A cone-beam CT beam center alignment device, calibration system and calibration method

Abstract

A cone-beam CT beam center alignment device, calibration system and calibration method belong to the technical field of CT beam alignment. The cone-beam CT beam center alignment device is characterized in that it includes a positioning body (8) and positioning blocks. The positioning body (8) has a front end face and a rear end face that are parallel to each other. On the front end face of the positioning body (8), there is a polygon positioning area that is centrosymmetric along the center of the front end face. Each side of the polygon positioning area is evenly provided with a positioning block, and a positioning block is provided at the center of the rear end face of the positioning body (8). The spatial distances between the positioning blocks on the front end face and the positioning block on the rear end face are all the same. The present invention can quickly and accurately find the beam center of the cone-beam CT system, making the X-ray tube focal point, turntable center, and flat panel detector center collinear and perpendicular to the flat panel detector plane. The technical solution of the present invention is easy to implement, the device structure is simple, the system debugging can be quickly completed, the accuracy of the cone-beam CT system can be improved, and the image quality can be improved.

Description

Technical Field

[0001] A cone-beam CT beam center alignment device, calibration system and calibration method belong to the technical field of CT beam alignment. Background Art

[0002] Since the discovery of X-rays by Roentgen in 1895, X-rays have been widely used in clinical medicine and industrial detection. Especially with the emergence of CT technology, as one of the greatest scientific and technological achievements in the late 20th century, CT technology has also developed by leaps and bounds in recent years, from parallel beam scanning to fan beam scanning, from single-row scanning to multi-row spiral scanning, etc. At the same time, with the development of detector technology, cone-beam CT technology has gradually become an important direction of CT development. Cone-beam CT has been gradually applied to clinical medicine and industrial detection and other fields due to its advantages such as fast scanning speed, high ray utilization rate, and simple operation.

[0003] A cone-beam CT system generally mainly includes a X-ray tube, a turntable and a flat panel detector, etc. Ideally, the X-ray tube focal point, the turntable center point, and the flat panel detector center point should be collinear and the connection line of the three points should be perpendicular to the flat panel detector plane. However, during the actual installation process, there are errors in the positions of these three components, resulting in the non-collinearity of the X-ray tube focal point, the turntable center point, and the flat panel detector center point or the non-perpendicularity to the flat panel detector plane after collinearity, seriously affecting the image quality. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a cone-beam CT beam center alignment device, calibration system and calibration method that can make the X-ray tube focal point, the turntable center, and the image center point of the flat panel detector collinear and perpendicular to the flat panel detector plane, and can assist in adjusting and verifying whether the centers are aligned.

[0005] A cone-beam CT beam center alignment device, characterized in that: it includes a positioning body and positioning blocks. The positioning body has a front end face and a rear end face that are parallel to each other. On the front end face of the positioning body, there is a polygon positioning area that is centrosymmetric along the center of the front end face. Each side of the polygon positioning area is evenly distributed with a positioning block. A positioning block is provided at the center of the rear end face of the positioning body. The spatial distances between the positioning blocks on the front end face and the positioning block on the rear end face are all the same.

[0006] The present invention aims to satisfy the collinearity of the tube focus, the center point of the turntable, and the center point of the flat panel detector. Through the cone beam CT beam center alignment device, the three points can be quickly and accurately aligned. The method is simple and fast, and the device structure is simple. By using the positioning blocks set at the fixed points on the front and rear end faces of the positioning body and the spatial geometric relationship between the front and rear positioning blocks, the position that needs to be collinearly calibrated can be accurately and quickly determined. According to the distances between multiple positioning blocks on the front surface and the center positioning block on the rear surface in the image, the horizontal or vertical position of the tube is adjusted. By continuously adjusting the position of the tube, continuously emitting beams, and continuously measuring the distances between the positioning blocks, until the distances between multiple positioning blocks on the front surface and the positioning block on the rear surface in the image are the same. At this time, it indicates that the beam central axis is perpendicular to the plane of the flat panel detector and passes through the image center of the detector. The beam center of the cone beam CT system can be quickly and accurately found, making the three points of the tube focus, the turntable center, and the flat panel detector center collinear and perpendicular to the plane of the flat panel detector. The technical solution of the present invention is easy to implement, the device structure is simple, the system debugging can be quickly completed, the accuracy of the cone beam CT system can be improved, and the image quality can be improved.

