Image processing apparatus, method, and program

Abstract

The present invention relates to an image processing apparatus, method, and program that reduce the difference in image quality between high-absorbent regions and adjacent regions in a tomographic image. [Solution] The system includes a processor, which identifies high-absorbent regions in a projection image obtained by imaging a subject containing high-absorbent materials using a CT scanner, and derives a corrected projection image by performing a correction on the high-absorbent regions in the projection image to suppress the image quality difference between the high-absorbent regions and other regions other than the high-absorbent regions.

Description

Technical Field

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

Background Art

[0002] In a CT (Computed Tomography) apparatus, when an object with a high X-ray absorption rate such as metal is included inside a subject, artifacts occur in the reconstructed image. Such artifacts hinder clinical diagnosis. For this reason, various methods for removing artifacts have been proposed. For example, in Patent Document 1, a peak on projection data, which is one of the characteristics of an artifact, is estimated by interpolation from data of a channel not affected by a high absorber such as a metal body, and the signal value of the peak of the projection data is interpolated with the estimated projection data, and an artifact-reduced tomographic image is obtained by reconstructing the interpolated projection data.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the method described in Patent Document 1 is a method of approximately interpolating projection data based on measured projection data adjacent to the peak of the projection data. For this reason, the position of the peak in the projection data and the position of the data for interpolating the data at the peak position are different. As a result, the data at the peak position does not match the surrounding measured projection data, and in the reconstructed tomographic image, a difference in image quality such as density or frequency characteristics occurs between a high absorber region such as metal and a region adjacent to the high absorber region.

[0005] This disclosure is made in view of the above circumstances and aims to reduce the difference in image quality between high-absorbent regions and adjacent regions in tomographic images. [Means for solving the problem]

[0006] The image processing apparatus according to this disclosure comprises a processor, The processor identifies high-attenuation regions in projection images obtained by imaging a subject containing high-attenuation materials using a CT scanner. A corrected projection image is derived by applying a correction to the high-absorbent regions of the projected image to suppress the image quality discrepancy between the high-absorbent regions and other regions.

[0007] In the image processing apparatus according to this disclosure, the processor may derive a corrected projection image by performing a correction on the high-absorbent region in the projection image based on at least one of the following: the hardening of the radiation quality transmitted through the subject, the scattered radiation from the radiation transmitted through the subject, and the frequency components of the tomographic image reconstructed from the projection image.

[0008] In the image processing apparatus according to this disclosure, the processor reconstructs a projected image to derive a provisional tomographic image, identifies a provisional high-absorbent region in the provisional tomographic image, and identifies a high-absorbent region in the projected image by projecting the provisional high-absorbent region forward. Alternatively, a de-absorbent tomographic image may be derived from a provisional tomographic image, from which the effects of high-absorbent regions have been removed. A corrected high-absorbent projection image may be derived by projecting the provisional high-absorbent regions forward onto the de-absorbent tomographic image while correcting it based on at least one of the following: the hardening of the radiation quality transmitted through the subject, the scattered radiation from the radiation transmitted through the subject, and the frequency components of the tomographic image reconstructed from the projection image. Finally, a corrected projection image may be derived by replacing the high-absorbent regions in the projection image with the corrected high-absorbent projection image.

[0009] In the image processing apparatus according to this disclosure, the processor may perform frequency component-based correction of the tomographic image based on at least one of the following: the channel frequency of the detector during back projection of the projected image for reconstruction of the tomographic image, a back projection algorithm, a reconstruction filter, the pixel size of the tomographic image, and a forward projection algorithm used for forward projection.

[0010] In the image processing apparatus according to this disclosure, the processor may derive a corrected tomographic image by reconstructing a corrected projection image.

[0011] The image processing method disclosed herein involves a computer identifying high-attenuation regions in a projection image obtained by imaging a subject containing high-attenuation materials using a CT scanner. A corrected projection image is derived by applying a correction to the high-absorbent regions of the projected image to suppress the image quality discrepancy between the high-absorbent regions and other regions.

