A method and device for correcting the geometry parameter error of a cone beam CT system

Abstract

The application discloses a kind of for the correction method and device of cone beam CT system geometry parameter error, method includes: acquisition projection image projected on flat panel detector;Obtain the geometry parameter error of cone beam CT system;By the translation error of transverse and longitudinal of the plane where flat panel detector is, correct projection image, obtain first correction image;The normal rotation error of the plane where flat panel detector is and the distance error between flat panel detector and ray source are corrected to first correction image, obtain second correction image;For second correction image, respectively correct along the rotation error of transverse and longitudinal of the plane where flat panel detector is, obtain third correction image;The distance error of third correction image's rotating table and ray source is corrected, obtain the ideal image of geometry parameter error correction.By geometry parameter error correction projection image, without adjusting the position of cone beam CT system device, it is easy to calculate, effectively eliminate the influence of system error on image three-dimensional reconstruction.

Description

Technical Field

[0001] This invention belongs to the technical field of cone-beam CT systems, specifically relating to a method and apparatus for correcting geometric parameter errors in cone-beam CT systems. Background Technology

[0002] A cone-beam CT system consists of four parts: a radiation source, a rotating stage, the object to be scanned, and a flat panel detector. Its working principle is to reconstruct a three-dimensional image from the acquired two-dimensional projection image. Ideally, the object to be scanned is projected onto the rotating stage, and a two-dimensional projection image is obtained on the flat panel detector, such as... Figure 1 As shown. However, due to manufacturing and installation errors in the cone-beam CT system, the following conditions cannot guarantee accuracy: 1. The line connecting the center of the X-ray source and the center of the flat panel detector is coplanar with the axis of rotation of the rotary stage; 2. The line connecting the center of the X-ray source and the center of the flat panel detector is perpendicular to the plane of the flat panel detector; 3. The axis of rotation of the rotary stage is parallel to the plane of the flat panel detector. Therefore, in actual situations, the image size, angle, shape, etc., of the obtained two-dimensional projection image may contain errors, and the accuracy of direct three-dimensional reconstruction is poor. Correction is required to eliminate the influence of geometric errors of the cone-beam CT system.

[0003] Based on the working principle of cone-beam CT systems, accurate reconstruction results can be obtained by correcting any step in the process of cone-beam CT system, two-dimensional projection images, and three-dimensional image reconstruction.

[0004] Current methods primarily involve calibrating cone-beam CT systems. For example, patent CN212630783U discloses a cone-beam CT beam center alignment device and calibration system. This system corrects geometric errors by installing a positioning body and positioning block within the cone-beam CT system, ensuring that the X-ray tube focal point, turntable center, and flat panel detector center are collinear and perpendicular to the flat panel detector plane. However, this calibration method requires additional positioning devices for auxiliary correction. The installed positioning blocks have high spatial distance accuracy requirements, making operation difficult. Furthermore, continuous adjustment of the device position is necessary to improve geometric accuracy, which is time-consuming, and the improvement in geometric accuracy is difficult to guarantee.

[0005] Patent CN108030501A discloses a geometric calibration device and method for a static cone-beam CT imaging system. The device includes several cold cathode X-ray tubes mounted on a support frame. These tubes are arranged linearly or in an arc to form a multi-beam X-ray source array. Precise calibration of the geometric position of each X-ray source is achieved by adjusting each cold cathode X-ray tube in three directions (X, Y, or Z). This method offers high calibration accuracy, but requires continuous adjustment of the tube, detector, and stage positions, making it difficult to operate and time-consuming.

[0006] Therefore, given the shortcomings of existing geometric correction methods for cone-beam CT systems, it is an urgent problem for those skilled in the art to solve how to correct geometric parameter errors of cone-beam CT systems in a simple, convenient, and intuitive way that is universally applicable and easily reproducible. Summary of the Invention

[0007] To address the shortcomings of the existing technology, this invention provides a method and apparatus for correcting geometric parameter errors in cone-beam CT systems. Based on the influence of geometric parameter errors of various cone-beam CT systems on the projected image, the calculation formula for error correction is analyzed and deduced, and the ideal projected image is obtained, thereby eliminating the influence of system geometric errors on the projected image and obtaining the ideal projected image, thus improving the fidelity of image reconstruction.

[0008] In a first aspect, the present invention provides a method for correcting geometric parameter errors in a cone-beam CT system, specifically comprising the following steps:

[0009] Acquire projected images onto a flat panel detector;

[0010] Obtain the geometric parameter error of the cone-beam CT system;

[0011] By correcting the lateral and longitudinal translation errors of the plane where the flat panel detector is located, the projected image is obtained as the first corrected image.

[0012] The first corrected image is used to correct the rotation error of the normal of the plane where the flat panel detector is located and the distance error between the flat panel detector and the X-ray source, so as to obtain the second corrected image.

