A method for automatically calculating and adjusting central projection parameters of a CT system

Abstract

The present invention discloses an automatic calculation and adjustment method for the central projection parameters of a CT system, and relates to the technical field of industrial CT. The light cone of the CT light-emitting base point is adjusted to irradiate into the detector sensing plate; the CT light-emitting base point is turned on, and the displacement of the Z and X of the first positioning platform is adjusted, and the displacement of the X and Y of the third positioning platform is adjusted, and the projection of the detection plate is adjusted to be displayed in the detector sensing plate; the point position of the detection ball projected onto the detector sensing plate is recorded; the offset detector sensing plate records and combines the four-point data on the multiple offset detector sensing plate, calculates four straight lines, and uses the four straight lines to calculate the central coordinates of the CT light-emitting base point; the center of the CT light-emitting base point is adjusted to be on the same axis as the center point of the detector sensing plate. The tedious operation of accurately calculating the four-point model used for correction is reduced, and the requirements can be met by manual processing only by using a simple four-point model with low precision requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial CT, and in particular to a method for automatically calculating and adjusting central projection parameters of a CT system. Background Art

[0002] Industrial CT, or computer tomography, is a high-precision, non-destructive detection method. It is based on radiation sources such as X-rays or gamma rays, and uses the differences in radiation absorption effects of different materials to collect data through a highly sensitive detector array, and then uses a computer to perform complex image reconstruction processing. This process can generate high-resolution cross-sectional layers or three-dimensional images of the object being inspected, allowing the subtle structures and differences hidden inside the object to be clearly displayed.

[0003] Specifically, when X-rays or gamma rays penetrate the object being inspected, their intensity will attenuate according to factors such as the density, thickness and atomic composition of different substances in the object. This attenuation information is captured by the detector and converted into digital signals, which are then processed by the computer system through complex mathematical operations and image reconstruction algorithms to ultimately generate a three-dimensional image reflecting the internal structure of the object.

[0004] It is worth noting that in order to obtain accurate image reconstruction results, the various parameter states of the CT system during the scanning process must be accurately mastered. These parameters include but are not limited to the intensity of the radiation source, the sensitivity of the detector, the scanning geometric parameters, etc., which are crucial to the quality of the final image. Therefore, in practical applications, it is usually necessary to perform a series of calibrations and measurements on the CT system in advance to ensure that all parameters are in the best state.

[0005] In order to further improve the calibration accuracy and efficiency of the CT system, researchers have also developed a variety of advanced parameter calculation models. For example, Chinese patent CN200910162329.7 proposed a CT system parameter calculation model based on four small balls. This model uses small balls of known size and material as calibration standards to accurately measure and calculate various parameters of the CT system, in order to improve the accuracy and reliability of image reconstruction. The four-point model of the four small balls has high accuracy requirements. It is not something that can be observed and adjusted by the human eye, but requires precise measurements together. In addition, the parameter calculation process of the four-point model is too complicated. Once there is an error in the calculated data of one point, it will affect all data detection results.

[0006] In addition, accurate CT projection geometric parameters need to be obtained, among which the center position of the one-dimensional projection is a very important parameter. In theory, the projection center and the center unit of the detector coincide with each other, but it is difficult to completely adjust the two during the installation of CT. Therefore, in practical applications, the detector center and the projection center often do not coincide. If this parameter is not corrected, the reconstructed image will have artifacts. Summary of the invention

[0007] The present application provides a method for automatically calculating and adjusting the central projection parameters of a CT system, which is used to solve the problem that the parameter calculation process of the four-point model in the prior art is too complicated and leads to a long time for adjusting the projection of industrial CT; in addition, there is a problem that the overlap adjustment method of the projection center and the central unit of the detector is not good.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for automatically calculating and adjusting central projection parameters of a CT system, comprising: a CT light-emitting base point, an object to be detected, and a detector sensing plate, wherein the object to be detected is located between the CT light-emitting base point and the detector sensing plate, wherein the method comprises: a first positioning platform, a second positioning platform, and a third positioning platform, wherein the CT light-emitting base point is located on the first positioning platform, the object to be detected is located on the second positioning platform, the detector sensing plate is located on the third positioning platform, and the first positioning platform, the second positioning platform, and the third positioning platform are located on the same axis;

[0010] A detection board is placed in the area of ​​the object to be detected. At least four detection balls are arranged in the detection board. The four detection balls form a detection area. The CT light-emitting base point emits a light cone toward the detection board. The projection of the detection board and the projection of the detection ball are both projected into the detector sensing board.

