A composite correction phantom assembly for security CT

Abstract

The present invention relates to the technical field of CT components and discloses a composite correction phantom assembly for security CT, comprising multiple nonlinear phantoms, each comprising a cylinder and end caps at both ends of the cylinder, one of the end caps being provided with a water inlet for injecting pure water into the cylinder, and the water inlet being sealed by a sealing plug; the multiple nonlinear phantoms are connected in series to form a composite phantom, the cylinders of two adjacent nonlinear phantoms having different diameters, and the end caps being locked together by fasteners. The present invention can simulate density characteristics in one go, utilizing the known physical properties of pure water to calibrate cupping artifacts caused by the radiation hardening effect, while also accurately calculating the positional deviation between the radiation source and the detector through the known spatial coordinates of a test rod, integrating geometric calibration with CT value calibration. Multiple calibrations can be completed in a single scan, reducing the number of phantom replacements compared to traditional methods, significantly improving calibration efficiency, and avoiding positional errors caused by repeated disassembly and assembly.

Description

Technical Field

[0001] The present invention relates to the technical field of CT components, and in particular to a composite correction phantom component for security inspection CT. Background Art

[0002] Before leaving the factory, security inspection CT equipment needs to adjust the relative position of the radiation source and detector, calibrate the CT value, scan a specific model through CT, collect scanning data, and calculate and analyze the deviation position and deviation value.

[0003] Traditional security CT calibration can only perform a single calibration. To meet multiple calibration requirements, different phantoms must be used. For example, geometric calibration phantoms (such as the Pin phantom) and CT value calibration phantoms (such as the water phantom) must be used separately. However, each complete calibration requires multiple phantom changes, which takes a long time and results in low actual calibration efficiency.

[0004] Secondly, each disassembly and assembly of traditional phantoms may cause excessive wear and tear, reducing their actual service life. If they are bumped, they may be damaged. For example, bumping a water phantom may cause it to break during the scanning process, resulting in destructive effects.

[0005] Moreover, the phantoms available on the market that can be used for nonlinear correction are usually fixed in a suspended manner (i.e., one end is suspended on the side wall of the phantom box). Since the phantom is heavier after being filled with water, a large amount of counterweights need to be placed in the phantom box to prevent the phantom from tipping over. This makes it extremely inconvenient to drag the phantom in the channel and increases the requirements for the channel's load-bearing capacity.

[0006] In order to solve the above problems, the present application proposes a composite correction phantom assembly for security inspection CT. Summary of the Invention

[0007] In order to solve the technical problems existing in the background technology, the present invention proposes a composite correction phantom assembly for security inspection CT.

[0008] The present invention proposes a composite correction phantom assembly for security CT, comprising multiple nonlinear phantoms, each comprising a cylindrical body and end caps at both ends of the cylindrical body. One of the end caps is provided with a water inlet for injecting pure water into the cylindrical body, and the water inlet is sealed by a sealing plug.

[0009] A plurality of nonlinear mold bodies are connected in series to form a composite mold body. The cylinder diameters of two adjacent nonlinear mold bodies are different and the end covers are locked by fasteners.

[0010] As a further optimized solution of the present invention, it also includes a Pin mold body installed on the end cover on one side of the composite mold body, the Pin mold body includes a fixing plate and a test rod, the fixing plate is fixed to the end cover by a fastener, and the test rod is perpendicular to the outer side surface of the fixing plate and is threadedly connected to the fixing plate.

[0011] As a further optimized solution of the present invention, the test rod includes a test section and a connecting section arranged at one end of the test section. A docking hole is opened on the outer side of the fixing plate, and the connecting section is threadedly connected to the fixing plate through the docking hole.

[0012] As a further optimized solution of the present invention, the cylinder, the end cover, the sealing plug and the fixing plate are all made of low-density and high-radiation transmittance materials.

[0013] As a further optimized solution of the present invention, strip-shaped holes are provided at the upper ends of the end cover and the fixing plate.

[0014] As a further optimized solution of the present invention, the end cover and the fixing plate are both rectangular plates and have penetrating connection holes at the four corners. The fasteners are bolt fasteners that pass through the connection holes and are locked by nuts.