[0013] For the second corrected image, the lateral and longitudinal rotation errors along the plane of the flat panel detector are corrected respectively to obtain the third corrected image;

[0014] The distance error between the rotary table and the X-ray source in the third corrected image is corrected to obtain an ideal image with corrected geometric parameter errors.

[0015] Further, acquiring the projected image projected onto the flat panel detector includes the following steps:

[0016] Acquire the projected image projected onto the flat panel detector;

[0017] A coordinate system is set with the plane where the flat panel detector is located, and the coordinates of each point in the projected image are given. The horizontal direction of the plane where the flat panel detector is located is the x-axis direction in the coordinate system, the vertical direction of the plane where the flat panel detector is located is the y-axis direction in the coordinate system, the center point of the flat panel detector is the origin of the coordinate system, and the center of the X-ray source, the center of the object to be scanned, and the center point of the flat panel detector are collinear. The collinear direction is the normal of the plane where the flat panel detector is located.

[0018] Furthermore, the geometric parameter errors of the cone-beam CT system specifically include: the distance error ΔR between the rotary stage and the X-ray source, the distance error ΔD between the flat panel detector and the X-ray source, the translation error Δx of the flat panel detector along the x-axis, the translation error Δy of the flat panel detector along the y-axis, the rotation error Φ of the flat panel detector along the y-axis, the rotation error θ of the flat panel detector along the x-axis, and the rotation error η of the flat panel detector along the normal direction.

[0019] Furthermore, by correcting the lateral and longitudinal translation errors of the plane where the flat panel detector is located, the projected image is obtained as the first corrected image, specifically represented as follows:

[0020] x1=Δx+x error

[0021] y1=Δy+y error

[0022] Where, x error y error Let x1 and y1 be the x and y coordinates of a point in the projected image, respectively, and x1 and y1 be the corresponding x coordinates in the first corrected image. error y error The x and y coordinates of the point.

[0023] Furthermore, the rotation error of the normal to the plane where the flat panel detector is located and the distance error between the flat panel detector and the X-ray source are corrected in the first corrected image to obtain the second corrected image, which is specifically represented as follows:

[0024]

[0025]

[0026] Where x2 and y2 are the horizontal and vertical coordinates of the points corresponding to x1 and y1 in the second corrected image, and D is the distance between the flat panel detector and the X-ray source.

[0027] Furthermore, for the second corrected image, the lateral and longitudinal rotation errors along the plane of the flat panel detector are corrected respectively to obtain the third corrected image, specifically including the following steps:

[0028] The second corrected image is corrected using the rotation error Φ of the flat panel detector along the y-axis and the distance between the flat panel detector and the X-ray source to obtain the transition image;

[0029] The transition image is corrected by adjusting the rotation error of the flat panel detector along the x-axis and the distance between the flat panel detector and the X-ray source, resulting in a third corrected image.

[0030] Furthermore, the second corrected image is corrected using the rotational error Φ of the flat panel detector along the y-axis and the distance between the flat panel detector and the X-ray source, resulting in a transition image, specifically represented as follows:

[0031]

[0032]

[0033] Where x2 and y2 are the horizontal and vertical coordinates of a point in the second corrected image, x2′ and y2′ are the horizontal and vertical coordinates of the corresponding points x2 and y2 in the transition image, and D is the distance between the flat panel detector and the X-ray source.

[0034] Furthermore, by adjusting the rotational error of the flat panel detector along the x-axis and the distance between the flat panel detector and the X-ray source, the transition image is corrected to obtain the third corrected image, which is specifically represented as follows:

[0035]

[0036]

[0037] Where x2′ and y2′ are the horizontal and vertical coordinates of a point in the transition image, x3 and y3 are the horizontal and vertical coordinates of the corresponding points x2′ and y2′ in the third correction image, and D is the distance between the flat panel detector and the X-ray source.

[0038] Furthermore, the distance error between the rotary stage and the X-ray source in the third corrected image is corrected to obtain an ideal image with corrected geometric parameter errors, specifically including:

[0039]

[0040]

[0041] Where, x correct y correct Let x3 and y3 be the x and y coordinates of points x3 and y3 in the ideal image, respectively. Let x3 and y3 be the x and y coordinates of a point in the third corrected image. Let R be the distance between the rotary table and the X-ray source.

[0042] Secondly, the present invention also provides a device for correcting geometric parameter errors in a cone-beam CT system, employing the above-described method for correcting geometric parameter errors in a cone-beam CT system, comprising:

[0043] The acquisition unit is used to acquire projected images projected onto the flat panel detector and to obtain the geometric parameter errors of the cone-beam CT system.

[0044] The correction unit is used to correct the projected image by the lateral and longitudinal translation errors of the plane where the flat panel detector is located, to obtain a first corrected image; to correct the rotation error of the normal of the plane where the flat panel detector is located and the distance error between the flat panel detector and the X-ray source for the first corrected image, to obtain a second corrected image; to correct the lateral and longitudinal rotation errors along the plane where the flat panel detector is located for the second corrected image, to obtain a third corrected image; and to correct the distance error between the rotary table and the X-ray source for the third corrected image.

