Geometric parameter calibration piece and calibration method of CT (computed tomography) equipment

Abstract

The invention discloses a geometric parameter calibration piece and calibration method of CT equipment, the geometric parameter calibration piece comprises at least one calibration unit, each calibration unit comprises a plurality of calibration wires, and the plurality of calibration wires are regularly arranged in the same plane. The geometric parameter calibration piece is easy to machine, geometric parameters of CT equipment can be calibrated, and calibration operation is simple and easy to implement.

Description

[0001] This application is a divisional application of the Chinese invention patent application with application number CN 201910226555.0 (application date: March 25, 2019; invention name: Geometric parameter calibration part and calibration method of CT equipment). Technical Field

[0002] The present disclosure relates to the field of security inspection technology, and in particular to a geometric parameter calibration component for a CT device and a calibration method for calibrating the geometric parameters of the CT device using the calibration component. Background Art

[0003] In recent years, X-ray computed tomography (CT) technology has been widely used in the fields of medical treatment and security inspection. At present, most CT devices use spiral cone beam scanning, that is, a single target light source and an arc detector are installed on a circular slip ring, the slip ring rotates to collect projection data at different angles, and then reconstructs a 3D CT image through an analytical method. This type of device usually has only a single scanning plane, the relative position of the optical target and the detector is fixed, and the system involves fewer geometric parameters. However, the geometric error of the device will cause problems such as structural distortion, numerical inaccuracy and ring artifacts in the reconstructed image. In addition to spiral cone beam CT devices, static CT devices using distributed light sources have also begun to be used in the field of security inspection. Static CT devices have single or multiple scanning planes, each of which contains multiple light source targets, which can be arranged in straight lines, arcs, etc.; the detector is composed of multiple detector arms, and a single detector arm can be a straight line, a broken line or an arc. Compared with spiral cone beam CT, the X-ray source and detector positions of static CT slip ring-free equipment are fixed, and the angle coverage of the rays is guaranteed through multi-plane scanning. It has the advantages of fast scanning speed and low noise. Due to the particularity of scanning geometry, static CT usually uses an iterative reconstruction method to obtain 3D images. This method does not require the geometric arrangement to meet specific conditions, but the positions of the optical and mechanical targets and the detector crystals need to be accurately positioned, and the coordinate systems of different scanning planes also need to be kept consistent. However, compared with single-target light sources, distributed light sources are larger in size and weight, and the mechanical errors of installation will also increase accordingly. Due to the wide distribution range of light source targets, the overall geometric deviation of the light source usually causes the target position to deviate seriously from the design value, and the offset distance and offset direction of each target may be different, causing deformation of the reconstructed object and inaccurate reconstruction values, affecting the spatial resolution and material recognition of the equipment. In addition, there will be errors in the installation of the detector arm, so it is necessary to perform geometric correction on the equipment. Summary of the invention

[0004] The purpose of the present disclosure is to solve at least one aspect of the above-mentioned problems and defects in the prior art.

[0005] According to an embodiment of one aspect of the present disclosure, a geometric parameter calibration component of a CT device is provided, the calibration component includes at least one calibration unit, each of the calibration units includes a plurality of calibration wires, and the plurality of calibration wires are regularly arranged in the same plane.

[0006] In some embodiments, the calibration wire is in the shape of a straight line, a broken line or an arc.

[0007] In some embodiments, each of the calibration units further includes: a fixing member configured to fix the plurality of calibration wires.

[0008] In some embodiments, the plurality of calibration wires are directly fixed on a conveyor belt of the CT device or a channel of the CT device.

[0009] In some embodiments, the multiple calibration wires in the calibration unit are arranged at equal intervals.

[0010] In some embodiments, the plurality of calibration wires are parallel to or at a certain angle to a conveying direction of a conveyor belt of the CT device.

[0011] In some embodiments, the at least one calibration unit includes a first calibration unit, and a plurality of calibration wires of the first calibration unit are arranged in a horizontal plane or a vertical plane parallel to a conveying direction of a conveyor belt of the CT device.

[0012] In some embodiments, the at least one calibration unit further includes a second calibration unit, and a plane where the multiple calibration wires of the second calibration unit are located is perpendicular to a plane where the multiple calibration wires of the first calibration unit are located.

