27 are the same (see the normal CL in FIGS. 4A and 4B). At the insertion position, the radiation R irradiated from the radiation source 37R is irradiated onto the radiation detector 28 through the grid 27. On the other hand, as shown in FIG. 3, at the retracted position, the radiation R irradiated from the radiation source 37R is irradiated onto the radiation detector 28 without passing through the grid 27.

[0026] The radiation irradiation unit 37 includes a radiation source 37R. As shown in FIG. 2, the radiation irradiation unit 37 is provided on the arm portion 32 together with the imaging table 30 and the compression unit 36. As shown in FIG. 2, a face guard 38 is detachably provided at a position close to the subject on the arm portion 32 corresponding to the lower side of the radiation irradiation unit 37. The face guard 38 is a protection member for protecting the subject from the radiation R emitted from the radiation source 37R.

[0027] As shown in FIG. 2, the mammography apparatus 10 of the present embodiment includes an arm portion 32, a base 34, and a shaft portion 35. The arm portion 32 is held by the base 34 so as to be movable in the vertical direction (Z-axis direction). Further, the arm portion 32 can be rotated with respect to the base 34 by the shaft portion 35. The shaft portion 35 is fixed to the base 34, and the shaft portion 35 and the arm portion 32 rotate integrally.

[0028] Gears are provided on the shaft portion 35 and the compression unit 36 respectively. By switching the meshing state and non-meshing state of these gears, the compression unit 36 and the shaft portion 35 are connected and rotated integrally, and the shaft portion 35 is separated from the compression unit 36 and the imaging table 30 and idles. Note that the switching of the transmission and non-transmission of power of the shaft portion 35 is not limited to the above gears, and various mechanical elements can be used.

[0029] The arm portion 32, the imaging table 30, and the compression unit 36 are each rotatable relative to the base 34 about the shaft portion 35 as a rotation axis. In the present embodiment, engaging portions (not shown) are provided on the base 34, the arm portion 32, the imaging table 30, and the compression unit 36, respectively. By switching the state of these engaging portions, the arm portion 32, the imaging table 30, and the compression unit 36 are each connected to the base 34. One or both of the arm portion 32, the imaging table 30, and the compression unit 36 connected to the shaft portion 35 rotate integrally about the shaft portion 35.

[0030] The compression unit 36 is provided with a compression plate drive unit 41 that moves the compression plate 40 in the vertical direction (Z-axis direction). The compression plate 40 of the present embodiment has a function of compressing the breast of the subject. The support portion 46 of the compression plate 40 is detachably attached to the compression plate drive unit 41, moves in the vertical direction (Z-axis direction) by the compression plate drive unit 41, and compresses the breast of the subject between the compression plate 40 and the imaging table 30.

[0031] The mammography apparatus 10 of the present embodiment has a function of performing general imaging and a function of performing so-called contrast imaging in which imaging is performed with a contrast agent injected into the breast of the subject. In the present embodiment, "contrast imaging" refers to imaging performed with a contrast agent injected into the breast (subject 9) of the subject, and "general imaging" refers to imaging other than contrast imaging.

[0032] Note that the mammography apparatus 10 of the present embodiment has a CEDM (Contrast Enhanced Digital Mammography) function of performing contrast imaging by energy subtraction imaging as a function of performing contrast imaging.

[0033] Further, the mammography apparatus 10 of the present embodiment has a function of performing so-called stereo imaging in which two types of contrast imaging, a first contrast imaging and a second contrast imaging, in which the positions of the radiation sources 37R are different, are performed as contrast imaging. The two types of contrast imaging will be described with reference to FIGS. 4A and 4B.

[0034] As shown in FIG. 4A, the first contrast imaging is contrast imaging performed with the radiation source 37R at a first position where the incident direction of the radiation R is the normal direction with respect to the grid 27 and the radiation detector 28. That is, in the first contrast imaging, the normal CL with respect to the grid 27 and the detection surface 28A of the radiation detector 28 coincides with the radiation axis RC. In the first contrast imaging, the breast W in a state where a contrast agent is injected is irradiated with radiation R of a first energy to capture a first low-energy image. Also, in the first contrast imaging, the breast W is irradiated with radiation R of a second energy higher than the first energy to capture a first high-energy image. In the present embodiment, a radiation image captured by irradiating with radiation R of the first energy is referred to as a "low-energy image", and a radiation image captured by irradiating with radiation R of the second energy is referred to as a "high-energy image". Also, when collectively referring to mammogram images obtained by the mammography apparatus 10 without distinguishing types such as low-energy images, high-energy images, and differential images described later, it is simply referred to as a "radiation image".

[0035] For example, as a contrast agent used for contrast imaging, an iodine contrast agent having a k absorption edge of 32 keV is generally used. In the contrast imaging in this case, a low-energy image is captured by irradiating with radiation R of a first energy lower than the k absorption edge of the iodine contrast agent. Also, a high-energy image is captured by irradiating with radiation R of a second energy higher than the k absorption edge of the iodine contrast agent.

[0036] The absorption characteristics of radiation are different between the contrast agent and body tissues such as the breast. Therefore, in the high-energy image captured as described above, in addition to body tissues such as the breast and fat being shown, the contrast agent is clearly shown. Also, in the low-energy image, the contrast agent is hardly shown, and body tissues such as the breast are clearly shown. Therefore, a differential image showing the difference between the low-energy image and the high-energy image can be an image in which the breast structure is removed and the contrast agent is clearly shown.

[0037] As shown in FIG. 4A, when performing the first contrast imaging, the grid 27 is in the insertion position, and the grid 27 is inserted between the radiation source 37R and the radiation detector 28. When the grid 27 is in the insertion position, the radiation R irradiated from the radiation source 37R and transmitted through the breast W is irradiated onto the detection surface 28A of the radiation detector 28 via the grid 27. Therefore, the radiation image obtained by the radiation detector 28 is an image in which the scattered ray component due to the scattered rays and the component due to the oblique incidence of the radiation are suppressed by the grid 27. Accordingly, the first low-energy image and the first high-energy image are images in which the artifact components including the scattered ray component and the component due to the oblique incidence of the radiation are suppressed.

[0038] On the other hand, as shown in FIG. 4B, the second contrast imaging is contrast imaging in which the radiation source 37R is at a position different from the first position. In other words, the second contrast imaging is contrast imaging in which the radiation R irradiated from the radiation source 37R is obliquely incident on the detection surface 28A of the radiation detector 28. That is, in the second contrast imaging, the normal CL of the detection surface 28A of the radiation detector 28 and the radiation axis RC do not coincide. In the second contrast imaging, the breast W in a state where the contrast agent is injected is irradiated with the radiation R of the first energy to capture the second low-energy image. Further, in the second contrast imaging, the radiation R of the second energy is irradiated to capture the second high-energy image.

