Method for monitoring x-ray source focal spot drift and ct imaging system

Abstract

The application discloses a kind of X-ray source focal point drift monitoring method and CT imaging system.The monitoring method includes the following steps: structure is arranged in the light path area between X-ray source and detector, so that structure is located in the illumination range of X-ray source, and is located outside the imaging FOV area;Focus calibration is carried out to X-ray source, and the theoretical center point coordinate value of the projection image of structure is obtained in the focal point calibration process;In the process of carrying out CT scanning, the actual center point coordinate value of each frame projection image of structure is obtained, to calculate the center point drift amount of each frame projection image of structure;Based on the preset geometric position relationship, according to the center point drift amount of each frame projection image, the focal point drift amount of each frame projection image of X-ray source is calculated out.Using the monitoring method, focal point drift amount can be detected in real time and image correction is carried out once scanning.

Description

Technical Field

[0001] This invention relates to a method for monitoring the focus drift of an X-ray source, and also to a CT imaging system employing this monitoring method, belonging to the field of computed tomography technology. Background Technology

[0002] An X-ray source, also known as an X-ray tube, is a vacuum diode operating at high voltage. It contains two electrodes: a filament that emits electrons (cathode) and a target that receives the electron bombardment (anode). X-ray source anodes can be classified as fixed anode tubes and rotating anode tubes. A fixed anode tube refers to an X-ray source where the anode target remains stationary during operation; a rotating anode tube refers to an X-ray source where the anode target rotates at high speed. Because the high-speed impact of electrons on the rotating anode target generates significant heat, rotating anode tubes dissipate this heat through the rotation of the anode target and radiate heat outwards in real time, achieving superior heat dissipation. Therefore, their heat capacity is higher than that of fixed anode tubes. Consequently, rotating anode tubes are more widely used than fixed anode tubes.

[0003] Because the anode target of a rotating anode tube typically rotates at high speeds, sometimes exceeding 10,000 rpm, deviations between the actual and ideal installation positions of the rotating shaft, or uneven weight distribution within the anode target itself, can cause it to sway during rotation. This swaying leads to focal point shift. This focal point drift in the X-ray source introduces errors into image reconstruction, affecting image quality. Therefore, detecting focal point shift is crucial.

[0004] Chinese invention patent ZL 201611042507.9 discloses a method for detecting the focal shift of an X-ray tube, which detects whether the effective focal spot of an X-ray tube has shifted. The method includes: performing a first scan using X-rays generated by the ideal effective focal spot of the X-ray tube, and obtaining a first parameter based on a first energy value output from a preset channel in the X-ray detector according to a preset rule; performing a second scan using X-rays generated by the actual effective focal spot of the X-ray tube, and obtaining a second parameter based on a second energy value output from a preset channel in the X-ray detector according to a preset rule; if the first parameter and the second parameter do not match, it is confirmed that the actual effective focal spot has shifted relative to the ideal effective focal spot.

[0005] However, the above-mentioned focus shift detection method corrects the image by analyzing the shift between the actual focus and the ideal focus. It requires two scans to analyze the amount of focus shift. However, in addition to the impact of focus shift on image quality, the fluctuations in the tube current and tube voltage of the radiation source also affect the image. Therefore, the principle of two scans not only increases the radiation dose to the patient, but also makes the calculated amount of shift incompletely accurate. Summary of the Invention

[0006] The primary technical problem to be solved by this invention is to provide a method for monitoring the focus drift of an X-ray source.

[0007] Another technical problem to be solved by the present invention is to provide a CT imaging system employing the above-described monitoring method.

[0008] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0009] According to a first aspect of the present invention, a method for monitoring the focus drift of an X-ray source is provided, comprising the following steps:

[0010] A structural component is provided in the optical path region between the X-ray source and the detector, such that the structural component is located within the irradiation range of the X-ray source and outside the imaging FOV region;

[0011] The X-ray source is calibrated to focus, and the theoretical center point coordinates of the projected image of the structure are obtained during the focus calibration process.

[0012] During the CT scan, the actual center point coordinates of each frame of the projected image of the structure are obtained in order to calculate the center point drift of each frame of the projected image of the structure.