[0007] The positioning block described above is a metal positioning ball.

[0008] Multiple positioning blocks on the front end face are respectively fixed at the midpoints of each side of the polygonal positioning area.

[0009] Multiple positioning blocks on the front end face are respectively fixed at multiple vertices of the polygonal positioning area.

[0010] The positioning body described above is a cylindrical, square, I-shaped, or rectangular box body, and the polygonal positioning area is square.

[0011] A cone beam CT system formed by using a cone beam CT beam center alignment device, characterized in that: it includes a tube, a turntable, a flat panel detector, and a CT beam center alignment device. The CT beam center alignment device is placed on the vertical plane of the flat panel detector, and the rear end face of the CT beam center alignment device is attached to the vertical side face of the flat panel detector. A calibration body is placed on the vertical axis of the turntable, and the top tip is in the same straight line as the beam central axis emitted by the tube and the positioning block at the center of the rear end face of the CT beam center alignment device.

[0012] The calibration body described above is a cone.

[0013] The cone beam CT calibration system described in the present invention can be divided into two forms. One is the form where the turntable rotates and the flat panel detector and the tube are fixed, and the other can be a structural form where the turntable does not move and the flat panel detector and the tube rotate around the turntable. Both forms of cone beam CT systems can adopt the cone beam CT beam center alignment device and alignment method described in the present invention. The first form of cone beam CT system is preferably described below.

[0014] A method for calibrating the beam center of cone-beam CT using a cone-beam CT calibration system, characterized by comprising the following steps:

[0015] (1) Determine the image center of the flat panel detector. Place the positioning body on the vertical plane of the flat panel detector, align the positioning block at the rear end face of the positioning body with the center of the flat panel detector and connect them. Let the X-ray tube emit beams, observe that the positioning block is at the center of the flat panel detector, and adjust the positioning block until it is at the center of the flat panel detector;

[0016] (2) Determine that the focal center of the X-ray tube and the image center of the flat panel detector are collinear and perpendicular to the plane of the flat panel detector. Let the X-ray tube emit beams, observe whether the beam central axis is perpendicular to the front and rear end faces of the positioning body and passes through the image center of the flat panel detector, adjust the position of the X-ray tube, and emit beams multiple times until the beam central axis is perpendicular to the front and rear end faces of the positioning body and passes through the image center of the flat panel detector;

[0017] (3) Determine the horizontal center of the turntable. Place the calibration body at the center of the turntable. While rotating the turntable, let the X-ray tube emit beams. Determine that during the rotation of the turntable, the image of the top tip of the calibration body on the flat panel detector remains stable and passes through the horizontal center of the flat panel detector;

[0018] (4) Determine the vertical center of the turntable. Observe whether the top tip of the calibration body coincides with the center of the flat panel detector in the image of the top tip of the calibration body on the flat panel detector, and adjust the vertical position of the calibration body until they coincide.

[0019] Regarding the observation in step (2) of whether the beam central axis is perpendicular to the front and rear end faces of the positioning body and passes through the image center of the flat panel detector, by measuring the distances from multiple positioning blocks on the front end face of the positioning body to the positioning block at the center of the rear end face, adjust the horizontal or vertical position of the X-ray tube, and emit beams from the X-ray tube multiple times to measure the distances between the positioning blocks on the front and rear end faces multiple times until the distances from multiple positioning blocks on the front end face to the positioning block at the center of the rear end face in the image of the flat panel detector are the same.

