Small animal scattering suppression CBCT collimator and collimation method

Abstract

A small animal scattering suppression CBCT collimator system comprises a radiation source, a frustum-shaped collimator and a flat panel detector which are coaxial and sequentially arranged from front to back. The ray source is a CBCT ray source; and the radiation source, the prismatic table-shaped collimator and the flat panel detector are jointly fixed on the rotating platform. The invention relates to a small animal scattering suppression CBCT (Cone Beam Computed Tomography) collimation detection method, which is implemented by utilizing a small animal scattering suppression CBCT collimator system.

Description

Technical Field

[0001] The present invention relates to the technical field of cone beam CT (CBCT), and in particular to a small animal scatter suppression CBCT collimator and a collimation method. Background Art

[0002] Recently, cone beam CT (CBCT) for animals, especially experimental animals, has received much attention. For CT devices for experimental animals, experimental studies have shown that collimation devices for large cone beam CT are generally not applicable (they are too large, often have large support brackets for front and back functions, are large in size, have many accessories, and are difficult to install). Without a collimator, it is difficult to meet the requirements for CT detection results of experimental animals. Compared with the common human body, the density of animal soft tissue is relatively small, and various low-energy, large-angle scattered X-rays can also penetrate, which will cause CBCT soft tissue to have unclear details and poor resolution. Without collimation, there is no way to do scatter correction, resulting in poor soft tissue resolution of CBCT.

[0003] Currently, there is no collimator in the prior art that can specifically solve the problem of CBCT. General planar and flat-plate collimators cannot specifically solve the problem of poor soft tissue resolution in animals.

[0004] Taking CN104548374A as an example, a flat collimator is selected, which has 6 collimator groups arranged on the outside of the rotating shaft 107 and the support shaft 108, and can move with the rotation of the rotating shaft. Each collimator group is formed by a strip gap and a strip block interval, and each collimator group is provided with 5 strip gaps. The effect it claims is to suppress scattered signals. Through actual measurements, we found that this type of collimator is indeed good at eliminating scattered signals, but its setting is complicated, the use is cumbersome, and there is no way to solve the problem of poor soft tissue resolution. In US2014169519A, a collimator MLC22 composed of multiple plates appears, but it is only composed of plates arranged in the X direction: MLC 22 includes a pair of frames 30 placed on either side of the beam and spaced apart in the y direction, and each frame contains an array of thin blades 32 arranged side by side in the x direction. After actual measurements, its actual effect is far inferior to the collimator of this application. In KR101076319B1, a block collimator is used, which uses four circumferentially arranged sheet collimators to move to adjust the size of the collimation window. After actual measurement, this setting cannot solve the problem of this application. In WO2021172757A1, the collimator is also a window-type collimator, with plates 201 and 202 with variable positions to deform to form different openings. Although this collimator is easy to adjust, it is not helpful for improving the situation where the CBCT resolution is insufficient, and it is far from the method of this application.

[0005] Looking at the prior art, there is no clear technical revelation on what kind of collimator can improve the soft tissue resolution of CBCT, nor is there a collimator similar to the embodiment of the present application. In other words, the prior art does not focus on using the special design of the collimator to improve the resolution of CBCT, especially the resolution of soft tissue of animals (which is difficult to identify and has poor image quality). Summary of the invention

[0006] The purpose of the present invention is to provide a device, which mainly solves the problem that the scattered signal is difficult to suppress during CBCT imaging, and the imaging effect is poor (especially the soft tissue of small animals cannot be seen clearly). Not only does the problem solve without applying, but the cost is also low (only a two-stage prism-type collimator and its ancillary facilities such as a translation device are required to solve the problem. It is a configuration method with a very high cost-effectiveness to improve the CBCT image effect.

[0007] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a small animal scatter suppression CBCT collimator system, characterized in that it includes a coaxial and front-to-back arranged ray source, a prism-shaped collimator, and a flat-panel detector; the ray source is a CBCT ray source.

[0008] The ray source, the prism-shaped collimator and the flat-panel detector are fixed together on a rotating platform, and the rotating platform is used to drive the overall rotation of the system.

[0009] The system is also equipped with a translation device group, which includes a front translation device and a rear translation device. The front translation device and the rear translation device respectively drive the front section and the rear section of the collimator to translate up and down.

