Radiation imaging processing device, method, and program

Abstract

In a radiation image processing device, method, and program, the scattered radiation component is removed from the image, taking into account the position of the contrast agent within the subject. [Solution] The processor obtains a post-contrast radiographic image by radiography of a subject including a tubular structure into which a contrast agent has been injected. Using the tubular structure as a reference, it derives a first scattered ray component on the incident side of the radiation and a second scattered ray component on the outgoing side of the radiation to the subject. Based on the first and second scattered ray components, it removes the scattered ray component from the post-contrast radiographic image in the region of the tubular structure into which the contrast agent has been injected to derive a post-contrast processed radiographic image.

Description

Technical Field

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

Background Art

[0002] Conventionally, for examining and treating the shape of blood vessels, blood vessel abnormalities, blood flow conditions, etc., a contrast radiography diagnostic apparatus has been used. The contrast radiography diagnostic apparatus is called an angiography apparatus. In the angiography apparatus, a contrast agent is injected into a blood vessel using a catheter, and a DSA (Digital Subtraction Angiography) image, which is a difference image between an image before injection of the contrast agent (mask image) and an image after injection of the contrast agent (live image), is acquired. In the DSA image, structures other than the region where the contrast agent is injected are removed. Therefore, by using the DSA image, a doctor can efficiently perform examinations and treatments of blood vessels while confirming the state of blood vessels such as the distribution of blood flow in the blood vessels and stenosis of blood vessels.

[0003] In the above-described DSA image, the state of blood vessels can be confirmed based on the region of the contrast agent injected into the blood vessels. However, due to the influence of scattered radiation generated when radiation passes through the subject, structures unnecessary for observation such as bones that overlap with the contrast agent in the subject may not be completely removed by the difference and may be included in the DSA image. For this reason, a method for removing scattered radiation of an acquired image based on the concentration and thickness of the contrast agent has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in live images, the behavior of scattered radiation differs between the scattered radiation component generated within the subject before reaching the blood vessel into which the contrast agent has been injected, and the scattered radiation component generated after passing through the blood vessel. For example, scattered radiation generated between the radiation source and the blood vessel is largely absorbed by the contrast agent, but scattered radiation generated on the detector side rather than the blood vessel is not absorbed by the contrast agent, and instead, the influence of scattered radiation generated by the contrast agent becomes greater.

[0006] This disclosure is made in view of the above circumstances and aims to enable the removal of scattered radiation components from images, taking into account the position of the contrast agent within the subject. [Means for solving the problem]

[0007] The radiation image processing apparatus according to this disclosure comprises a processor, The processor acquires post-contrast radiographic images by radiography of a subject containing a tubular structure into which a contrast agent has been injected. Using a tubular structure as a reference, the first scattered ray component on the incident side of the radiation and the second scattered ray component on the exit side of the radiation are derived. In the region of the tubular structure into which the contrast agent was injected in the post-contrast radiographic image, the scattered radiation component of the post-contrast radiographic image is removed based on the first and second scattered radiation components to derive the post-contrast processed radiographic image.

[0008] In the radiation image processing apparatus according to this disclosure, the processor may derive the first scattered ray component and the second scattered ray component, respectively, based on the first body thickness of the subject on the radiation incident side with respect to a tubular structure on the radiation transmission path within the subject, and the second body thickness on the radiation exit side with respect to the tubular structure.

[0009] In the radiation image processing apparatus according to this disclosure, the processor may derive a first scattered ray component based on a first coefficient that takes into account scattered rays absorbed by the contrast agent, which is determined according to the concentration of the contrast agent, and a second scattered ray component based on a second coefficient that takes into account scattered rays generated from the contrast agent, which is determined according to the concentration of the contrast agent.

[0010] In the radiographic image processing apparatus according to this disclosure, the processor may derive other scattered radiation components in areas other than the tubular structure into which the contrast agent was injected in the post-contrast radiographic image, and derive a post-contrast processed radiographic image by removing scattered radiation components in other areas of the post-contrast radiographic image based on the derived other scattered radiation components.

[0011] In the radiation image processing apparatus according to this disclosure, the processor derives, in other areas, the first scattered radiation component on the incident side of the radiation of the subject and the second scattered radiation component on the exit side of the radiation, with respect to a tubular structure. Other scattered ray components may be derived based on the first scattered ray component and the pre-second scattered ray component.

[0012] In the radiographic image processing apparatus according to this disclosure, the processor may derive a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image only in the region of tubular structures in the post-contrast radiographic image.

[0013] In the radiographic image processing apparatus according to this disclosure, the processor acquires a pre-contrast radiographic image by radiography of a subject including a tubular structure before the injection of a contrast agent. The pre-contrast scattered radiation component contained in the pre-contrast radiographic image is derived, Based on the pre-contrast scattered radiation component, the scattered radiation component of the pre-contrast radiographic image is removed to derive the pre-contrast processed radiographic image. It may also be possible to derive a difference image between a pre-processed radiographic image and a post-processed radiographic image.

[0014] In the radiographic image processing apparatus according to this disclosure, the processor acquires a pre-contrast radiographic image by radiography of a subject including a tubular structure before the injection of a contrast agent. The pre-contrast scattered radiation component included in the region of the tubular structure in the pre-contrast radiographic image was derived. Based on the pre-contrast scattered radiation component, the scattered radiation component in the region of the tubular structure in the pre-contrast radiographic image is removed to derive the pre-contrast processed radiographic image. It may also be possible to derive a difference image between a pre-processed radiographic image and a post-processed radiographic image.

[0015] The radiographic image processing method disclosed herein involves a computer acquiring a post-contrast radiographic image by radiography of a subject including a tubular structure into which a contrast agent has been injected. Using a tubular structure as a reference, the first scattered ray component on the incident side of the radiation and the second scattered ray component on the exit side of the radiation are derived. In the region of the tubular structure into which the contrast agent was injected in the post-contrast radiographic image, the scattered radiation component of the post-contrast radiographic image is removed based on the first and second scattered radiation components to derive the post-contrast processed radiographic image.