[0013] Based on the preset geometric positional relationship, the focal drift of each frame of the X-ray source is calculated according to the center point drift of each frame of the projected image.

[0014] Preferably, the X-ray source is focused, and the theoretical center point coordinates of the projected image of the structure are obtained during the focus calibration process, specifically including:

[0015] The X-ray source is calibrated to adjust the focal position to the theoretical position in the X and Z directions of a preset coordinate system; wherein the center of the preset coordinate system is the center of the detector, the Z direction is the axial direction of the detector, the X direction is the horizontal direction perpendicular to the Z direction, and the Y direction is the vertical direction perpendicular to the Z direction.

[0016] Based on the theoretical position of the focus, the structural component is scanned during the focus calibration process to obtain multiple scan images;

[0017] Calculate the X and Z coordinates of the center point of the projection area of ​​the structural component in each frame of the image in the preset coordinate system;

[0018] The average X-coordinate of the center point of the projection area of ​​the structural component in each frame image is obtained by averaging the X-coordinate; and the average Z-coordinate of the center point of the projection area of ​​the structural component in each frame image is obtained by averaging the Z-coordinate.

[0019] The average value of the X-coordinate and the average value of the Z-coordinate together constitute the theoretical center point coordinates of the projected image of the structural component.

[0020] Preferably, the center point drift of each frame of the projected image is obtained in the following way:

[0021] During the CT scan, the actual X coordinate and actual Z coordinate of the center point of each frame of the projected image of the structural component in the preset coordinate system are obtained.

[0022] For any frame of the projected image, the actual X coordinate of the center point is subtracted from the average value of the X coordinates to obtain the drift amount ΔX of the center point in the X direction; and the actual Z coordinate of the center point is subtracted from the average value of the Z coordinates to obtain the drift amount ΔZ of the center point in the Z direction; wherein, the drift amount ΔX in the X direction and the drift amount ΔZ in the Z direction together constitute the center point drift amount of the projected image frame.

[0023] Preferably, the focus shift of each frame of the projected image is calculated in the following way:

[0024] Obtain the first distance D1 in the Y direction from the focal point of the X-ray source to the structural component;

[0025] Obtain the second distance D2 from the structural component to the detector in the Y direction;

[0026] Based on the similar triangle geometry, the focus drift ΔX_FS and ΔZ_FS of each frame of projected image are calculated using the following formula;

[0027]

[0028] Preferably, the monitoring method further includes:

[0029] The image reconstruction algorithm is adapted based on the focus drift of each frame of the projected image from the X-ray source to correct the image.

[0030] Preferably, the adaptation includes at least the following steps:

[0031] For each voxel point f(x, y, z) within the reconstructed object, a line is constructed from the X-ray source to the voxel point f(x, y, z) using the adjusted X-ray source position S(X_FS+ΔX_FS, Y_FS, Z+ΔZ_FS), and extended to intersect the detector at point p(u, v); the pixel value of the ray along this direction at point p(u, v) on the detector plane is calculated, and the same calculation is performed for all voxels;

[0032] Alternatively, find the projection value at the intersection point p(u,v) of the line connecting the adjusted ray source position S(X_FS+ΔX_FS,Y_FS,Z+ΔZ_FS) and the voxel point f(x,y,z) with the projection map, and accumulate it in reverse to the corresponding voxel point f. Perform the same calculation on all pixels in each projection map and on projection maps at all angles.

[0033] Preferably, multiple structural components are provided in the optical path region between the X-ray source and the detector, so as to calculate the focal drift of each frame of the projection image of the multiple X-ray sources based on the multiple structural components.

[0034] For any given frame of projected image, the average of multiple focus drift values ​​is taken as the final focus drift value of that frame of projected image.

[0035] Preferably, the distance between the structural member and the detector is proportional to the drift of the projection of the structural member.

[0036] According to a second aspect of the present invention, a CT imaging system employing the above-described monitoring method is provided, comprising:

[0037] Detector, used for image detection;

[0038] An X-ray source is positioned on one side of the detector to emit X-rays toward the detector;

[0039] At least one structural component is disposed in the optical path region between the X-ray source and the detector, the structural component being located within the irradiation range of the X-ray source and outside the imaging FOV region.