[0039] As shown in FIG. 4B, when performing the second contrast imaging, the grid 27 is in the retracted position and is retracted from between the radiation source 37R and the radiation detector 28. When the grid 27 is in the retracted position, the radiation R irradiated from the radiation source 37R and transmitted through the breast W is irradiated onto the detection surface 28A of the radiation detector 28 without passing through the grid 27. Therefore, the radiation image obtained by the radiation detector 28 is an image including the scattered component due to the scattered rays and the oblique incidence component due to the oblique incidence of the radiation. Accordingly, the second low-energy image and the second high-energy image are images including the scattered ray component and the oblique incidence component, which are artifact components. Such artifact components appear as white-looking images in the radiation image.

[0040] An explanation will be given for such artifact components. As described above, the artifact components mainly include a scattered ray component and an oblique incidence component caused by the oblique incidence of radiation.

[0041] First, with reference to FIG. 5A, an explanation will be given for the scattered ray component caused by the scattered rays of the radiation R. FIG. 5A shows a schematic diagram for explaining an example of an artifact due to the scattered ray component of the radiation R. In the image of the inner region of the breast W, the dose increases because the scattered rays generated by the breast W overlap. Therefore, the pixel value of the image of the inner region of the breast W becomes large, and the image becomes black. On the other hand, in the image of the end region of the breast W, since some of the scattered rays escape outside the breast W, the dose decreases. Therefore, the image of the cool air on the end side of the breast W, in other words, on the skin line side, has a smaller pixel value and the image becomes smaller. In other words, in the vicinity of the skin line of the breast W, the pixel value becomes smaller compared to the inner region. In the case of the breast W, since it is difficult for the scattered rays to escape outside on the chest wall side, the dose increases and the pixel value becomes large, so the image tends to be black. On the other hand, on the nipple side, since the scattered rays easily escape outside, the dose decreases and the pixel value becomes small, so the image tends to be white. Therefore, the scattered ray component of the radiation R becomes an artifact component. Note that the thicker the thickness h of the breast W, the more scattered rays are generated.

[0042] Next, with reference to FIG. 5B, an explanation will be given for the oblique incidence component caused by the oblique incidence of the radiation R on the breast W. FIG. 5B shows a schematic diagram for explaining an example of an artifact due to the oblique incidence component of the radiation R. When the radiation R1 with an incident angle of 0 degrees is incident from the radiation source 37R on the breast W with a thickness h, the length of the transmission path through which the radiation R1 passes through the breast W is h. On the other hand, when the radiation R2 with an incident angle of θ is incident from the radiation source 37R, the length of the transmission path is h / cosθ. Therefore, when the radiation R2 is incident, the transmission path is longer by the length x represented by the following formula (1) compared to the case when the radiation R1 is incident. x=(1 / cosθ - 1)×h ···(1)

[0043] When the transmission path becomes longer, the dose of the radiation R reaching the radiation detector 28 decreases. Therefore, the dose of the radiation R2 passing through the breast W and reaching the radiation detector 28 is smaller than that of the radiation R1. Since the dose decreases, the image generated by the radiation detector 28 in response to the radiation R2 becomes whiter than the image generated by the radiation detector 28 in response to the radiation R1. As shown in the above formula (1), the pixel value of the radiation image decreases in response to the oblique incidence of the radiation R. Also, as the thickness h of the breast W increases, the transmission path becomes longer and the pixel value of the radiation image decreases. Therefore, the oblique incidence component of the radiation R becomes an artifact component.

[0044] Furthermore, with reference to FIG. 6, the configurations of the mammography apparatus 10 and the console 12 will be described. FIG. 6 shows a block diagram representing an example of the configurations of the mammography apparatus 10 and the console 12 of the present embodiment. As shown in FIG. 6, the mammography apparatus 10 of the present embodiment includes a control unit 20, a storage unit 22, an I / F unit 24, an operation unit 26, a grid movement unit 31, a radiation source movement unit 39, and a compression plate drive unit 41, which are connected to each other via a bus 29 such as a system bus or a control bus so as to be able to exchange various information.

[0045] The control unit 20 controls the overall operation of the mammography apparatus 10 in response to the control of the console 12. The control unit 20 includes a CPU (Central Processing Unit) 20A, a ROM (Read Only Memory) 20B, and a RAM (Random Access Memory) 20C. The ROM 20B stores in advance various programs including a shooting processing program for controlling the shooting of radiation images, which is executed by the CPU 20A. The RAM 20C temporarily stores various data.

[0046] The storage unit 22 stores the image data of the radiation image captured by the radiation detector 28, as well as various other information. Specific examples of the storage unit 22 include an HDD (Hard Disk Drive), an SSD (Solid State Drive), and the like. The I / F unit 24 communicates various information with the console 12 through wireless communication or wired communication. The image data of the radiation image captured by the radiation detector 28 in the mammography apparatus 10 is transmitted to the console 12 through the I / F unit 24 by wireless communication or wired communication.

[0047] As described above, the grid moving unit 31 has a function of moving the grid 27 between the insertion position and the retracted position according to the instruction of the control unit 20. The radiation source moving unit 39 has a function of moving the position of the radiation source 37R from the first position to the second position or from the second position to the first position by rotating the shaft portion 35 to rotate the arm portion 32. As described above, the compression plate driving unit 41 has a function of moving the compression plate 40 in the vertical direction (the direction of compressing the breast ~ the direction away from the breast).

[0048] On the other hand, the console 12 of the present embodiment has a function of controlling the mammography apparatus 10 by using the imaging order and various information acquired from the RIS (Radiology Information System) 2 or the like via a wireless communication LAN (Local Area Network) or the like, and the instructions given by the user through the operation unit 56 or the like.

[0049] The console 12 of the present embodiment is, for example, a server computer. As shown in FIG. 5, the console 12 includes a control unit 50, a storage unit 52, an I / F unit 54, an operation unit 56, and a display unit 58. The control unit 50, the storage unit 52, the I / F unit 54, the operation unit 56, and the display unit 58 are connected to each other via a bus 59 such as a system bus or a control bus so as to be able to exchange various information.

[0050] The control unit 50 of the present embodiment controls the overall operation of the console 12. The control unit 50 includes a CPU 50A, a ROM 50B, and a RAM 50C. In the ROM 50B, various programs including a contrast imaging processing program 51A and a differential image generation program 51B, which are executed by the CPU 50A and will be described later, are stored in advance. The RAM 50C temporarily stores various data. The CPU 50A of the present embodiment is an example of the processor of the present disclosure. The differential image generation program 51B of the present embodiment is an example of the image processing program of the present disclosure.

[0051] The storage unit 52 stores image data of radiation images taken by the mammography apparatus 10, as well as various other information. Specific examples of the storage unit 52 include HDDs, SSDs, and the like.

[0052] The operation unit 56 is used for the user to input instructions and various information related to the taking of radiation images, including irradiation instructions for radiation R. The operation unit 56 is not particularly limited, and examples include various switches, touch panels, touch pens, and mice. The display unit 58 displays various information. Note that the operation unit 56 and the display unit 58 may be integrated into a touch panel display.

[0053] The I / F unit 54 communicates various information between the mammography apparatus 10 and the RIS 2 through wireless communication or wired communication. In the radiation image imaging system 1 of the present embodiment, the image data of the radiation image taken by the mammography apparatus 10 is received by the console 12 from the mammography apparatus 10 through the I / F unit 54 by wireless communication or wired communication.