[0016] The radiographic image processing program disclosed herein includes a procedure for acquiring a post-contrast radiographic image by radiography of a subject including a tubular structure into which a contrast agent has been injected, A procedure for deriving the first scattered radiation component on the incident side of radiation and the second scattered radiation component on the exit side of radiation to an object, using a tubular structure as a reference, The computer is instructed to perform a procedure to derive a post-processed radiographic image by removing the scattered radiation component from the post-contrast radiographic image based on the first and second scattered radiation components in the region of the tubular structure into which the contrast agent was injected, in the region of the post-contrast radiographic image.

[0017] Furthermore, the technology disclosed herein may be applied to computer products. [Effects of the Invention]

[0018] According to the present disclosure, the scattered ray component can be removed from the image according to the position of the contrast agent in the subject.

Brief Description of the Drawings

[0019] [Figure 1] Fig. showing an overview of an angiography system to which a radiation image processing apparatus according to an embodiment of the present disclosure is applied [Figure 2] Fig. showing a schematic configuration of a radiation image processing apparatus according to the present embodiment [Figure 3] Fig. showing a functional configuration of a radiation image processing apparatus according to the present embodiment [Figure 4] Fig. for explaining derivation of position information of blood vessels [Figure 5] Fig. for explaining extraction of blood vessel regions [Figure 6] Fig. showing the relationship between the amount of contrast agent and coefficients α and β [Figure 7] Flowchart showing the processing performed in the present embodiment [Figure 8] Flowchart showing the processing performed in the present embodiment [Figure 9] Conceptual diagram of the processing performed in the present embodiment

Embodiments of the Invention

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic block diagram showing the configuration of an angiography system to which a radiation image processing apparatus according to an embodiment of the present disclosure is applied. As shown in Fig. 1, the angiography system 100 according to the present embodiment includes an angiography apparatus 1 and a radiation image processing apparatus 10 according to the present embodiment.

[0021] The angiography apparatus 1 is a device for examining and treating the shape of blood vessels, abnormalities in blood vessels, and the state of blood flow in a subject. In this embodiment, the angiography apparatus 1 is used to examine and treat, for example, the aorta and arteries branching from the aorta. The angiography apparatus 1 has a C-arm 3 attached to the main body 2 so as to be rotatable around axis X0, i.e., in the direction of arrow A, by a mounting part 4. The C-arm 3 is also attached to the mounting part 4 so as to be movable in the direction of arrow B shown in Figure 1. A radiation source 5 is attached to one end of the C-arm 3, and an imaging unit 6 is attached to the other end. The imaging unit 6 has a built-in radiation detector 8 for detecting radiation transmitted through the subject H on the imaging table 7 and generating a radiation image of the subject H. The main body 2 contains the radiation image processing device 10 according to this embodiment. Blood vessels are an example of tubular structures.

[0022] In this embodiment, imaging is performed by injecting a contrast agent into a blood vessel. First, before injecting the contrast agent, the subject H is imaged to obtain a radiographic image of the subject H before contrast agent injection (hereinafter referred to as the mask image). Then, after injecting the contrast agent, the subject H is imaged again to obtain a radiographic image of the subject H after contrast agent injection (hereinafter referred to as the live image). The mask image is an example of a pre-contrast radiographic image, and the live image is an example of a post-contrast radiographic image.

[0023] Next, a radiation image processing apparatus according to this embodiment will be described. First, the hardware configuration of the radiation image processing apparatus according to this embodiment will be described with reference to Figure 2. As shown in Figure 2, the radiation image processing apparatus 10 is a computer such as a workstation, server computer, or personal computer, and includes a CPU (Central Processing Unit) 11, non-volatile storage 13, and memory 16 as a temporary storage area. The radiation image processing apparatus 10 also includes a display 14 such as a liquid crystal display, input devices 15 such as a keyboard and mouse, and an interface 17 such as a network I / F (Interface) connected to a network and an imaging unit 6. The CPU 11, storage 13, display 14, input devices 15, memory 16, and network I / F 17 are connected to a bus 18. Note that the CPU 11 is an example of a processor in this disclosure.

[0024] The storage 13 is implemented using an HDD (Hard Disk Drive), an SSD (Solid State Drive), and flash memory, etc. The storage 13, as a storage medium, stores the radiation image processing program 12 installed in the radiation image processing device 10. The CPU 11 reads the radiation image processing program 12 from the storage 13, expands it into memory 16, and executes the expanded radiation image processing program 12.

[0025] The radiation image processing program 12 is stored in a memory device of a server computer connected to the network, or in network storage, in a state that allows external access, and is downloaded and installed on the computers comprising the radiation image processing device 10 upon request. Alternatively, it is recorded on a recording medium such as a DVD (Digital Versatile Disc) or CD-ROM (Compact Disc Read Only Memory) and distributed, and then installed from that recording medium on the computers comprising the radiation image processing device 10.

[0026] Next, the functional configuration of the radiation image processing apparatus according to this embodiment will be described. Figure 3 is a diagram showing the functional configuration of the radiation image processing apparatus according to this embodiment. As shown in Figure 3, the radiation image processing apparatus 10 includes an image acquisition unit 20, a scattered radiation removal unit 21, an image output unit 22, and a display control unit 23. The CPU 11 executes the radiation image processing program 12, and the CPU 11 functions as the image acquisition unit 20, the scattered radiation removal unit 21, the image output unit 22, and the display control unit 23.

[0027] The image acquisition unit 20 acquires the mask image G1 and live image G2 described above by causing the angiography device 1 to take images of the subject H. During the imaging process, imaging conditions such as the radiation dose, tube voltage, and SID (Source-to-Image receptor Distance) are set. The set imaging conditions are stored in the storage device 13.