[0040] Preferably, the CT imaging system further includes:

[0041] A collimator is disposed between the X-ray source and the detector, and close to the X-ray source; the structural component is mounted on the collimator.

[0042] Compared with the prior art, the present invention has the following technical effects:

[0043] 1. During X-ray scanning, the amount of focus drift is detected in real time, and the image is corrected based on the amount of focus drift in each frame of the projected image.

[0044] 2. Focus drift can be detected in a single scan, eliminating the need for multiple scans that would increase the radiation dose to the patient, and the calculated drift is more accurate.

[0045] 3. The structure is simple and easy to implement, and can effectively solve the impact of X-ray source focus drift on image quality. Attached Figure Description

[0046] Figure 1 A flowchart illustrating a method for monitoring X-ray source focus drift according to the first embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of the structural components in the first embodiment of the present invention;

[0048] Figure 3 This is a projection relationship diagram between the structural component and the focal point in the first embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram illustrating the calculation principle of the focus offset in the first embodiment of the present invention;

[0050] Figure 5 This is a geometric schematic diagram of the algorithm reconstruction in the first embodiment of the present invention;

[0051] Figure 6 A structural diagram of a CT imaging system employing this monitoring method is provided in the second embodiment of the present invention;

[0052] Figure 7 This is a structural diagram of a CT imaging system employing the monitoring method, provided in the third embodiment of the present invention. Detailed Implementation

[0053] The technical content of the present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0054] First Embodiment

[0055] like Figure 1 As shown, the first embodiment of the present invention provides a method for monitoring the focus drift of an X-ray source, specifically including steps S1 to S5:

[0056] S1: Set up structural components.

[0057] Specifically, refer to Figure 2As shown, a structural component 30 is provided in the optical path region between the X-ray source 10 and the detector 20 so that the structural component 30 is located within the irradiation range of the X-ray source 10 and outside the imaging FOV (Field of View) region.

[0058] It is understandable that the structural component 30 can be installed inside the filter surface of the front collimator or at other locations. Since the structural component 30 is not within the imaging FOV region but near its edge, its projection will not appear within the imaging range, thus not affecting the reconstructed image. Furthermore, referring to… Figure 3 As shown, since the relative position of the structural component 30 is fixed, if the focus shifts, the projection of the structural component 30 will change accordingly. Therefore, the amount of focus shift can be deduced by using the positional change of the projection of the structural component 30. Then, based on the amount of focus shift, the algorithm control program can be used to correct and reconstruct the image, thereby obtaining a higher quality image.

[0059] In this embodiment, the structural component 30 is a small ball made of high-density tungsten alloy or stainless steel, and the diameter of the ball is adaptively selected as needed. This allows for the formation of a projection image with significant contrast on the detector, which is more advantageous for accurately extracting the projection position of the ball and thus enabling more accurate acquisition of the focus drift.

[0060] Furthermore, regarding the position of the sphere, it can be selected anywhere along the optical path between the X-ray source 10 and the detector 20, as long as it is not within the field of view (FOV). Preferably, it can be placed on the filter surface in the front collimator, thus eliminating the need for additional support structures and allowing it to participate in the system scanning process along with the filter, resulting in a simple and compact structure. Of course, the sphere can also be placed closer to the detector, but the closer it is to the detector, the smaller the drift of the sphere's projection, which is less favorable for accurately calculating the drift of the focal point.

[0061] S2: Obtain the theoretical center point coordinates of the projected image of the structural component.

[0062] Specifically, this includes steps S21 to S24:

[0063] S21: Perform focus calibration on the X-ray source 10 to adjust the focus position to the theoretical position in the X and Z directions of the preset coordinate system; wherein, the center of the preset coordinate system is the center of the detector 20, the Z direction is the axial direction of the detector 20, the X direction is the horizontal direction perpendicular to the Z direction, and the Y direction is the vertical direction perpendicular to the Z direction.