[0012] The image processing program disclosed herein includes a procedure for identifying high-attenuation regions in projection images obtained by imaging a subject containing high-attenuation materials using a CT scanner, and The computer is instructed to perform a procedure to derive a corrected projection image by applying a correction to the high-absorbent regions of the projected image, thereby suppressing the image quality difference between the high-absorbent regions and other regions.

[0013] Furthermore, the technology disclosed herein may be applied to program products. [Effects of the Invention]

[0014] According to this disclosure, it is possible to reduce the difference in image quality between high-absorbent regions and adjacent regions in tomographic images. [Brief explanation of the drawing]

[0015] [Figure 1] Schematic diagram of an image processing device according to an embodiment of the present disclosure. [Figure 2]Diagram showing the hardware configuration of the image processing apparatus according to the present embodiment [Figure 3] Functional configuration diagram of the image processing apparatus according to the present embodiment [Figure 4] Diagram showing raw data obtained by photographing the head of a subject containing metal with a CT apparatus [Figure 5] Diagram showing the flow of processing performed by the specifying unit, correction unit, and reconstruction unit in the present embodiment [Figure 6] Diagram for explaining the specification of the metal region [Figure 7] Diagram for explaining the forward projection of the metal region [Figure 8] Diagram for explaining the correction of the metal region [Figure 9] Flowchart showing the processing performed in the present embodiment

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. First, an example of the configuration of a medical image capturing system including an image processing apparatus according to an embodiment of the present disclosure will be described. FIG. 1 is a schematic configuration diagram of a medical image capturing system including an image processing apparatus according to the present embodiment.

[0017] As shown in FIG. 1, the medical image capturing system 1 of the present embodiment includes a CT apparatus 2 and a console 3. The CT apparatus 2 includes a gantry 4 and a couch 8. In the following description, the horizontal direction in FIG. 1 is the X-axis, the vertical direction is the Y-axis, and the direction orthogonal to the XY plane is the Z-axis. The CT apparatus 2 is an example of a radiation imaging apparatus.

[0018] The gantry 4 has an opening 4A, and the subject H to be imaged is placed in the opening 4A while being placed on the couch 8. The gantry 4 and the couch 8 are relatively movable in the Z-axis direction.

[0019] Inside the gantry 4, a radiation source 5, which has a radiation tube 6 and a bowtie filter 7, and a detector 9 are arranged facing each other with the subject H in between. The bowtie filter 7 optimizes the radiation dose by increasing the dose near the center and decreasing the dose around the periphery in order to reduce the dose in the peripheral area. The radiation emitted from the radiation tube 6 is shaped into a beam shape suitable for the size of the subject H by the bowtie filter 7 and irradiated onto the subject H.

[0020] The detector 9 detects radiation transmitted through the subject H and generates projection data corresponding to the detected radiation dose. In the detector 9, multiple detection elements 9P are arranged in an arc shape centered on the focal point of the radiation tube 6. The direction in which the multiple detection elements 9P are aligned in the arc is defined as the channel direction.

[0021] In this embodiment, X-rays are used as an example of radiation, but the invention is not limited to this, and gamma rays or other types of radiation can also be used.

[0022] The radiation source 5 and detector 9 are mounted on a rotating plate 4B inside the gantry 4 and are rotated around the subject H by a rotation drive unit (not shown). As radiation irradiation from the radiation source 5 and detection of radiation by the detector 9 are repeated along with the rotation of both, raw data is acquired in multiple view units with different projection angles of radiation onto the subject H, and projection data is generated from the raw data. The generated projection data is output to the console 3. The projection data is derived by arranging the raw data with the horizontal axis representing the channel of the detector 9 and the vertical axis representing the rotation angle of the CT device 2.

[0023] The radiation dose emitted from the radiation tube 6, the rotation speed of the gantry 4, and the relative movement speed between the gantry 4 and the patient bed 8 are all set by the console 3 based on the imaging conditions entered by the operator, such as a technician.

