CN107730569B - Medical image artifact correction method and device - Google Patents
Medical image artifact correction method and device Download PDFInfo
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- G06T11/003—Reconstruction from projections, e.g. tomography
- G06T11/008—Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
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Abstract
The invention discloses a medical image artifact correction method, which comprises the following steps: receiving die body scanning data, and preprocessing the die body scanning data to obtain a die body measurement projection value; reconstructing a measured projection value of the phantom to obtain an image with an artifact; obtaining a section equation of the die body according to the image with the artifact; determining an ideal projection value of the die body according to a cross section equation of the die body and a scanning ray equation; determining a correction coefficient corresponding to each detector by adopting polynomial fitting according to the measured projection value and the ideal projection value of the phantom; and determining a correction table according to the correction coefficient.
Description
Technical Field
The present invention relates to the field of medical image processing, and in particular, to a method and an apparatus for correcting an image artifact.
Background
In a Computed Tomography (CT) imaging process, artifacts have been an important factor affecting the quality of CT reconstructed images. Artifact refers to the presence of artifacts and interferences in the CT reconstructed image that are not present in the actual object, i.e., the image that is not related to the actual scanned object. Among them, ringing artifacts are one of the most common artifacts. The ring artifacts are mainly formed due to the non-uniformity of the response of the detector units to radiation intensities and to the non-uniformity of the response of photons of different energies. The ring artifacts greatly reduce the quality of the CT image, and particularly, the ring artifacts seriously affect the accuracy of CT values (the CT values represent attenuation values after X-rays are absorbed through tissues) of the CT image, and affect the uniformity of the CT image, thereby affecting clinical diagnosis. Thus, removing or minimizing ringing artifacts becomes a problem that must be addressed.
In the conventional ring artifact correction method, a phantom having a circular cross section is first placed in a scan field between an X-ray tube and an X-ray detector, the phantom is scanned from a plurality of directions to obtain a plurality of views, then an ideal projection value, i.e., second projection information, is obtained by mathematical processing (e.g., fitting or filtering) using a scan result, i.e., first projection information, and then a correction coefficient for correcting projection information obtained from a subject is calculated from the first projection information and the second projection information. The process of obtaining the ideal projection value by the method depends on the processing of the first projection information, a clear physical model is not generated, and the generated ideal projection value is easy to be inaccurate due to various errors of the first projection information and the difference of mathematical processing methods, so that the correction result is influenced.
Disclosure of Invention
In view of the above problems, the present invention is directed to calculating a correction coefficient using phantom projection data and phantom ideal projection data, and using the correction coefficient to correct projection data of a subject, thereby solving the problem that the correction coefficient cannot accurately correct projection information of the subject in the prior art.
In order to achieve the above object, one aspect of the present invention provides a method for correcting artifacts in medical imaging, including: receiving die body scanning data, and preprocessing the die body scanning data to obtain a die body measurement projection value; reconstructing a measured projection value of the phantom to obtain an image with an artifact; obtaining a section equation of the die body according to the image with the artifact; determining an ideal projection value of the die body according to a cross section equation of the die body and a scanning ray equation; determining a correction coefficient corresponding to each detector by adopting polynomial fitting according to the measured projection value and the ideal projection value of the phantom; and determining a correction table according to the correction coefficient.
In the invention, the medical imaging artifact correction method further comprises the step of placing the phantom at different positions in the scanning range to obtain the scanning data of the phantom at different positions.
In the present invention, the phantom is an elliptic cylinder phantom, and the determining an ideal projection value of the phantom includes:
the method comprises the following three conditions of simultaneous solution according to an elliptic cylinder phantom section equation and a scanning ray equation:
a. the ray and the ellipse have no intersection point, the equation system has no solution, and the ideal projection value is 0.
b. The ray is tangent to the ellipse, the equation set has a unique solution, and the ideal projection value is 0;
c. the ray intersects the ellipse, the system of equations has two solutions, and then the ideal projection value is determined based on the distance between the two intersection points at the intersection.