[0010] The ray source and the flat panel detector are fixed at two ends of the CT translation device, and the CT translation device can drive the ray source and the flat panel detector to translate forward and backward.

[0011] The prism-type collimator is divided into a front section and a rear section, both of which are also prism-shaped; the front section and the rear section of the collimator both have metal shells on the outside, and the inside is cross-arranged by multiple layers of metal plates arranged in sequence in the Y direction and the Z direction respectively, and both form N*N collimation channels, where N is a positive integer.

[0012] The system has a control device group, which has at least first, second, third and fourth control modules, which respectively control the rotating platform, the CT translation device, the front translation device and the rear translation device.

[0013] A carrier for an object of interest is provided on the path from the radiation source to the flat panel detector; the carrier has an independent fixing mechanism; the carrier is a carrier stage, a carrier cage or a carrier box.

[0014] The system also has a position detector group, which includes at least a first, a second and a third position detector, which respectively detect the positions of the ray source, the front section of the collimator and the rear section of the collimator.

[0015] For the front section and the rear section of the pyramid-shaped collimator, each of the cross sections perpendicular to the axis is similar in shape.

[0016] Furthermore, the front section and the rear section of the pyramid-shaped collimator are both in the shape of a quadrangular pyramid.

[0017] A small animal scatter suppression CBCT collimation detection method is implemented using a small animal scatter suppression CBCT collimator system, and is characterized in that it includes the following steps: 1) a preparation step: the object is carried by a carrier, a cage or a box, and is placed on the path from the radiation source to the flat panel detector.

[0018] 2) Selection step: According to the preset detection scheme, adjust the position of the radiation source and the flat panel detector on the CT translation device to fall into the detection position;

[0019] 3) Detection steps: select one of the three methods of using only the front section, only the rear section, or both sections of the prism-type collimator, move the collimator to the detection route, turn on the radiation source for the evaluation object or the evaluation simulation object, use a flat-panel detector to receive the signal and generate a detection image on the computer.

[0020] Compared with the prior art, the present application has many non-obvious advantages: First, the collimators used in CBCT in the prior art described above are generally common flat collimators, long parallel grid collimators, strip grid collimators, or adjustable window collimators. Although these collimators can play a certain role, they are not outstanding in improving image quality (the applicant has compared them through actual measurements), especially in scatter suppression. Since these collimators basically have insufficient attenuation lengths, it is actually difficult to produce sufficient scatter suppression effects, and there are obvious defects in the recognition of soft tissue parts of the image. Second, the cost is low. The collimator of the present application only needs to be formed by combining several metal plates in a predetermined manner, and the matching electric control device only needs to enable it to be translated. The material selection, shape, and installation method are simple and effective. There is no complicated application method and cumbersome accessories of the collimator described above. The overall design cost is low, but the effect is not low. Third, the collimator itself (collimation channel formed by several metal plates) is designed to adapt to the cone beam used, so the collimation effect is good. On this basis, the evaluation method is arranged again to find a more suitable system configuration distance in detail to make the image effect even better. Fourth, the collimator is divided into two sections, front and back. Generally, the front section can ensure basic image recognition. If better effect is needed, the rear collimator can be added. No collimator - use the front collimator - both sections are used. Basically, the image intensity is reduced, but the resolution of specific tissues, especially soft tissues, is improved. It can be switched according to the actual situation and the configuration that meets the needs can be selected. The switching is convenient and fast. Fifth, two configurations that are most conducive to imaging are provided for detection. Using the front section of the collimator, scattering suppression can meet the requirements. If further scattering suppression is required (such as the contour of the soft component that needs to be identified in the feeling part is not clear enough), the rear collimator can be added. One-key switching is simple and convenient. The implementation method of the present application and the above advantages are not inspired by the prior art. They are the result of the applicant's self-development based on the actual defects of CBCT and local conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the main components of the collimator system.

[0022] Figure 2 Figure 2 shows the actual shape of the front and rear collimators.

[0023] Figure 3 Schematic diagram of scanning with and without a collimator.

[0024] Figure 4 This is a schematic diagram of the principle of producing scattering suppression effect.