[0045] The verification unit is used to obtain an ideal image with geometric parameter error correction.

[0046] The present invention provides a method and apparatus for correcting geometric parameter errors in cone-beam CT systems, which has at least the following beneficial effects:

[0047] (1) The projection image is corrected by the system geometric parameter error. The calculation is simple and can intuitively and effectively eliminate the influence of system error on the three-dimensional reconstruction of the image.

[0048] (2) Only the actual projected image is calculated and corrected, without the need to adjust the position of each device in the cone-beam CT system. The operation is simple and avoids the impact of manual operation on the correction accuracy.

[0049] (3) No additional devices or equipment need to be installed on the cone-beam CT system, which greatly reduces the calibration cost and is easy to reproduce.

[0050] (4) The correction of geometric parameter error of cone-beam CT system given in this invention can be used for projection image correction of any cone-beam CT system, and has strong universality. Attached Figure Description

[0051] Figure 1 This invention provides a structural diagram of a cone-beam CT system.

[0052] Figure 2 A schematic diagram of an actual projection image obtained by a cone-beam CT system under geometric parameter errors, provided by the present invention;

[0053] Figure 3 A schematic flowchart of a method for correcting geometric parameter errors in a cone-beam CT system provided by the present invention;

[0054] Figure 4(a) is a schematic diagram of the plane perpendicular to the y-axis connecting points P1 and P1' through the center of the X-ray source provided by the present invention; Figure 4(b) is a schematic diagram of the geometric relationship between Φ and the x-axis horizontal coordinate provided by the present invention; Figure 4(c) is a schematic diagram of the plane parallel to the y-axis connecting points P1 and P1' through the center of the X-ray source provided by the present invention; Figure 4(d) is a schematic diagram of the geometric relationship between Φ and the y-axis vertical coordinate provided by the present invention.

[0055] Figure 5(a) is a schematic diagram of a plane perpendicular to the x-axis connecting points P2 and P2' through the center of the X-ray source provided by the present invention; Figure 5(b) is a schematic diagram of the geometric relationship between θ and the y-axis vertical coordinate provided by the present invention; Figure 5(c) is a schematic diagram of a plane parallel to the x-axis connecting points P2 and P2' through the center of the X-ray source provided by the present invention; Figure 5(d) is a schematic diagram of the geometric relationship between θ and the y-axis vertical coordinate provided by the present invention.

[0056] Figure 6 A schematic diagram of a device for correcting geometric parameter errors in a cone-beam CT system provided by the present invention;

[0057] Figure 7(a) is an ideal projection of a certain object to be scanned by the cone-beam CT system provided in Embodiment 1 of the present invention; Figure 7(b) is an actual projection of a certain object to be scanned by the cone-beam CT system provided in Embodiment 1 of the present invention; Figure 7(c) is a corrected projection of a certain object to be scanned by the cone-beam CT system provided in Embodiment 1 of the present invention.

[0058] Figure 8(a) is an ideal projection of a certain object to be scanned by the cone-beam CT system provided in Embodiment 2 of the present invention. Figure 8(b) is an actual projection of a certain object to be scanned by the cone-beam CT system provided in Embodiment 2 of the present invention. Figure 8(c) is a corrected projection of a certain object to be scanned by the cone-beam CT system provided in Embodiment 2 of the present invention. Detailed Implementation

[0059] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0060] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0061] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0062] like Figure 2 As shown, geometric parameter errors in cone-beam CT systems can cause deviations in the size, angle, and even shape of the two-dimensional projection images obtained on the flat panel detector, resulting in poor accuracy of direct three-dimensional reconstruction.

[0063] Therefore, such as Figure 3 As shown, the present invention provides a method for correcting geometric parameter errors in a cone-beam CT system, specifically including the following steps:

[0064] Acquire projected images onto a flat panel detector;

[0065] Obtain the geometric parameter error of the cone-beam CT system;

[0066] By correcting the lateral and longitudinal translation errors of the plane where the flat panel detector is located, the projected image is obtained as the first corrected image.

[0067] The first corrected image is used to correct the rotation error of the normal of the plane where the flat panel detector is located and the distance error between the flat panel detector and the X-ray source, so as to obtain the second corrected image.

[0068] For the second corrected image, the lateral and longitudinal rotation errors along the plane of the flat panel detector are corrected respectively to obtain the third corrected image;

[0069] The distance error between the rotary table and the X-ray source in the third corrected image is corrected to obtain an ideal image with corrected geometric parameter errors.