[0011] The steps for calculating and adjusting the position of the CT light emitting base point and the detector sensing plate are as follows:

[0012] Step 100: The first positioning platform and the third positioning platform are a moving point, and the second positioning platform is a fixed point. The first positioning platform, the second positioning platform, and the third positioning platform are manually placed in a straight line to form an initial position;

[0013] Step 200: Adjust the light cone of the CT light emitting base point to irradiate the detector sensing plate;

[0014] Turn on the CT light-emitting base point, adjust the Z and X displacements of the first positioning platform, adjust the X and Y displacements of the third positioning platform, and adjust the projection of the detection board to be displayed in the detector sensing board;

[0015] Step 300: Record the point where the detection ball is projected onto the detector sensing plate;

[0016] When the detector sensing plate is at the initial position, the first four-point data collection is performed;

[0017] The detector sensing plate faces the CT light emitting base point and performs surface offset to collect the second four-point data;

[0018] Step 400: Combine the first four-point data with the second four-point data to calculate four straight lines;

[0019] Step 500: Calculate the intersection of four straight lines, and set the intersection of the four straight lines as the center coordinate of the CT light emitting base point;

[0020] Step 600: preset the center point of the detector sensing plate, and adjust the position of the detector sensing plate by moving the third point so that the coordinates of the center point of the detector sensing plate and the CT light emitting base point are adjusted to the same axis.

[0021] Step 700: Perform a calibration, and perform a sensing calibration on the area of ​​the detector sensing plate that is hit by the light cone rays.

[0022] In the above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, in step 100, the first positioning platform can be automatically controlled to move in the X and Z directions, and the third positioning platform can be automatically controlled to move in the Y and Z directions.

[0023] In the above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, in step 200, the detection board is embedded with sensing balls A, B, C, and D; the density of sensing balls A, B, C, and D is significantly greater than the density of the detection board.

[0024] In the above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, in step 300, after the light cone of the CT light-emitting base point is irradiated onto the detection board, the projection points of the sensing ball A, the sensing ball B, the sensing ball C, and the sensing ball D are left on the sensing board surface of the detector at the initial position, forming the initial four-point data respectively: AP0 (APx0, APy0, APz0), BP0 (BPx0, BPy0, BPz0), CP0 (CPx0, CPy0, CPz0), DP0 (DPx0, DPy0, DPz0);

[0025] The detector sensing plate surface is offset for the first time toward the second positioning platform, leaving the projection points of sensing ball A, sensing ball B, sensing ball C, and sensing ball D on the detector sensing plate surface, forming the first four points of data respectively: AP1 (APx1, APy1, APz1), BP1 (BPx1, BPy1, BPz1), CP1 (CPx1, CPy1, CPz1), DP1 (DPx1, DPy1, DPz1).

[0026] The above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, wherein, in step 400, the projection straight line of the sensing sphere A is calculated using AP0 (APx0, APy0, APz0) and AP1 (APx1, APy1, APz1);

[0027] Use BP0 (BPx0, BPy0, BPz0) and BP1 (BPx1, BPy1, BPz1) to calculate the projection line of the sensing ball B;

[0028] Using CP0 (CPx0, CPy0, CPz0) and CP1 (CPx1, CPy1, CPz1), calculate the projection line of the sensing ball C;

[0029] Using DP0 (DPx0, DPy0, DPz0) and DP1 (DPx1, DPy1, DPz1), calculate the projection line of the sensing ball D.

[0030] In the above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, in step 500, the steps of calculating the center point of the CT light-emitting base point based on the vector method from the intersection of the four straight lines are as follows:

[0031] Step 510: select any two projection lines from the four projection lines as the first group;

[0032] Step 520: using the two projection lines of the first group, calculating the least common perpendicular line of the two projection lines;

[0033] Step 530: Calculate the center point of the two perpendicular feet and set it as the center point of the CT light emitting base point.

[0034] In the above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, in step 600, the coordinates of the center point of the detector sensing plate are (midpoint of width, midpoint of height);

[0035] The center point of the CT light emitting base point and the center point of the detector sensing plate are located on the same horizontal line and on the same axis.

[0036] In the above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, in step 600, when adjusting the center point of the CT light-emitting base point and the center point of the detector sensing plate surface, when the movement of the third positioning platform reaches the limit position, the first positioning platform is displaced for adjustment until the center point of the CT light-emitting base point and the center point of the detector sensing plate surface are located on the same axis.

[0037] The axis is formed by the center point of the CT light emitting base point, the center of the object being detected and the center point of the detector sensing plate.

[0038] In the above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, in step 700, the center point of the displaced CT light emitting base point and the center point of the detector sensing plate are checked in the following way:

[0039] The detector sensing plate is deflected toward the second positioning platform at least four times, which are the second four-point data, the third four-point data, the fourth four-point data, and the fifth four-point data;

[0040] The second four-point data are: AP2 (APx2, APy2, APz2), BP2 (BPx2, BPy2, BPz2), CP2 (CPx2, CPy2, CPz2), DP2 (DPx2, DPy2, DPz2);

[0041] The four-point data for the third time are: AP3 (APx3, APy3, APz3), BP3 (BPx3, BPy3, BPz3), CP3 (CPx3, CPy3, CPz3), DP3 (DPx3, DPy3, DPz3);

[0042] The fourth four-point data are: AP4 (APx4, APy4, APz4), BP4 (BPx4, BPy4, BPz4), CP4 (CPx4, CPy4, CPz4), DP4 (DPx4, DPy4, DPz4);