[0020] During the process of rotating the turntable in step (3), if the image of the top tip of the calibration body on the flat panel detector shakes, adjust the position of the calibration body on the turntable. If the image of the top tip of the calibration body on the flat panel detector is stable but does not pass through the horizontal center of the flat panel detector, adjust the horizontal positions of the turntable and the calibration body as a whole.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] The present invention aims to satisfy the collinearity of the tube focus, the center point of the turntable, and the center point of the flat panel detector. Through the cone beam CT beam center alignment device, the three points can be quickly and accurately aligned. The method is simple and fast, and the device structure is simple. By using the positioning blocks set at the fixed points on the front and rear end faces of the positioning body and the spatial geometric relationship between the front and rear positioning blocks, the position that needs to be collinearly calibrated can be accurately and quickly determined. According to the distances between multiple positioning blocks on the front surface and the center positioning block on the rear surface in the image, the horizontal or vertical position of the tube is adjusted. By continuously adjusting the position of the tube, continuously emitting beams, and continuously measuring the distances between the positioning blocks, until the distances between multiple positioning blocks on the front surface and the positioning block on the rear surface in the image are the same. At this time, it indicates that the beam central axis is perpendicular to the plane of the flat panel detector and passes through the image center of the detector. The beam center of the cone beam CT system can be quickly and accurately found, making the tube focus, the turntable center, and the flat panel detector center collinear and perpendicular to the plane of the flat panel detector. The technical solution of the present invention is easy to implement, the device structure is simple, the system debugging can be quickly completed, the accuracy of the cone beam CT system can be improved, and the image quality can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a cone beam CT system.

[0024] Figure 2 It is a diagram for determining the state of the center of the flat panel detector.

[0025] Figure 3 It is a schematic diagram of the projection relationship between the tube and the flat panel detector.

[0026] Figure 4 It is a schematic diagram for determining the position of the turntable.

[0027] Figure 5 It is a schematic diagram of the structure of the positioning body.

[0028] Among them, 1. Tube; 2. Turntable; 3. Flat panel detector; 4. Cone; 5. Tube focus; 6. Beam central axis; 7. Center of the flat panel detector; 8. Positioning body; 9. Front surface; 10. Metal positioning ball; 11. Rear surface. DETAILED DESCRIPTION OF THE INVENTION

[0029] Figures 1 to 5 This is the best embodiment of the present invention. The following further describes the present invention in conjunction with the attached Figures 1 to 5 drawings.

[0030] Referring to the attached Figure 1: A cone-beam CT beam center alignment device, comprising a positioning body 8 and positioning blocks. The positioning body 8 has a front end face and a rear end face that are parallel to each other. On the front end face of the positioning body 8, there is a polygonal positioning area that is centrosymmetric along the center of the front end face. A positioning block is evenly distributed on each side of the polygonal positioning area. At the center of the rear end face of the positioning body 8, there is a positioning block. The spatial distances between the positioning blocks on the front end face and the positioning block on the rear end face are all the same.

[0031] The positioning blocks are metal positioning balls 10. Multiple positioning blocks are respectively fixed at the midpoints of each side of the polygonal positioning area. Preferably, multiple positioning blocks are respectively fixed at multiple vertices of the polygonal positioning area. The positioning body 8 is a cylindrical, square, I-shaped or rectangular box body, and the polygonal positioning area is square.

[0032] A cone-beam CT system formed by a cone-beam CT beam center alignment device, comprising an X-ray tube 1, a turntable 2, a flat panel detector 3 and a CT beam center alignment device. The CT beam center alignment device is placed on the vertical plane of the flat panel detector 3, and the rear end face of the CT beam center alignment device is attached to the vertical side face of the flat panel detector. A calibration body is placed on the vertical axis of the turntable 2, and the top tip is in the same straight line as the beam central axis 6 emitted by the X-ray tube 1 and the positioning block at the center of the rear end face of the CT beam center alignment device. The calibration body is a cone 4.