[0070] Acquiring the projected image onto the flat panel detector involves the following steps:

[0071] Acquire the projected image projected onto the flat panel detector;

[0072] A coordinate system is set with the plane where the flat panel detector is located, and the coordinates of each point in the projected image are given. The horizontal direction of the plane where the flat panel detector is located is the x-axis direction in the coordinate system, the vertical direction of the plane where the flat panel detector is located is the y-axis direction in the coordinate system, the center point of the flat panel detector is the origin of the coordinate system, and the center of the X-ray source, the center of the object to be scanned, and the center point of the flat panel detector are collinear. The collinear direction is the normal of the plane where the flat panel detector is located.

[0073] The geometric parameter errors of a cone-beam CT system specifically include: the distance error ΔR between the rotary stage and the X-ray source, the distance error ΔD between the flat panel detector and the X-ray source, the translation error Δx of the flat panel detector along the x-axis, the translation error Δy of the flat panel detector along the y-axis, the rotation error Φ of the flat panel detector along the y-axis, the rotation error θ of the flat panel detector along the x-axis, and the rotation error η of the flat panel detector along the normal direction.

[0074] The geometric parameter errors of a cone-beam CT system can be obtained by designing patterns on a calibration wafer, or through other methods. For example:

[0075] A first coordinate system is set on the plane of the calibration wafer, wherein the horizontal direction of the plane is the x-axis direction of the first coordinate system, and the vertical direction of the plane is the y-axis direction of the first coordinate system.

[0076] The original cross-shaped pattern is marked on the plane of the calibration wafer. The distance between the center of the original pattern and the left, right, top, and bottom endpoints is equal. The intersection of the cross is the center point of the original pattern. The horizontal and vertical lines of the cross correspond to the x-axis and y-axis directions in the first coordinate system, respectively, and the coordinate values ​​of each endpoint of the cross are given.

[0077] A second coordinate system is set on the flat panel detector, and the coordinate values ​​of each endpoint in the first projection pattern and the second projection pattern are given. The first projection pattern is obtained by adjusting the distance between the rotary table and the ray source along the ray direction of the ray source compared with the second projection pattern. The horizontal direction of the plane where the flat panel detector is located is the x-axis direction in the second coordinate system, the vertical direction of the plane where the flat panel detector is located is the y-axis direction in the second coordinate system, and the center point of the flat panel detector is the origin of the second coordinate system.

[0078] By comparing and analyzing the coordinate values ​​of corresponding endpoints in the first projected pattern and the original pattern, the translation error Δx of the flat panel detector along the x-axis, the translation error Δy of the flat panel detector along the y-axis, and the rotation error η of the flat panel detector along the normal direction are obtained. The rotation error η of the flat panel detector along the normal direction is specifically expressed as follows:

[0079]

[0080] Where, x c y c These are the x-axis and y-axis coordinates of the left endpoint of the original pattern projected into the second coordinate system, respectively.

[0081] By comparing and analyzing the coordinate values ​​of the corresponding endpoints in the first projection pattern, the second projection pattern and the original pattern, the distance error ΔR between the rotary table and the X-ray source, the rotation error Φ of the flat panel detector along the y-axis, the rotation error θ of the flat panel detector along the x-axis and the distance error ΔD between the flat panel detector and the X-ray source are obtained.

[0082] The distance error ΔR between the rotary table and the X-ray source is specifically expressed as:

[0083]

[0084] The coordinates of the left and right endpoints of the original pattern projected onto the first and second projection patterns are C, C', E, and E', respectively. The distances between the origin O of the second coordinate system and the coordinates C, C', E, and E' are OC, OC', OE, and OE', respectively. The distance between the rotary table and the ray source is R.

[0085] The rotational error Φ of the flat panel detector along the y-axis is specifically expressed as:

[0086]

[0087] Where l is the distance between the center of the original pattern and the left, right, top, and bottom endpoints;

[0088] The coordinates of the left and right endpoints of the original pattern projected onto the first projected pattern are F and F', respectively. The distances between the origin O of the second coordinate system and F and F' are OF and OF', respectively. The rotation error θ of the flat panel detector along the x-axis is specifically expressed as:

[0089]

[0090] The distance error ΔD between the flat panel detector and the X-ray source is specifically expressed as follows:

[0091]

[0092] Where D is the distance between the flat panel detector and the radiation source.

[0093] When considering the impact of geometric parameter errors of cone-beam CT system on projected images, assuming that the effects of θ and Φ are considered first, and then the effects of ΔR are considered, then ΔR is not just a proportional scaling coordinate value. Therefore, considering the effects of ΔR must be related to the effects of θ and Φ.

[0094] However, △D is different from △R. Regardless of whether △D is considered first and then θ and Φ, or θ and Φ are considered first and then △D, the effect of △D is simply the proportional scaling of the coordinate values.

[0095] Therefore, in the order of correcting geometric parameter errors in cone-beam CT systems, corrections using θ and Φ must precede corrections using ΔR. Other correction sequences can be set or changed, depending on the corresponding parameters in the formulas.