In the present invention, the medical image artifact correction method further comprises correcting the projection data of the detected patient by a correction table, wherein the correcting comprises:
receiving projection data of a detected patient; acquiring an artifact correction table, wherein the artifact correction table comprises one or more correction coefficients; correcting the projection data of the detected patient according to a correction table to obtain corrected projection data; an image is reconstructed from the corrected projection data.
In the present invention, the mold body further comprises the following shapes: cylindroid, cylindrical, conical, and elliptical cone structures.
The invention also provides a medical image artifact correction device, comprising: the data receiving module is used for receiving the projection data of the elliptic cylinder mould body; the preprocessing module is used for preprocessing the scanning data of the model; a reconstruction module for reconstructing a medical image; a correction module configured to generate an artifact correction table, the generating an artifact correction table comprising:
preprocessing the scanning data of the elliptic cylinder mould body by a preprocessing module to obtain a measured projection value of the elliptic cylinder mould body; reconstructing the measured projection value of the elliptic cylinder model by a reconstruction module to obtain an image with an artifact; obtaining a section equation of the die body according to the image with the artifact; determining an ideal projection value of the elliptic cylinder mould body according to an elliptic cylinder mould body section equation and a scanning ray equation; determining a correction coefficient corresponding to each detector by adopting polynomial fitting according to the measured projection value and the ideal projection value of the elliptic cylinder model; and determining a correction table according to the correction coefficient.
In the invention, the data receiving module can be further used for acquiring the die body scanning data of the elliptical cylinder die body placed at different positions in the scanning range.
In the present invention, the correction module may be configured to determine a phantom ideal projection value, where the determining a phantom ideal projection value includes:
the method comprises the following three conditions of simultaneous solution according to an elliptic cylinder phantom section equation and a scanning ray equation:
a. the ray and the ellipse have no intersection point, the equation system has no solution, and the ideal projection value is 0.
b. The ray is tangent to the ellipse, the equation set has a unique solution, and the ideal projection value is 0;
c. the ray intersects the ellipse, the system of equations has two solutions, and then the ideal projection value is determined based on the distance between the two intersection points at the intersection.
In the present invention, the correction module may be configured to correct the detected patient projection data using a correction table, the correcting comprising: receiving projection data of a detected patient; acquiring an artifact correction table, wherein the artifact correction table comprises one or more correction coefficients; correcting the projection data of the detected patient according to a correction table to obtain corrected projection data; an image is reconstructed from the corrected projection data.
In the present invention, the medical image artifact correction apparatus further includes: and preprocessing the projection data of the detected patient by the preprocessing module to obtain initial projection data.
Compared with the prior art, the invention has the following beneficial effects:
the ideal projection value is generated by modeling the elliptic die body, so that the calculation of the ideal projection value has a definite basis, and the ideal projection value is not only dependent on mathematical processing of an observed projection value, and is further calculated to obtain a correction coefficient, thereby achieving higher precision and improving the correction accuracy.
Secondly, the shape of the elliptic phantom is closer to the shape of a human body, and the physical effect (such as scattering) in the correction is closer to the actual condition of clinical scanning, thereby achieving better correction effect.
Drawings
FIG. 1 is a schematic view of an imaging system provided by the present invention;
FIG. 2 is a schematic diagram of a ring artifact correction apparatus provided in the present invention;
FIG. 3 is an exemplary flow chart for creating a correction table provided by the present invention;
FIG. 4 is a schematic view of an imaging system scan provided by the present invention;
fig. 5 is an exemplary flowchart of a ring artifact correction provided by the present invention.
FIG. 1 labels: 100 is an imaging system, 110 is a cavity, 120 is a bed frame, 130 is a high voltage generator, 140 is an operation control computer device, 150 is an image generator, 160 is a control display device, 170 is a detector, and 180 is a radiation generator;
FIG. 2 labels: 200 is a ring artifact correction device, 210 is a data receiving module, 220 is a preprocessing module, 230 is a correction module, 240 is a reconstruction module, and 250 is a storage module;
FIG. 4 labels: an X-ray tube 401, an X-ray detector 402 and a phantom 403.