[0054] Furthermore, FIG. 7 shows a functional block diagram of an example of the configuration of the console 12 of the present embodiment. As shown in FIG. 7, the console 12 includes a first acquisition unit 60, a second acquisition unit 62, a first difference image generation unit 64, a thickness estimation unit 66, a second difference image generation unit 68, and a display control unit 70. As an example, in the console 12 of the present embodiment, the CPU 50A of the control unit 50 executes the difference image generation program 51B stored in the ROM 50B, so that the CPU 50A functions as the first acquisition unit 60, the second acquisition unit 62, the first difference image generation unit 64, the thickness estimation unit 66, the second difference image generation unit 68, and the display control unit 70.

[0055] The first acquisition unit 60 has a function of acquiring a first low-energy image and a first high-energy image obtained by the first contrast imaging. Specifically, the first acquisition unit 60 acquires image data representing the first low-energy image and image data representing the first high-energy image, which are taken in the first contrast imaging by the radiation detector 28 of the mammography apparatus 10, via the I / F unit 24 and the I / F unit 54. The first acquisition unit 60 outputs the acquired first low-energy image and first high-energy image to the first difference image generation unit 64.

[0056] The first difference image generation unit 64 has a function of generating a first difference image showing the difference between the first high-energy image and the first low-energy image. As an example, the first difference image generation unit 64 of the present embodiment generates the image data of the first difference image by subtracting, for each corresponding pixel, the image data obtained by multiplying the first low-energy image by a predetermined coefficient from the image data obtained by multiplying the first high-energy image by a predetermined coefficient. As an example of the weight coefficient, a weight coefficient based on the absorption coefficient μg of the breast for the radiation R of the first energy, the absorption coefficient μa of fat for the radiation R of the first energy, the absorption coefficient μg of the breast for the radiation R of the second energy, and the absorption coefficient μa of fat for the radiation R of the second energy is used. Specifically, the weight coefficient γ obtained by the following formula (2) is used. L , the absorption coefficient μa of fat for the radiation R of the first energy L , the absorption coefficient μg of the breast for the radiation R of the second energy H , and the absorption coefficient μa of fat for the radiation R of the second energy H is used. Specifically, the weight coefficient γ obtained by the following formula (2) is used. γ=(μgL -μa L ) / (μg H -μa H ) ···(2)

[0057] The first difference image is an image in which breast tissue is removed and the contrast agent is emphasized. The first difference image generation unit 64 outputs the generated first difference image to the thickness estimation unit 66 and the display control unit 70.

[0058] The thickness estimation unit 66 has a function of estimating the thickness of the breast from the first low-energy image and the first high-energy image. In other words, the thickness estimation unit 66 has a function of estimating the thickness of the breast in a state compressed by the compression plate 40 based on the first difference image. As an example, the thickness estimation unit 66 in the present embodiment derives the thickness of the breast W by calculating a coefficient at which the contrast between the mammary gland and fat disappears. As a specific method, for example, the method described in Japanese Patent No. 6667462 can be applied. Note that the method by which the thickness estimation unit 66 estimates the thickness of the breast is not limited to this embodiment, and existing methods can be used. For example, as described in Japanese Unexamined Patent Application Publication No. 2007-300964, the thickness of the breast may be estimated by simulating the scattering of radiation based on thickness information and the density distribution of the subject. The thickness estimation unit 66 outputs the estimated thickness of the breast to the second difference image generation unit 68.

[0059] Also, the second acquisition unit 62 has a function of acquiring the second low-energy image and the second high-energy image obtained by the second contrast imaging. Specifically, the second acquisition unit 62 acquires image data representing the second low-energy image and image data representing the second high-energy image, which are captured in the second contrast imaging by the radiation detector 28 of the mammography apparatus 10, via the I / F unit 24 and the I / F unit 54. The second acquisition unit 62 outputs the acquired second low-energy image and second high-energy image to the second difference image generation unit 68.

[0060] The second difference image generation unit 68 has a function of generating a second difference image showing the difference between a second high-energy image with artifact components suppressed and a second low-energy image based on the thickness of the breast estimated by the thickness estimation unit 66. As an example, the second difference image generation unit 68 of the present embodiment generates a second difference image from the second low-energy image and the second high-energy image in the same manner as the above-described first difference image generation unit 64 generates the first difference image. Further, the second difference image generation unit 68 removes the above-described artifact components from the generated second difference image based on the thickness of the breast estimated by the thickness estimation unit 66. The method by which the second difference image generation unit 68 removes the artifact components from the second difference image is not particularly limited. As an example, the second difference image generation unit 68 of the present embodiment applies a low-pass filter corresponding to the scattered ray component and the obliquely incident component according to the thickness of the breast to the second difference image to remove the scattered ray component and the obliquely incident component.

[0061] The scattered ray component and the obliquely incident component occur as low-frequency non-uniformities. Therefore, by applying a low-pass filter that removes the low-frequency component corresponding to the scattered ray component and the obliquely incident component to the second difference image, the scattered ray component and the obliquely incident component are removed from the second difference image. Note that the degree of the scattered ray component and the obliquely incident component changes according to the thickness of the breast. Specifically, as the breast becomes thicker, the scattered ray component and the obliquely incident component increase. Therefore, it is preferable to apply a low-pass filter that removes lower frequency components as the breast becomes thicker. The second difference image generation unit 68 of the present embodiment prepares a plurality of low-pass filters corresponding to the thickness of the breast. Then, the second difference image generation unit 68 applies a low-pass filter corresponding to the thickness of the breast estimated by the thickness estimation unit 66 to remove the scattered ray component and the obliquely incident component from the second difference image. Note that the threshold value of the low-pass filter may be changeable according to the scattered ray component, the obliquely incident component, a user's instruction, or the like. In this way, the second difference image generation unit 68 generates a second difference image with artifact components suppressed. The second difference image generation unit 68 outputs the generated second difference image to the display control unit 70.

[0062] The display control unit 70 has a function of causing the display unit 58 to display the first difference image and the second difference image.

[0063] Next, the operation of the console 12 in the contrast imaging by the radiation imaging system 1 of the present embodiment will be described with reference to the drawings. FIG. 8 shows a flowchart illustrating an example of the flow of contrast imaging by the radiation imaging system 1 of the present embodiment. When performing contrast imaging, first, as shown in step S10 of FIG. 8, the user injects a contrast agent into the breast to be imaged. Next, as shown in step S12, the user positions the breast of the subject on the imaging table 30 of the mammography apparatus 10 and compresses the breast with the compression plate 40.

[0064] Next, in step S14, the first contrast imaging process shown in FIG. 9 for performing the first contrast imaging described above is performed by the console 12 using the mammography apparatus 10. Since the first contrast imaging process and the second contrast imaging process, the details of which will be described later, are the same processes, both will be described with reference to FIG. 9.

[0065] As described above, in the first contrast imaging (see FIGS. 3 and 4A), the grid 27 is in the insertion position, and the grid 27 is inserted between the radiation source 37R and the detection surface 28A of the radiation detector 28.