[0064] S22: Based on the theoretical position of the focus, scan the structural component 30 during the focus calibration process to acquire multiple scan images.

[0065] S23: Calculate the X and Z coordinates of the center point of the projection area of ​​the structural component in each frame of the image in the preset coordinate system;

[0066] Specifically, the metal ball is scanned during the rack rotation, resulting in hundreds or thousands of scan images. The center point of the projected area of ​​the metal ball in each frame is calculated using the X and Z coordinates in a preset coordinate system.

[0067] S24: Obtain the theoretical center point coordinates of the projected image of structural component 30.

[0068] Specifically, the X-coordinates of the center point of the projection area of ​​the structural component 30 in each frame image are averaged to obtain the average X-coordinate. Similarly, the Z-coordinates of the center point of the projection area of ​​the structural component 30 in each frame image are averaged to obtain the average Z-coordinate. Thus, the average X-coordinate and the average Z-coordinate together constitute the theoretical center point coordinate value of the projection image of the structural component 30.

[0069] S3: Calculate the center point drift of each frame of the projected image of the structural component.

[0070] Specifically, this includes steps S31 to S33:

[0071] S31: During the CT scan, the actual X coordinate and actual Z coordinate of the center point of each frame of the projected image of the structural component 30 in the preset coordinate system are obtained.

[0072] S32: Obtain the center point drift of any frame of the projected image.

[0073] Specifically, for any frame of the projected image, the actual X-coordinate of the center point is subtracted from the average of the X-coordinates to obtain the center point's drift ΔX in the X direction. Similarly, the actual Z-coordinate of the center point is subtracted from the average of the Z-coordinates to obtain the center point's drift ΔZ in the Z direction. Thus, the drift ΔX in the X direction and the drift ΔZ in the Z direction of this frame of the projected image together constitute the center point drift of this frame of the projected image.

[0074] S33: Obtain the center point drift of each frame of the projected image.

[0075] Repeat step S32 above to obtain the center point drift of each frame of the projected image.

[0076] S4: Calculate the focal drift of each frame of the X-ray source projection image.

[0077] In this embodiment, based on the preset geometric positional relationship, the focal drift of each frame of the X-ray source is calculated according to the center point drift of each frame of the projected image.

[0078] Specifically, refer to Figure 4 As shown, steps S41 to S43 are included:

[0079] S41: Obtain the first distance D1 from the focal point of the X-ray source to the structural component in the Y direction;

[0080] S42: Obtain the second distance D2 from the structural component to the detector in the Y direction;

[0081] S43: Based on similar triangle geometry, calculate the focus drift ΔX_FS and ΔZ_FS for each frame of projected image using the following formula;

[0082]

[0083] S5: Adapt the image reconstruction algorithm based on the focus drift of each frame of the X-ray source to correct the image.

[0084] Reference Figure 5 As shown, in this embodiment, after obtaining the focus drift of each frame of the X-ray source projection image based on step S4, the reconstruction algorithm is adapted in the following two ways:

[0085] The first method: orthographic projection algorithm.

[0086] Specifically, for each voxel point f(x, y, z) within the reconstructed object, a line is established from the X-ray source to the voxel point f(x, y, z) using the adjusted X-ray source position S(X_FS+ΔX_FS, Y_FS, Z+ΔZ_FS), and extended to intersect the detector at point p(u, v); the pixel value of the ray along this direction at point p(u, v) on the detector plane is calculated, and the same calculation is performed for all voxels.

[0087] The second method: back projection algorithm.

[0088] Specifically, the projection value at the intersection point p(u,v) of the line connecting the adjusted ray source position S(X_FS+ΔX_FS,Y_FS,Z+ΔZ_FS) and the voxel point f(x,y,z) with the projection map is found, and then accumulated in reverse to the corresponding voxel point f. The same calculation is performed on all pixels on each projection map and on projection maps at all angles.

[0089] It is understood that the focus drift obtained by the monitoring method provided in this embodiment of the invention only affects the reconstruction algorithm by changing the assignment of X-ray source coordinates during forward and reverse projection operations. It requires almost no modification to the reconstruction algorithm itself, thus improving the convenience of projection operations.