Detailed Description
The invention is further described by means of specific embodiments in conjunction with the accompanying drawings.
FIG. 1 is a schematic view of an imaging system provided by the present invention. In some embodiments, the imaging system 100 may scan a target, obtain scan data and generate an image associated therewith. In some embodiments, imaging system 100 may be a medical imaging system, such as a pet (positional Emission tomography) device, a ct (computed tomography) device, an mri (magnetic resonance imaging) device, or the like.
In some embodiments, imaging system 100 may include a chamber 110, a bed frame 120, a high voltage generator 130, an operation control computer device 140, an image generator 150, and a control display device 160. The interior of the cavity 110 may house components for generating and detecting radioactive emissions. In some embodiments, the cavity 110 may house one radiation generator 180 and one detector 170. The radiation generator 180 may emit radioactive rays. The radioactive emissions may be emitted at an object disposed in the cavity 110 and received by the detector 170 through the object. By way of example, the radiation generator 180 may be an X-ray tube. The X-ray tube may emit X-rays that are transmitted through an object disposed inside the cavity 110 and received by the detector 170. In some embodiments, the detector 170 may be a circular detector, a square detector, an arc detector, or the like.
The bed frame 120 may support an object to be inspected (e.g., a patient to be inspected, a mold, etc.). In some embodiments, the bed frame 120 may be moved inside the chamber 110 during the testing process. As shown in FIG. 1, during the examination, the bed frame 120 may be moved in the Z-axis direction. The patient may be supine, prone, head-in-front, or foot-in-front, as desired for the test. In some embodiments, the bed frame 120 may move inside the chamber 110 at a constant speed. The speed at which the bed frame 120 moves may be related to the scanning time, the scanning area, and the like. In some embodiments, the speed at which the bedframe 120 moves may be a system default or may be set by the user.
The high voltage generator 130 may generate a high voltage or a high current. In some embodiments, the high voltage or high current generated may be transmitted to the radiation generator 180.
The operation control computer device 140 may be associated with the chamber 110, the radiation generator 180, the detector 170, the high voltage generator 130, the bed frame 120, the image generator 150, and/or the control display device 160. The devices may be connected directly or indirectly. In some embodiments, the operation control computer device 140 may control the rotation of the chamber 110 to a certain position. The position may be a default value of the system or may be set by a user (e.g., a doctor, a nurse, or the like). In some embodiments, the operation control computer device 140 may control the high voltage generator 130. For example, the operation control computer device 140 may control the intensity of the voltage or current produced by the high voltage generator 130. In some embodiments, the operation control computer device 140 may control the display device 160. For example, the operation control computer device 140 may control display related parameters. The parameters may include display size, display scale, display order, number of displays, and the like.
The image generator 150 may generate an image. In some embodiments, the image generator 150 may perform image preprocessing, image reconstruction, and/or artifact correction, among other operations. The image generator 150 may be associated with the detector 170, the operation control computer device 140, the display device 160, and/or an external data source (not shown). In some embodiments, the image generator 150 may receive data from the detector 170 or an external data source and generate an image based on the received data. In some embodiments, the image generator 150 may transmit the generated image to the display device 160 for display.
It should be noted that the above description of the imaging system 100 is merely for convenience of description and is not intended to limit the present invention to the scope of the illustrated embodiments. It will be understood by those skilled in the art that, having the benefit of the teachings of this system, various modifications and changes in the form and details of the application of the method and system described above may be made without departing from this concept, with any combination of the various modules or sub-systems being constructed to interface with other modules.
Fig. 2 is a schematic diagram of a ring artifact correction apparatus according to the present invention. In some embodiments, the ring artifact correction device 200 may be included within the image generator 150.