[0028] In addition, the mask image G1 and live image G2 may be acquired by a program separate from the radiation image processing program of this embodiment. In this case, the mask image G1 and live image G2 are stored in the storage 13, and the image acquisition unit 20 reads the mask image G1 and live image G2 stored in the storage 13 from the storage 13 for processing.

[0029] Here, when imaging subject H using the angiography device 1, scattered radiation is generated as the radiation passes through subject H, and the scattered radiation component is included in the mask image G1 and the live image G2. The mask image G1 is acquired before the injection of the contrast agent, while the live image G2 is acquired after the injection of the contrast agent. Since the contrast agent absorbs radiation, the scattered radiation component of the radiation is also absorbed by the contrast agent. As a result, the scattered radiation component in the vascular region where the contrast agent was injected in the live image G2 is less than the scattered radiation component in the vascular region in the mask image G1.

[0030] Furthermore, in the live image G2, the behavior of scattered radiation differs between the scattered radiation component generated within subject H before reaching the blood vessel into which the contrast agent was injected and the scattered radiation component generated after the contrast agent has passed through the blood vessel. Specifically, scattered radiation generated between the radiation source 5 and the blood vessel is largely absorbed by the contrast agent, but scattered radiation generated on the radiation detector 8 side rather than the blood vessel is not absorbed by the contrast agent, and instead the influence of scattered radiation generated by the contrast agent becomes greater.

[0031] In situations where the scattered radiation components present differ, applying the same scattered radiation removal process to both the mask image G1 and the live image G2 results in different degrees of scattered radiation removal in the vascular region where the contrast agent was injected. This leads to differences in the contrast of the vascular region between the mask image G1 and the live image G2. As a result, when deriving the DSA image, which is the difference image between the mask image G1 and the live image G2 from which the scattered radiation components have been removed, unwanted structures such as bone overlapping the vascular region where the contrast agent was injected may remain in the DSA image without being completely removed. Such unwanted structures can hinder the examination of the vascular condition.

[0032] In this embodiment, the scattered radiation removal unit 21 derives the scattered radiation components of the mask image G1 and the live image G2, respectively, and removes the scattered radiation components from the mask image G1 and the live image G2. In this embodiment, the scattered radiation removal unit 21 derives the first scattered radiation component on the incident side of the radiation in the subject H, i.e., the radiation source 5 side, with respect to the blood vessel into which the contrast agent was injected, for the live image G2. The scattered radiation removal unit 21 also derives the second scattered radiation component on the emission side of the radiation in the subject H, i.e., the radiation detector 8 side, with respect to the blood vessel into which the contrast agent was injected, for the live image G2. Then, the scattered radiation removal unit 21 removes the scattered radiation components from the live image G2 based on the first and second scattered radiation components.

[0033] First, the removal of scattered radiation components from the mask image G1 will be explained. In this embodiment, the scattered radiation removal unit 21 removes scattered radiation components from the mask image G1 using a method described in, for example, Japanese Patent Application Publication No. 2015-043959. Note that the method for removing scattered radiation components is not limited to this, and any method can be used. The following describes the scattered radiation removal process when using the method described in Japanese Patent Application Publication No. 2015-043959. When using the method described in Japanese Patent Application Publication No. 2015-043959, the derivation of the thickness distribution of the subject H and the derivation of scattered radiation components for removal are performed simultaneously.

[0034] Furthermore, when removing scattered radiation components, a low-frequency image representing the low-frequency components of the mask image G1 and the live image G2 may be generated, and the body thickness distribution may be derived using the low-frequency image.

[0035] First, the scatter removal unit 21 acquires a virtual model K of the subject H having an initial thickness distribution Ts(x,y). The virtual model K is data that virtually represents the subject H, in which the thickness according to the initial thickness distribution Ts(x,y) is associated with the coordinate position of each pixel in the mask image G1. The virtual model K of the subject H having an initial thickness distribution Ts(x,y) is assumed to be stored in the storage 13 in advance, but it may also be acquired from an external server where the virtual model K is stored.

[0036] Alternatively, the Source Image receptor Distance (SID), which is the distance between the radiation source 5 and the surface of the radiation detector 8 in the angiography apparatus 1, and the Source Object Distance (SOD), which is the distance between the radiation source 5 and the surface of the subject H, may be measured, and the initial body thickness distribution Ts(x, y) of the subject H may be calculated based on the SID and SOD. In this case, the body thickness distribution can be obtained by subtracting SOD from the SID.

[0037] Next, the scattered radiation removal unit 21 derives an estimated primary line image Ip(x,y) obtained by estimating the primary line image obtained by imaging the virtual model K, and an estimated scattered radiation image Is(x,y) obtained by estimating the scattered radiation image obtained by imaging the virtual model K, based on the virtual model K, as shown in equations (1) and (2) below. Furthermore, as shown in equation (3) below, the scattered radiation removal unit 21 derives an estimated image Im(x,y) obtained by estimating the mask image G1 obtained by imaging the subject H, by combining the estimated primary line image Ip(x,y) and the estimated scattered radiation image Is(x,y). Ip(x,y) = Io(x,y)×exp(-μls×T(x,y)) (1) Is(x,y) = Io(x,y)*Sσ(T(x,y)) (2) Im(x,y) = Is(x,y)+Ip(x,y) (3)

[0038] Here, (x,y) are the coordinates of the pixel position in the mask image G1, Ip(x,y) is the primary component at the pixel position (x,y), Is(x,y) is the scattered component at the pixel position (x,y), Io(x,y) is the incident dose to the surface of the subject H at the pixel position (x,y), μls is the attenuation coefficient of the subject H, and Sσ(T(x,y)) is a convolution kernel that represents the scattering characteristics according to the thickness distribution T(x,y) of the subject H at the pixel position (x,y). Note that when deriving the first estimated image Im(x,y), the initial thickness distribution Ts(x,y) is used as the thickness distribution T(x,y) in equations (1) and (2). Equation (1) is based on the known exponential attenuation law, and equation (2) is based on the method described in "JM Boon et al, An analytical model of the scattered radiation distribution in diagnostic radiolog, Med. Phys. 15(5), Sep / Oct 1988" (Reference 1). The incident dose Io(x,y) to the surface of subject H is the irradiation dose derived based on the imaging conditions. Furthermore, the attenuation coefficient μls for subject H in equation (1) is the attenuation coefficient for soft tissue for the mask image G1 of subject H.