[0033] The positioning body 8 and the metal positioning balls 10 are made of materials with a large density difference. For example, the positioning body 8 is made of materials such as plastic. The metal positioning balls 10 block more rays, and the rays of the material of the positioning body 8 are more easily penetrated, so as to ensure that the metal positioning balls 10 form obvious marks on the flat panel detector 3 through the rays, which is convenient for observation.

[0034] The cone-beam CT system described in the present invention can be divided into two forms. One is the type in which the turntable 2 rotates and the flat panel detector 3 and the X-ray tube 1 are fixed. It can also be a structural form in which the turntable 2 does not move and the flat panel detector 3 and the X-ray tube 1 rotate around the turntable 2. Both types of cone-beam CT systems can adopt the cone-beam CT beam center alignment device and alignment method described in the present invention. Hereinafter, the first type of cone-beam CT system is preferably described.

[0035] A cone-beam CT beam center calibration method performed by a cone-beam CT system, comprising the following steps:

[0036] 1. Determine the image center of the flat panel detector 3. Place the positioning body 8 on the vertical plane of the flat panel detector 3. Align the positioning block on the rear end face of the positioning body 8 with and connect it to the center of the flat panel detector 3. The X-ray tube 1 emits a beam, and observe that the positioning block is at the center of the flat panel detector 3. Adjust the positioning block until it is at the center of the flat panel detector 3; as Figure 2As shown, it is fixed at the center of the flat panel detector with a metal positioning ball 10. The X-ray tube 1 emits a beam, and observe whether the center of the metal positioning ball 10 is at the center of the image. If not, adjust the position of the metal positioning ball 10. The X-ray tube 1 emits a beam again, and then observe whether the center of the metal positioning ball 10 is at the center of the image. Repeat the above process until the center of the metal positioning ball 10 is at the image center of the flat panel detector. At this time, it indicates that the position marked by the metal positioning ball 10 is the image center position of the flat panel detector 3.

[0037] 2. Ensure that the focal center of the X-ray tube 1 and the image center of the flat panel detector 3 are collinear and perpendicular to the plane of the flat panel detector 3. The X-ray tube 1 emits a beam, and observe whether the central axis 6 of the beam is perpendicular to the front and rear end faces of the positioning body 8 and passes through the image center of the flat panel detector 3. Adjust the position of the X-ray tube 1 and emit the beam multiple times until the central axis 6 of the beam is perpendicular to the front and rear end faces of the positioning body 8 and passes through the image center of the flat panel detector 3; observe whether the central axis 6 of the beam is perpendicular to the front and rear end faces of the positioning body 8 and passes through the image center of the flat panel detector 3. By measuring the distances from multiple positioning blocks on the front end face of the positioning body 8 to the positioning block at the center of the rear end face, adjust the horizontal or vertical position of the X-ray tube 1, and emit the beam from the X-ray tube 1 multiple times and measure the distances between the positioning blocks on the front and rear end faces multiple times until the distances from multiple positioning blocks on the front end face in the image of the flat panel detector 3 to the positioning block at the center of the rear end face are the same.