The ring artifact correction device 200 may include a data receiving module 210, a preprocessing module 220, a correction module 230, a reconstruction module 240, and a storage module 250. The data receiving module 210 may receive data related to the object under test. The data associated with the subject may include scan data, basic information (e.g., name, age, gender, height, weight, medical history, etc.), scan parameters, and the like. In some embodiments, the scan data may be collected by the detector 170 and transmitted to the data receiving module 210. In some embodiments, the scan data may be transmitted to the storage module 250 after being collected by the detector 170, and then transmitted to the data receiving module 210 by the storage module 250. In some embodiments, the data receiving module 210 may receive scan parameter data from the operation control computer device 140. In some embodiments, the data receiving module 210 may receive data (e.g., patient base information) from an external data source (not shown).
The preprocessing module 220 may perform analysis processing on the received data. The preprocessing module 220 may receive data from the data receiving module 210, the storage module 250, and/or an external data source and perform analysis processing. In some embodiments, the pre-processing module 220 may perform pre-processing operations on the received data. As an example, the pre-processing module 220 may perform pre-processing such as air correction, beam hardening correction, defocus correction, and the like.
The correction module 230 may perform artifact correction on the processed data. The correction module 230 may receive data from the pre-processing module 220, the storage module 250, and/or an external data source and perform analysis processing. In some embodiments, the correction module 230 may be used to calculate phantom ideal projection values. The model body is a model similar to a human body structure. It is common practice in the medical field to irradiate a phantom with radiation from a radiation source and to determine the radiation dose applied to a particular tissue of a patient during actual patient treatment by imaging images formed by varying degrees of attenuation of the radiation on an imaging panel disposed behind the phantom. In some embodiments, the correction module 230 may derive the correction coefficients based on the phantom scan data and the phantom ideal projection data. In some embodiments, the correction module 230 may obtain a correction factor and correct the scan data of the detected patient after the processing according to the correction factor.
The reconstruction module 240 may generate and/or process images. In some embodiments, the image processing module may receive the scan data processed by the correction module 230 and generate an image from the processed scan data. In some embodiments, the reconstruction module 240 may perform image reconstruction.
The storage module 250 may store data, images, and/or related parameters, etc. The stored data may be in various forms. Such as one or more of values, signals, images, information relating to a given object, commands, algorithms, programs, etc. As an example, phantom scan data, phantom ideal projection data, artifact corrected projection data may be stored in the storage module 250. In some embodiments, the storage module 250 may include a fixed storage system (e.g., a disk), a removable storage system, and so forth. In some embodiments, the storage module 250 may store phantom images with artifacts, images after artifact correction, and the like. Further, the storage module 250 may be a temporary storage of data, that is, data is transferred for the next data processing; or long-term storage of data, i.e. storing the final data processing results.
Fig. 3 is an exemplary flowchart for creating a correction table according to the present invention.