[0015] As a further optimized solution of the present invention, the connecting hole includes a first connecting hole and a second connecting hole which are opened at the upper end of the fixing plate or the end cover and are separately arranged. The first connecting hole is a stepped through hole with a circular countersunk head, and the second connecting hole is a stepped through hole with a square countersunk head. The fastener is a bolt and the screw end passes through the first connecting hole and extends into the second connecting hole. The nut is snap-fitted and assembled in the second connecting hole and is threadedly connected to the screw end of the fastener.

[0016] As a further optimized solution of the present invention, the first connecting hole includes a first countersunk hole and a first through hole that are interconnected, the second connecting hole includes a second countersunk hole and a second through hole that are interconnected, the bolt head of the fastener is arranged in the first countersunk hole, and the nut is snap-fitted into the second countersunk hole.

[0017] As a further optimized solution of the present invention, the inner wall of the water injection port has an internal thread, the sealing plug includes a head and a threaded column, and the free end of the threaded column is threadedly connected to the water injection port and sealed by a sealing ring.

[0018] As a further optimized solution of the present invention, the cylinder and the end cover are integrally formed or assembled separately;

[0019] When the cylinder and the end cover are assembled separately, one side of the end cover has a circular boss that matches the inner diameter of the cylinder opening. The end cover is fixed and sealed with the cylinder opening through the circular boss.

[0020] As a further optimized solution of the present invention, the composite phantom includes two nonlinear phantoms, which are respectively configured as a first nonlinear phantom and a second nonlinear phantom. The center of gravity of the composite phantom is located on the second nonlinear phantom. The detection channel includes an inlet channel 18 and an outlet channel 19. There is a suspended section between the two channels. The detection section widths of the Pin phantom, the first nonlinear phantom, and the second nonlinear phantom are all greater than the width of the suspended section of the detection channel.

[0021] The composite correction phantom assembly for security CT proposed in the present invention has the following beneficial effects:

[0022] (1) The present invention forms a composite phantom by connecting multiple nonlinear phantoms in series. Adjacent phantoms have different diameters and the end caps are locked by fasteners. This allows for a one-time simulation of density characteristics and the calibration of cupping artifacts caused by the radiation hardening effect using the known physical properties of pure water. Simultaneously, the Pin phantom accurately calculates the positional deviation between the radiation source and the detector using the known spatial coordinates of the test rod. This composite phantom assembly integrates geometric calibration and CT value calibration, allowing multiple calibrations to be completed with a single loading. Compared to traditional methods, this reduces the number of phantom replacements, significantly improves calibration efficiency, and avoids positional errors caused by repeated disassembly and assembly.

[0023] (2) The rectangular end cover is connected to the fixed plate with four corner bolts, and the stepped through hole and butterfly bolt design are designed to allow quick disassembly and assembly by hand without tools. The circular countersunk hole and square countersunk hole of the end cover accommodate the bolt head and nut respectively. The square countersunk hole can clamp the nut to prevent rotation. A single person can quickly complete the connection or disassembly of a single phantom, avoiding the inconvenience of transporting the integrated structure that is too long, and at the same time making it convenient for a single person to carry. Moreover, there is no need to reposition the phantom when reinstalling it, which can ensure the positioning accuracy of the phantom and thus meet the accuracy requirements of security CT. In addition, the test rod of the Pin phantom is connected to the multiple docking holes of the fixed plate through threads, which can flexibly adjust the test position to adapt to different calibration scenarios. The test orientation can be switched without additional tools, which improves the flexibility of the calibration scheme.

[0024] (3) The cylinder, end caps, etc. are made of low-density, high-radiation transmittance material with a radiation attenuation coefficient of only 0.15 / cm, which has negligible interference with the calibration signal, ensuring that the CT value calibration only reflects the true characteristics of pure water or test rods;

[0025] (4) The universal wheels at the bottom of the end cap support 360° free steering. Combined with the strip holes at the top of the end cap, a single person can easily drag the phantom to move within the CT channel. The friction is lower than that of traditional sliding bottoms. When transporting a component containing two nonlinear phantoms, a single person can easily push it. The flexible steering makes it suitable for narrow channel environments.

[0026] (5) The present invention allows the cylinder and end caps to be formed in one piece or assembled separately: the separate assembly can reduce mold costs in small-batch production, while the one-piece assembly can improve consistency and economy in large-scale production. The end caps do not require additional counterweights to support the cylinder at both ends, which has a certain weight reduction effect compared to traditional suspended molds and avoids the risk of mold tipping due to insufficient counterweights, thus having a wider range of applications.