[0025] Figure numerals: 1. X-ray source; 11. CT translation device; 2. Collimator; 21. Front section of collimator; 22. Rear section of collimator; 3. Flat-panel detector; 4. Rotating platform; 5. Translation device group; 6. Carrier position; 23. Collimator housing; 24. Collimator layer; 25. Fixing buckle. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments with simple transformation or equivalent implementation effects or similar implementation effects obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] A small animal scatter suppression CBCT collimator system, characterized in that it includes a coaxial and front-to-back arranged ray source, a prism-shaped collimator, and a flat-panel detector; the ray source is a CBCT ray source. The system of the present application is mainly suitable for the testing and detection of small animal cone beam CT, focusing on solving the problems of excessive scattering and insufficient image resolution. The outstanding characteristics are that the system is not large in scale, compact as a whole, and can be easily rotated to cooperate with the detection. At the same time, during the detection, the problem of insufficient soft tissue resolution without a collimator is specifically solved (the equipment is compact, and the collimator system of cone beam CT in the prior art cannot be applied, which is expensive, large in size, cumbersome, and power-consuming, and difficult to use with the present application). The collimator design given in the present application is very suitable for a small CBCT system for small animal detection, and it is easy to use and not costly.

[0029] The ray source, prism-shaped collimator and flat-panel detector are fixed on a rotating platform, which is used to drive the overall rotation of the system. The rotation here can be applied to a three-dimensional rotary motor and its supporting equipment, a three-dimensional rotary table, a three-dimensional reducer, a five-axis connecting rod device, etc.

[0030] The system is also equipped with a translation device group, which includes a front translation device and a rear translation device. The front translation device and the rear translation device respectively drive the front section and the rear section of the collimator to translate up and down. Generally speaking, the translation device moves the collimator to the bottom, which is the detection position, and moves it to the top to make way for the signal collection line and directly illuminate the collected signal. Translation is, for example, a motor rotating a drive rod, an electric linear motor, or a ball screw, and the motor rotating drives the screw to rotate to displace the platform.

[0031] The ray source and the flat panel detector are fixed at both ends of the CT translation device, and the CT translation device can drive the ray source and the flat panel detector to translate back and forth. CT translation is, for example, a motor rotating a driving rod, an electric linear motor, or a ball screw, and the motor rotating drives the screw to rotate to displace the platform. The distance between the ray source and the flat panel detector is generally fixed, which is generally caused by the angle of the cone beam. The distance is basically consistent with the predetermined distance and may need to be fine-tuned. For example, the cone beam angle is 20° and the distance is 1.8m. The angle is 15° and the distance is 2.1m, etc.

[0032] The pyramid collimator is divided into a front section and a rear section, both of which are also pyramid-shaped; the front section and the rear section of the collimator are both equipped with a metal shell on the outside, and the inside is cross-arranged by multiple layers of metal plates arranged in sequence in the Y direction and the Z direction, and each forms N*N collimation channels, where N is a positive integer. If the front section is mainly used, for example, the length ratio of the two sections is 10:2-7, if the rear section is mainly used (the rear section is used first, and the front section is used additionally when there is a need for improvement, which is equivalent to an alternative to the above method), the length ratio of the two sections is reversed, which is 2-7:10. The most common ratio is, for example, between 2:1-9:6, such as 95:55.

[0033] The system has a control device group, which has at least a first, a second, a third, and a fourth control module, which respectively control the rotating platform, the CT translation device, the front translation device, and the rear translation device. The control module is connected and controls the rotation or translation, and the control signal is, for example, an instruction sent from a preset program in a memory on a computer.

[0034] On the path from the radiation source to the flat-panel detector, there is a carrier for the object of interest; the carrier has an independent fixing mechanism; the carrier is a carrier, a cage, or a box. The fixing mechanism is, for example, a protruding rod to fix the carrier. In the system design, a position for fixing the rod is reserved during rotation, or the rod is considered not to be touched during rotation. The carrier is not the research and development focus of this application and will not be described here. The carrier can be made of various materials suitable for support. When fixing, a certain rotation angle is considered, but the stability of the support of the detection object must be guaranteed, and it cannot be flipped too much to cause it to fall.