In step 302, the data receiving module 210 may receive phantom scan data. The scan data may also be referred to as projection data. The phantom may have a structure similar to a human body part, and an elliptical cylinder phantom having an elliptical cross section is selected here as an example, because most human body parts have an approximately elliptical cross section, and when the interface of the phantom is elliptical, each detector may receive X-ray intensities passing through different thicknesses of the phantom during one rotation of the frame, and the weight of the phantom may be reduced by increasing the ratio of the major axis to the minor axis of the ellipse. In some embodiments, the mold body may be a homogeneous mold body composed of a material, such as polypropylene, polyethylene, polytetrafluoroethylene, and the like. In some embodiments, the module may be a large cylinder in a small cylinder configuration, where one material is inside the small cylinder and another material is between the small cylinder and the large cylinder. In some embodiments, the phantom may be scanned by placing the phantom at different positions within the scanning range of the imaging system to simulate different positions of different parts of the human body within the scanning range of the imaging system. For example, the phantom is positioned at the center of the scanning range of the imaging system, 50mm off center, 100mm off center, etc. And then, respectively acquiring tomography data of different placement positions of the phantom at least once and using the tomography data for later image correction, for example, obtaining a correction coefficient according to the phantom scanning data of different placement positions, and correcting the scanning data of the detected patient according to the correction coefficient at later stage. In some embodiments, fig. 4 is a schematic scanning diagram of an imaging system according to the present invention, where 401 is an X-ray tube, 402 is an X-ray detector, and 403 is a phantom. In the figure, the phantom 403 is placed at the center of the scanning range of the imaging system (even if the center of the ellipse is at the center of the gantry rotation), the X-ray tube 401 radiates X-rays to the X-ray detector 402, and the X-ray detector 402 detects the X-rays passing through the phantom 403 to obtain the scanning data of the phantom placed at the center. The phantom is positioned such that it is fully exposed to X-rays propagating in a fan 404 from the X-ray tube 401 to the X-ray detector 402, which X-ray detector 402 may comprise a plurality of detection channels. During scanning, the X-ray tube 401 and the X-ray detector 402 may rotate around a rotation center of a gantry of the imaging system 100, and after the X-ray tube 401 and the X-ray detector 402 rotate for one circle, scanning data of a phantom placed at a central position is obtained. And then placing the die body at different positions in the scanning range of the imaging system to obtain die body scanning data of different placing positions. For example, phantom scan data is 50mm off center and phantom scan data is 100mm off center.
In step 304, the preprocessing module 220 may process the phantom scan data to obtain measured projection values of the phantom. The processing can be pre-correcting the received die body scanning data such as air correction, beam hardening correction, defocusing correction and the like, eliminating the influence of known physical factors on the data, and recording the processed data as a measured projection value ProjMi,j,kWherein, in the step (A),
1,2, …, nChannel; j ═ 1,2, …, nView; k is 1,2, …, nScan; nChannel is the number of detector units; nView is the projection angle of each tomography; nScan is the number of tomographic scans.
In step 306, the correction module 230 may obtain ideal projection values of the phantom. Before obtaining ideal phantom projection values, the reconstruction module 240 first determines the measured projection values ProjM for each tomographyi,j,kCarrying out Image reconstruction to obtain an Image with artifactsk. Then extracting the Image with the artifactkThe normal ellipse equation is used to fit the pixels of the interface to obtain the ellipse equation of the phantom section, as shown in formula (1):
wherein (x)0,y0) The central position of the die body is shown, and t is the inclined angle between the long axis of the cross section of the die body and a coordinate system formed by an X axis and a Y axis in the figure 1.
For the X-rays emitted from the X-ray tube and irradiated on the detector after being attenuated by the die body, the straight line equation of each ray can pass through the focal point coordinate (X) of the X-ray tubeS,YS) And coordinates (X) of the detector IdI,YdI) To be uniquely determined. The equation of the line of the ray is shown in equation (2):
Ax+By+C＝0 (2)
wherein, A, B and C are parameters containing X-ray rotation information, and A ═ YdI-Ys；
B＝Xs-XdI；C＝XdI*Ys-Xs*YdI。
Simultaneous equations (1) and (2) are solved for three cases:
1. the equation set has no solution, which shows that at the moment, the straight line (X ray) and the ellipse have no intersection point, and the ideal projection value of the corresponding die body is 0
2. The equation set has unique solution, which shows that the straight line (X-ray) is tangent to the ellipse at the moment, and the ideal projection value of the corresponding die body is also 0
3. There are two sets of solutions to the system of equations, denoted as (X) respectively1，Y1) And (X)2，Y2) At this time, the straight line (X-ray) intersects the ellipse. The ideal phantom projection value can be determined by the distance between two intersection points, as shown in equation (3):
wherein mu0Is a die body with energy of E0Linear attenuation coefficient of rays of kev, E0Kev (kilo-electron volts) is the unit of energy, ProjII,j,kIs the ideal projection value of the phantom.