[0038] As Figure 3 shown, multiple metal positioning balls 10 are fixedly installed on the front surface of the positioning body 8, and one metal positioning ball 10 is fixedly installed on the rear surface. The multiple metal positioning balls 10 on the front surface are respectively located at the vertices of a polygon, and the center of the polygon coincides with the center of the front surface of the polyhedron. The metal positioning ball 10 on the rear surface is located at the center of the rear surface. Press the rear surface of the positioning body 8 closely against the surface of the flat panel detector 3, and the metal positioning ball 10 fixed at the center of the rear surface coincides with the image center of the flat panel detector 3, that is, coincides with the image center found in step 1. Due to the spatial geometric relationship of the five metal positioning balls 10 in the positioning body 8, if the central axis 6 of the beam is perpendicular to the front and rear surfaces of the positioning body 8 and passes through the image center of the flat panel detector 3, the distances from the multiple metal positioning balls 10 on the front surface to the metal positioning ball 10 on the rear surface in the image should be the same. If the distances are not the same, it indicates that the central axis 6 of the beam does not pass through the image center of the flat panel detector 3. At this time, according to the distances from the multiple metal positioning balls 10 on the front surface to the metal positioning ball 10 at the center of the rear surface in the image, adjust the horizontal or vertical position of the X-ray tube 1. By continuously adjusting the position of the X-ray tube 1, continuously emitting the beam, and continuously measuring the distances between the metal positioning balls 10, until the distances from the multiple metal positioning balls 10 on the front surface to the metal positioning ball 10 on the rear surface in the image are the same. At this time, it indicates that the central axis 6 of the beam is perpendicular to the plane of the flat panel detector 3 and passes through the image center of the flat panel detector 3.

[0039] 3. Determine the lateral center of the turntable. Place a calibration body at the center of the turntable 2. While rotating the turntable 2, the X-ray tube 1 emits beams. During the rotation of the turntable 2, ensure that the image of the top tip of the calibration body on the flat panel detector 3 remains stable and passes through the lateral center of the flat panel detector. During the rotation of the turntable 2, if the image of the top tip of the calibration body on the flat panel detector 3 shakes, adjust the position of the calibration body on the turntable 2. If the image of the top tip of the calibration body on the flat panel detector 3 does not shake but does not pass through the lateral center of the flat panel detector, adjust the lateral positions of the turntable 2 and the cone 4 as a whole. As Figure 4 shown in the figure, place the cone 4 on the turntable 2. Rotate the turntable 2 while the X-ray tube 1 emits beams. Observe whether the image of the tip of the cone 4 on the flat panel detector 3 shakes and passes through the lateral center of the flat panel detector. If it shakes, adjust the cone 4 until the image of the tip of the cone 4 on the flat panel detector 3 remains stationary during the rotation of the turntable 2. If the image of the top tip of the calibration body on the flat panel detector 3 does not shake but does not pass through the lateral center of the flat panel detector, adjust the lateral positions of the turntable 2 and the cone 4 as a whole until the image of the top tip of the calibration body on the flat panel detector 3 remains stable and passes through the lateral center of the flat panel detector 3 during the rotation of the turntable 2. At this time, it indicates that the tip of the cone 4 indicates the position of the central axis of the turntable 2 in the lateral direction.

[0040] 4. Determine the vertical center of the turntable. Observe whether the top tip of the calibration body coincides with the center of the flat panel detector 3 in the image of the top tip of the calibration body on the flat panel detector 3. Adjust the vertical position of the calibration body until they coincide. As Figure 1 shown in the figure, the X-ray tube 1 emits beams. Observe whether the tip of the cone 4 coincides with the center of the flat panel detector 3 in the image. If not, adjust the vertical position of the tip of the cone 4 until the tip of the cone 4 coincides with the center of the flat panel detector 3 in the image. According to steps 3 and 4, the tip of the cone 4 indicates the intersection of the central axis of the turntable 2 and the central axis of the beam 6.

[0041] By implementing the above steps, the central axis of the beam 6 can be accurately found and the central axis of the beam 6 can be made perpendicular to the plane of the flat panel detector 3. The implementation of the present invention is easy, the device structure is simple, and it is convenient and fast to use. It can quickly and accurately complete the alignment of the beam center of the cone beam CT system.