[0043] The fifth four-point data are: AP5 (APx5, APy5, APz5), BP5 (BPx5, BPy5, BPz5), CP5 (CPx5, CPy5, CPz5), DP5 (DPx5, DPy5, DPz5);

[0044] Collect four-point data for four times, combine the four-point data for four times with the first four-point data and the initial four-point data, and use straight-line fitting to calculate the straight-line fitting projection line of the sensing ball A, the straight-line fitting projection line of the sensing ball B, the straight-line fitting projection line of the sensing ball C, and the straight-line fitting projection line of the sensing ball D respectively;

[0045] Using the projection straight line fitted by the four straight lines, refer to the steps in step 500 to calculate the center coordinates of the CT light emitting base point for the second time;

[0046] If the threshold between the center coordinates of the CT luminous base point calculated for the second time and the center coordinates of the CT luminous base point calculated for the first time is less than or equal to 10 pixels, the adjustment is considered qualified;

[0047] If the difference between the center coordinates of the CT luminous base point calculated for the second time and the center coordinates of the CT luminous base point calculated for the first time is greater than 10 pixels, it is considered unqualified, and the process enters step 300 to enter the cycle test phase.

[0048] In the above-mentioned method for automatically calculating and adjusting the central projection parameters of the CT system, in step 700, the points referenced by the straight line fitting projection line of the sensing sphere A are: AP0 (APx0, APy0, APz0), AP1 (APx1, APy1, APz1), AP2 (APx2, APy2, APz2), AP3 (APx3, APy3, APz3), AP4 (APx4, APy4, APz4), AP5 (APx5, APy5, APz5);

[0049] The reference points of the straight line fitting projection line of the sensing ball B are: BP0 (BPx0, BPy0, BPz0), BP1 (BPx1, BPy1, BPz1), BP2 (BPx2, BPy2, BPz2), BP3 (BPx3, BPy3, BPz3), BP4 (BPx4, BPy4, BPz4), BP5 (BPx5, BPy5, BPz5);

[0050] The reference points of the straight line fitting projection line of the sensing ball C are: CP0 (CPx0, CPy0, CPz0), CP1 (CPx1, CPy1, CPz1), CP2 (CPx2, CPy2, CPz2), CP3 (CPx3, CPy3, CPz3), CP4 (CPx4, CPy4, CPz4), CP5 (CPx5, CPy5, CPz5);

[0051] The reference points of the straight line fitting projection line of the sensing ball D are: DP0 (DPx0, DPy0, DPz0), DP1 (DPx1, DPy1, DPz1), DP2 (DPx2, DPy2, DPz2), DP3 (DPx3, DPy3, DPz3), DP4 (DPx4, DPy4, DPz4), DP5 (DPx5, DPy5, DPz5);

[0052] Straight line fitting The projection straight line is obtained by fitting using the least squares method.

[0053] The method for automatically calculating and adjusting the central projection parameters of a CT system of the present invention adopts the above scheme and has the following effects:

[0054] 1. The tedious operation of accurate calculation of the four-point model used for correction is reduced. As long as a simple four-point model with low precision requirements is adopted, the requirements can be met only by manual processing;

[0055] 2. By utilizing the automatic displacement of the CT light-emitting base point and the detector sensing plate, as well as the linear fitting verification method, the current projection parameters can be obtained in real time, and the automatic adjustment of the alignment between the center point of the CT light-emitting base point and the center point of the detector sensing plate can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The present invention is a flowchart of a method for automatically calculating and adjusting central projection parameters of a CT system;

[0057] Figure 2 Four projection straight line diagrams for a method for automatic calculation and adjustment of central projection parameters of a CT system;

[0058] Figure 3 A schematic diagram of a method for automatically calculating and adjusting central projection parameters of a CT system, wherein the detector sensing plate is offset 1, 3, and 5 times;

[0059] Figure 4 A schematic diagram of a detector sensing plate offset 2 and 4 times in a method for automatically calculating and adjusting central projection parameters of a CT system;

[0060] Figure 5 A schematic diagram of the center point of a detector sensing plate of a method for automatically calculating and adjusting the center projection parameters of a CT system;

[0061] Figure 6 A schematic diagram of a method for automatically calculating and adjusting central projection parameters of a CT system using the least square method to calculate four straight lines to fit the projection straight line;

[0062] Figure 7 A projection straight line diagram of a straight line fitting of a method for automatic calculation and adjustment of central projection parameters of a CT system;

[0063] Figure 8 A schematic diagram of a method for automatically calculating and adjusting central projection parameters of a CT system using the least square method to calculate four straight lines;

[0064] The reference numerals in the accompanying drawings of the specification are as follows:

[0065] First positioning platform 1, second positioning platform 2, third positioning platform 3, CT light emitting base point 4, detector sensing plate 6, projection straight line 7 of sensing ball A, projection straight line 8 of sensing ball B, projection straight line 9 of sensing ball C, projection straight line 10 of sensing ball D, common perpendicular line 11, common perpendicular line 12, common perpendicular line 13, common perpendicular line 14, common perpendicular line 15, common perpendicular line 16, sensing surface 21, straight line fitting projection straight line 7' of sensing ball A, straight line fitting projection straight line 8' of sensing ball A, straight line fitting projection straight line 9' of sensing ball A, straight line fitting projection straight line 10' of sensing ball A, common perpendicular line 11', common perpendicular line 12', common perpendicular line 13', common perpendicular line 14', common perpendicular line 15', common perpendicular line 16'. DETAILED DESCRIPTION

[0066] In order to make the technical means, creative features, objectives and effects of the invention easy to understand, the present invention is further explained below with reference to specific illustrations.