And establishing a corresponding linear equation through the focal coordinates of the X-ray tube and the coordinates of the detector I, and solving the linear equation and the elliptic equation simultaneously to obtain the ideal projection value of the die body corresponding to the detector I.
In step 308, the correction module 230 may determine a correction factor based on the ideal projection values and the measured projection values. In some embodiments, a correction factor for each detector is determined based on the measured projection values detected by each detector and its corresponding ideal projection values. In particular, for each detector I, all the measured projection values proj m of this detector I are comparedI,j,kAs independent variable, the ideal projection value ProjII,j,kAs a dependent variable, fitting by adopting an N-order polynomial to obtain a correction coefficient alphaI,nAs shown in equation (4):
j ═ 1,2, …, nView; k is 1,2, …, nScan; nView is the projection angle of each tomography; nScan is the number of tomographic scans.
In step 310, the correction module 230 may generate a correction table according to the correction coefficient. Finally, the correction table is stored in any one of the storage devices described in the present invention, and is further used for artifact correction. In some implementations, the artifact correction table may be saved in the form of a file in the storage module 250 or an external data source.
The above description of determining the correction coefficients is merely a specific example and should not be considered the only possible embodiment. It will be obvious to those having skill in the art that, after understanding the underlying principles, the embodiments and steps may be modified and varied in form and detail without departing from such principles, but that such modifications and variations are within the scope of the foregoing description. By way of example, the phantom structure may also be a cylinder, cone, elliptical cone, or the like.
Fig. 5 is an exemplary flowchart of a ring artifact correction provided by the present invention.
In step 502, the data receiving module 210 may receive scan data of a detected patient. The object to be detected may be a different part of the human body, for example, the head, chest, abdomen, heart, liver, upper limb, lower limb, spine, bone, etc., or any combination thereof. In some embodiments, the subject scan data may come from the detector 170, the memory module 250, or an external data source.
In step 504, the pre-processing module 220 may process the scan data of the patient under examination to obtain initial projection values. The processing may be pre-correcting the received scanned data of the object to be detected by air correction, beam hardening correction, defocusing correction, etc., eliminating the influence of known physical factors on the data, and recording the processed data as the initial projection value proj orig.
In step 506, the correction module 230 may obtain a correction table. The correction table includes one or more correction coefficients. In some embodiments, the correction factor may be determined in step 308 of fig. 3. In some embodiments, the correction coefficients may originate from the storage module 250 or an external data source.
In step 508, the correction module 230 may obtain a corrected projection value according to the correction table. Corrected projection value ProjCorrIThis can be obtained by equation (5):
wherein ProjOrig is the initial projection value, alphaI,nThe correction coefficient is corresponding to the detector I.
In step 510, the reconstruction module 240 reconstructs an image from the corrected projection values. In some embodiments, the algorithms used for image reconstruction may include one or more of Filtered Back Projection (FBP), Ordered Subsets Expectation Maximization (OSEM), FDK algorithms, and the like. In the process of reconstructing the image, one or more of the above reconstruction methods may be adopted, and finally an artifact-free image is obtained.
The above examples merely illustrate the application of the ring artifact correction method provided by the present invention to a computed tomography apparatus, and those skilled in the art understand that the correction method and apparatus of the present invention can be applied to, for example, a C-arm system using X-rays, a combined medical imaging system (e.g., combined positron emission tomography-computed tomography), or a tomography apparatus using other types of rays, and the present invention is not limited to the type and structure of the computed tomography apparatus.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (12)
1. A medical image artifact correction method, comprising:
receiving the scanning data of the phantom body,
preprocessing the die body scanning data to obtain a die body measurement projection value;
reconstructing a measured projection value of the phantom to obtain an image with an artifact;
obtaining a section equation of the die body according to the image with the artifact;
simultaneously solving and determining an ideal projection value of the die body according to a cross section equation of the die body and a scanning ray equation;
determining a correction coefficient corresponding to each detector by adopting polynomial fitting according to the measured projection value and the ideal projection value of the phantom; and
and determining a correction table according to the correction coefficient.