[0039] Furthermore, * in equation (2) is an operator representing a convolution operation. The properties of the kernel change not only with respect to the thickness of the subject H, but also with respect to the distribution of the irradiation field in the angiography apparatus 1 (if an irradiation field aperture is used), the distribution of the composition of the subject H, the irradiation dose during imaging, the tube voltage, the imaging distance, and the characteristics of the radiation detector 8 used in the imaging unit 6. According to the method described in Reference 1, scattered radiation can be approximated by the convolution of the point spread function (Sσ(T(x,y)) in equation (3)) with respect to the primary radiation. Note that Sσ(T(x,y)) can be determined experimentally depending on the irradiation field information, subject information, and imaging conditions.

[0040] In this embodiment, Sσ(T(x,y)) may be calculated based on the illumination field information, subject information, and shooting conditions at the time of shooting. Alternatively, a table associating various illumination field information, various subject information, and various shooting conditions with Sσ(T(x,y)) may be stored in the storage 13, and Sσ(T(x,y)) may be obtained by referring to this table based on the illumination field information, subject information, and shooting conditions at the time of shooting. Furthermore, Sσ(T(x,y)) may be approximated by T(x,y).

[0041] Next, the scattered radiation removal unit 21 modifies the initial thickness distribution Ts(x,y) of the virtual model K so that the difference between the estimated image Im and the mask image G1 is small. The scattered radiation removal unit 21 repeatedly generates the estimated image Im using the modified thickness distribution T(x,y) and modifies the thickness distribution T(x,y) until the difference between the estimated image Im and the mask image G1 satisfies a predetermined termination condition. When the termination condition is met, the scattered radiation removal unit 21 subtracts the scattered radiation component Is(x,y) derived by equation (2) from the mask image G1. The scattered radiation component derived for the mask image G1 will be referred to as the scattered radiation component Is1(x,y) in the following description. This removes the scattered radiation component contained in the mask image G1. G11 will be used as the reference code for the processed mask image from which the scattered radiation component has been removed. The processed mask image G11 is an example of a pre-processed radiographic image according to this disclosure.

[0042] In the angiography apparatus 1, air is present because the distance between the subject H and the radiation detector 8 is relatively large. Air has its own unique radiation properties. Therefore, the quality of the primary and scattered radiation components that pass through the subject H changes according to the radiation properties of the air. Accordingly, in this embodiment, it is preferable to consider the radiation properties of the air interposed between the subject H and the radiation detector 8 when removing the scattered radiation component.

[0043] As a method for removing scattered radiation while considering the radiation properties of air, for example, the method described in International Publication 2021 / 100413 can be used. Specifically, for the air interposed between the subject H and the radiation detector 8, the primary radiation transmittance and scattered radiation transmittance are generated in advance as a table or the like, according to various air thicknesses, various imaging conditions, and the thickness distribution of the subject H, and stored in storage 13. The air thickness is the distance d between the imaging table 7 and the radiation detector 8 (see Figure 1), and can be measured and obtained in advance.

[0044] In this case, when the scattered radiation removal unit 21 estimates the thickness distribution of the subject H and removes scattered radiation, it refers to a table to obtain the radiation characteristics of the air corresponding to the thickness distribution, i.e., the primary radiation transmittance and scattered radiation transmittance. The scattered radiation removal unit 21 also uses the acquired radiation characteristics, shooting conditions, and thickness distribution to obtain an estimated primary radiation image and an estimated scattered radiation image, and adds the estimated primary radiation image and the estimated scattered radiation image to generate an estimated image. Furthermore, the scattered radiation removal unit 21 repeatedly generates an estimated image and corrects the thickness distribution until the difference between the estimated image and the mask image G1 satisfies a predetermined termination condition. The scattered radiation removal unit 21 then removes the scattered radiation component from the mask image G1 by subtracting the estimated scattered radiation image obtained when the thickness distribution satisfying the termination condition was acquired from the mask image G1. In this way, the scattered radiation component can be removed from the mask image G1 while also considering the radiation characteristics of the air interposed between the subject H and the radiation detector 8.

[0045] Next, the removal of scattered radiation components from the live image G2 will be explained. In this embodiment, the scattered radiation removal unit 21 separately derives scattered radiation components from the vascular region where the contrast agent is injected and from other regions other than the vascular region of the live image G2. First, the deriving of scattered radiation components from the vascular region will be explained. In order to derive scattered radiation components from the vascular region, the scattered radiation removal unit 21 first acquires positional information representing the location of the blood vessels on the radiation transmission path within the subject H. The positional information of the blood vessels can be obtained based on a three-dimensional image of the subject H obtained by imaging the subject H with a CT (Computed Tomography) device, an MRI (Magnetic Resonance Imaging) device, etc.

[0046] Figure 4 is a diagram illustrating the positional information of blood vessels. In Figure 4, an axial cross-section in a 3D image is schematically shown for illustrative purposes. The upper side of Figure 4 is the anterior side of subject H. As shown in Figure 4, in a 3D image, the blood vessels 30 of subject H can be extracted and the centerline 31 of the blood vessels can be determined. In Figure 4, the blood vessel 30 is, for example, the abdominal aorta. Since subject H is lying supine when the 3D image is taken, the distance z1 from the anterior body surface of subject H to the centerline 31 of the blood vessels 30 on a perpendicular line passing through the centerline 31 of the blood vessels 30, and the distance z2 from the posterior body surface of subject H to the centerline 31 of the blood vessels 30 can be derived as positional information of the blood vessels. The former is called the first distance and the latter the second distance.