[0067] like Figure 1 , 2 The method for automatically calculating and adjusting the central projection parameters of a CT system includes: a CT light-emitting base point 4, an object to be detected, and a detector sensing plate 6. The object to be detected is located between the CT light-emitting base point 4 and the detector sensing plate 6. The object to be detected is illuminated by the CT light-emitting base point 4, so that the projection of the object to be detected is projected onto the detector sensing plate 6 for imaging.

[0068] In this embodiment, the positions of the platforms need to be adjusted first so that the first positioning platform 1, the second positioning platform 2 and the third positioning platform 3 are located on the same axis. The first positioning platform 1 drives the CT light emitting base point 4 to move in the X and Z directions, and the third positioning platform 3 drives the detector sensing plate 6 to move in the X and Y directions.

[0069] The adjustment of each platform can be done manually, without being very precise. The main reason for adjusting the initial position formed on the same axis is to reduce the displacement distance of the first positioning platform 1 and the third positioning platform 3 in the later stage.

[0070] The object to be detected on the second positioning platform 2 is replaced with a detection plate 5, and at least four balls are placed in the detection plate 5. The area surrounded by the four balls needs to be larger than the original object to be detected. The detection plate 5 and the four balls are used to calculate the center point of the CT light emitting base point 4.

[0071] In specific embodiment 2 of the present invention, in the process steps of calculation:

[0072] like Figure 2 , Figure 5As shown, the four sensing balls in the detection board 5 are set as sensing ball A, sensing ball B, sensing ball C, and sensing ball D. The light cone rays emitted by the CT light emitting base point 4 project the detection board 5 and its four sensing balls onto the detector sensing board 6, forming a sensing surface 21 and a projection line 7 of the sensing ball A, a projection line 8 of the sensing ball B, a projection line 9 of the sensing ball C, and a projection line 10 of the sensing ball D.

[0073] The projection straight line 7 of the sensing ball A, the projection straight line 8 of the sensing ball B, the projection straight line 9 of the sensing ball C, and the projection straight line 10 of the sensing ball D fall on the surface of the detector sensing plate 6 at the initial position, leaving the projection point of the sensing ball A, the projection point of the sensing ball B, the projection point of the sensing ball C, and the projection point of the sensing ball D, forming the initial four point data respectively: AP0 (APx0, APy0, APz0), BP0 (BPx0, BPy0, BPz0), CP0 (CPx0, CPy0, CPz0), DP0 (DPx0, DPy0, DPz0);

[0074] The detector sensing plate 6 is offset toward the detection plate 5, and the projection straight line 7 of the sensing ball A, the projection straight line 8 of the sensing ball B, the projection straight line 9 of the sensing ball C, and the projection straight line 10 of the sensing ball D fall on the surface of the detector sensing plate 6 that has been offset once, forming the first four points of data respectively: AP1 (APx1, APy1, APz1), BP1 (BPx1, BPy1, BPz1), CP1 (CPx1, CPy1, CPz1), DP1 (DPx1, DPy1, DPz1).

[0075] Combine the first four-point data with the second four-point data to calculate the equations of the four straight lines. The points involved in the calculation are:

[0076] Use AP0 (APx0, APy0, APz0) and AP1 (APx1, APy1, APz1) to calculate the projection line of the sensing ball A;

[0077] Use BP0 (BPx0, BPy0, BPz0) and BP1 (BPx1, BPy1, BPz1) to calculate the projection line of the sensing ball B;

[0078] Using CP0 (CPx0, CPy0, CPz0) and CP1 (CPx1, CPy1, CPz1), calculate the projection line of the sensing ball C;

[0079] Using DP0 (DPx0, DPy0, DPz0) and DP1 (DPx1, DPy1, DPz1), calculate the projection line of the sensing ball D.

[0080] like Figure 6As shown in the figure, the intersection point where all four straight lines pass is defined as the center coordinate of the CT luminous base point. In the actual calculation process, there will be errors when four rays intersect at one point. Therefore, it is necessary to find the center of the two perpendicular feet of the least common perpendicular line of any two 3D space straight lines. In the actual calculation, these four rays pass through the intersection point and leave four points. The four points are combined into six pairs. The six pairs are:

[0081] The least common perpendicular 11 between the projection straight line 7 of the induction sphere A and the projection straight line 8 of the induction sphere A, the least common perpendicular 15 between the projection straight line 7 of the induction sphere A and the projection straight line 10 of the induction sphere A, the least common perpendicular 14 between the projection straight line 7 of the induction sphere A and the projection straight line 9 of the induction sphere A, the least common perpendicular 12 between the projection straight line 8 of the induction sphere A and the projection straight line 10 of the induction sphere A, the least common perpendicular 16 between the projection straight line 8 of the induction sphere A and the projection straight line 9 of the induction sphere A, and the least common perpendicular 13 between the projection straight line 9 of the induction sphere A and the projection straight line 10 of the induction sphere A.