[0066] As an example, the console 12 of the present embodiment executes the first contrast imaging process shown as an example in FIG. 9 by the CPU 50A of the control unit 50 executing the contrast imaging process program 51A stored in the ROM 50B. FIG. 9 shows a flowchart illustrating an example of the flow of the first contrast imaging process executed in the console 12 of the present embodiment.

[0067] In step S100 of FIG. 9, the control unit 50 determines whether or not an irradiation instruction for radiation R has been received. The determination in step S100 remains a negative determination until an irradiation instruction is received. On the other hand, when an irradiation instruction is received, the determination in step S100 becomes an affirmative determination, and the process proceeds to step S102.

[0068] In step S102, the control unit 50 outputs an instruction for irradiating the radiation R of the first energy to the mammography apparatus 10. In the mammography apparatus 10, based on the instruction input from the console 12, the control unit 20 irradiates the radiation R of the first energy from the radiation source 37R toward the breast, and the first low-energy image is taken by the radiation detector 28.

[0069] In the next step S104, the control unit 50 outputs an instruction for irradiating the radiation R of the second energy to the mammography apparatus 10. In the mammography apparatus 10, based on the instruction input from the console 12, the control unit 20 irradiates the radiation R of the second energy from the radiation source 37R toward the breast, and the first high-energy image is taken by the radiation detector 28. When the process of step S104 ends, the first contrast imaging process ends.

[0070] Note that the order of taking the first low-energy image and the first high-energy image is not limited to this embodiment, and the first high-energy image may be taken before the first low-energy image. That is, the order of the process of step S102 and the process of step S104 may be swapped.

[0071] When the first contrast imaging process shown in FIG. 9 ends in this way, the first contrast imaging process of step S14 shown in FIG. 8 ends. Note that the control unit 50 may notify the user that the first contrast imaging has ended.

[0072] In the next step S16, the mammography apparatus 10 moves the grid 27 from the insertion position to the retracted position by the grid moving unit 31 and retracts it from between the radiation source 37R and the radiation detector 28 (see FIGS. 3 and 4A).

[0073] In the next step S18, the mammography apparatus 10 moves the radiation source 37R to the second position by the radiation source moving unit 39 (see FIGS. 3 and 4A).

[0074] Note that the order of the process in step S16 and the process in step S18 may be swapped, or the process in step S16 and the process in step S18 may be performed in parallel.

[0075] In the next step S20, the console 12 performs a second contrast imaging process for performing the second contrast imaging described above by the mammography apparatus 10. As described above, the flow of the second contrast imaging process is the same as that of the first contrast imaging process, and the second contrast imaging process shown in FIG. 9 is performed by the console 12.

[0076] Specifically, in the second contrast imaging process, in step S100 of FIG. 9, the control unit 50 determines whether or not an irradiation instruction for the radiation R has been received. The determination in step S100 remains a negative determination until an irradiation instruction is received. On the other hand, when an irradiation instruction is received, the determination in step S100 becomes an affirmative determination, and the process proceeds to step S102.

[0077] In step S102, the control unit 50 outputs an instruction for irradiating the radiation R of the first energy to the mammography apparatus 10. In the mammography apparatus 10, a second low-energy image is taken by the radiation detector 28.

[0078] In the next step S104, the control unit 50 outputs an instruction for irradiating the radiation R of the second energy to the mammography apparatus 10. In the mammography apparatus 10, a second high-energy image is taken by the radiation detector 28. When the process in step S104 ends, the second contrast imaging process ends.

[0079] When the second contrast imaging process shown in FIG. 9 ends in this way, the second contrast imaging process in step S20 shown in FIG. 8 ends. Note that the control unit 50 may notify the user that the second contrast imaging has ended.

[0080] In the next step S22, the console 12 performs the differential image generation process shown in FIG. 10. As an example, in the console 12 of the present embodiment, the CPU 50A of the control unit 50 executes the differential image generation program 51B stored in the ROM 50B to execute the differential image generation process shown as an example in FIG. 10. FIG. 10 shows a flowchart representing an example of the flow of the differential image generation process executed in the console 12 of the present embodiment.

[0081] In step S200, as described above, the first acquisition unit 60 acquires the first low-energy image and the first high-energy image obtained by the first contrast imaging.

[0082] In the next step S202, the first differential image generation unit 64 generates a first differential image from the first low-energy image and the first high-energy image. As described above, the first differential image generation unit 64 of the present embodiment generates the image data of the first differential image by subtracting, for each corresponding pixel, the image data obtained by multiplying the first low-energy image by a predetermined coefficient from the image data obtained by multiplying the first high-energy image by a predetermined coefficient.

[0083] In the next step S204, the thickness estimation unit 66 estimates the thickness of the breast based on the first differential image generated in step S204. As described above, the thickness estimation unit 66 of the present embodiment derives the thickness of the breast by calculating the coefficient at which the contrast between the mammary gland and the fat disappears in the first differential image.

[0084] In this way, by the processes of steps S200 to S204, the thickness of the breast is estimated from the first low-energy image and the first high-energy image obtained by the first contrast imaging performed using the grid.

[0085] In the next step S206, the second acquisition unit 62 acquires the second low-energy image and the second high-energy image obtained by the second contrast imaging, as described above.

[0086] In the next step S208, the second difference image generation unit 68 generates a second difference image including an artifact component from the second low-energy image and the second high-energy image. As described above, the second difference image generation unit 68 of the present embodiment multiplies the image data obtained by multiplying the second low-energy image by a predetermined coefficient by the corresponding pixel from the image data obtained by multiplying the second high-energy image by a predetermined coefficient, thereby generating the image data of the second difference image.

[0087] In the next step S210, the second difference image generation unit 68 removes the artifact component from the second difference image generated in the step S208 based on the breast thickness estimated in the step S204. As described above, the second difference image generation unit 68 of the present embodiment selects a low-pass filter corresponding to the breast thickness estimated by the thickness estimation unit 66 from a plurality of low-pass filters prepared according to the breast thickness, and applies the selected low-pass filter to the second difference image to remove the scattered ray component and the obliquely incident component.

[0088] In the next step S212, the display control unit 70 performs control to cause the display unit 58 to display the first difference image generated in the step S202 and the second difference image from which the artifact component has been removed in the step S210.

[0089] Note that the display form for displaying the first difference image and the second difference image on the display unit 58 is not particularly limited. For example, the second difference image before removing the artifact component, that is, the second difference image including the artifact component generated by the process of step S208 above, may also be used as a form to be displayed on the display unit 58. Also, the first difference image and the second difference image may be arranged side by side for medical use without overlapping, or may be arranged side by side in a state where a part of them is overlapped. Further, either one of the first difference image and the second difference image may be displayed on the display unit 58 in a form that can be switched according to a user's instruction. Note that the first low-energy image, the first high-energy image, the first difference image, the second low-energy image, the second high-energy image, the second difference image including the artifact component, and the second difference image from which the artifact component has been removed, etc., may also be stored in the storage unit 52 of the console 12 or in a PACS (Picture Archiving and Communication Systems), etc.