[0024] The console 3 in this embodiment controls the imaging of the subject H, generates projection data from the raw data acquired by imaging, reconstructs tomographic images from the projection data, and sets the storage of image data for the projection data and tomographic images. The console 3 is an example of an image processing apparatus in this disclosure.

[0025] Next, an image processing device according to this embodiment will be described. First, with reference to Figure 2, the hardware configuration of the image processing device according to this embodiment, which is contained within the console 3, will be described. As shown in Figure 2, the image processing device 10 contained within the console 3 is a computer such as a workstation, server computer, or personal computer, and is equipped with a CPU (Central Processing Unit) 11, non-volatile storage 13, and memory 16 as a temporary storage area.

[0026] The image processing device 10 also includes a display 14, an input device 15, and an I / F (Interface) 17. The CPU 11, storage 13, display 14, input device 15, memory 16, and I / F 17 are connected to a bus 18. The CPU 11 is an example of a processor in this disclosure.

[0027] The storage 13 is implemented using an HDD (Hard Disk Drive), an SSD (Solid State Drive), and flash memory, etc. The image processing program 12 installed on the image processing device 10 is stored in the storage 13 as a storage medium. The CPU 11 reads the image processing program 12 from the storage 13, expands it into memory 16, and executes the expanded image processing program 12.

[0028] The display 14 is a device that displays various types of screens, such as a liquid crystal display or an EL (Electro Luminescence) display.

[0029] The input device 15 is used by the operator to input instructions and various information regarding the shooting conditions, image generation and display, etc., when photographing the subject H. Examples of input devices 15 include various switches, buttons, touch panels, styluses, keyboards, and mice. The display 14 and the input device 15 may be integrated to form a touch panel display.

[0030] I / F17 communicates various types of information with the rotational drive unit (not shown) of the gantry 4, the radiation source 5, and the detector 9 via wired or wireless communication.

[0031] The 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 image processing device 10 upon request. Alternatively, it may be 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 image processing device 10.

[0032] Next, the functional configuration of the image processing apparatus according to this embodiment will be described. Figure 3 is a diagram showing the functional configuration of the image processing apparatus according to this embodiment. As shown in Figure 3, the image processing apparatus 10 includes an image capture control unit 21, an information acquisition unit 22, an identification unit 23, a correction unit 24, and a reconstruction unit 25. The CPU 11 functions as the image capture control unit 21, the information acquisition unit 22, the identification unit 23, the correction unit 24, and the reconstruction unit 25 by executing the image processing program 12.

[0033] The imaging control unit 21 controls each part of the CT scanner 2 to perform imaging of the subject H based on instructions from the input device 15. In this embodiment, the head of the subject H is to be imaged. For illustrative purposes, the head is assumed to contain metal. The metal is an example of a highly absorbent material in this disclosure.

[0034] The information acquisition unit 22 acquires projection data obtained by imaging the subject H from the CT device 2. The image represented by the projection data is the projection image.

[0035] Figure 4 shows the raw data obtained by imaging the head of subject H containing metal using the CT scanner 2. In Figure 4, the raw data 30 is shown when radiation is irradiated to the head 31 in the direction of arrow A. In the raw data 30 shown in Figure 4, the horizontal axis represents the channel direction of the detector 9, and the vertical axis represents the data value. In the raw data 30, the data value is small in the channel that detected radiation that did not pass through the head 31 (i.e., the detection element 9P), the data value is large in the channel that detected radiation that passed through the head 31, and there is a peak in the data value in the channel that detected radiation that passed through the metal 32 inside the head 31. When such raw data is arranged with the horizontal axis representing the channel direction of the detector 9 and the vertical axis representing the rotation angle, it becomes projection data.

[0036] Figure 5 is a diagram showing the processing flow performed by the identification unit 23, the correction unit 24, and the reconstruction unit 25 in this embodiment. As shown in Figure 5, first, the metallic region A0 is extracted from the projection image P0 represented by projection data. Next, the metallic region A0 in the projection image P0 is corrected to derive a corrected projection image P1. Furthermore, the corrected projection image P1 is reconstructed to derive a corrected tomographic image D1. The individual processes performed by the identification unit 23, the correction unit 24, and the reconstruction unit 25 will be described below.