[0013] In some embodiments, the at least one calibration unit also includes a third calibration unit, the plane where the multiple calibration wires of the third calibration unit are located is perpendicular to the plane where the multiple calibration wires of the first calibration unit are located, and the second calibration unit and the third calibration unit are respectively located at both ends of the first calibration unit in a direction perpendicular to the conveying direction of the conveyor belt.

[0014] In some embodiments, the calibration wire is cylindrical.

[0015] In some embodiments, the diameter of the calibration wire is 0.5 mm-5 mm.

[0016] According to an embodiment of another aspect of the present disclosure, a method for calibrating geometric parameters of a CT device using the geometric parameter calibration component of the CT device is provided, comprising the following steps:

[0017] S1: Calculate the theoretical position of the center of mass of the calibration wire according to the geometric parameters of the calibration piece;

[0018] S2: Scanning the calibration part, extracting at least one group of projection slices including the calibration wire projection on the scanning plane;

[0019] S3: acquiring the position of the center of mass of each calibration wire of the calibration component on the projection slice;

[0020] S4: for each calibration wire, taking the optical machine as a reference system, establishing an optimization problem about the detector parameters and the position of the center of mass of the calibration wire according to the intersection of the target point and the center of mass of the calibration wire and the detector, and the position of the center of mass of the calibration wire obtained in S3, and solving the optimization problem to obtain the positions of the center of mass of all calibration wires in the scanning plane;

[0021] S5: using a position matching algorithm to match the position of the center of mass of the calibration wire obtained by S4 with the theoretical position calculated by S1, and then correcting the position of the center of mass of the calibration wire obtained by S4;

[0022] S6: Based on the corrected position of the center of mass of the calibration wire, an optimization problem about the detector parameters is established through all the calibration wires, and the optimization problem is solved to obtain the detector geometric parameters of the scanning plane.

[0023] In some embodiments, when there are multiple scanning planes, in step S2, at least one group of projection slices containing the calibration wire projection is extracted from each scanning plane, and the projection slices extracted from different scanning planes correspond to the same slice position of the calibration object; after step S6, the following steps are also included:

[0024] S7: Repeat S3 to S6 for each scanning plane to obtain the detector geometric parameters and the position of the center of mass of the calibration wire of each scanning plane; and

[0025] S8: By using a position matching algorithm, the position of the center of mass of the calibration wire obtained in S6 is expressed in a unified coordinate system, so that the position of the center of mass of the calibration wire in different scanning planes is the same, so as to obtain the position of the optomechanical target and the detector crystal.

[0026] According to the geometric parameter calibration piece of the CT device and the calibration method thereof described in the above embodiment of the present disclosure, the calibration piece includes at least one calibration unit, each of which includes a plurality of calibration wires, and the plurality of calibration wires are regularly arranged in the same plane. When in use, the calibration piece is placed on the conveyor belt or in the channel of the CT device to scan the calibration piece, calibrate the relative position of the optical machine and the detector through the projection position of the calibration wire on the detector plane, and obtain the position of the calibration wire to obtain the optical machine target point of the device and the crystal position of the detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is a schematic structural diagram of a geometric parameter calibration component of a CT device according to an exemplary embodiment of the present disclosure.

[0028] Figure 2 It is a schematic structural diagram of a geometric parameter calibration component of a CT device according to another exemplary embodiment of the present disclosure.

[0029] Figure 3 It is a schematic structural diagram of a geometric parameter calibration component of a CT device according to another exemplary embodiment of the present disclosure.

[0030] Figure 4 It is a schematic structural diagram of a geometric parameter calibration component of a CT device according to another exemplary embodiment of the present disclosure.

[0031] Figure 5 A flowchart of a method for calibrating geometric parameters of a CT device according to an exemplary embodiment of the present disclosure.

[0032] Figure 6 Another flowchart of a method for calibrating geometric parameters of a CT device according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] Although the present invention will be fully described with reference to the accompanying drawings containing preferred embodiments of the present invention, it should be understood before this description that a person of ordinary skill in the art may modify the invention described herein while obtaining the technical effects of the present invention. Therefore, it should be understood that the above description is a broad disclosure to a person of ordinary skill in the art, and its contents are not intended to limit the exemplary embodiments described in the present invention.

[0034] In addition, in the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the disclosed embodiments. However, it is apparent that one or more embodiments may be implemented without these specific details. In other cases, known structures and devices are embodied in a schematic manner to simplify the accompanying drawings.