[0090] When the process of step S212 ends in this way, the difference image generation process shown in FIG. 10 ends, and the difference image generation process of step S22 shown in FIG. 8 ends.

[0091] When the contrast imaging being performed is stereo imaging for biopsy, the user reads the first difference image and the second difference image displayed on the display unit 28 and performs sampling of the lesion while confirming the position of the lesion.

[0092] In the next step S24, the compression of the breast is released. Specifically, the control unit 50 outputs an instruction to move the compression plate 40 in a direction away from the imaging table 30 to the mammography apparatus 10. The mammography apparatus 10 moves the compression plate 40 in a direction away from the imaging table 30 based on the input instruction. Thereby, the compression of the breast is released. Note that the release of the compression of the breast may be performed according to a user's instruction or may be automatically performed according to the end of the contrast imaging.

[0093] In the next step S26, the mammography apparatus 10 moves the grid 27 to the insertion position by the grid moving unit 31 and inserts it between the radiation source 37R and the radiation detector 28. In the present embodiment, the insertion position of the grid 27 is set as the initial position. Therefore, the mammography apparatus 10 moves the grid 27 that has moved to the retracted position after the second contrast imaging to the insertion position, which is the initial position, by the grid moving unit 31.

[0094] In the next step S28, the mammography apparatus 10 moves the radiation source 37R to the first position by the radiation source moving unit 39. In the present embodiment, the first position of the radiation source 37R is set as the initial position. Therefore, the mammography apparatus 10 moves the radiation source 37R that has moved to the second position after the second contrast imaging to the first position, which is the initial position, by the radiation source moving unit 39.

[0095] When the process of step S28 is completed, a series of processes related to the contrast imaging in the embodiment shown in FIG. 8 is completed.

[0096] As described above, according to the present embodiment, based on the thickness of the breast estimated from the first difference image showing the difference between the first high-energy image and the first low-energy image in which the artifact component is suppressed by the grid 27, a second difference image in which the artifact component is removed is obtained. Therefore, according to the present embodiment, a difference image in which the contrast agent is clearly shown and the artifact component is suppressed can be obtained.

[0097] Note that the above embodiment is an example, and various modifications are possible. For example, the following modifications may be made.

[0098] (Modification Example 1: Modification Example of Difference Image Generation Process) In the difference image generation process (see FIG. 10) of the above embodiment, the form of removing the artifact component from the second difference image has been described. In this modification example, the form of removing the artifact component from the second low-energy image and the second high-energy image will be described.

[0099] The second difference image generation unit 68 of the present embodiment removes the artifact component from each of the second low-energy image and the second high-energy image based on the thickness of the breast estimated by the thickness estimation unit 66.

[0100] Note that the method for removing the artifact component from the second low-energy image and the method for removing the artifact component from the second high-energy image by the second difference image generation unit 68 are not particularly limited. For example, the second difference image generation unit 68 applies a low-pass filter corresponding to the scattered ray component according to the breast thickness and a low-pass filter corresponding to the obliquely incident component to each of the second low-energy image and the second high-energy image to remove the artifact component, in the same manner as the method of removing the artifact component from the second difference image. Note that the low-pass filter applied to the second low-energy image and the low-pass filter applied to the second high-energy image may be the same or different.

[0101] FIG. 11 shows a flowchart representing an example of the flow of the difference image generation process of this modified example. The difference image generation process shown in FIG. 11 is different from the difference image generation process (see FIG. 10) of the above embodiment in that it includes the processes of steps S207 and S209 instead of the processes of steps S208 and S210.

[0102] In step S207 of FIG. 11, the second difference image generation unit 68 removes artifact components from each of the second low-energy image and the second high-energy image generated in step S206 based on the breast thickness estimated in step S204 above. As described above, the second difference image generation unit 68 selects a low-pass filter corresponding to the breast thickness estimated by the thickness estimation unit 66 from a plurality of low-pass filters prepared according to the breast thickness, and applies the selected low-pass filter to the second low-energy image to remove scattered ray components and obliquely incident components. Further, the second difference image generation unit 68 selects a low-pass filter corresponding to the breast thickness estimated by the thickness estimation unit 66 from a plurality of low-pass filters prepared according to the breast thickness, and applies the selected low-pass filter to the second high-energy image to remove scattered ray components and obliquely incident components.

[0103] In the next step S209, the second difference image generation unit 68 generates a second difference image with the artifact components removed from the second low-energy image and the second high-energy image with the artifact components removed in step S207 above. The second difference image generation unit 68 generates the image data of the second difference image with the artifact components removed by subtracting, for each corresponding pixel, the image data obtained by multiplying the second low-energy image with the artifact components removed by a predetermined coefficient from the image data obtained by multiplying the second high-energy image with the artifact components removed by the predetermined coefficient.

[0104] Thus, according to this modification example, since the second difference image is generated from the second low-energy image and the second high-energy image with the artifact components removed, the generated second difference image is the second difference image with the artifact components removed.

[0105] (Modification Example 2: Tomosynthesis Imaging) In the above-described embodiment, the form in which the technology of the present disclosure is applied to stereo imaging has been described. In this modification example, the form in which the technology of the present disclosure is applied to tomosynthesis imaging will be described.

[0106] The mammography apparatus 10 of the present embodiment has a function of performing tomosynthesis imaging. When performing tomosynthesis imaging with the mammography apparatus 10, the radiation source 37R is sequentially moved to each of a plurality of irradiation positions with different irradiation angles by the rotation of the arm portion 32. The radiation source 37R has a radiation tube (not shown) that generates radiation R, and the radiation tube is moved to each of the plurality of irradiation positions according to the movement of the radiation source 37R. FIG. 12 shows a diagram for explaining an example of tomosynthesis imaging. In FIG. 12, the compression plate 40 is not shown. In the present embodiment, as shown in FIG. 12, the radiation source 37R is at irradiation positions 19 with different irradiation angles by a predetermined angle β t (t = 1, 2, ···, the maximum value is 7 in FIG. 12), in other words, it is moved to a position where the irradiation angle of the radiation R with respect to the detection surface 28A of the radiation detector 28 is different. Each irradiation position 19 t at, the radiation R is irradiated from the radiation source 37R toward the breast W according to the instruction of the console 12, and a radiation image is taken by the radiation detector 28. In the radiation image imaging system 1, when tomosynthesis imaging is performed by moving the radiation source 37R to each of the irradiation positions 19 t and taking a radiation image at each irradiation position 19 t , in the example of FIG. 12, seven radiation images are obtained. In the following, in tomosynthesis imaging, when the radiation image taken at each irradiation position 19 t is described separately from other radiation images, it is also referred to as a "projection image".

[0107] Note that, as shown in FIG. 12, the irradiation angle of the radiation R refers to the angle α formed by the normal line CL of the detection surface 28A of the radiation detector 28 and the radiation axis RC. The radiation axis RC refers to an axis connecting a preset position such as the focal point of the radiation source 37R at each irradiation position 19 t and the center of the detection surface 28A. Here, the detection surface 28A of the radiation detector 28 is a surface substantially parallel to the imaging surface 24A.