[0082] The mean value is calculated as:

[0083] X mean=(X1+ X 2+X3+X4+X5+X6) / 6;

[0084] Y mean=(Y1+Y2+Y3+Y4+Y5+Y6) / 6;

[0085] Z mean=(Z1+ xZ 2+Z3+Z4+Z5+Z6) / 6;

[0086] Get the center coordinates of the mean CT luminescence base point ( X meanYmean,Zmean).

[0087] In addition, the coordinates of the center point of the detector sensing plate are obtained as (midpoint of width, midpoint of height).

[0088] Adjust the CT light emitting base point to the center point of the detector sensing plate.

[0089] Finally, the verification stage is entered, and the detector sensing plate 6 is offset multiple times with equal or non-equal spacing, and the detector sensing plate 6 is offset at least four times toward the second positioning platform 2. The four-point data of the four times are collected and combined with the first four-point data and the initial four-point data.

[0090] like Figure 7 As shown, the linear fitting projection straight line of the sensing ball A, the linear fitting projection straight line of the sensing ball B, the linear fitting projection straight line of the sensing ball C, and the linear fitting projection straight line of the sensing ball D are calculated respectively by linear fitting;

[0091] like Figure 3 , 4 As shown, the second four-point data are: AP2 (APx2, APy2, APz2), BP2 (BPx2, BPy2, BPz2), CP2 (CPx2, CPy2, CPz2), DP2 (DPx2, DPy2, DPz2);

[0092] The four-point data for the third time are: AP3 (APx3, APy3, APz3), BP3 (BPx3, BPy3, BPz3), CP3 (CPx3, CPy3, CPz3), DP3 (DPx3, DPy3, DPz3);

[0093] The fourth four-point data are: AP4 (APx4, APy4, APz4), BP4 (BPx4, BPy4, BPz4), CP4 (CPx4, CPy4, CPz4), DP4 (DPx4, DPy4, DPz4);

[0094] The fifth four-point data are: AP5 (APx5, APy5, APz5), BP5 (BPx5, BPy5, BPz5), CP5 (CPx5, CPy5, CPz5), DP5 (DPx5, DPy5, DPz5);

[0095] The six-point data are: AP6 (APx6, APy6, APz6), BP6 (BPx6, BPy6, BPz6), CP6 (CPx6, CPy6, CPz6), DP6 (DPx6, DPy6, DPz6);

[0096] The center coordinates of the CT luminous base point calculated by the projection line of the four straight line fitting are used as a reference to verify the center coordinates of the CT luminous base point calculated by the projection line passing through the four straight lines.

[0097] Further, if the threshold between the center coordinates of the CT luminous base point calculated for the second time and the center coordinates of the CT luminous base point calculated for the first time is less than or equal to 10 pixels, it is considered as qualified and completed adjustment;

[0098] If the difference between the center coordinates of the CT luminous base point calculated for the second time and the center coordinates of the CT luminous base point calculated for the first time is greater than 10 pixels, it is considered unqualified. The detector sensing plate 6 is then offset to the initial position, and the first four-point data is collected again to enter the cyclic test phase.

[0099] In specific embodiment 2 of the present invention, in the process steps of calculation:

[0100] like Figure 2 , Figure 5 As shown, the four sensing balls in the detection board 5 are set as sensing ball A, sensing ball B, sensing ball C, and sensing ball D. The light cone rays emitted by the CT light emitting base point 4 project the detection board 5 and its four sensing balls onto the detector sensing board 6, forming a sensing surface 21 and a projection line 7 of the sensing ball A, a projection line 8 of the sensing ball B, a projection line 9 of the sensing ball C, and a projection line 10 of the sensing ball D.

[0101] The projection straight line 7 of the sensing ball A, the projection straight line 8 of the sensing ball B, the projection straight line 9 of the sensing ball C, and the projection straight line 10 of the sensing ball D fall on the surface of the detector sensing plate 6 at the initial position, leaving the projection point of the sensing ball A, the projection point of the sensing ball B, the projection point of the sensing ball C, and the projection point of the sensing ball D, forming the initial four point data respectively: AP0 (APx0, APy0, APz0), BP0 (BPx0, BPy0, BPz0), CP0 (CPx0, CPy0, CPz0), DP0 (DPx0, DPy0, DPz0);

[0102] The detector sensing plate 6 is shifted multiple times with equal or non-equal spacing, and the detector sensing plate 6 faces the second positioning platform 2 and is shifted at least five times.