[0047] Furthermore, since the subject H is lying supine when capturing a 3D image, if a horizontal plane 32 passing through the center line 31 is set within the blood vessel 30, and a perpendicular line is set to the horizontal plane 32, then within the blood vessel 30, the first distance z1 and the second distance z2 from each of the two points where the perpendicular line intersects the anterior and posterior body surfaces of the subject H to the horizontal plane 32 can be derived as positional information of the blood vessel.

[0048] In the CT scanner and angiography system 1 for acquiring three-dimensional images, the subject H is imaged in a supine position. Therefore, the first distance z1 derived using the three-dimensional image is the body thickness on the radiation incidence side of the subject H, with reference to the centerline 31 of the blood vessel 30, for the live image G2. The second distance z2 is the body thickness on the radiation emission side of the subject H, with reference to the centerline 31 of the blood vessel 30, for the live image G2.

[0049] In this embodiment, a three-dimensional image of the subject H is acquired in advance, and the first distance z1 and second distance z2 to each point on the horizontal plane 32 corresponding to the center line 31 of the blood vessel 30 to which the contrast agent is injected are derived in advance as positional information of the blood vessel and stored in the storage 13.

[0050] The scattered radiation removal unit 21 extracts vascular regions from the live image G2 when removing scattered radiation components from the live image G2. Figure 5 is a diagram illustrating the extraction of vascular regions. As shown in Figure 5, in the live image G2, vascular regions are enhanced and therefore have higher brightness than the surrounding areas. For this reason, the scattered radiation removal unit 21 extracts regions in the live image G2 that have a brightness higher than a predetermined threshold Th1 as vascular regions A0. Alternatively, the vascular regions may be extracted using an extraction model that has been machine-learned to extract vascular regions A0. As a result, the live image G2 is divided into vascular regions A0 and other regions A1 other than vascular regions A0.

[0051] In the vascular region A0 of the live image G2, the scattered radiation removal unit 21 derives the first scattered radiation component Is21(x,y) on the radiation incident side of subject H and the second scattered radiation component Is22(x,y) on the radiation exit side of subject H, using the blood vessel as a reference. Then, as shown in equation (4) below, the scattered radiation component Is2(x,y) of the live image G2 is derived by weighted addition of the first scattered radiation component Is21(x,y) and the second scattered radiation component Is22(x,y). The coefficients α and β will be described later. Is2(x,y)=(1-α)·Is21(x,y)+(1+β)·Is22(x,y) (4)

[0052] The scattered radiation removal unit 21 uses the first body thickness T1 from the body surface on the source side of the subject H to the horizontal plane 32 corresponding to the center line 31 of the blood vessel 30 to derive the first scattered radiation component Is21(x,y) by the following equation (5). The scattered radiation removal unit 21 also uses the second body thickness T2 from the body surface on the detector side of the subject H to the horizontal plane 32 corresponding to the center line 31 of the blood vessel 30 to derive the second scattered radiation component Is22(x,y) by the following equation (6). Is21(x,y) = Io(x,y)*Sσ(T1(x,y)) (5) Is22(x,y) = Io(x,y)*Sσ(T2(x,y)) (6)

[0053] In this embodiment, the scattered radiation removal unit 21 acquires the position information of blood vessels stored in the storage 13. The scattered radiation removal unit 21 then aligns the live image G2 with a previously acquired 3D image and uses the first distance z1 and the second distance z2 at the pixel positions of the 3D image corresponding to the pixel positions of the live image G2 as the first body thickness T1 and the second body thickness T2, respectively. When deriving the first scattered radiation component Is21(x,y) and the second scattered radiation component Is22(x,y), it is preferable to consider the thickness of the air between the subject H and the radiation detector 8, similar to the mask image G1.

[0054] In equation (4), α and β are coefficients determined according to the concentration of the contrast agent. Coefficient α takes into account the scattered radiation absorbed by the contrast agent; it is 0 when there is no contrast agent and approaches 1 as the amount of contrast agent increases. Coefficient β takes into account the scattered radiation generated from the contrast agent; it is 0 when there is no contrast agent and increases proportionally to the amount of contrast agent. Figure 6 shows the relationship between the amount of contrast agent and coefficients α and β. α = 1 - exp(-C0q) and β = C1q. q is the amount of contrast agent and is derived from the contrast agent concentration × blood vessel diameter. The contrast agent concentration can be obtained by receiving input from the input device 15 for the concentration of the contrast agent to be used, and the blood vessel diameter can be obtained by measuring the blood vessel diameter in a 3D image. C0 and C1 are constants and are derived by measuring scattered radiation by pre-photographing a phantom that simulates a human body injected with contrast agent.

[0055] For regions A1 other than vascular region A0 in the live image G2, the scattered radiation removal unit 21 derives the scattered radiation component Is2(x,y) using the live image G2, similar to the mask image G1. In this case, the body thickness used in equation (2) should be the body thickness T(x,y) that satisfies the termination condition when deriving the scattered radiation component Is(x,y) of the mask image G1. In this case, it is also preferable to derive the scattered radiation component considering the thickness of the air between the subject H and the radiation detector 8, similar to the mask image G1. The scattered radiation component Is2(x,y) for other regions A1 is an example of other scattered radiation components in this disclosure.

[0056] Furthermore, the scattered radiation removal unit 21 may derive the first scattered radiation component Is21(x,y) on the radiation incident side of the subject H and the second scattered radiation component Is22(x,y) on the radiation exit side of the subject H in another region A1 of the live image G2, using the center line 31 of the blood vessel 30 as a reference, and then derive the scattered radiation component Is2(x,y) in equation (4) above by setting α=0 and β=0.