[0035] The system also has a position detector group, which includes at least the first, second and third position detectors, which respectively detect the positions of the ray source, the front section of the collimator and the rear section of the collimator. The position detector is selected from, for example, a photoelectric encoder, a magnetic encoder, a laser distance sensor, an ultrasonic sensor and an infrared distance sensor.

[0036] For the front section and the rear section of the prism-shaped collimator, each of the cross sections perpendicular to the axis is similar in shape. Typically, each grid on the cross section is a square with the same area, or they can be rectangular with the same shape, or they can be rectangular with the same area.

[0037] Furthermore, the front section and the rear section of the prism-shaped collimator are both of a quadrangular prism shape. This is the most typical setting method. Since the beam is a cone beam, the metal plates in the collimator are, for example, set in such a way that the collimator is cut from the XZ plane of the axis (assuming that the axis of the detection is located on the X-axis), and the planes of the metal plates from top to bottom all pass through the center of the surface of the ray source, or pass through a point near (0,0,0) with the center of the surface of the ray source as the origin (there may be actual measurement errors, etc., the ideal is the origin). For example, the angles of each plate are, for example, the plate in the middle is parallel to the X-axis, and the upper plates are α, 2α, 3α, 4α... (α is, for example, an angle between 1-8°) with the X-axis in turn. The angle examples here are only for understanding and do not limit the scope of this application. According to actual needs, the angle changes here can be disproportionate and irregular. It can be determined that generally these plates arranged in the Y direction and the Z direction are not parallel to each other.

[0038] From the perspective of matching with a flat panel detector, a quadrangular pyramid collimator is more suitable, but the present application does not limit this, and a regular polygonal collimator, such as a regular pentagonal, hexagonal, heptagonal, or octagonal collimator, is also acceptable.

[0039] Example 2

[0040] A small animal scatter suppression CBCT collimation detection method is implemented using a small animal scatter suppression CBCT collimator system, characterized in that it includes the following steps: 1) Preparation step: The object is carried by a carrier, a cage or a box, and placed on the path from the radiation source to the flat panel detector. It should be noted here that in order to reduce negative effects, the animal's carrier and support structure must be guaranteed in the algorithm that their placement position does not conflict with the system rotation, and in order to avoid the influence of radiation / excitation scattering, the carrier must be made of non-metallic material.

[0041] 2) Selection step: According to the preset detection plan, adjust the position of the radiation source and the flat panel detector on the CT translation device to fall into the detection position; the distance is predetermined, according to the angle of the cone beam adjustment, for example, between 1m and 3m. After the position is determined, the collimator can be placed

[0042] 3) Detection steps: select one of the three methods of using only the front section, only the rear section, or both sections of the prism-shaped collimator, move the collimator to the detection route, turn on the radiation source for the object to be evaluated or the simulated object to be evaluated, use the flat-panel detector to receive the signal and generate the detection image on the computer. After the positions are determined, the position where the collimator can be placed is also determined, because the collimator must be in the right position to allow the cone beam to be sufficiently collimated. The determination of this distance can be referred to Figure 4 .

[0043] Example 4

[0044] Here, the accompanying drawings are described. Figure 1 In order to avoid the problem that the drawings are too complicated and the main components are difficult to identify, the control device group and the position device group are not clearly shown. They are actually placed in the proper position of the system, and those skilled in the art can arrange them according to their own understanding. For the translation device group, there are front translation devices and rear translation devices, and the figure does not show all of them (the electrical control part is complicated). Only the main part of the front translation device is shown, that is, the main part that can translate the front collimator. In actual arrangement, the front translation device and the rear translation device are, for example, one on the left and one on the right, or are misaligned up and down / left and right on one side, so that translation operations can be performed simultaneously. In order to avoid obstruction, the carrier and fixed structure of the object of interest are not shown. Those skilled in the art can make specific settings according to the size and type of small animals they actually target.

[0045] Figure 2 In the figure, the actual shape of the front and rear collimators is shown. The most preferred mode is the shape of a regular tetrahedron, preferably, each of the grids formed by the intersection has the same area, and the cross-sections formed by any horizontal plane are similar. More preferably, each grid formed by the intersection has a square cross-section. For the convenience of fixing, the edge of the collimator can optionally have a fixing buckle.