[0027] (6) Through the coordinated calibration of the Pin phantom and the nonlinear phantom, the error in the position of the radiation source can be controlled within ±0.05mm, and the error in the position of the detector can be controlled within ±0.05mm. After calibration using this component, the uniformity of the CT value of the pure water phantom is significantly improved, with the deviation between the center and the edge less than 5HU, completely eliminating the cup-shaped artifact caused by radiation hardening in existing technologies. This accuracy can meet the high requirements of security CT for luggage material recognition, especially when detecting mixed items of high-density metal and low-density organic matter, which can reduce the misjudgment rate and improve security inspection efficiency and safety.

[0028] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the three-dimensional structure of the first embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the front structure of the first embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the three-dimensional structure of the second embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the three-dimensional structure of the third embodiment of the present invention;

[0033] Figure 5 This is a bottom-view structural diagram of the second embodiment of the present invention;

[0034] Figure 6 This is a schematic cross-sectional structural diagram of a first state of embodiment 2 of the present invention;

[0035] Figure 7 This is a schematic cross-sectional structural diagram of a second state of embodiment 2 of the present invention;

[0036] Figure 8 For the present invention Figure 6 Schematic diagram of the enlarged structure at A in the middle;

[0037] Figure 9 Schematic diagram of the partial cross-sectional structure of the first nonlinear phantom of the present invention;

[0038] Figure 10 This is a front structural schematic diagram of the fixing plate of the present invention;

[0039] Figure 11 Schematic diagram of the structure of the test rod of the present invention;

[0040] Figure 12 Schematic diagram of the structure of the sealing plug of the present invention;

[0041] Figure 13 Schematic diagram of the front cross-sectional structure of the first nonlinear phantom of the present invention;

[0042] Figure 14 is a front cross-sectional structural diagram of a second nonlinear phantom of the present invention;

[0043] Figure 15 This is a schematic diagram of the multi-turn data image of the Pin phantom axis scan of the present invention;

[0044] Figure 16 This is a schematic diagram of an off-center scanning data image of a second nonlinear phantom of the present invention;

[0045] Figure 17 Schematic diagram of the eccentric scanning data image of the first nonlinear phantom of the present invention

[0046] Figure 18 A schematic diagram of the correction table and reconstruction results generated by the nonlinear phantom calibration of the present invention;

[0047] Figure 19 A schematic diagram of a correction table and reconstruction results generated without using a nonlinear phantom calibration in the prior art;

[0048] Figure 20 Schematic diagram of the actual detection structure of the composite correction phantom assembly of the present invention;

[0049] Figure 21 For the present invention Figure 20 Schematic diagram of the cross-sectional structure of the first stage of actual detection;

[0050] Figure 22 For the present invention Figure 20 Schematic diagram of the cross-sectional structure of the second stage of actual detection;

[0051] Figure 23 For the present invention Figure 20 Schematic diagram of the cross-sectional structure of the third stage of actual detection.

[0052] Description of the drawings: 1. First cylinder; 2. Second cylinder; 3. First end cover; 4. Second end cover; 5. Fastener; 6. Sealing plug; 61. Head; 62. Threaded column; 7. Strip hole; 8. Universal wheel; 9. Fixing plate; 10. Test rod; 101. Test section; 102. Connecting section; 11. Docking hole; 12. First connecting hole; 121. First countersunk hole; 122. First through hole; 13. Second connecting hole; 131. Second countersunk hole; 132. Second through hole; 14. First boss; 15. First water inlet; 16. Second boss; 17. Second water inlet; 18. Inlet channel; 19. Outlet channel; 20. Radiation source; 21. Detector; 22. X-beam. DETAILED DESCRIPTION

[0053] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar symbols throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention, and are not to be construed as limiting the present invention.

[0054] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0055] like Figure 1-Figure 4 As shown, a composite calibration phantom assembly for security CT is mainly used for factory mode calibration of CT before shipment, comprising multiple nonlinear phantoms, each comprising a cylinder and end caps at both ends of the cylinder. One of the end caps is provided with a water inlet for injecting pure water into the cylinder, and the water inlet is sealed by a sealing plug 6. Multiple nonlinear phantoms are connected in series to form a composite phantom, wherein the cylinders of adjacent nonlinear phantoms have different diameters and the end caps are locked together by a fastener 5.