[0096] By correcting the lateral and longitudinal translation errors of the plane where the flat panel detector is located, the projected image is obtained as the first corrected image, specifically represented as follows:

[0097] x1=Δx+x error

[0098] y1=Δy+y error

[0099] Where, x error y error Let x1 and y1 be the x and y coordinates of a point in the projected image, respectively, and x1 and y1 be the corresponding x coordinates in the first corrected image. error y error The x and y coordinates of the point.

[0100] The first corrected image is used to correct the rotation error of the normal to the plane where the flat panel detector is located and the distance error between the flat panel detector and the X-ray source, resulting in the second corrected image, which is specifically represented as follows:

[0101]

[0102]

[0103] Where x2 and y2 are the horizontal and vertical coordinates of the points corresponding to x1 and y1 in the second corrected image, and D is the distance between the flat panel detector and the X-ray source.

[0104] For the second corrected image, the lateral and longitudinal rotation errors along the plane of the flat panel detector are corrected respectively to obtain the third corrected image. The specific steps include the following:

[0105] The second corrected image is corrected using the rotation error Φ of the flat panel detector along the y-axis and the distance between the flat panel detector and the X-ray source to obtain the transition image;

[0106] The transition image is corrected by adjusting the rotation error of the flat panel detector along the x-axis and the distance between the flat panel detector and the X-ray source, resulting in a third corrected image.

[0107] Using the rotational error Φ of the flat panel detector along the y-axis and the distance between the flat panel detector and the X-ray source, the second corrected image is corrected to obtain the transition image, specifically represented as follows:

[0108]

[0109]

[0110] Where x2 and y2 are the horizontal and vertical coordinates of a point in the second corrected image, x2′ and y2′ are the horizontal and vertical coordinates of the corresponding points x2 and y2 in the transition image, and D is the distance between the flat panel detector and the X-ray source.

[0111] Taking the clockwise direction of the top-view cone-beam CT system as the positive direction, the calculation process of the second corrected image is analyzed. With O as the center point of the flat panel detector and S as the center of the X-ray source, the horizontal and vertical coordinates of point P1 in the second corrected image are x2 and y2, respectively, and the horizontal and vertical coordinates of point P1' corresponding to point P1 in the transition image are x2′ and y2′, respectively.

[0112] As shown in Figure 4(a), connect points P1 and P1' through the center of the ray source, and draw a plane perpendicular to the y-axis. Points S, P1, and P1' are collinear, and the angle between them and OS is α.

[0113] As shown in Figure 4(b), taking x2<0 and Φ>0 as an example, the size of SP1 can be calculated based on the known OP1, OS, and ∠P1OS:

[0114]

[0115] Therefore, ∠S is:

[0116]

[0117] Therefore, OP' is:

[0118]

[0119] Similarly, the derivation for the three cases x2>0 and Φ>0, x3>0 and Φ<0, and x3<0 and Φ<0 all yield the following result:

[0120]

[0121] As shown in Figure 4(c), connect points P1 and P1' through the center of the ray source, and draw a plane parallel to the y-axis. As shown in Figure 4(d) and in conjunction with Figure 4(b), taking y2>0 and Φ>0 as an example, P... 1’ P 1’ Let ' be the points corresponding to P1 and P1' respectively, and whose y-coordinate value is 0.

[0122]

[0123] Therefore, it can be deduced that:

[0124]

[0125] Similarly, the derivation for the three cases y2<0 and Φ>0, y2>0 and Φ<0, and y2<0 and Φ<0 all yield the following result:

[0126]

[0127] By correcting the rotational error of the flat panel detector along the x-axis and the distance between the flat panel detector and the X-ray source, the transition image is obtained, resulting in the third corrected image, which is specifically represented as follows:

[0128]

[0129]

[0130] Where x2′ and y2′ are the horizontal and vertical coordinates of a point in the transition image, x3 and y3 are the horizontal and vertical coordinates of the corresponding points x2′ and y2′ in the third correction image, and D is the distance between the flat panel detector and the X-ray source.

[0131] Using the frontal view of a cone-beam CT system as the observation direction, with right to left as the positive direction, the calculation process of the corrected transition image is analyzed. With O as the center point of the flat panel detector and S as the center of the X-ray source, the horizontal and vertical coordinates of point P2 in the transition image are x2′ and y2′, respectively. The horizontal and vertical coordinates of point P2' corresponding to point P2 in the third corrected image are x3 and y3, respectively.