[0108] In the case of contrast imaging and tomosynthesis imaging, the mammography apparatus 10 of the present embodiment, as the first contrast imaging, captures a projection image that is a first low-energy image and a projection image that is a first high-energy image with the radiation source 37R disposed at the irradiation position 194. Further, as the second contrast imaging, the mammography apparatus 10 captures a projection image that is a second low-energy image and a projection image that is a second high-energy image with the radiation source 37R disposed at each of the irradiation positions 191 to 193 and 195 to 197. That is, in the example shown in FIG. 12, in the case of contrast imaging and tomosynthesis imaging, a set of a first low-energy image and a first high-energy image, and six sets of a second low-energy image and a second high-energy image are obtained. t (t≠4), it captures a projection image that is a second low-energy image and a projection image that is a second high-energy image. That is, in the example shown in FIG. 12, in the case of contrast imaging and tomosynthesis imaging, a set of a first low-energy image and a first high-energy image, and six sets of a second low-energy image and a second high-energy image are obtained.

[0109] FIG. 13 shows a flowchart illustrating an example of the flow of contrast imaging by the radiation image imaging system 1 of this modified example. The flow of contrast imaging in this modified example differs from the flow of contrast imaging in the above-described embodiment (see FIG. 8) in that it includes the process of step S21 instead of step S20 and the process of step S23 instead of step S22. That is, in this modified example, the second contrast imaging process and the differential image generation process are different from the second contrast imaging process and the differential image generation process (see FIG. 9) of the above-described embodiment.

[0110] FIG. 14 shows a flowchart illustrating an example of the flow of the second contrast imaging process executed on the console 12 of this modified example. In this modified example, when starting the second contrast imaging process, that is, at the above step S18, the radiation source 37R is moved to the position where the movement of the radiation source 37R is started in tomosynthesis imaging. For example, in the example shown in FIG. 12, it is moved to the irradiation position 191.

[0111] In step S100 of FIG. 14, as described above, the control unit 50 determines whether or not it has received an irradiation instruction for the radiation R. Until the irradiation instruction is received, the determination in step S100 is a negative determination. On the other hand, when the irradiation instruction is received, the determination in step S100 becomes an affirmative determination, and the process proceeds to step S105.

[0112] In step S105, the control unit 50 starts the movement of the radiation source 37R. For example, in the example shown in FIG. 12, the movement of the radiation source 37R is started from the irradiation position 191 toward the end position, which is the irradiation position 197.

[0113] In step S107, as described above, the control unit 50 outputs an instruction for irradiating the radiation R of the first energy to the mammography apparatus 10. In the mammography apparatus 10, the control unit 20 irradiates the breast with the radiation R of the first energy from the radiation source 37R, and the radiation detector 28 captures a second low-energy image.

[0114] In the next step S109, as described above, the control unit 50 outputs an instruction for irradiating the radiation R of the second energy to the mammography apparatus 10. In the mammography apparatus 10, the control unit 20 irradiates the breast with the radiation R of the second energy from the radiation source 37R, and the radiation detector 28 captures a second high-energy image.

[0115] In the next step S111, the control unit 50 determines whether or not the position of the radiation source 37R is the end position. In the example shown in FIG. 12, it is determined whether or not the position of the radiation source 37R is the irradiation position 197. In other words, with the position of the radiation source 37R being the irradiation position 197, it is determined whether or not the processes of steps S107 and S109 have been performed. If the position of the radiation source 37R is not the irradiation position 197, the determination in step S111 is a negative determination, and the process proceeds to step S113.

[0116] In step S113, the control unit 50 determines whether the position of the moving radiation source 37R is the irradiation position 19 tDetermine whether (t≠4) has been reached. The radiation source 37R is at the irradiation position 19 t Until (t≠4) is reached, the determination in step S113 is a negative determination. On the other hand, when the radiation source 37R is at the irradiation position 19 t When (t≠4) is reached, the determination in step S113 is an affirmative determination, and the process returns to step S107, and at the reached irradiation position 19 t At (t≠4), the processes of steps S107 and S109 are repeated.

[0117] On the other hand, in step S111, when the position of the radiation source 37R is the end position, in the example shown in FIG. 12, when it is the irradiation position 197, the determination is an affirmative determination, and the process proceeds to step S115.

[0118] In step S115, the control unit 50 stops the movement of the radiation source 37R. When the process of step S115 ends, the second contrast imaging process shown in FIG. 14 ends.

[0119] On the other hand, FIG. 15 shows a flowchart representing an example of the flow of the differential image generation process executed on the console 12 of this modified example.

[0120] The differential image generation process of this modified example shown in FIG. 15 is different from the differential image generation process (see FIG. 10) of the above embodiment in that it includes the processes of steps S213 and S215 instead of the process of step S212.

[0121] In step S213 of FIG. 15, the second differential image generation unit 68 further generates a tomographic image from the first differential image generated in step S202 and the plurality of second differentials generated in step S208. The method by which the second differential image generation unit 68 generates a tomographic image from the first differential image and the plurality of second differential images is not particularly limited. For example, the second differential image generation unit 68 can generate a plurality of tomographic images by reconstructing the first differential image and the plurality of second differential images by an inverse projection method such as the FBP (Filter Back Projection) method or the successive approximation reconstruction method.

[0122] In the next step S215, the display control unit 70 performs control to cause the display unit 58 to display the tomographic image generated in step S213. When the processing of step S215 ends, the differential image generation process shown in FIG. 15 ends.

[0123] Thus, the first differential image of this modification example is a projection image taken using the grid 27, and is a projection image in which artifact components including scattered ray components and components caused by oblique incidence of radiation are suppressed. Also, each of the plurality of second differential images is a projection image from which artifact components have been removed. Therefore, according to this modification example, a tomographic image in which artifact components are suppressed can be obtained.

[0124] Note that also in this modification example, similar to the first modification example, after removing the artifact components from each of the second low-energy image and the second high-energy image, a second differential image may be generated.

[0125] (Modification Example 3: Tomosynthesis Imaging) In addition to the above configuration, the position of the object of interest stained with the contrast agent may be specified. FIG. 16 shows a functional block diagram of an example of the configuration of the console 12 of this modification example. As shown in FIG. 16, the console 12 of this modification example is different from the console 12 of the above configuration in that it further includes a position specifying unit 69.

[0126] The position specifying unit 69 has a function of specifying the position of an object of interest stained with a contrast agent, more specifically, the position in the depth direction, from the first difference image and the second difference image. As described above, both the first difference image and the second difference image are images in which breast tissue is removed and the contrast agent is emphasized, so that an object of interest such as a tumor stained with the contrast agent can be easily detected. The position specifying unit 69 detects an object of interest from each of the first difference image and the second difference image. Note that the method by which the position specifying unit 69 detects an object of interest from each of the first difference image and the second difference image is not particularly limited. For example, the position specifying unit 69 may detect an object of interest by applying a known CAD (Computer-Aided Diagnosis) algorithm to each of the first difference image and the second difference image.