[0103] The first four points of data are: AP1 (APx1, APy1, APz1), BP1 (BPx1, BPy1, BPz1), CP1 (CPx1, CPy1, CPz1), DP1 (DPx1, DPy1, DPz1);

[0104] The second four-point data are: AP2 (APx2, APy2, APz2), BP2 (BPx2, BPy2, BPz2), CP2 (CPx2, CPy2, CPz2), DP2 (DPx2, DPy2, DPz2);

[0105] The four-point data for the third time are: AP3 (APx3, APy3, APz3), BP3 (BPx3, BPy3, BPz3), CP3 (CPx3, CPy3, CPz3), DP3 (DPx3, DPy3, DPz3);

[0106] The fourth four-point data are: AP4 (APx4, APy4, APz4), BP4 (BPx4, BPy4, BPz4), CP4 (CPx4, CPy4, CPz4), DP4 (DPx4, DPy4, DPz4);

[0107] The four points of data for the fifth time are: AP5 (APx5, APy5, APz5), BP5 (BPx5, BPy5, BPz5), CP5 (CPx5, CPy5, CPz5), and DP5 (DPx5, DPy5, DPz5).

[0108] Collect four-point data five times, and combine the five-point data with the initial four-point data. Use linear fitting to calculate the linear fitting projection line of the sensing ball A, the linear fitting projection line of the sensing ball B, the linear fitting projection line of the sensing ball C, and the linear fitting projection line of the sensing ball D respectively;

[0109] like Figure 7 As shown, a representation of the straight line fitting projection line of the example sensing sphere A is shown, passing through points AP1 (APx1, APy1, APz1), AP2 (APx2, APy2, APz2), AP3 (APx3, APy3, APz3), AP4 (APx4, APy4, APz4), and AP5 (APx5, APy5, APz5).

[0110] like Figure 8 As shown in the figure, the intersection point where the four straight-line fitting projection lines pass through is defined as the central coordinate of the CT luminous base point. In the actual calculation process, there will be errors when the four straight-line fitting projection lines intersect at one point. Therefore, it is necessary to find the center of the two perpendicular feet of the least common perpendicular line of any two 3D space lines. In the actual calculation, these four straight-line fitting projection lines pass through the intersection point, leaving 4 points. The four points are combined in pairs to form a total of 6 pairs. The 6 pairs are: the least common perpendicular 11' between the straight line fitting projection line 7' and the straight line fitting projection line 8' of the sensing sphere A, the least common perpendicular 15' between the straight line fitting projection line 7' and the straight line fitting projection line 10' of the sensing sphere A, the least common perpendicular 14' between the straight line fitting projection line 7' and the straight line fitting projection line 9' of the sensing sphere A, the least common perpendicular 12' between the straight line fitting projection line 8' and the straight line fitting projection line 10' of the sensing sphere A, the least common perpendicular 16' between the straight line fitting projection line 8' and the straight line fitting projection line 9' of the sensing sphere A, and the least common perpendicular 13' between the straight line fitting projection line 9' and the straight line fitting projection line 10' of the sensing sphere A.

[0111] The mean value is calculated as:

[0112] X mean=(X1+ X 2+X3+X4+X5+X6) / 6;

[0113] Y mean=(Y1+Y2+Y3+Y4+Y5+Y6) / 6;

[0114] Z mean=(Z1+ xZ 2+Z3+Z4+Z5+Z6) / 6;

[0115] Get the center coordinates of the mean CT luminescence base point ( X mean, Ymean, Zmean).

[0116] In addition, the coordinates of the center point of the detector sensing plate are (midpoint of width (W / 2), midpoint of height (H / 2)).

[0117] Adjust the CT light emitting base point toward the center point of the detector sensing plate 6.

[0118] Finally, the calibration phase is entered, and the detector sensing plate 6 is offset multiple times with equal or non-equal spacing, and the detector sensing plate 6 is offset once more toward the second positioning platform 2. Four-point data are collected four times, and the four-point data once is combined with the initial four-point data.

[0119] Combine the initial four-point data with the first four-point data to calculate the equations of the four straight lines. The value points involved in the calculation are:

[0120] Use AP0 (APx0, APy0, APz0) and AP1 (APx1, APy1, APz1) to calculate the projection line of the sensing ball A;

[0121] Use BP0 (BPx0, BPy0, BPz0) and BP1 (BPx1, BPy1, BPz1) to calculate the projection line of the sensing ball B;

[0122] Using CP0 (CPx0, CPy0, CPz0) and CP1 (CPx1, CPy1, CPz1), calculate the projection line of the sensing ball C;

[0123] Using DP0 (DPx0, DPy0, DPz0) and DP1 (DPx1, DPy1, DPz1), calculate the projection line of the sensing ball D.

[0124] The center coordinates of the CT luminous base points calculated by the four straight lines are used as a reference to verify the center coordinates of the CT luminous base points calculated by the projection straight line fitted by the four straight lines. Here, the straight line appearing above can be interpreted as the trajectory equation of the X-ray.

[0125] Further, if the threshold between the center coordinates of the CT luminous base point calculated for the second time and the center coordinates of the CT luminous base point calculated for the first time is less than or equal to 10 pixels, it is considered as qualified and completed adjustment;

[0126] If the difference between the center coordinates of the CT luminous base point calculated for the second time and the center coordinates of the CT luminous base point calculated for the first time is greater than 10 pixels, it is considered unqualified. The detector sensing plate 6 is then offset to the initial position, and the first four-point data is collected again to enter the cyclic test phase.