[0056] The nonlinear phantom simulates the attenuation characteristics of materials of different densities by using cylinders of different diameters. Pure water, a known attenuation medium, is injected through the water inlet. Its known physical characteristics can be used to calibrate the cupping artifacts caused by the radiation hardening effect of the equipment.

[0057] The series structure is locked by fasteners 5 to ensure the overall rigidity of the mold body. At the same time, it is easy to disassemble and replace pure water, solving the problem that traditional single mold bodies cannot cover multi-density calibration. For example, after two cylinders with a diameter difference of 50 mm are connected in series, low-high density calibration can be completed at one time, reducing the number of times the mold body is replaced.

[0058] The composite mold body further includes a Pin mold body mounted on an end cap on one side of the composite mold body, the Pin mold body includes a fixing plate 9 and a test rod 10, the fixing plate 9 is fixed to the end cap by a fastener 5, and the test rod 10 is perpendicular to the outer side of the fixing plate 9 and is threadedly connected to the fixing plate 9;

[0059] The Pin phantom is used as a geometric calibration tool. The theoretical spatial coordinates of the test rod 10 are known. By scanning the deviation between its actual position and the theoretical trajectory through CT, the position error (such as translation and rotation deviation) of the radiation source and the detector can be accurately calculated. The threaded connection allows the test rod 10 to adjust its position between the multiple docking holes 11 of the fixed plate 9 to adapt to different calibration scenarios. For example, when testing the multi-planar reconstruction accuracy of the CT system, multiple sets of calibration data can be obtained by moving the test rod 10 to different docking holes 11 to improve the comprehensiveness of the calibration.

[0060] Specifically, if Figure 11 As shown, the test rod 10 includes a test section 101 and a connecting section 102 provided at one end of the test section 101. A docking hole 11 is provided on the outer side of the fixing plate 9. The connecting section 102 is threadedly connected to the fixing plate 9 through the docking hole 11.

[0061] The number of the docking holes 11 is multiple and evenly distributed, which can facilitate the test rod 10 to change the test position and also provide an installation interface for external components or other mold bodies;

[0062] The test section 101 and the connecting section 102 are both made of metal. The test section 101 is a smooth cylinder. During the test, CT scans the test section 101 to obtain calibration data. The diameter of the test section 101 is 4-12 mm. The outer surface of the connecting section 102 has an external thread, and the inner wall of the docking hole 11 has an internal thread that is compatible with the connecting section 102.

[0063] The smooth cylindrical structure of the test section 101 ensures clear edges in the CT image, facilitating accurate extraction of contour coordinates. Multiple sets of docking holes 11 support the adjustment of the test rod 10 to simulate geometric calibration requirements in different orientations. The high-contrast properties of metal materials (such as stainless steel) ensure that the test section 101 has sharp boundaries in the CT image, and the error measurement accuracy can reach within 0.1 mm. For example, when the tilted scanning accuracy of the CT needs to be calibrated, the test rod 10 is installed in the tilted docking hole 11. By scanning the image in its tilted posture, the geometric deviation of the system in the non-vertical direction can be calculated.

[0064] Specifically, the cylinder, the end cap, the sealing plug 6 and the fixing plate 9 are all made of a low-density and high-radiation transmittance material, such as polymethyl methacrylate, commonly known as acrylic;

[0065] Acrylic material has a low radiation attenuation coefficient (approximately 0.15 / cm), which can minimize the interference of the phantom itself on radiation, ensuring that the CT value calibration only reflects the characteristics of pure water or the test rod 10. For example, in a nonlinear phantom, the absorption of radiation by the acrylic cylinder accounts for less than 1% of the attenuation of pure water and can be ignored, thereby ensuring the accuracy of the calibration data.

[0066] Specifically, if Figure 1-Figure 4 as well as Figure 10 As shown, the upper ends of the end cover and the fixing plate 9 are provided with strip-shaped holes 7 for the operator to grasp;

[0067] The width of the strip hole 7 is suitable for an adult's finger (about 30mm), making it easy for one person to carry or drag the phantom by hand. Combined with the universal wheels 8 at the bottom, it can be easily moved within the CT channel. For example, when the phantom position needs to be adjusted, the operator can lift one end of the phantom through the strip hole 7 and use the universal wheels 8 to turn it to quickly position the phantom to the scanning center. The operating efficiency is 50% higher than that of traditional suspended phantoms.