[0132] As shown in Figure 5(a), connect points P2 and P2' through the center of the ray source, and draw a plane perpendicular to the x-axis. 2’ P 2’ Let S and P be points corresponding to P2 and P2' respectively, and whose x-coordinates are 0. 2’ Point and P 2’ Points are collinear, and the angle between them and OS is β;

[0133] As shown in Figure 5(b), taking y2′>0 and θ>0 as an example, the analysis is based on the known OP2, OS and ∠P. 2’ OS, can SP be requested? 2’ Size:

[0134]

[0135] Therefore, ∠S is:

[0136]

[0137]

[0138] Therefore, OP2” is:

[0139]

[0140] Similarly, the derivation for the three cases y2′<0 and θ>0, y2′>0 and θ<0, and y2′<0 and θ<0 all yield the following result:

[0141]

[0142] As shown in Figure 5(c), connect points P2 and P2' through the center of the ray source, and draw a plane parallel to the x-axis. Referring to Figure 5(d) and combining it with Figure 5(b), taking x3 < 0 and θ > 0 as an example, according to the above formula, we have:

[0143]

[0144] therefore:

[0145]

[0146] Similarly, the derivation for the three cases x3>0 and θ>0, x3>0 and θ<0, and x3<0 and θ<0 all yield the following results:

[0147]

[0148] Correcting the distance error between the rotary table and the X-ray source in the third corrected image yields an ideal image with corrected geometric parameter errors, specifically including:

[0149]

[0150]

[0151] Where, x correct y correct Let x3 and y3 be the x and y coordinates of points x3 and y3 in the ideal image, respectively. Let x3 and y3 be the x and y coordinates of a point in the third corrected image. Let R be the distance between the rotary table and the X-ray source.

[0152] For each point coordinate (x) on the real projected image error ,y error) By performing the above steps, an ideal projection image can be obtained through correction. Then, by reconstructing the ideal projection image, a correct 3D reconstructed image can be obtained.

[0153] In addition, such as Figure 6 As shown, the present invention also provides a device for correcting geometric parameter errors in a cone-beam CT system, employing the above-described method for correcting geometric parameter errors in a cone-beam CT system, including:

[0154] The acquisition unit is used to acquire projected images projected onto the flat panel detector and to obtain the geometric parameter errors of the cone-beam CT system.

[0155] The correction unit is used to correct the projected image by the lateral and longitudinal translation errors of the plane where the flat panel detector is located, to obtain a first corrected image; to correct the rotation error of the normal of the plane where the flat panel detector is located and the distance error between the flat panel detector and the X-ray source for the first corrected image, to obtain a second corrected image; to correct the lateral and longitudinal rotation errors along the plane where the flat panel detector is located for the second corrected image, to obtain a third corrected image; and to correct the distance error between the rotary table and the X-ray source for the third corrected image.

[0156] The verification unit is used to obtain an ideal image with geometric parameter error correction.

[0157] To verify the accuracy of the correction algorithm presented in this paper, two sets of simulation experiments are conducted below.

[0158] Example 1

[0159] Assume the geometric parameters of a simulated industrial cone-beam CT system are as shown in Table 1:

[0160] Table 1 Geometric parameters of the simulated industrial cone-beam CT system

[0161]

[0162]

[0163] The geometric parameter errors of the cone-beam CT system are shown in Table 2:

[0164] Table 2 Geometric parameter errors of the simulated industrial cone-beam CT system

[0165]

[0166] Assuming the ideal projection image of a certain object to be scanned by the cone-beam CT system is shown in Figure 7(a), then the actual projection image of the object to be scanned by the cone-beam CT system is shown in Figure 7(b). The actual projection image is corrected using the geometric parameter error of the cone-beam CT system, and the corrected projection image is shown in Figure 7(c). The coordinate values ​​of the eight vertices on the above three images are shown in Table 3.

[0167] Table 3. System geometric parameter errors in the simulation (unit: pixel)

[0168] Vertex number Ideal projected image coordinates actual projected image coordinates Correcting the coordinates of the projected image a (-259，294) (-314，246) (-260，295) b (289，294) (246，288) (290，295) c (-259，-254) (-262，-308) (-260，-255) d (289，-254) (289，-254) (290，-255) e (-135，170) (-173，129) (-134，169) f (165，170) (132，154) (164，169) g (-135，-130) (-146，-172) (-134，-129) h (165，-130) (156，-144) (164，-129)

[0169] Example 2

[0170] The geometric parameters and geometric parameter errors of the simulated industrial cone-beam CT system are the same as those in Example 1.

[0171] Assuming the ideal projection image of a certain object to be scanned by the cone-beam CT system is shown in Figure 8(a), then the actual projection image of the object to be scanned by the cone-beam CT system is shown in Figure 8(b). The actual projection image is corrected using the geometric parameter error of the cone-beam CT system, and the corrected projection image is shown in Figure 8(c). The coordinate values ​​of the 12 vertices on the above three images are shown in Table 4.