[0037] The identification unit 23 identifies metallic regions in the projected image. Figure 6 is a diagram illustrating the identification of metallic regions. The identification unit 23 first derives a provisional tomographic image D0 by reconstructing the projected image P0 using the reconstruction unit 25. Here, the provisional tomographic image D0 includes metallic regions and artifacts due to the influence of metal. The identification unit 23 removes artifacts from the provisional tomographic image D0. For example, the identification unit 23 removes artifacts from the provisional tomographic image D0 using a removal model constructed to remove artifacts from tomographic images.

[0038] The identification unit 23 identifies the metallic region A1 in the provisional tomographic image from which artifacts have been removed (hereinafter referred to as the removed tomographic image D2). Since the metallic region A1 is a high-brightness region in the removed tomographic image D2, the identification unit 23 extracts the metallic region A1 using an extraction model constructed to extract such high-brightness regions. Then, as shown in Figure 7, the identification unit 23 identifies the metallic region A1 in the projected image P0 by projecting the metallic region A1 in the direction of arrow B.

[0039] The correction unit 24 derives a corrected projected image P1 by performing corrections on the metallic region in the projected image P0. Figure 8 is a diagram illustrating the correction of the metallic region. The correction unit 24 derives a provisional corrected tomographic image (let's call it D3) in which the metallic region has been corrected by correcting the metallic region A1 in the de-articulated tomographic image D2 from which artifacts have been removed. The correction of the metallic region A1 is performed, for example, by interpolating the pixel values ​​of the metallic region A1 with the pixel values ​​of the region adjacent to the metallic region A1, as described in Patent Document 1, or by using a correction model that has been trained to estimate the pixel values ​​of the metallic region A1. Then, the corrected metallic region projected image A3 is derived by forward projecting only the region A2 corresponding to the metallic region in the provisional corrected tomographic image D3. In Figure 8, the forward projection of region A2 is shown by adding an arrow to the provisional tomographic image D3. Alternatively, instead of projecting only region A2 forward, a provisional projection image may be derived by projecting the entire provisional corrected tomographic image D3 forward, and the corrected metallic region projection image A3 may be derived by extracting the region corresponding to the metallic region in the provisional projection image.

[0040] The correction unit 24 corrects the metal region A0 in the projected image P0 by replacing it with the corrected metal region projected image A3, thereby deriving the corrected projected image P1 (see Figure 5).

[0041] In this process, the correction unit 24 performs a correction to suppress the discrepancy in image quality between the metallic region and other regions. Here, the projected image P0 includes the effects of beam quality due to beam hardening and the effects of scattered radiation from the subject H. The effects of beam quality due to beam hardening and scattered radiation differ between the metallic region and other regions within the subject H. Therefore, if the corrected metallic region projection image A3 is derived by simply performing a forward projection by integral calculation of the provisional corrected tomographic image D3, the effects of beam quality and scattered radiation will differ between the corrected metallic region projection image A3 and the region adjacent to the metallic region A0 in the projected image P0. As a result, the image quality will differ between the corrected metallic region projection image A3 and the region adjacent to the metallic region A0 in the projected image P0.

[0042] Therefore, the correction unit 25 derives a corrected metal region projection image A3, taking into account the effects of the beam quality and scattered radiation. This process is referred to as the first process.

[0043] In this embodiment, regarding beam quality, the effect of beam hardening on beam quality is derived in advance by simulating the radiation transmission process from when the radiation emitted from the radiation tube 6 passes through the subject H and reaches the detector 9. For example, the radiation transmission process within subject H is derived using the energy spectrum of the radiation at irradiation and the absorption spectrum of subject H for each energy. In this case, since the tissue of subject H is complex, it is assumed that subject H consists of three substances: water, bone, and air, and the composition of subject H in the radiation transmission path is derived as the radiation transmission process using the pixel values ​​of a provisional corrected tomographic image D3. Then, based on the derived radiation transmission process, the correction unit 24 projects the provisional corrected tomographic image D3 forward, correcting the effect of beam quality in region A2 corresponding to the metallic region to derive a corrected metallic region projection image A3.