[0057] The scattered radiation removal unit 21 derives a processed live image from which scattered radiation components have been removed by subtracting the scattered radiation component Is2(x,y) derived in the vascular region A0 and other regions A1 other than the vascular region A0 from the live image G2. G22 is used as the reference code for the processed live image from which scattered radiation components have been removed. The processed live image G22 is an example of a post-processed radiographic image according to this disclosure.

[0058] The image derivation unit 22 derives a difference image, i.e., a DSA image Gp, in which the vascular region within the subject H into which the contrast agent was injected is enhanced, by subtracting the processed mask image G11 from the processed live image G22, as shown in equation (7) below. Gp(x,y) = G22(x,y) - G11(x,y) (7)

[0059] The display control unit 23 displays the DSA image Gp on the display 14. The physician performs vascular examinations and treatments while viewing the DSA image Gp displayed on the display.

[0060] Next, the processing performed in this embodiment will be described. Figures 7 and 8 are flowcharts showing the processing performed in this embodiment, and Figure 9 is a conceptual diagram of the processing performed in this embodiment. It is assumed that the mask image G1 and the live image G2 are acquired by photography and stored in storage 13.

[0061] When an instruction to start processing is input from the input device 15, the image acquisition unit 20 acquires the mask image G1 and the live image G2 from the storage 13 (step ST1). Next, the scattered radiation removal unit 21 derives the scattered radiation component Is1 contained in the mask image G1 (step ST2), and derives the processed mask image G11 by subtracting the derived scattered radiation component Is1 from the mask image G1 to remove the scattered radiation component from the mask image G1 (step ST3).

[0062] Next, the scattered radiation removal unit 21 extracts the vascular region A0 into which the contrast agent has been injected from the live image G2 (step ST4). Then, the scattered radiation removal unit 21 derives the scattered radiation components for the live image G2 (step ST5).

[0063] Moving on to Figure 8, the scattered radiation removal unit 21 derives the first scattered radiation component for vascular region A0 on the incident side of the radiation in subject H, i.e., on the radiation source 5 side (step ST11). The scattered radiation removal unit 21 also derives the second scattered radiation component for vascular region A0 on the emission side of the radiation in subject H, i.e., on the radiation detector 8 side, using the vascular region to which the contrast agent was injected as a reference (step ST12). Then, for vascular region A0, the scattered radiation component Is2 is derived by adding the first and second scattered radiation components (step ST13). Meanwhile, for regions A1 other than vascular region A0, the scattered radiation component Is2 is derived in the same way as for the mask image G1 (step ST14), and the deriving of scattered radiation components from the live image is completed.

[0064] Returning to Figure 7, the scattered radiation removal unit 21 subtracts the derived scattered radiation component Is2(x,y) from the live image G2 to remove the scattered radiation component from the live image G2, thereby deriving the processed live image G22 (step ST6). Next, the image derivation unit 22 derives the DSA image Gp by subtracting the processed mask image G11 from the processed live image G22 (step ST7). Then, the display control unit 23 displays the DSA image Gp on the display 14 (step ST8), and the process ends.

[0065] Thus, in this embodiment, for the live image G2, the first scattered radiation component Is21 on the incident side of the radiation in the subject H and the second scattered radiation component Is22 on the exit side of the radiation are derived, using the blood vessel region into which the contrast agent was injected as a reference. Based on the first scattered radiation component Is21 and the second scattered radiation component Is22, the scattered radiation component Is2 of the live image G2 is removed. Here, the first scattered radiation component Is21 represents the scattered radiation from the radiation source 5 side with respect to the blood vessel into which the contrast agent was injected, and the second scattered radiation component Is22 represents the scattered radiation from the radiation detector 8 side with respect to the blood vessel into which the contrast agent was injected. Therefore, even if the behavior of scattered radiation differs between the scattered radiation component generated before reaching the blood vessel into which the contrast agent was injected within the subject H and the scattered radiation component generated after passing through the blood vessel, the scattered radiation component can be accurately derived by considering this effect and the scattered radiation component of the live image G2 can be removed. Therefore, according to this embodiment, when a difference image such as a DSA image Gp is ​​derived, it is possible to suppress the retention of structures such as bone superimposed on the contrast agent in the contrast agent region, thereby preventing unnecessary structures from interfering with the confirmation of the blood vessel condition.

[0066] In the above embodiment, the scattered radiation component is removed from the entire area of ​​the live image G2, but this is not the only way. Alternatively, the scattered radiation component Is2(x,y) may be derived using equation (4) only in the vascular region A0 of the live image G2, and the processed live image G22 may be derived by removing the scattered radiation component Is2(x,y) only in the vascular region A0 of the live image G2. In this case, for the mask image G1, the vascular region may be extracted, and the processed mask image G11 may be derived by removing the scattered radiation component only in the vascular region of the mask image G1 in the same manner as above. Then, the DSA image Gp may be derived using equation (7) from the processed live image G22, from which the scattered radiation component has been removed only in the vascular region A0, and the processed mask image G11, from which the scattered radiation component has been removed only in the vascular region. Even in this case, it is possible to suppress the remaining presence of structures such as bone superimposed on the contrast agent in the vascular region A0 where the contrast agent has been injected.

[0067] The radiation in the above embodiment is not particularly limited, and in addition to X-rays, alpha rays or gamma rays may also be used.

[0068] Furthermore, while blood vessels are used as tubular structures in the above embodiments, the invention is not limited to them. Any tubular structure that is subjected to examination and treatment using contrast agents, such as the esophagus, large intestine, pancreatic duct, and bile duct, can be targeted. Endoscopic retrograde cholangiopancreatography (ERCP) is an example of an examination and treatment in which contrast agents are injected into the pancreatic and bile ducts. Endoscopic retrograde cholangiopancreatography is a method in which an endoscope is inserted through the mouth, advanced through the esophagus and stomach to the duodenum, and a contrast agent is injected directly into the bile duct or pancreatic duct via a thin tube to examine or treat abnormalities in the gallbladder, bile duct, and pancreatic duct.