[0035] According to the general inventive concept of the present disclosure, a geometric parameter calibration component of a CT device is provided, comprising at least one calibration unit, each of which comprises a plurality of calibration wires, and the plurality of calibration wires are regularly arranged in the same plane.

[0036] Figure 1 FIG. 1 is a schematic diagram of a geometric parameter calibration component of a CT device according to an exemplary embodiment of the present disclosure. Figure 1As shown, the geometric parameter calibration part of the CT device includes a calibration unit 10, and the calibration unit 10 includes a plurality of calibration wires 2 and a fixing part 1. The plurality of calibration wires 2 are regularly arranged in a horizontal plane parallel to the conveying direction of the conveyor belt. The calibration wires 2 are usually made of highly absorbent materials, such as metal. The calibration wires 2 can be flexible (such as steel wires, etc.) or rigid (such as steel rods, etc.). Each calibration wire 2 is in a straight line shape, and the shape of the calibration wire 2 includes but is not limited to a cylindrical shape, and its diameter can be, for example, 0.5mm-5mm. The fixing part 1 is configured to fix the plurality of calibration wires 2 to ensure that the position of the calibration wires 2 is fixed, so that the relative positions between different calibration wires 2 are consistent with the theoretical design value. The fixing part 1 can be made of a low-absorption material.

[0037] It should be noted that, although the calibration wire shown in this embodiment is in a straight line shape, those skilled in the art should understand that in some other embodiments of the present disclosure, the calibration wire 2 may also be in a broken line, arc shape or other regular shape. In addition, it should be noted that those skilled in the art should understand that in some other embodiments of the present disclosure, the calibration wire 2 may also be directly fixed on the conveyor belt of the CT device or the channel of the CT device.

[0038] like Figure 1 As shown, in this exemplary embodiment, the multiple calibration wires 2 in the calibration unit 10 are parallel to each other and arranged at equal intervals to facilitate subsequent calculations. In addition, in this embodiment, the multiple calibration wires 2 are at a certain angle to the conveying direction of the conveyor belt of the CT device. However, it should be noted that those skilled in the art should understand that in some other embodiments of the present disclosure, the multiple calibration wires 2 in the calibration unit 10 may also be parallel to the conveying direction of the conveyor belt.

[0039] Figure 2 FIG. 1 is a schematic diagram of a geometric parameter calibration component of a CT device according to another exemplary embodiment of the present disclosure. Figure 2 As shown, the multiple calibration wires 2 in the calibration unit 10 are parallel to each other and parallel to the conveying direction of the conveyor belt of the CT device (such as Figure 2 The multiple calibration wires 2 are arranged at equal intervals in a vertical plane (as indicated by the middle arrow), and form a certain angle with the conveying direction of the conveyor belt.

[0040] Figure 3 FIG. 1 is a schematic diagram of a geometric parameter calibration component of a CT device according to another exemplary embodiment of the present disclosure. Figure 3As shown, the calibration device includes two calibration units: a first calibration unit 11 and a second calibration unit 12, wherein the first calibration unit 11 and the second calibration unit 12 each include a plurality of calibration wires 2 and a fixing member 1, wherein the plurality of calibration wires 2 are regularly arranged, and each calibration wire 2 is in a straight line. The fixing member 1 is configured to fix the plurality of calibration wires 2. The plurality of calibration wires 2 in the first calibration unit 11 are arranged parallel to the conveying direction of the conveyor belt of the CT device (e.g., Figure 3 The plane where the multiple calibration wires 2 of the second calibration unit 12 are located is perpendicular to the plane where the multiple calibration wires 2 of the first calibration unit 11 are located, so that the entire calibration piece is L-shaped.

[0041] Figure 4 FIG. 1 is a schematic diagram of a geometric parameter calibration component of a CT device according to another exemplary embodiment of the present disclosure. Figure 4 As shown, the calibration device includes three calibration units: a first calibration unit 11, a second calibration unit 12 and a third calibration unit 13, wherein the first calibration unit 11, the second calibration unit 12 and the third calibration unit 13 each include a plurality of calibration wires 2 and a fixing member 1, wherein the plurality of calibration wires 2 are regularly arranged and each calibration wire 2 is in a straight line; the fixing member 1 is configured to fix the plurality of calibration wires 2. The plurality of calibration wires 2 in the first calibration unit 11 are parallel to the conveying direction of the conveyor belt of the CT device (such as Figure 4 The plane where the multiple calibration wires 2 of the second calibration unit 12 are located is perpendicular to the plane where the multiple calibration wires 2 of the first calibration unit 11 are located, the plane where the multiple calibration wires 2 of the third calibration unit 13 are located is perpendicular to the plane where the multiple calibration wires 2 of the first calibration unit 11 are located, and the second calibration unit 11 and the third calibration unit 13 are respectively located at both ends of the first calibration unit 11 in a direction perpendicular to the conveying direction of the conveyor belt, so that the entire calibration piece is U-shaped.