[0044] Regarding scattered radiation, the scattered radiation component is derived in advance, for example, using a provisional corrected tomographic image D3, as a component that deviates from the radiation transmission path by passing through the subject H, relative to the process in which radiation passes through the radiation tube 6 and the detector 9 in a straight line. Then, the correction unit 24, based on the derived scattered radiation component, corrects the effect of scattered radiation in region A2 corresponding to the metal region when projecting the provisional corrected tomographic image D3 forward, thereby deriving a corrected metal region projection image A3.

[0045] The correction unit 24 may, as a first process, correct either the line quality or the scattered radiation, or it may correct both the line quality and the scattered radiation. When correcting both the line quality and the scattered radiation, the effects of both can be derived simultaneously in advance, thereby preventing errors that would occur if only the effect of the line quality or only the effect of the scattered radiation were corrected separately.

[0046] Furthermore, the correction unit 24 may perform correction to suppress the image quality difference between the metallic region and the non-metallic region based on the frequency components of the derived tomographic image. This process is referred to as the second process. The frequency components of the derived tomographic image change depending on, for example, the channel frequency of the detector during back projection, the back projection algorithm, the reconstruction filter, the pixel size of the tomographic image, and the forward projection algorithm.

[0047] Regarding the channel frequency of the detector, the tomographic image is reconstructed by back-projecting the projected image of the path connecting the radiation tube 6 and each channel (i.e., each detection element 9P) of the detector 9 in the projected image. Therefore, the wider the width of the detector 9, i.e., the lower the channel frequency, the greater the blurring of the projected image in the channel direction of the detector 9, and the more high-frequency components are lost in the reconstructed tomographic image.

[0048] Regarding the backprojection algorithm, both the pixels of the tomographic image and the channels of the detector 9 are discrete pieces of information with a constant width. Therefore, when backprojecting a projection image along a path passing between pixels of the tomographic image or between channels of the detector 9, interpolation is required to interpolate the images between pixels of the tomographic image or between channels of the detector 9. Depending on the type of interpolation performed, the degree of reduction in the high-frequency components of the reconstructed tomographic image will differ.

[0049] Furthermore, when the identification unit 23 identifies a metallic region, a provisional tomographic image D0 is derived by reconstructing the projected image P0. The back projection algorithm is an algorithm for reconstructing the projected image P0.

[0050] Regarding reconstruction filters, known FBP (Filtered Back Projection) methods use filters with differential characteristics that emphasize high-frequency components (such as ramp filters) when back-projecting the projected image. Theoretically, a reconstruction filter that can obtain a correct reconstructed image is defined, but multiple reconstruction filters may be available to obtain the desired frequency range of the tomographic image, depending on the purpose, such as suppressing noise in the projected image or emphasizing structural information of frequency components desired by the user. Therefore, the degree of high-frequency components in the reconstructed tomographic image differs depending on the reconstruction filter used.

[0051] Regarding the pixel size of the tomographic image, similar to the channel frequency of the detector 9, the smaller the pixel size of the tomographic image (i.e., the higher the sampling frequency), the smaller the discrepancy between the projected image and the pixel position in the path connecting the radiation tube 6 and the detector 9 channels, thus reducing the loss of high-frequency components in the tomographic image. On the other hand, the larger the pixel size (i.e., the lower the sampling frequency), the lower the high-frequency components in the tomographic image, and the more the fine structure is averaged out. For this reason, the degree of high-frequency components in the tomographic image differs depending on the pixel size of the tomographic image.

[0052] Regarding the forward projection algorithm, both the pixels of the projected image and the channels of the detector 9 are discrete information with a constant width. Therefore, when projecting a tomographic image forward along a path passing between pixels of the tomographic image or between channels of the detector 9, interpolation is required to interpolate the images between pixels of the projected image or between channels of the detector 9. Depending on the type of interpolation process used, different frequency components are lost due to the forward projection.