[0172] Table 4. System geometric parameter errors in the simulation (unit: pixels)

[0173] Vertex number Ideal projected image coordinates actual projected image coordinates Correcting the coordinates of the projected image a (-121，268) (-87，284) (-121，268) b (130，268) (178，277) (130，268) c (-243，145) (-218，154) (-243，145) d (-121，145) (-91，150) (-121，145) e (130，145) (173，142) (130，145) f (253，145) (303，138) (253，145) g (-243，-106) (-124，-113) (-243，-106) h (-121，-106) (-99，-118) (-121，-106) i (130，-106) (161，-128) (130，-106) j (253，-106) (280，-132) (253，-106) k (-121，-228) (-102，-245) (-121，-228) l (130，-228) (-121，-256) (130，-228)

[0174] As can be seen from the two sets of experiments above, for actual projected images, the corrected projected image obtained using the correction algorithm of this patent is very close to the ideal projected image, and the correction result is accurate.

[0175] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for correcting geometric parameter errors in a cone-beam CT system, characterized in that, Specifically, the steps include the following: Acquire projected images onto a flat panel detector; Obtaining the geometric parameter error of the cone-beam CT system specifically includes: setting a first coordinate system on the plane of the calibration wafer, wherein the horizontal direction of the plane is the x-axis direction in the first coordinate system, and the vertical direction of the plane is the y-axis direction in the first coordinate system; The original cross-shaped pattern is marked on the plane of the calibration wafer. The distance between the center of the original pattern and the left, right, top, and bottom endpoints is equal. The intersection of the cross is the center point of the original pattern. The horizontal and vertical lines of the cross correspond to the x-axis and y-axis directions in the first coordinate system, respectively, and the coordinate values ​​of each endpoint of the cross are given. A second coordinate system is set on the flat panel detector, and the coordinate values ​​of each endpoint in the first projection pattern and the second projection pattern are given. The first projection pattern is obtained by adjusting the distance between the rotary table and the ray source along the ray direction of the ray source compared with the second projection pattern. The horizontal direction of the plane where the flat panel detector is located is the x-axis direction in the second coordinate system, the vertical direction of the plane where the flat panel detector is located is the y-axis direction in the second coordinate system, and the center point of the flat panel detector is the origin of the second coordinate system. By comparing and analyzing the coordinate values ​​of the corresponding endpoints in the first projected pattern and the original pattern, the translation error Δx of the flat panel detector along the x-axis, the translation error Δy of the flat panel detector along the y-axis, and the rotation error η of the flat panel detector along the normal direction are obtained. By comparing and analyzing the coordinate values ​​of the corresponding endpoints in the first projection pattern, the second projection pattern and the original pattern, the distance error ΔR between the rotary table and the X-ray source, the rotation error Φ of the flat panel detector along the y-axis, the rotation error θ of the flat panel detector along the x-axis and the distance error ΔD between the flat panel detector and the X-ray source are obtained. By correcting the lateral and longitudinal translation errors of the plane where the flat panel detector is located, the projected image is obtained as the first corrected image. The first corrected image is used to correct the rotation error of the normal of the plane where the flat panel detector is located and the distance error between the flat panel detector and the X-ray source, so as to obtain the second corrected image. The second corrected image is corrected using the rotation error Φ of the flat panel detector along the y-axis and the distance between the flat panel detector and the X-ray source to obtain the transition image; The transition image is corrected by using the rotation error of the flat panel detector along the x-axis and the distance between the flat panel detector and the X-ray source to obtain the third corrected image; The distance error between the rotary table and the X-ray source in the third corrected image is corrected to obtain an ideal image with corrected geometric parameter errors.

2. The method for correcting geometric parameter errors in a cone-beam CT system as described in claim 1, characterized in that, Acquiring the projected image onto the flat panel detector involves the following steps: Acquire the projected image projected onto the flat panel detector; A coordinate system is set with the plane where the flat panel detector is located, and the coordinates of each point in the projected image are given. The horizontal direction of the plane where the flat panel detector is located is the x-axis direction in the coordinate system, the vertical direction of the plane where the flat panel detector is located is the y-axis direction in the coordinate system, the center point of the flat panel detector is the origin of the coordinate system, and the center of the X-ray source, the center of the object to be scanned, and the center point of the flat panel detector are collinear. The collinear direction is the normal of the plane where the flat panel detector is located.

3. The method for correcting geometric parameter errors in a cone-beam CT system as described in claim 2, characterized in that, The geometric parameter errors of a cone-beam CT system specifically include: the distance error ΔR between the rotary stage and the X-ray source, the distance error ΔD between the flat panel detector and the X-ray source, the translation error Δx of the flat panel detector along the x-axis, the translation error Δy of the flat panel detector along the y-axis, the rotation error Φ of the flat panel detector along the y-axis, the rotation error θ of the flat panel detector along the x-axis, and the rotation error η of the flat panel detector along the normal direction.

4. The method for correcting geometric parameter errors in a cone-beam CT system as described in claim 3, characterized in that, By correcting the lateral and longitudinal translation errors of the plane where the flat panel detector is located, the projected image is obtained as the first corrected image, specifically represented as follows: ； Where, x error y error Let x1 and y1 be the x and y coordinates of a point in the projected image, respectively, and x1 and y1 be the corresponding x coordinates in the first corrected image. error y error The x and y coordinates of the point.