[0090] Furthermore, in another embodiment of the present invention, preferably, a plurality of structural components 30 may be provided in the optical path region between the X-ray source and the detector. Thus, the focus drift of each frame of the X-ray source can be calculated using each structural component 30. Therefore, for any given frame of the projected image, the average of the multiple focus drifts can be taken as the final focus drift of that frame, thereby improving the accuracy of the focus drift calculation.

[0091] Second Embodiment

[0092] like Figure 6 As shown, based on the first embodiment described above, the second embodiment of the present invention also provides a CT imaging system employing this monitoring method. The CT imaging system includes an X-ray source 10, a detector 20, at least one structural component 30, and a collimator 40.

[0093] Detector 20 is used for image detection. X-ray source 10 is disposed on one side of detector 20 to emit X-rays toward detector 20. Structural component 30 is disposed in the optical path region between X-ray source 10 and detector 20, and is located within the irradiation range of X-ray source 10 but outside the imaging field of view (FOV). Collimator 40 is disposed between X-ray source 10 and detector 20, and close to X-ray source 10; structural component 30 is mounted on collimator 40.

[0094] Third Embodiment

[0095] Based on the aforementioned method for monitoring X-ray source focus drift, this invention further provides a CT imaging system employing this monitoring method. For example... Figure 7 As shown, the CT imaging system includes one or more processors 21 and a memory 22. The memory 22 is coupled to the processors 21 and is used to store one or more programs. When the one or more programs are executed by the one or more processors 21, the one or more processors 21 implement the X-ray source focus drift monitoring method as described in the above embodiment.

[0096] The processor 21 controls the overall operation of the CT imaging system to complete all or part of the steps of the X-ray source focus drift monitoring method described above. The processor 21 can be a central processing unit (CPU), graphics processing unit (GPU), field-programmable gate array (FPGA), application-specific integrated circuit (ASIC), digital signal processing (DSP) chip, etc. The memory 22 stores various types of data to support the operation of the CT imaging system. This data may include, for example, instructions for any application or method used to operate on the CT imaging system, as well as application-related data. The memory 22 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, etc.

[0097] In one exemplary embodiment, the CT imaging system may be implemented by a computer chip or physical entity, or by a product with certain functions, for performing the X-ray source focus drift monitoring method described above and achieving the same technical effect as the method described above. A typical embodiment is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, an in-vehicle human-machine interface device, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0098] In another exemplary embodiment, the present invention also provides a computer-readable storage medium including program instructions that, when executed by a processor, implement the steps of the X-ray source focus drift monitoring method in any of the above embodiments. For example, the computer-readable storage medium may be the memory including the program instructions described above, which can be executed by a processor of a CT imaging system to complete the X-ray source focus drift monitoring method described above and achieve the same technical effects as the method described above.

[0099] In summary, the X-ray source focus drift monitoring method and CT imaging system provided in this embodiment of the invention have the following beneficial effects:

[0100] 1. During X-ray scanning, the amount of focus drift is detected in real time, and the image is corrected based on the amount of focus drift in each frame of the projected image.

[0101] 2. Focus drift can be detected in a single scan, eliminating the need for multiple scans that would increase the radiation dose to the patient, and the calculated drift is more accurate.

[0102] 3. The structure is simple and easy to implement, and can effectively solve the impact of X-ray source focus drift on image quality.

[0103] The X-ray source focus drift monitoring method and CT imaging system provided in the embodiments of the present invention have been described in detail above. Any obvious modifications made by those skilled in the art without departing from the essence of the present invention will constitute an infringement of the patent rights of the present invention and will incur corresponding legal liability.