[0053] From the above, when projecting a tomographic image forward, the frequency components lost due to forward projection can be derived by interpolating the pixels generated by the calculations during forward projection and the frequency components of the tomographic image. In this embodiment, the frequency components lost due to forward projection are derived in advance.

[0054] The correction unit 24 derives a corrected metal region projection image A3 by forward projection of a provisional corrected tomography image D3 that includes region A2 corresponding to metal in the provisional corrected tomography image D3, along the path connecting the radiation tube 6 and the detector 9. In order to match the frequency components of the metal region A0 and adjacent regions in the projection image P0 with the frequency components of the corrected metal region projection image A3, the unit emphasizes the frequency components of the provisional corrected tomography image D3 that includes region A2, along the path connecting the radiation tube 6 and the detector 9, based on at least one of the following: the detector channel frequency during back projection, the back projection algorithm, the reconstruction filter, the pixel size of the tomography image, and the forward projection algorithm. This makes it possible to match the frequency components of the corrected metal region projection image A3 with the frequency components of the metal region A0 and adjacent regions in the projection image P0 when the corrected metal region projection image A3 is derived by forward projection of a provisional corrected tomography image D3 that includes region A2, along the path connecting the radiation tube 6 and the detector 9.

[0055] Furthermore, the correction unit 24 may derive a corrected metal region projection image A3 by correcting the influence of beam quality and scattered radiation from non-metallic structures included in the projection image P0. This process is referred to as the third process. In the decompressed tomographic image D2 described above, artifacts caused by metal are removed, while the influence of beam quality and scattered radiation from non-metallic high-absorbent materials is not removed. As a result, the influence of beam quality and scattered radiation from non-metallic high-absorbent materials cannot be completely removed and remains in the provisional corrected tomographic image D3. For example, between two bones, the influence of beam quality and scattered radiation from the bone cannot be completely removed and remains. In this case, as described above, when projecting the provisional corrected tomographic image D3 forward, the provisional corrected tomographic image D3, which still contains the influence of beam quality and scattered radiation from non-metallic high-absorbent materials, is used to further correct the influence of beam quality and scattered radiation. Therefore, when deriving the corrected metal region projection image A3, the influence of beam quality and scattered radiation cannot be correctly corrected.

[0056] Therefore, when the correction unit 24 projects the provisional corrected tomographic image D3 forward, it is preferable to remove the effects of the beam quality and scattered radiation of non-metallic high-absorbent materials, and then correct the effects of the beam quality and scattered radiation as described above to derive the corrected metallic region projection image A3.

[0057] Furthermore, when the correction unit 24 derives the corrected metal region projection image A3 by correcting the effects of the radiation quality and scattered radiation as described above, it may also correct the scattered radiation component that enters the metal region A0 from a region adjacent to the metal region A0 in the projection image P0. This process is referred to as the fourth process. In the fourth process, as described above, the component that deviates from the transmission path of the radiation by passing through the subject H is pre-determined as the scattered radiation component, in the process of the radiation passing in a straight line through the path connecting the radiation tube 6 and the detector 9. When the correction unit 24 forward projects the provisional corrected tomographic image D3, it should correct the effect of scattered radiation in the region A2 corresponding to the metal based on the scattered radiation component that enters the metal region A0 from a region adjacent to the metal region A0, and obtain the corrected metal region projection image A3. Note that by considering the effect of the radiation quality when correcting the effect of scattered radiation, the effect of scattered radiation can be corrected with greater accuracy.

[0058] Furthermore, when the correction unit 24 derives the corrected metal region projection image A3 by correcting the effects of the radiation quality and scattered radiation as described above, it may also correct the scattered radiation component that enters the region adjacent to metal region A0 in the projection image P0. This process is referred to as the fifth process. In the fifth process, as described above, the component that deviates from the transmission path of radiation by passing through the subject H is pre-determined as the scattered radiation component, relative to the process in which radiation passes through the path connecting the radiation tube 6 and the detector 9 in a straight line. Then, when the correction unit 24 forward-projects a provisional corrected tomographic image D3 based on the scattered radiation component that enters the region adjacent to metal region A0 from metal region A0, it should correct the effects of scattered radiation that enters the region adjacent to metal region A0 from metal region A0 to derive the corrected metal region projection image A3 and further corrected projection image P1. Note that by considering the effect of the radiation quality when correcting the effects of scattered radiation, the effects of scattered radiation can be corrected with greater accuracy.