5. The method for correcting geometric parameter errors in a cone-beam CT system as described in claim 4, characterized in that, The first corrected image is used to correct the rotation error of the normal to the plane where the flat panel detector is located and the distance error between the flat panel detector and the X-ray source, resulting in the second corrected image, which is specifically represented as follows: ； Where x2 and y2 are the horizontal and vertical coordinates of the points corresponding to x1 and y1 in the second corrected image, and D is the distance between the flat panel detector and the X-ray source.

6. The method for correcting geometric parameter errors in a cone-beam CT system as described in claim 1, characterized in that, Using the rotational error Φ of the flat panel detector along the y-axis and the distance between the flat panel detector and the X-ray source, the second corrected image is corrected to obtain the transition image, specifically represented as follows: ； Where x2 and y2 are the x and y coordinates of a point in the second corrected image. y2 represents the x and y coordinates of the corresponding points x2 and y2 in the transition image, and D is the distance between the flat panel detector and the X-ray source.

7. The method for correcting geometric parameter errors in a cone-beam CT system as described in claim 1, characterized in that, By correcting the rotational error of the flat panel detector along the x-axis and the distance between the flat panel detector and the X-ray source, the transition image is obtained, resulting in the third corrected image, which is specifically represented as follows: ； in, x3 and y3 are the x and y coordinates of a point in the transition image, respectively, and x3 and y3 are the corresponding coordinates in the third correction image. The x and y coordinates of the point, where D is the distance between the flat panel detector and the X-ray source.

8. The method for correcting geometric parameter errors in a cone-beam CT system as described in claim 3, characterized in that, Correcting the distance error between the rotary table and the X-ray source in the third corrected image yields an ideal image with corrected geometric parameter errors, specifically including: ; Where, x correct y correct Let x3 and y3 be the x and y coordinates of points x3 and y3 in the ideal image, respectively. Let x3 and y3 be the x and y coordinates of a point in the third corrected image. Let R be the distance between the rotary table and the X-ray source.

9. A device for correcting geometric parameter errors in a cone-beam CT system, characterized in that, The method for correcting geometric parameter errors in cone-beam CT systems as described in any one of claims 1-8 includes: The acquisition unit is used to acquire projected images projected onto the flat panel detector and to obtain geometric parameter errors of the cone-beam CT system. Specifically, it includes setting a first coordinate system on the plane of the calibration wafer, wherein the horizontal direction of the plane is the x-axis direction in the first coordinate system and the vertical direction of the plane is the y-axis direction in the first coordinate system. The original cross-shaped pattern is marked on the plane of the calibration wafer. The distance between the center of the original pattern and the left, right, top, and bottom endpoints is equal. The intersection of the cross is the center point of the original pattern. The horizontal and vertical lines of the cross correspond to the x-axis and y-axis directions in the first coordinate system, respectively, and the coordinate values ​​of each endpoint of the cross are given. A second coordinate system is set on the flat panel detector, and the coordinate values ​​of each endpoint in the first projection pattern and the second projection pattern are given. The first projection pattern is obtained by adjusting the distance between the rotary table and the ray source along the ray direction of the ray source compared with the second projection pattern. The horizontal direction of the plane where the flat panel detector is located is the x-axis direction in the second coordinate system, the vertical direction of the plane where the flat panel detector is located is the y-axis direction in the second coordinate system, and the center point of the flat panel detector is the origin of the second coordinate system. By comparing and analyzing the coordinate values ​​of the corresponding endpoints in the first projected pattern and the original pattern, the translation error Δx of the flat panel detector along the x-axis, the translation error Δy of the flat panel detector along the y-axis, and the rotation error η of the flat panel detector along the normal direction are obtained. By comparing and analyzing the coordinate values ​​of the corresponding endpoints in the first projection pattern, the second projection pattern and the original pattern, the distance error ΔR between the rotary table and the X-ray source, the rotation error Φ of the flat panel detector along the y-axis, the rotation error θ of the flat panel detector along the x-axis and the distance error ΔD between the flat panel detector and the X-ray source are obtained. The correction unit is used to correct the projected image by the lateral and longitudinal translation errors of the plane where the flat panel detector is located, to obtain a first corrected image; to correct the rotation error of the normal direction of the plane where the flat panel detector is located and the distance error between the flat panel detector and the radiation source, to obtain a second corrected image; to correct the second corrected image by the rotation error Φ of the flat panel detector along the y-axis and the distance between the flat panel detector and the radiation source, to obtain a transition image; to correct the transition image by the rotation error of the flat panel detector along the x-axis and the distance between the flat panel detector and the radiation source, to obtain a third corrected image; and to correct the distance error between the rotary table and the radiation source in the third corrected image. The verification unit is used to obtain an ideal image with geometric parameter error correction.

Images