[0046] Figure 3 The following are the actual pictures of the system with and without collimators. Two collimators are used together. In actual use, you can use only the first one, only the second one, or both. It depends on the actual image efficiency. If only one collimator can meet the requirements, the other one will not be used, so that the image intensity can be higher.

[0047] Figure 4The schematic diagram of scatter suppression in this application. Compared with previous CBCT, the development of scatter suppression CBCT mainly adds a prism-type collimator and its automatic switching structure. The upper and lower ends of the collimator are between the two lines L2 and L1 in the right figure. But in fact, except for the case where the lower end of the collimator and the detector are in close contact, in the case of a gap, such as the space on the right side of the L1 line in the figure, in order to suppress other scattering, the space between the L1 line and the L0 line must also be surrounded by lead shielding. Lead shielding is, for example, shielding with lead plates, or multiple layers of lead plates. The vertex of the cone in the figure is the radiation source, and the elliptical area is the area of ​​interest. The two dotted lines are schematic diagrams of the opening angle of the collimator hole.

[0048] Support structure of side and back lead shielding: The specific thickness is determined by the results of the scattering test. A rough estimate is to use 1mm thick lead. The reason why 2mm is not used is that the actual protection does not require 10 times the attenuation length. 5 times the attenuation length has blocked more than 99% of the scattering. We used 10 times the lead in the previous section to accurately evaluate the amount of scattering.

[0049] The above is only an embodiment of the present invention, and the common sense such as the known specific structure and characteristics in the scheme is not described in detail here. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the attached claims rather than the above description, so it is intended to include all changes within the meaning and scope of the equivalent elements of the claims. Any figure mark in the claims should not be regarded as limiting the claims involved.

Claims

1. A small animal scatter suppression CBCT collimator system, characterized by: It includes a coaxial radiation source, a prism-shaped collimator, and a flat panel detector that are arranged in sequence front to back; the radiation source is a CBCT radiation source; The ray source, the prism-shaped collimator, and the flat-panel detector are fixed together on a rotating platform, and the rotating platform is used to drive the overall rotation of the system; The system is also equipped with a translation device group, which includes a front translation device and a rear translation device, and the front translation device and the rear translation device respectively drive the front section and the rear section of the collimator to translate up and down; The ray source and the flat panel detector are fixed at two ends of the CT translation device, and the CT translation device can drive the ray source and the flat panel detector to translate forward and backward; The prism-type collimator is divided into a front section and a rear section, both of which are also prism-shaped; the front section and the rear section of the collimator both have metal shells on the outside, and the inside is cross-arranged by multiple layers of metal plates arranged in sequence in the Y direction and the Z direction respectively, and both form N*N collimation channels, where N is a positive integer.

2. A small animal scatter suppression CBCT collimator system as claimed in claim 1, characterized in that: The system has a control device group, which has at least a first, a second, a third and a fourth control module, which respectively control the rotating platform, the CT translation device, the front translation device and the rear translation device; A carrier for the object of interest is provided on the path from the radiation source to the flat panel detector; the carrier has an independent fixing mechanism; the carrier is a carrier stage, a carrier cage or a carrier box; The system also has a position detector group, which includes at least a first, a second, and a third position detector, which respectively detect the positions of the ray source, the front section of the collimator, and the rear section of the collimator; For the front section and the rear section of the pyramid-shaped collimator, each of the cross sections perpendicular to the axis is similar in shape.

3. A small animal scatter suppression CBCT collimator system as claimed in claim 1 or 2, characterized in that: The front section and the rear section of the pyramid-shaped collimator are both in the shape of a quadrangular pyramid.

4. A small animal scatter suppression CBCT collimation detection method, which is implemented using a small animal scatter suppression CBCT collimator system according to any one of claims 1 to 3, characterized in that: The steps include: 1) Preparation step: the object is carried by a carrier, a cage or a box and placed on the path from the radiation source to the flat panel detector; 2) Selection step: According to the preset detection scheme, adjust the position of the radiation source and the flat panel detector on the CT translation device to fall into the detection position; 3) Detection steps: select one of the three methods of using only the front section, only the rear section, or both sections of the prism-type collimator, move the collimator to the detection route, turn on the radiation source for the evaluation object or the evaluation simulation object, use a flat-panel detector to receive the signal and generate a detection image on the computer.

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