[0059] The correction unit 24 may perform all of the first to fifth processes, or it may perform one or more of the first to fifth processes.

[0060] The reconstruction unit 25 derives a corrected tomographic image D1 by reconstructing the corrected projection image P1 at multiple projection angles.

[0061] Next, the processing performed in this embodiment will be described. Figure 9 is a flowchart showing the processing performed in this embodiment. First, the imaging control unit 21 performs imaging of the subject H in the CT device 2 according to the operator's instructions (step ST1), and the information acquisition unit 22 acquires projection data (step ST2). The identification unit 23 identifies the metallic region A0 in the projection image P0 represented by the projection data (step ST3). The correction unit 24 corrects the metallic region A0 in the projection image P0 to derive a corrected projection image P1 (step ST4). The reconstruction unit 25 reconstructs the corrected projection image P1 to derive a corrected tomographic image D1 (step ST5), and the process ends.

[0062] Thus, in this embodiment, a corrected projection image P0 is derived by applying a correction to the metal region in the projection image to suppress the image quality difference between the metal region and other non-metallic regions. Therefore, the difference in image quality between the metal region and the region adjacent to the metal region in the corrected tomographic image D1 derived by reconstructing the corrected projection image P0 can be reduced.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Furthermore, although the above embodiment describes an embodiment in which the image processing program 12 is pre-stored (installed) in the storage 13, the invention is not limited to this. The 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 image processing program 12 may be provided in the form of a download from an external device via a network.

[0067] 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.

[0068] The following are additional notes to this disclosure. (Additional note 1) Equipped with a processor, The aforementioned processor, By imaging a subject containing a highly attenuating material using a CT scanner, we can identify the highly attenuating regions in the projection image. An image processing apparatus that derives a corrected projection image by performing a correction on the high-absorbent region in the projection image to suppress the image quality difference between the high-absorbent region and other regions other than the high-absorbent region. (Additional note 2) The image processing apparatus according to Appendix 1, wherein the processor derives the corrected projection image by performing a correction on the high-absorbent region in the projection image based on at least one of the hardening of the radiation quality of the radiation passing through the subject, the scattered radiation of the radiation passing through the subject, and the frequency components of the tomographic image reconstructed from the projection image. (Additional note 3) The processor reconstructs the projection image to derive a provisional tomographic image, identifies a provisional high-absorbent region in the provisional tomographic image, and identifies the high-absorbent region in the projection image by projecting the provisional high-absorbent region forward. The image processing apparatus according to Appendix 2, comprising: deriving a decompressed tomographic image from the provisional tomographic image from which the influence of the high-absorbent region has been removed; deriving a corrected high-absorbent projection image by projecting the provisional high-absorbent region forward while correcting the decompressed tomographic image based on at least one of the hardening of the radiation quality of the radiation passing through the subject, the scattered radiation of the radiation passing through the subject, and the frequency components of the tomographic image reconstructed from the projection image; and deriving the corrected projection image by replacing the high-absorbent region in the projection image with the corrected high-absorbent projection image. (Additional note 4) The image processing apparatus according to Appendix 3, wherein the processor performs a correction based on the frequency components of the tomographic image based on at least one of the following: the channel frequency of the detector during back projection of the projection image for reconstruction of the tomographic image, a back projection algorithm, a reconstruction filter, the pixel size of the tomographic image, and a forward projection algorithm used for forward projection. (Additional note 5) The image processing apparatus according to any one of the appendices 1 to 4, wherein the processor derives a corrected tomographic image by reconstructing the corrected projection image. (Additional note 6) A computer identifies high-attenuation regions in projection images obtained by scanning a subject containing high-attenuation materials using a CT scanner. An image processing method for deriving a corrected projected image by performing a correction on the high-absorbent region in the projected image to suppress the image quality difference between the high-absorbent region and other regions other than the high-absorbent region. (Additional note 7) A procedure for identifying high-attenuation regions in projection images obtained by imaging a subject containing high-attenuation materials using a CT scanner, An image processing program that causes a computer to perform a procedure to derive a corrected projection image by performing a correction on the high-absorbent region in the projection image to suppress the difference in image quality between the high-absorbent region and other regions other than the high-absorbent region. [Explanation of Symbols]