[0042] like Figure 5 As shown, the present disclosure also provides a calibration method for calibrating the geometric parameters of a CT device using the above calibration component, comprising the following steps:

[0043] S1: Calculate the theoretical position of the center of mass of calibration wire 2 according to the design parameters of the calibration part .

[0044] S2: Scan the calibration piece, extract the projection slice containing the projection of the calibration wire 2 on the scanning plane. Specifically, place the calibration piece on the transmission belt of the CT device to scan the calibration piece. During the scanning process, the transmission belt runs at a low speed, and the starting position of the calibration piece is detected to ensure that the projections obtained in different scanning planes correspond to the projection slices at the same position of the calibration piece. In addition, each scanning plane can extract, for example, more than 3 pairs of projection slices at equal intervals.

[0045] S3: Use image processing methods to obtain the position of the center of mass of the calibration wire 2 on each projection slice. Due to the limitation of the detector crystal size, the detection accuracy of the position of the center of mass of the calibration wire 2 is half the crystal width. Assuming that the calibration part contains N calibration wires 2, a total of M groups of projection slices are collected. Due to the movement of the conveyor belt, the position of the center of mass of the calibration wire 2 in each projection slice is different, so each scanning plane package collects M*N calibration wire projection data. If the target k is out of the beam, the crystal number of the actual projection of the center of mass of the calibration wire m on the detector plane is recorded as .

[0046] S4: For a single calibration wire m in the scanning plane, take the optical machine as the reference system, and establish an optimization problem about the detector parameters and the position of the calibration wire according to the intersection of the target point and the center of mass of the calibration wire m and the detector, as well as the position of the center of mass of the calibration wire m obtained in S3, and solve the optimization problem to obtain the position of all calibration wires in the scanning plane. The geometric parameters related to the detector are related to the arrangement of the detector crystals. For example, the linear detector is determined by the starting position of the detector and the crystal arrangement direction, and the arc detector is determined by the center of the circle, the radius and the starting angle. Taking the linear detector as an example, the parameters of the detector are recorded as , where y is the detector starting position and d is the detector crystal arrangement direction vector. The detector linear equation is recorded as , the crystal size is recorded as The position of the calibration wire m is recorded as , the position of the target point k is recorded as The line connecting the calibration wire and the target point is recorded as . and The two lines intersect at position , corresponding to the crystal According to S3, the actual projected crystal positions of the target point k and the calibration wire m on the detector plane are By minimizing Parameters and Optimize. The above process can be described as the following optimization problem

[0047]

[0048] in represents the coordinates of the intersection of two straight lines, For each calibration wire, solve the above optimization problem to obtain the position of all calibration wires The above optimization problem can be solved using simulated annealing method.

[0049] S5: Use the position matching algorithm to match the position of the center of mass of the calibration wire m obtained by S4 with the theoretical position calculated by S1, and then correct the position of the center of mass of the calibration wire m obtained by S4. Since there are errors in S3 and S4, and the calibration part is placed in an uncertain posture, there is a deviation between the position of the center of mass of the calibration wire m obtained by S4 and the theoretical position calculated by S1. The position value of the center of mass of the calibration wire m calculated by S4 is corrected by the position matching algorithm. The theoretical position calculated by S1 To align Perform calibration to obtain the final position of the calibration wire m .

[0050] S6: In S4, the position of the calibration wire m is replaced with the position corrected in S5, and an optimization problem about the detector parameters is established through all the calibration wires, and the detector geometric parameters of the scanning plane are obtained by solving the optimization problem. For example, the following optimization problem is established based on the intersection relationship:

[0051]

[0052] Solving the above optimization problem obtains the detector geometric parameters y and d.