[0042] The above is only a preferred embodiment of the present invention, and it is not intended to limit the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A cone-beam CT beam center calibration method, characterized in that: Comprising a cone beam CT calibration system, the cone beam CT calibration system includes an X-ray tube (1), a turntable (2), a flat panel detector (3) and a CT beam center alignment device. The CT beam center alignment device is placed on the vertical plane of the flat panel detector (3), and the rear end face of the CT beam center alignment device is attached to the vertical side face of the flat panel detector. A calibration body is placed on the vertical axis of the turntable (2), and its top tip is in the same straight line as the beam central axis (6) emitted by the X-ray tube (1) and the positioning block at the center of the rear end face of the CT beam center alignment device; The cone beam CT beam center alignment device includes a positioning body (8) and positioning blocks. The positioning body (8) has a front end face and a rear end face that are parallel to each other. On the front end face of the positioning body (8), a polygon positioning area that is centrosymmetric along the center of the front end face is provided. A positioning block is evenly distributed on each side of the polygon positioning area. A positioning block is provided at the center of the rear end face of the positioning body (8). The spatial distances between the positioning blocks on the front end face and the positioning block on the rear end face are all the same; The positioning block is a metal positioning ball (10); The cone beam CT beam center calibration method includes the following steps:

1. Determine the image center of the flat panel detector (3). Place the positioning body (8) on the vertical plane of the flat panel detector (3). Align the positioning block on the rear end face of the positioning body (8) with and connect it to the center of the flat panel detector (3). The X-ray tube (1) emits a beam. Observe that the positioning block is at the center of the flat panel detector (3), and adjust the positioning block until it is at the center of the flat panel detector (3); 2. Determine that the focal center of the X-ray tube (1) and the image center of the flat panel detector (3) are collinear and perpendicular to the plane of the flat panel detector (3). The X-ray tube (1) emits a beam. Observe whether the beam central axis (6) is perpendicular to the front and rear end faces of the positioning body (8) and passes through the image center of the flat panel detector (3). Adjust the position of the X-ray tube (1). Emit the beam multiple times until the beam central axis (6) is perpendicular to the front and rear end faces of the positioning body (8) and passes through the image center of the flat panel detector (3); 3. Determine the transverse center of the turntable. Place a calibration body at the center of the turntable (2). While rotating the turntable (2), the X-ray tube (1) emits a beam. Determine that during the rotation of the turntable (2), the top tip of the calibration body remains stable in the image of the flat panel detector (3) and passes through the transverse center of the flat panel detector (3); 4. Determine the vertical center of the turntable. Observe whether the top tip of the calibration body coincides with the center of the flat panel detector (3) in the image of the flat panel detector (3). Adjust the vertical position of the calibration body until they coincide; Regarding the observation in step 2 of whether the beam central axis (6) is perpendicular to the front and rear end faces of the positioning body (8) and passes through the image center of the flat panel detector (3), by measuring the distances from multiple positioning blocks on the front end face of the positioning body (8) to the positioning block at the center of the rear end face, adjust the horizontal or vertical position of the X-ray tube (1), and emit the beam from the X-ray tube (1) multiple times. Measure the distances between the positioning blocks on the front and rear end faces multiple times until the distances from multiple positioning blocks on the front end face to the positioning block at the center of the rear end face in the image of the flat panel detector (3) are all the same.

2. The cone-beam CT beam center calibration method according to claim 1, wherein: The multiple positioning blocks on the front end face are respectively fixed at the midpoints of each side of the polygonal positioning area.

3. A cone-beam CT beam center calibration method according to claim 1, characterized in that: The multiple positioning blocks on the front end face are respectively fixed at the respective vertices of the polygonal positioning area.

4. A cone beam CT beam center calibration method according to claim 1, characterized in that: The positioning body (8) is cylindrical, I-shaped or square, and the polygonal positioning area is square.

5. A cone-beam CT beam center calibration method according to claim 1, characterized in that: The calibration body is a cone (4).

6. A cone-beam CT beam center calibration method according to claim 1, characterized in that: During the process of rotating the turntable (2) in Step 3, if the image of the top tip of the calibration body shakes in the flat panel detector (3), adjust the position of the calibration body on the turntable (2). If the image of the top tip of the calibration body is stable but does not pass through the horizontal center of the flat panel detector, adjust the horizontal positions of the turntable (2) and the calibration body as a whole.

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