[0069] 1. Medical imaging system 2 CT device 3 Console 4 Gantry 4A opening 4B Rotating Plate 5 Radiation source 6 Radiation tubes 7 Bowtie Filter 8 berths 9 Detectors 9P detection element 10 Image Processing Device 11 CPU 12 Image Processing Programs 13 Storage 14 displays 15 Input Devices 16 memory 17 I / F 18 bus 21. Image capture control unit 22 Information Acquisition Department 23 Specific section 24 Correction section 25 Reconstruction part 30 Raw data 31 Head 32 metal A0,A1 Metal area A2 Region corresponding to the metallic region A3 Corrected Metal Area Projection Image D0 Provisional fault image D1 Corrected Tomographic Image D2 Removal Tomographic Image D3 Provisional corrected tomographic image P0 Projection Image P1 Corrected projection image

Claims

1. Equipped with a processor, The aforementioned processor, By imaging a subject containing a highly attenuating material using a CT scanner, the highly attenuating regions in the projection image are identified. An image processing apparatus that derives a corrected projection image by performing a correction on the high-absorbent region in the projection image to suppress the image quality difference between the high-absorbent region and other regions other than the high-absorbent region.

2. The image processing apparatus according to claim 1, wherein the processor derives the corrected projection image by performing a correction on the high-absorbent region in the projection image based on at least one of the hardening of the radiation quality of the radiation passing through the subject, the scattered radiation of the radiation passing through the subject, and the frequency components of the tomographic image reconstructed from the projection image.

3. The processor reconstructs the projection image to derive a provisional tomographic image, identifies a provisional high-absorbent region in the provisional tomographic image, and identifies the high-absorbent region in the projection image by projecting the provisional high-absorbent region forward. The image processing apparatus according to claim 2, comprising: deriving a decompressed tomographic image from the provisional tomographic image from which the influence of the high-absorbent region has been removed; deriving a corrected high-absorbent projection image by projecting the provisional high-absorbent region forward while correcting the decompressed tomographic image based on at least one of the hardening of the radiation quality of the radiation passing through the subject, the scattered radiation of the radiation passing through the subject, and the frequency components of the tomographic image reconstructed from the projection image; and deriving the corrected projection image by replacing the high-absorbent region in the projection image with the corrected high-absorbent projection image.

4. The image processing apparatus according to claim 3, wherein the processor performs correction based on the frequency components of the tomographic image based on at least one of the following: the channel frequency of the detector during back projection of the projection image for reconstruction of the tomographic image, a back projection algorithm, a reconstruction filter, the pixel size of the tomographic image, and a forward projection algorithm used for forward projection.

5. The image processing apparatus according to any one of claims 1 to 4, wherein the processor derives a corrected tomographic image by reconstructing the corrected projection image.

6. A computer identifies high-attenuation regions in projection images obtained by scanning a subject containing high-attenuation materials using a CT scanner. An image processing method for deriving a corrected projected image by performing a correction on the high-absorbent region in the projected image to suppress the image quality difference between the high-absorbent region and other regions other than the high-absorbent region.

7. A procedure for identifying high-attenuation regions in projection images obtained by imaging a subject containing high-attenuation materials using a CT scanner, An image processing program that causes a computer to perform a procedure to derive a corrected projection image by performing a correction on the high-absorbent region in the projection image to suppress the difference in image quality between the high-absorbent region and other regions other than the high-absorbent region.

Images