[0069] In this embodiment, each process is executed on any computer. Furthermore, any computer may execute these processes using a processor as hardware, a program as software, or a combination thereof. In that case, the processor is configured to work in cooperation with the program to execute the various processes in this embodiment, and can function as a unit or means in this embodiment. Also, the execution order of the processes by the processor is not limited to the order described and may be changed as appropriate. Any computer may be a general-purpose computer, a computer designed for a specific purpose, a workstation, or any other system capable of executing each process.

[0070] A processor may consist of one or more hardware components, and the type of hardware is not limited. For example, a processor may consist of a CPU (Central Processing Unit), an MPU (Micro Processing Unit), a programmable logic device such as an FPGA (Field Programmable Gate Array), a dedicated circuit for executing a specific process such as an ASIC (Application Specific Integrated Circuit), a GPU (Graphic Processing Unit), or an NPU (Neural Processing Unit). Furthermore, the type of hardware may be a combination of different types of hardware. When multiple hardware components are configured to execute one or more processes of a given processor, these components may reside in physically separate devices or in the same device. Also, in any embodiment, the order of each process performed by the processor is not limited to the order described above and may be changed as appropriate. Hardware is composed of electrical circuits (circuitry) that combine circuit elements such as semiconductor elements.

[0071] Furthermore, the program may be firmware or software such as microcode. Alternatively, the program may be, for example, a set of program modules, each function of which may be implemented by a processor configured to perform its respective function. The program may be program code or multiple code segments stored on one or more non-temporary computer-readable media (e.g., storage media or other storage). The program may be divided and stored on multiple non-temporary computer-readable media located in physically separate devices. Program code or code segments may represent any combination of procedures, functions, subprograms, routines, subroutines, modules, software packages, classes, or instructions, data structures, or program statements. Program code or code segments may be connected to other code segments or hardware circuits by sending and receiving information, data, arguments, parameters, or memory contents.

[0072] Furthermore, although the above embodiment describes a configuration in which the radiation image processing program 12 is pre-stored (installed) in the storage 13, the invention is not limited to this configuration. The radiation image processing program 12 may be provided in the form of a recording medium such as a CD-ROM (Compact Disc Read Only Memory), DVD-ROM (Digital Versatile Disc Read Only Memory), or USB (Universal Serial Bus) memory. Alternatively, the radiation image processing program 12 may be provided in the form of a download from an external device via a network.

[0073] The technology disclosed herein extends to all program products. Program products include all forms of products for providing programs. For example, program products include programs provided via networks such as the Internet, and non-temporary computer-readable recording media such as CD-ROMs, DVDs, and USB memory sticks on which programs are stored.

[0074] The following are additional notes to this disclosure. (Additional note 1) Equipped with a processor, The aforementioned processor, Post-contrast radiographic images are obtained by radiography of a subject containing a tubular structure into which a contrast agent has been injected. Using the tubular structure as a reference, the first scattered ray component on the incident side of the radiation to the subject and the second scattered ray component on the exit side of the radiation are derived. A radiographic image processing apparatus that derives a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image based on the first scattered radiation component and the second scattered radiation component in the region of the tubular structure into which the contrast agent was injected in the post-contrast radiographic image. (Additional note 2) The radiation image processing apparatus according to Appendix 1, wherein the processor derives the first scattered ray component and the second scattered ray component, respectively, based on the first body thickness of the subject on the incident side of the radiation with respect to the tubular structure on the radiation transmission path within the subject, and the second body thickness on the exit side of the radiation with respect to the tubular structure. (Additional note 3) The radiographic image processing apparatus according to appendix 1 or 2, wherein the processor derives a first scattered ray component based on a first coefficient that takes into account scattered rays absorbed by the contrast agent, which is determined according to the concentration of the contrast agent, and derives a second scattered ray component based on a second coefficient that takes into account scattered rays generated from the contrast agent, which is determined according to the concentration of the contrast agent. (Additional note 4) The radiographic image processing apparatus according to any one of the appendices 1 to 3, wherein the processor derives other scattered radiation components in areas other than the tubular structure into which the contrast agent was injected in the post-contrast radiographic image, and derives the post-contrast processed radiographic image by removing the scattered radiation components in the other areas of the post-contrast radiographic image based on the other scattered radiation components. (Additional note 5) The processor, in the other region, derives the first scattered ray component on the incident side of the radiation and the second scattered ray component on the outgoing side of the radiation of the object, with respect to the tubular structure. The radiation image processing apparatus according to Appendix 4, which derives the other scattered radiation components based on the first scattered radiation component and the previous second scattered radiation component. (Additional note 6) The radiographic image processing apparatus according to any one of the appendices 1 to 3, wherein the processor derives a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image only in the region of the tubular structure in the post-contrast radiographic image. (Additional note 7) The processor acquires a pre-contrast radiographic image by radiography of the subject, including the tubular structure, before the contrast agent is injected. The pre-contrast scattered radiation component included in the pre-contrast radiographic image is derived, Based on the pre-contrast scattered radiation component, the scattered radiation component of the pre-contrast radiographic image is removed to derive a pre-contrast processed radiographic image. A radiographic image processing apparatus according to appendix 4 or 5, which derives a difference image between the pre-processed radiographic image and the post-processed radiographic image. (Additional note 8) The processor acquires a pre-contrast radiographic image by radiography of the subject, including the tubular structure, before the contrast agent is injected. The pre-contrast scattered radiation component included in the region of the tubular structure in the pre-contrast radiographic image is derived, Based on the pre-contrast scattered radiation component, the scattered radiation component in the region of the tubular structure in the pre-contrast radiographic image is removed to derive a pre-contrast processed radiographic image. A radiographic image processing apparatus according to appendix 6, which derives a difference image between the pre-processed radiographic image and the post-processed radiographic image. (Additional note 9) The computer acquires post-contrast radiographic images by radiography of a subject containing a tubular structure into which a contrast agent has been injected. Using the tubular structure as a reference, the first scattered ray component on the incident side of the radiation to the subject and the second scattered ray component on the exit side of the radiation are derived. A radiographic image processing method for deriving a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image based on the first scattered radiation component and the second scattered radiation component in the region of the tubular structure in which the contrast agent was injected in the post-contrast radiographic image. (Additional note 10) A procedure for obtaining post-contrast radiographic images by radiography of a subject containing a tubular structure into which a contrast agent has been injected, A procedure for deriving the first scattered ray component on the incident side of the radiation to the subject and the second scattered ray component on the exit side of the radiation, using the tubular structure as a reference, A radiographic image processing program that causes a computer to perform a procedure to derive a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image based on the first scattered radiation component and the second scattered radiation component in the region of the tubular structure in which the contrast agent was injected in the post-contrast radiographic image. [Explanation of Symbols]