[0127] Here, in a simplified case, if the equation of the line is calculated by sampling each point in the offset surface, it can be solved directly by observation or algebraic methods. In order to calculate the least common perpendicular between two lines, we only need the direction vectors of the two lines and a point.

[0128] In summary, the present invention provides a method for automatically calculating and adjusting the central projection parameters of a CT system, which reduces the tedious operation of accurately calculating the four-point model used for correction. As long as a simple four-point model with low precision requirements is adopted, the requirements can be met only through manual processing. The automatic displacement of the CT light-emitting base point and the detector sensing plate, as well as the calibration method of the straight line fitting are utilized, so that the current projection parameters can be obtained in real time, and the automatic adjustment of the alignment of the center point of the CT light-emitting base point and the center point of the detector sensing plate is realized.

[0129] The above describes the specific embodiments of the invention. It should be understood that the invention is not limited to the above specific embodiments, and the devices and structures not described in detail should be understood to be implemented in a common manner in the art; those skilled in the art can make various modifications or modifications within the scope of the claims, and make some simple deductions, deformations or substitutions, which does not affect the essence of the invention.

Claims

1. A method for automatically calculating and adjusting central projection parameters of a CT system, comprising: A CT light emitting base point, an object to be detected, and a detector sensing plate, wherein the object to be detected is located between the CT light emitting base point and the detector sensing plate, and is characterized in that it comprises: a first positioning platform, a second positioning platform, and a third positioning platform, wherein the CT light emitting base point is arranged on the first positioning platform, the object to be detected is arranged on the second positioning platform, and the detector sensing plate is arranged on the third positioning platform, and the first positioning platform, the second positioning platform, and the third positioning platform are located on the same axis; a detection plate is placed in the area of ​​the object to be detected, at least four detection balls are arranged in the detection plate, and a detection area is surrounded by the four detection balls, and the CT light emitting base point emits a light cone toward the detection plate, and the projection of the detection plate and the projection of the detection ball are both projected into the detector sensing plate; the steps of the method for calculating and adjusting the position of the CT light emitting base point and the detector sensing plate are as follows: Step 100: The first positioning platform and the third positioning platform are a moving point, and the second positioning platform is a fixed point. The first positioning platform, the second positioning platform, and the third positioning platform are manually placed in a straight line to form an initial position; Step 200: Adjust the light cone of the CT light emitting base point to irradiate the detector sensing plate; Turn on the CT light-emitting base point, adjust the Z and X displacements of the first positioning platform, adjust the X and Y displacements of the third positioning platform, and adjust the projection of the detection board to be displayed in the detector sensing board; Step 300: Record the point where the detection ball is projected onto the detector sensing plate; When the detector sensing plate is at the initial position, the first four-point data collection is performed; The detector sensing plate faces the CT light emitting base point and performs surface offset to collect the second four-point data; Step 400: Combine the first four-point data with the second four-point data to calculate four straight lines; Step 500: Calculate the intersection of four straight lines, and set the intersection of the four straight lines as the center coordinate of the CT light emitting base point; Step 600: preset the center point of the detector sensing plate, and adjust the position of the detector sensing plate by moving the third point so that the coordinates of the center point of the detector sensing plate and the CT light emitting base point are adjusted to the same axis; Step 700: Perform a calibration, and perform a sensing calibration on the area of ​​the detector sensing plate that is hit by the light cone rays.

2. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 1, characterized in that: In step 100, the first positioning platform may be automatically controlled to move in the X and Z directions, and the third positioning platform may be automatically controlled to move in the Y and Z directions.

3. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 2, characterized in that: In step 200, the detection board is embedded with sensing balls A, B, C and D; the density of sensing balls A, B, C and D is significantly greater than the density of the detection board.

4. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 3, characterized in that: In step 300, after the light cone of the CT light emitting base point is irradiated onto the detection board, the projection points of the sensing ball A, the sensing ball B, the sensing ball C, and the sensing ball D are left on the sensing board surface of the detector at the initial position, forming the initial four-point data respectively: AP0 (APx0, APy0, APz0), BP0 (BPx0, BPy0, BPz0), CP0 (CPx0, CPy0, CPz0), DP0 (DPx0, DPy0, DPz0); The detector sensing plate surface is offset for the first time toward the second positioning platform, leaving the projection points of sensing ball A, sensing ball B, sensing ball C, and sensing ball D on the detector sensing plate surface, forming the first four points of data respectively: AP1 (APx1, APy1, APz1), BP1 (BPx1, BPy1, BPz1), CP1 (CPx1, CPy1, CPz1), DP1 (DPx1, DPy1, DPz1).

5. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 4, characterized in that: In step 400, the projection line of the sensing ball A is calculated using AP0 (APx0, APy0, APz0) and AP1 (APx1, APy1, APz1); Use BP0 (BPx0, BPy0, BPz0) and BP1 (BPx1, BPy1, BPz1) to calculate the projection line of the sensing ball B; Using CP0 (CPx0, CPy0, CPz0) and CP1 (CPx1, CPy1, CPz1), calculate the projection line of the sensing ball C; Using DP0 (DPx0, DPy0, DPz0) and DP1 (DPx1, DPy1, DPz1), calculate the projection line of the sensing ball D.

6. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 5, characterized in that: In step 500, the steps of calculating the center point of the CT light emitting base point based on the vector method from the intersection of the four straight lines are as follows: Step 510: select any two projection lines from the four projection lines as the first group; Step 520: using the two projection lines of the first group, calculating the least common perpendicular line of the two projection lines; Step 530: Calculate the center point of the two perpendicular feet and set it as the center point of the CT light emitting base point.

7. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 6, characterized in that: In step 600, the coordinates of the center point of the detector sensing plate are (midpoint of width, midpoint of height); the center point of the CT light emitting base point and the center point of the detector sensing plate are located on the same horizontal line and on the same axis.

8. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 7, characterized in that: In step 600, when adjusting the center point of the CT light-emitting base point and the center point of the detector sensing plate surface, when the movement of the third positioning platform reaches the limit position, the first positioning platform is displaced for adjustment until the center point of the CT light-emitting base point and the center point of the detector sensing plate surface are located on the same axis; the axis is formed by the center point of the CT light-emitting base point, the center of the object to be detected and the center point of the detector sensing plate surface.

9. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 8, characterized in that: In step 700, the center point of the displaced CT light emitting base point and the center point of the detector sensing plate are checked in the following way: The detector sensing plate is deflected toward the second positioning platform at least four times, which are the second four-point data, the third four-point data, the fourth four-point data, and the fifth four-point data; The second four-point data are: AP2 (APx2, APy2, APz2), BP2 (BPx2, BPy2, BPz2), CP2 (CPx2, CPy2, CPz2), DP2 (DPx2, DPy2, DPz2); The four-point data for the third time are: AP3 (APx3, APy3, APz3), BP3 (BPx3, BPy3, BPz3), CP3 (CPx3, CPy3, CPz3), DP3 (DPx3, DPy3, DPz3); The fourth four-point data are: AP4 (APx4, APy4, APz4), BP4 (BPx4, BPy4, BPz4), CP4 (CPx4, CPy4, CPz4), DP4 (DPx4, DPy4, DPz4); The fifth four-point data are: AP5 (APx5, APy5, APz5), BP5 (BPx5, BPy5, BPz5), CP5 (CPx5, CPy5, CPz5), DP5 (DPx5, DPy5, DPz5); Collect four-point data for four times, combine the four-point data for four times with the first four-point data and the initial four-point data, and use straight-line fitting to calculate the straight-line fitting projection line of the sensing ball A, the straight-line fitting projection line of the sensing ball B, the straight-line fitting projection line of the sensing ball C, and the straight-line fitting projection line of the sensing ball D respectively; Using the projection straight line fitted by the four straight lines, refer to the steps in step 500 to calculate the center coordinates of the CT light emitting base point for the second time; If the threshold between the center coordinates of the CT luminous base point calculated for the second time and the center coordinates of the CT luminous base point calculated for the first time is less than or equal to 10 pixels, the adjustment is considered qualified; If the threshold between the center coordinates of the CT luminous base point calculated for the second time and the center coordinates of the CT luminous base point calculated for the first time is greater than 10 pixels, it is considered unqualified, and the process enters step 300 to enter the cycle test phase.

10. The method for automatically calculating and adjusting central projection parameters of a CT system according to claim 9, characterized in that: In step 700, the points referenced by the straight line fitting projection line of the sensing ball A are: AP0 (APx0, APy0, APz0), AP1 (APx1, APy1, APz1), AP2 (APx2, APy2, APz2), AP3 (APx3, APy3, APz3), AP4 (APx4, APy4, APz4), AP5 (APx5, APy5, APz5); The reference points of the straight line fitting projection line of the sensing ball B are: BP0 (BPx0, BPy0, BPz0), BP1 (BPx1, BPy1, BPz1), BP2 (BPx2, BPy2, BPz2), BP3 (BPx3, BPy3, BPz3), BP4 (BPx4, BPy4, BPz4), BP5 (BPx5, BPy5, BPz5); The reference points of the straight line fitting projection line of the sensing ball C are: CP0 (CPx0, CPy0, CPz0), CP1 (CPx1, CPy1, CPz1), CP2 (CPx2, CPy2, CPz2), CP3 (CPx3, CPy3, CPz3), CP4 (CPx4, CPy4, CPz4), CP5 (CPx5, CPy5, CPz5); The reference points of the straight line fitting projection line of the sensing ball D are: DP0 (DPx0, DPy0, DPz0), DP1 (DPx1, DPy1, DPz1), DP2 (DPx2, DPy2, DPz2), DP3 (DPx3, DPy3, DPz3), DP4 (DPx4, DPy4, DPz4), DP5 (DPx5, DPy5, DPz5); Straight line fitting The projection straight line is obtained by fitting using the least squares method.

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