Claims

1. A method for monitoring the focus drift of an X-ray source, characterized in that... Includes the following steps: A structural component is provided in the optical path region between the X-ray source and the detector, such that the structural component is located within the irradiation range of the X-ray source and outside the imaging FOV region; The X-ray source is calibrated to obtain the theoretical center point coordinates of the projected image of the structure during the calibration process. Specifically, this includes: calibrating the X-ray source to adjust the focal position to the theoretical position in the X and Z directions of a preset coordinate system; wherein the center of the preset coordinate system is the center of the detector, the Z direction is the axial direction of the detector, the X direction is the horizontal direction perpendicular to the Z direction, and the Y direction is the vertical direction perpendicular to the Z direction; based on the theoretical position of the focal point, the structure is scanned during the calibration process to obtain multiple scanned images; the X and Z coordinates of the center point of the projected area of ​​the structure in each frame are calculated in the preset coordinate system; the X coordinates of the center point of the projected area of ​​the structure in each frame are averaged to obtain an average X coordinate; and the Z coordinates of the center point of the projected area of ​​the structure in each frame are averaged to obtain an average Z coordinate; wherein the average X coordinate and the average Z coordinate together constitute the theoretical center point coordinates of the projected image of the structure. During a CT scan, the actual center point coordinates of each frame of the projected image of the structural component are acquired to calculate the center point drift of each frame of the projected image. Specifically, this includes: during the CT scan, acquiring the actual X-coordinate and actual Z-coordinate of the center point of each frame of the projected image of the structural component in a preset coordinate system; for any given frame of the projected image, subtracting the average value of the actual X-coordinate of the center point from the average value of the X-coordinates to obtain the drift ΔX of the center point in the X direction; and subtracting the average value of the actual Z-coordinate of the center point from the average value of the Z-coordinates to obtain the drift ΔZ of the center point in the Z direction; wherein, the drift ΔX in the X direction and the drift ΔZ in the Z direction together constitute the center point drift of that frame of the projected image. Based on the preset geometric positional relationship, the focal drift of each frame of the X-ray source is calculated according to the center point drift of each frame of the projected image.

2. The monitoring method as described in claim 1, characterized in that... The focus shift amount of each frame of the projected image is obtained in the following way: Obtain the first distance D1 in the Y direction from the focal point of the X-ray source to the structural component; Obtain the second distance D2 from the structural component to the detector in the Y direction; Based on the similar triangle geometry, the focus drift ΔX_FS and ΔZ_FS of each frame of projected image are calculated using the following formula; ； 。 3. The monitoring method as described in claim 1, characterized in that... Also includes: The image reconstruction algorithm is adapted based on the focus drift of each frame of the projected image from the X-ray source to correct the image.

4. The monitoring method as described in claim 3, characterized in that... The adaptation includes at least the following steps: For each voxel point f(x, y, z) within the reconstructed object, a line is constructed from the X-ray source to the voxel point f(x, y, z) using the adjusted X-ray source position S(X_FS ​​+ ΔX_FS, Y_FS, Z + ΔZ_FS), and extended to intersect the detector at point p(u, v); the pixel value of the ray along this direction at point p(u, v) on the detector plane is calculated, and the same calculation is performed for all voxels; Alternatively, find the projection value at the intersection point p(u,v) of the line connecting the adjusted ray source position S (X_FS ​​+ ΔX_FS, Y_FS, Z + ΔZ_FS) and the voxel point f(x, y, z) with the projection map, and accumulate it in reverse to the corresponding voxel point f. Perform the same calculation on all pixels in each projection map and on projection maps at all angles.

5. The monitoring method as described in claim 1, characterized in that: Multiple structural components are arranged in the optical path region between the X-ray source and the detector, so as to calculate the focal drift of each frame of the projection image of the multiple X-ray sources based on the multiple structural components. For any given frame of projected image, the average of multiple focus drift values ​​is taken as the final focus drift value of that frame of projected image.

6. The monitoring method as described in claim 1, characterized in that: The distance between the structural component and the detector is proportional to the drift of the structural component's projection.

7. A CT imaging system for performing the monitoring method as described in claim 1, characterized in that... include: Detector, used for image detection; An X-ray source is positioned on one side of the detector to emit X-rays toward the detector; At least one structural component is disposed in the optical path region between the X-ray source and the detector, the structural component being located within the irradiation range of the X-ray source and outside the imaging FOV region.

8. The CT imaging system as described in claim 7, characterized in that... Also includes: A collimator is positioned between the X-ray source and the detector, and close to the X-ray source; The structural component is mounted on the collimator.

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