2. The method of claim 1, wherein the scan ray equation is a corresponding line equation established by the X-ray tube's focal point coordinates and detector I coordinates.
3. The method of claim 1, further comprising positioning the phantom at different positions within the scanning range, obtaining phantom scan data at the different positions.
4. The method of claim 1, the phantom being an elliptical cylinder phantom, the determining ideal projection values of the phantom comprising:
the method comprises the following three conditions of simultaneous solution according to an elliptic cylinder phantom section equation and a scanning ray equation:
a. the ray and the ellipse have no intersection point, the equation system has no solution, and the ideal projection value is 0.
b. The ray is tangent to the ellipse, the equation set has a unique solution, and the ideal projection value is 0;
c. the ray intersects the ellipse, the system of equations has two solutions, and then the ideal projection value is determined based on the distance between the two intersection points at the intersection.
5. The method of claim 1, further comprising correcting the detected patient projection data with a correction table, the correcting comprising:
receiving projection data of a detected patient;
acquiring an artifact correction table, wherein the artifact correction table comprises one or more correction coefficients;
correcting the projection data of the detected patient according to a correction table to obtain corrected projection data; and
an image is reconstructed from the corrected projection data.
6. The method of claim 1, wherein the mold body further comprises the following shapes: cylindroid, cylindrical, conical, and elliptical cone structures.
7. A medical image artifact correction apparatus, comprising:
the data receiving module is used for receiving the projection data of the elliptic cylinder model body;
the preprocessing module is used for preprocessing the scanning data of the model;
a reconstruction module for reconstructing a medical image;
a correction module for generating an artifact correction table, said generating an artifact correction table comprising:
preprocessing the scanning data of the elliptic cylinder mould body by the preprocessing module to obtain a measured projection value of the elliptic cylinder mould body;
reconstructing the measured projection value of the elliptic cylinder model by the reconstruction module to obtain an image with an artifact;
obtaining a section equation of the die body according to the image with the artifact;
simultaneously solving and determining an ideal projection value of the elliptic cylinder phantom according to an elliptic cylinder phantom section equation and a scanning ray equation;
determining a correction coefficient corresponding to each detector by adopting polynomial fitting according to the measured projection value and the ideal projection value of the elliptic cylinder model; and
and determining a correction table according to the correction coefficient.
8. The apparatus of claim 7, wherein the scan ray equation is a corresponding line equation established by the X-ray tube's focal point coordinates and detector I coordinates.
9. The apparatus of claim 7, wherein the data receiving module is further configured to obtain phantom scan data for positioning an elliptical cylinder phantom at different positions within a scan range.
10. The apparatus of claim 9, wherein the determining a phantom ideal projection value comprises:
the method comprises the following three conditions of simultaneous solution according to an elliptic cylinder phantom section equation and a scanning ray equation:
a. the ray and the ellipse have no intersection point, the equation system has no solution, and the ideal projection value is 0.
b. The ray is tangent to the ellipse, the equation set has a unique solution, and the ideal projection value is 0;
c. the ray intersects the ellipse, the system of equations has two solutions, and then the ideal projection value is determined based on the distance between the two intersection points at the intersection.
11. The apparatus of claim 10, wherein the correction module is further configured to correct the detected patient projection data using a correction table, the correcting comprising:
receiving projection data of a detected patient;
acquiring an artifact correction table, wherein the artifact correction table comprises one or more correction coefficients;
correcting the projection data of the detected patient according to a correction table to obtain corrected projection data; and
an image is reconstructed from the corrected projection data.
12. The apparatus of claim 11 wherein the detected patient projection data is pre-processed by the pre-processing module to obtain initial projection data.
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| US16/205,152 US10922855B2 (en) | 2017-11-30 | 2018-11-29 | Systems and methods for determining at least one artifact calibration coefficient |
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