[0053] like Figure 6 As shown, in an exemplary embodiment of the present disclosure, when there are multiple scanning planes, in step S2, at least one group of projection slices containing calibration wire projections is extracted from each scanning plane, and the projection slices extracted from different scanning planes correspond to the same slice position of the calibration part, and the starting position of the calibration part is detected to ensure that the projections obtained by different scanning planes correspond to the projection slices at the same position of the calibration part. In addition, each scanning plane can extract, for example, more than 3 pairs of projection slices at equal intervals. After step S6, the following steps are also included:

[0054] S7: Repeat S3 to S6 for each scanning plane to obtain the detector geometric parameters and the position of the center of mass of the calibration wire for each scanning plane, and

[0055] S8: Through the position matching algorithm, the position of the center of mass of the calibration wire 2 obtained in S6 is expressed in a unified coordinate system, so that the position of the center of mass of the calibration wire 2 in different scanning planes is the same, so as to obtain the optical target and the detector crystal position. The conveying direction of the conveyor belt is the z-axis direction. Since the position of the calibration part remains unchanged and moves with the conveyor belt, the position of the calibration wire in different planes in the xy plane is consistent. Through the position matching algorithm, the calibration wire obtained in S6 is expressed in a unified coordinate system, so that the positions of different planes are consistent, and the optical target and the detector crystal position are obtained accordingly.

[0056] According to the geometric parameter calibration part of the CT device and the calibration method thereof described in the above embodiment of the present disclosure, the calibration part includes at least one calibration unit, each of the calibration units includes a plurality of calibration wires, the plurality of calibration wires are arranged according to preset rules in a plane perpendicular to the conveying direction of the conveyor belt of the CT device, and each of the calibration wires is in a straight line or other preset shape. When in use, the calibration part is placed on the conveyor belt or in the channel of the CT device to scan the calibration part, calibrate the relative position of the optical machine and the detector through the projection position of the calibration wire on the detector plane, and obtain the position of the calibration wire to obtain the optical machine target point of the device and the detector crystal position. The geometric parameter calibration part of the CT device is easy to process and can be applied to area array and linear array detectors, and can be used for the geometric parameter calibration of spiral cone beam CT devices and static CT devices.

[0057] Those skilled in the art can understand that the embodiments described above are exemplary and can be improved by those skilled in the art. The structures described in various embodiments can be freely combined without causing conflicts in structure or principle.

[0058] After describing the preferred embodiments of the present invention in detail, those skilled in the art can clearly understand that various changes and modifications can be made without departing from the scope and spirit of the appended claims, and the present invention is not limited to the exemplary embodiments described in the specification.

Claims

1. A geometric parameter calibration part for a static CT device, comprising at least one calibration unit, each of which comprises a plurality of calibration wires and a fixing part, wherein the plurality of calibration wires are regularly arranged in a horizontal plane parallel to a conveying direction of a conveyor belt, and the fixing part is configured to fix the plurality of calibration wires to ensure that the positions of the calibration wires are fixed, the plurality of calibration wires are parallel to each other and arranged at equal intervals, and the plurality of calibration wires are parallel to or at a certain angle to the conveying direction of the conveyor belt of the CT device.

2. The calibration piece according to claim 1, wherein: The calibration wire is in the shape of a straight line, a broken line or an arc.

3. The calibration piece according to any one of claims 1 to 2, wherein: The at least one calibration unit includes a first calibration unit, and a plurality of calibration wires of the first calibration unit are arranged in a horizontal plane or a vertical plane parallel to a conveying direction of a conveyor belt of the CT device.

4. The calibration piece according to claim 3, wherein: The at least one calibration unit further includes a second calibration unit, wherein a plane where the multiple calibration wires of the second calibration unit are located is perpendicular to a plane where the multiple calibration wires of the first calibration unit are located.

5. The calibration piece according to claim 4, wherein: The at least one calibration unit also includes a third calibration unit, wherein a plane where the multiple calibration wires of the third calibration unit are located is perpendicular to a plane where the multiple calibration wires of the first calibration unit are located, and the second calibration unit and the third calibration unit are respectively located at two ends of the first calibration unit in a direction perpendicular to the conveying direction of the conveyor belt.

6. The calibration piece according to any one of claims 1 to 2, wherein: The calibration wire is cylindrical.

7. The calibration piece according to claim 6, wherein: The diameter of the calibration wire is 0.5mm-5mm.

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