[0075] 1. Angiography equipment 2 Main unit 3 Arms 4. Mounting part 5 Radiation source 6. Photography Department 7. Shooting platform 8. Radiation detector 10. Radiation image processing device 11 CPU 12. Radiation Image Processing Program 13 Storage 14 displays 15 Input Devices 16 memory 17 Network Interface 18 bus 20 Image acquisition unit 21 Scattered radiation removal section 22 Image output unit 23 Display Control Unit 100 Angiography System A0 Vascular area A1 Other areas G1 Mask Image G2 Live Images G11 Processed Mask Image G22 Processed Live Image GP DSA images α,β coefficients

Claims

1. Equipped with a processor, The aforementioned processor, Post-contrast radiographic images are obtained by radiography of a subject containing a tubular structure into which a contrast agent has been injected. Using the tubular structure as a reference, the first scattered ray component on the incident side of the radiation to the subject and the second scattered ray component on the outgoing side of the radiation are derived. A radiographic image processing apparatus that derives a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image based on the first scattered radiation component and the second scattered radiation component in the region of the tubular structure in which the contrast agent was injected in the post-contrast radiographic image.

2. The radiation image processing apparatus according to claim 1, wherein the processor derives the first scattered ray component and the second scattered ray component, respectively, based on the first body thickness of the subject on the radiation incident side with respect to the tubular structure on the radiation transmission path within the subject, and the second body thickness on the radiation exit side with respect to the tubular structure.

3. The radiation image processing apparatus according to claim 1 or 2, wherein the processor derives a first scattered ray component based on a first coefficient that takes into account scattered rays absorbed by the contrast agent, which is determined according to the concentration of the contrast agent, and derives a second scattered ray component based on a second coefficient that takes into account scattered rays generated from the contrast agent, which is determined according to the concentration of the contrast agent.

4. The radiographic image processing apparatus according to claim 1, wherein the processor derives other scattered radiation components in areas other than the tubular structure into which the contrast agent was injected in the post-contrast radiographic image, and derives the post-contrast processed radiographic image by removing the scattered radiation components in the other areas of the post-contrast radiographic image based on the other scattered radiation components.

5. The processor, in the other region, derives a first scattered ray component on the incident side of the radiation and a second scattered ray component on the outgoing side of the radiation of the subject, with respect to the tubular structure. The radiation image processing apparatus according to claim 4, wherein the other scattered radiation components are derived based on the first scattered radiation component and the previous second scattered radiation component.

6. The radiographic image processing apparatus according to claim 1, wherein the processor derives a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image only in the region of the tubular structure in the post-contrast radiographic image.

7. The processor acquires a pre-contrast radiographic image by radiography of the subject, including the tubular structure, before the contrast agent is injected. The pre-contrast scattered radiation component included in the pre-contrast radiographic image is derived, Based on the pre-contrast scattered radiation component, the scattered radiation component of the pre-contrast radiographic image is removed to derive a pre-contrast processed radiographic image. The radiographic image processing apparatus according to claim 4 or 5, which derives a difference image between the pre-processed radiographic image and the post-processed radiographic image.

8. The processor acquires a pre-contrast radiographic image by radiography of the subject, including the tubular structure, before the contrast agent is injected. The pre-contrast scattered radiation component included in the region of the tubular structure in the pre-contrast radiographic image is derived, Based on the pre-contrast scattered radiation component, the scattered radiation component in the region of the tubular structure in the pre-contrast radiographic image is removed to derive a pre-contrast processed radiographic image. The radiographic image processing apparatus according to claim 6, which derives a difference image between the pre-processed radiographic image and the post-processed radiographic image.

9. The computer acquires post-contrast radiographic images by radiography of a subject containing a tubular structure into which a contrast agent has been injected. Using the tubular structure as a reference, the first scattered ray component on the incident side of the radiation to the subject and the second scattered ray component on the outgoing side of the radiation are derived. A radiographic image processing method for deriving a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image based on the first scattered radiation component and the second scattered radiation component in the region of the tubular structure in which the contrast agent was injected in the post-contrast radiographic image.

10. A procedure for obtaining post-contrast radiographic images by radiography of a subject containing a tubular structure into which a contrast agent has been injected, A procedure for deriving the first scattered ray component on the incident side of the radiation to the subject and the second scattered ray component on the exit side of the radiation, using the tubular structure as a reference, A radiographic image processing program that causes a computer to perform a procedure to derive a post-contrast processed radiographic image by removing the scattered radiation component of the post-contrast radiographic image based on the first scattered radiation component and the second scattered radiation component in the region of the tubular structure in which the contrast agent was injected in the post-contrast radiographic image.

Images