[0127] Further, the position specifying unit 69 specifies the position of the object of interest in the depth direction, that is, the height from the detection surface 28A of the radiation detector 28, from the position of the object of interest in the first difference image and the position of the object of interest in the second difference image. Note that the method by which the position specifying unit 69 specifies the position of the object of interest in the depth direction is not particularly limited. For example, the position specifying unit 69 may specify the position of the object of interest in the depth direction from the deviation between the position of the object of interest in the first difference image and the position of the object of interest in the second difference image by a method applying triangulation by stereo matching. The position specifying unit 69 outputs the specified position of the object of interest in the depth direction to the display control unit 70.

[0128] As an example, in the console 12 of the present embodiment, the CPU 50A of the control unit 50 functions as the position specifying unit 69 by executing the difference image generation program 51B stored in the ROM 50B.

[0129] Next, the differential image generation process for specifying the position of the object of interest, more specifically the depth direction position, will be described. FIG. 17 shows a flowchart representing an example of the flow of the differential image generation process of this modification. The differential image generation process shown in FIG. 17 is different from the differential image generation process (see FIG. 10) of the above-described embodiment in that the processes of steps S214 and S216 are provided instead of step S212.

[0130] In step S214 of FIG. 17, as described above, the position specifying unit 69 specifies the depth direction position of the object of interest stained with the contrast agent from the first differential image generated in step S202 and the second differential image generated in step S208.

[0131] In the next step S216, the display control unit 70 performs control to cause the display unit 58 to display the first differential image generated in step S202, the second differential image from which the artifact component has been removed in step S210, and the depth direction position of the object of interest specified in step S214.

[0132] Note that the display form for displaying the depth direction position of the object of interest on the display unit 58 is not particularly limited. For example, information representing the depth direction position of the object of interest may be displayed by superimposing it on the first differential image and the second differential image. Note that at least one of the first low energy image, the first high energy image, the first differential image, the second low energy image, the second high energy image, the second differential image including the artifact component, and the second differential image from which the artifact component has been removed is associated with the depth direction position of the object of interest, and it may be stored in the storage unit 52 of the console 12 or in a PACS (Picture Archiving and Communication Systems) or the like.

[0133] When the process of step S216 ends in this way, the differential image generation process shown in FIG. 17 ends.

[0134] As described above, according to this modification example, by using the grid 27, the depth direction position of the object of interest can be derived using the first difference image in which the artifact component is suppressed and the second difference image in which the artifact component is removed according to the breast thickness, and thus the derivation accuracy can be improved.

[0135] In this modification example, the case of performing stereoscopic imaging has been described. When performing tomosynthesis imaging as in the above-described modification example 3, the position specifying unit 69 may derive the depth direction position of the object of interest from the generated tomographic image. For example, the position specifying unit 69 may detect the object of interest from each of a plurality of tomographic images and specify the depth direction position of the object of interest based on the height of the tomographic image in which the object of interest is detected.

[0136] As described above, the mammography apparatus 10 according to each of the above-described embodiments performs imaging in which the subject in a state where a contrast agent is injected is irradiated with radiation of a first energy from the radiation source 37R and a low energy image is acquired by the radiation detector 28, and imaging in which the subject in a state where a contrast agent is injected is irradiated with radiation of a second energy higher than the first energy from the radiation source 37R and a high energy image is acquired by the radiation detector 28.

[0137] The console 12 processes the radiation image captured by the mammography apparatus 10. The first acquisition unit 60 acquires the first low-energy image and the first high-energy image captured by the mammography apparatus 10 in a state where the grid 27 for removing scattered radiation is inserted between the radiation source 37R and the radiation detector 28, and the radiation source 37R is arranged at a first position where the incident direction of the radiation with respect to the grid 27 is the normal direction. The second acquisition unit 62 acquires the second low-energy image and the second high-energy image captured by the mammography apparatus 10 in a state where the grid 27 is retracted from between the radiation source 37R and the radiation detector 28, and the radiation source 37R is arranged at a second position different from the first position. The thickness estimation unit 66 estimates the thickness of the subject from the first low-energy image and the first high-energy image. The second difference image generation unit 68 generates a second difference image indicating the difference between the second high-energy image and the second low-energy image from the second low-energy image and the second high-energy image based on the estimated thickness.

[0138] As described above, the console 12 of each of the above embodiments estimates the thickness of the breast from the first low-energy image and the first high-energy image captured using the grid 27. Further, the console 12 generates a second difference image from which the artifact component is removed based on the estimated thickness of the breast from the second low-energy image and the second high-energy image captured without using the grid 27.

[0139] When the radiation obliquely enters the radiation detector 28, in other words, when the radiation source 37R is positioned at a position different from the first position where the incident direction of the radiation is the normal direction, imaging cannot be performed using the grid 27. However, according to the console 12 of each of the above embodiments, a second difference image with suppressed artifact components can be obtained from the second low-energy image and the second high-energy image captured without using the grid 27. Therefore, according to the console 12 of each of the above embodiments, a difference image in which the contrast agent is clearly shown and the artifact components are suppressed can be obtained.

[0140] In each of the above embodiments, a form has been described in which a second difference image from which artifact components have been removed is generated based on the thickness of the breast. However, further, the ratio of dead tissue to breast tissue (composition ratio) may be derived for each pixel, and the influence of scattered radiation may be corrected.

[0141] Also, in each of the above embodiments, a form has been shown in which the difference image generation process is performed as step S20 after the process of step S20 in FIG. 8 has ended. However, the timing at which the difference image generation process is performed, that is, the timing at which the first difference image and the second difference image are generated, is not limited to each of the above embodiments. For example, immediately after the first contrast imaging process of step S14 has ended, the difference image generation process may be started in parallel with the processes after step S16. Also, a form may be adopted in which the difference image generation process is performed at a timing according to the user's desire after the contrast imaging.

[0142] Also, in each of the above embodiments, a form has been described in which a breast is applied as an example of the subject of the present disclosure, and a mammography apparatus 10 is applied as an example of the radiation imaging apparatus of the present disclosure. However, the subject is not limited to the breast, and the radiation imaging apparatus is not limited to the mammography apparatus. For example, the subject may be the chest, abdomen, or the like, or a form may be adopted in which a radiation imaging apparatus other than the mammography apparatus is applied as the radiation imaging apparatus.

[0143] Also, in each of the above embodiments, a form has been described in which the console 12 is an example of the image processing apparatus of the present disclosure. However, a device other than the console 12 may have the functions of the image processing apparatus of the present disclosure. In other words, some or all of the functions of the first acquisition unit 60, the second acquisition unit 62, the first difference image generation unit 64, the thickness estimation unit 66, the second difference image generation unit 68, and the display control unit 70 may be provided in a device other than the console 12, such as the mammography apparatus 10 or an external device.

[0144] Also, in each of the above embodiments, for example, as the hardware structure of a processing unit that executes various processes such as the first acquisition unit 60, the second acquisition unit 62, the first differential image generation unit 64, the thickness estimation unit 66, the second differential image generation unit 68, and the display control unit 70, the following various processors can be used. As described above, among the above various processors, in addition to the CPU which is a general-purpose processor that executes software (program) and functions as various processing units, there are also programmable logic devices (PLDs) such as FPGAs (Field Programmable Gate Arrays), which are processors whose circuit configuration can be changed after manufacturing, and dedicated electric circuits and the like, which are processors having a circuit configuration specifically designed to execute specific processes such as ASICs (Application Specific Integrated Circuits).

[0145] One processing unit may be composed of one of these various processors, or may be composed of a combination of two or more processors of the same type or different types (for example, a combination of multiple FPGAs, or a combination of a CPU and an FPGA). Also, multiple processing units may be composed of one processor.

[0146] As an example of configuring multiple processing units with one processor, first, as represented by computers such as clients and servers, there is a form in which one processor is configured by a combination of one or more CPUs and software, and this processor functions as multiple processing units. Second, as represented by system on chips (SoCs), there is a form in which a processor that realizes the functions of the entire system including multiple processing units with one IC (Integrated Circuit) chip is used. Thus, the various processing units are configured using one or more of the above various processors as the hardware structure.

[0147] Furthermore, as the hardware structure of these various processors, more specifically, circuitry combining circuit elements such as semiconductor elements can be used.

[0148] In addition, in each of the above embodiments, the mode in which the contrast imaging processing program 51A and the differential image generation program 51B are pre-stored (installed) in the ROM 50B has been described, but the present invention is not limited thereto. Each of the contrast imaging processing program 51A and the differential image generation program 51B may be provided in a form recorded on a recording medium such as a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disc Read Only Memory), and a USB (Universal Serial Bus) memory. Further, each of the contrast imaging processing program 51A and the differential image generation program 51B may be in a form downloaded from an external device via a network.

Explanation of Reference Numerals

[0149] 1 Radiation image imaging system 2 RIS 10 Mammography device 12 Console 191~197 Irradiation positions 20, 50 Control unit, 20A, 50A CPU, 20B, 50B ROM, 20C, 50C RAM 22, 52 Storage unit 24, 54 I / F unit 26, 56 Operation unit 27 Grid 28 Radiation detector, 28A Detection surface 29, 59 Bus 30 Imaging table, 30A Imaging surface 31 Grid moving unit 32 Arm unit 34 Base 35 Shaft unit 36 Compression unit 37 Radiation irradiation unit, 37R Radiation source 38 Face guard 39 Radiation source moving part 40 Compression plate 41 Compression plate drive part 46 Support part 51A Contrast imaging processing program, 51B Differential image generation program 58 Display part 60 First acquisition part 62 Second acquisition part 64 First differential image generation part 66 Thickness estimation part 68 Second differential image generation part 69 Position specifying part 70 Display control part CL Normal line R, R1, R2 Radiation, RC Radiation axis W Breast h Thickness α, β, θ Angles

Claims

1. Imaging that irradiates a subject injected with a contrast agent with radiation of a first energy from a radiation source and acquires a low-energy image with a radiation detector, and imaging that irradiates the subject injected with the contrast agent with radiation of a second energy higher than the first energy from the radiation source and acquires a high-energy image with the radiation detector, and an image processing apparatus that processes a radiation image captured by a radiation imaging apparatus that performs the imaging, comprising at least one processor, wherein the processor, acquires a first low-energy image and a first high-energy image captured by the radiation imaging apparatus in a state where a grid for removing scattered radiation is inserted between the radiation source and the radiation detector and the radiation source is disposed at a first position where the incident direction of the radiation with respect to the grid is the normal direction, acquires a second low-energy image and a second high-energy image captured by the radiation imaging apparatus in a state where the grid is retracted from between the radiation source and the radiation detector and the radiation source is disposed at a second position different from the first position, estimates the thickness of the subject from the first low-energy image and the first high-energy image, generates a difference image indicating the difference between the second high-energy image and the second low-energy image from the second low-energy image and the second high-energy image based on the estimated thickness Image processing apparatus.

2. wherein the processor, removes an artifact component from each of the second high-energy image and the second low-energy image based on the thickness, generates the difference image from the second low-energy image and the second high-energy image from which the artifact component has been removed The image processing apparatus according to claim 1.

3. wherein the processor, generates the difference image from the second low-energy image and the second high-energy image, removes an artifact component from the difference image based on the thickness The image processing apparatus according to claim 1.

4. The artifact component is an obliquely incident component caused by the oblique incidence of the radiation The image processing apparatus according to claim 2 or claim 3.

5. The artifact component is a scattered radiation component caused by the scattered radiation The image processing apparatus according to claim 2 or claim 3.

6. The processor estimates the thickness from a difference image showing a difference between the first high-energy image and the first low-energy image. The image processing apparatus according to any one of claims 1 to 5. **Claim 7** The processor identifies a position in the depth direction of an object stained with the contrast agent from a difference image showing a difference between the first high-energy image and the first low-energy image and a difference image showing a difference between the second high-energy image and the second low-energy image. The image processing apparatus according to any one of claims 1 to 6. **Claim 8** An image processing method in which a computer executes image processing of a radiation image taken by a radiation image imaging apparatus that performs: imaging for irradiating a subject in a state where a contrast agent is injected with radiation of a first energy from a radiation source and acquiring a low-energy image with a radiation detector; and imaging for irradiating the subject in the state where the contrast agent is injected with radiation of a second energy higher than the first energy from the radiation source and acquiring a high-energy image with the radiation detector, the method including: acquiring a first low-energy image and a first high-energy image taken by the radiation image imaging apparatus with a grid for removing scattered radiation inserted between the radiation source and the radiation detector and the radiation source arranged at a first position where an incident direction of the radiation with respect to the grid is a normal direction; acquiring a second low-energy image and a second high-energy image taken by the radiation image imaging apparatus with the grid retracted from between the radiation source and the radiation detector and the radiation source arranged at a second position different from the first position; estimating a thickness of the subject from the first low-energy image and the first high-energy image; generating a difference image showing a difference between the second high-energy image and the second low-energy image from the second low-energy image and the second high-energy image based on the estimated thickness; and a process executed by a computer. **Claim 9** An imaging program for causing a computer to execute image processing of a radiation image captured by a radiation imaging apparatus that performs imaging for obtaining a low-energy image with a radiation detector by irradiating a subject in a state where a contrast agent is injected with radiation of a first energy from a radiation source, and imaging for obtaining a high-energy image with the radiation detector by irradiating the subject in the state where the contrast agent is injected with radiation of a second energy higher than the first energy from the radiation source, obtaining a first low-energy image and a first high-energy image captured by the radiation imaging apparatus in a state where a grid for removing scattered radiation is inserted between the radiation source and the radiation detector and the radiation source is disposed at a first position where the incident direction of the radiation with respect to the grid is the normal direction, obtaining a second low-energy image and a second high-energy image captured by the radiation imaging apparatus in a state where the grid is retracted from between the radiation source and the radiation detector and the radiation source is disposed at a second position different from the first position, estimating the thickness of the subject from the first low-energy image and the first high-energy image, generating a difference image showing the difference between the second high-energy image and the second low-energy image from the second low-energy image and the second high-energy image based on the estimated thickness An image processing program for causing a computer to execute the processing.

Images