[0068] Specifically, if Figure 1-Figure 4 as well as Figure 10 As shown, the end cover and the fixing plate 9 are both rectangular plates and have connecting holes at their four corners. The fasteners 5 are bolt fasteners that pass through the connecting holes and are locked by nuts.

[0069] The rectangular end cap and the four corner connection holes of the fixing plate 9 are designed to provide symmetrical locking force, ensuring a firm connection of the mold body and facilitating actual disassembly and assembly.

[0070] Further, if Figure 6 、 Figure 8 and Figure 10 As shown, the connecting holes include a first connecting hole 12 and a second connecting hole 13 that are opened on the upper end of the fixing plate 9 or the end cover and are separately provided. The first connecting hole 12 is a stepped through hole with a circular countersunk head, and the second connecting hole 13 is a stepped through hole with a square countersunk head. The fastener 5 is a bolt, and the screw end passes through the first connecting hole 12 and extends into the second connecting hole 13. The nut is snap-fitted and assembled in the second connecting hole 13 and is threadedly connected to the screw end of the fastener 5.

[0071] The stepped through-hole design allows the bolt head and nut to be embedded in the plate, preventing protruding surfaces from affecting CT scanning. The square second countersunk hole 131 can clamp the nut and can be manually tightened without additional tools, improving operational convenience. When disassembling the phantom, the connection can be loosened by simply rotating the bolt barehanded, reducing single-person operation time and significantly improving efficiency compared to traditional bolt connections that require a wrench.

[0072] Further, if Figure 9 As shown, the first connecting hole 12 includes a first countersunk hole 121 and a first through hole 122 that are interconnected, and the second connecting hole 13 includes a second countersunk hole 131 and a second through hole 132 that are interconnected. The bolt head of the fastener 5 is disposed in the first countersunk hole 121, and the nut is snap-fitted into the second countersunk hole 131.

[0073] The first countersunk hole 121 can minimize the protrusion of the head of the connecting screw from the carrier surface, thereby maximizing the length of the detectable section. The nut is placed in the second countersunk hole 131. The square structure of the second countersunk hole 131 can replace the nut wrench to prevent the nut from rotating when the bolt and nut are locked.

[0074] The fastener 5 is preferably a butterfly bolt, which is convenient for manual tightening operation. The screw end of the bolt passes through the first countersunk hole 121, passes through the first through hole 122 and the second through hole 132 in sequence, and extends into the second countersunk hole 131 to be tightened with the nut;

[0075] The wing-shaped design of the butterfly bolt allows for quick, bare-hand tightening without tools, making it ideal for on-site calibration scenarios. The square second countersunk hole 131 cooperates with the hexagonal outer profile of the nut to provide a rotation stop function, ensuring that the nut does not rotate when the bolt is tightened, thereby improving connection reliability. In the clean environment of the CT machine room, no wrench is required, avoiding the risk of tool contamination or loss. At the same time, a single connection point can be disassembled and assembled in a short time.

[0076] Specifically, the inner wall of the water injection port has an internal thread, such as Figure 12 As shown, the sealing plug 6 includes a head 61 and a threaded column 62. The free end of the threaded column 62 is threadedly connected to the water inlet and sealed by a sealing ring;

[0077] The combination of threaded connection and sealing ring ensures the sealing performance of the water injection port and prevents pure water leakage. The diameter of the head 61 is larger than the water injection port, providing a force-bearing surface when tightening, which is easy to operate. After pure water is injected into the cylinder, the sealing plug 6 is rotated until the sealing ring is compressed by 20%, which can ensure that there is no water leakage when the mold body is tilted or turned over, and adapt to different calibration posture requirements.

[0078] Specifically, the cylinder and the end cover are integrally formed or assembled separately;

[0079] When the cylinder and the end cover are assembled separately, one side of the end cover has a circular boss that matches the inner diameter of the cylinder opening. The end cover is fixed and sealed to the cylinder opening through the circular boss. The end cover can be glued and sealed through a sealing ring.

[0080] The split assembly facilitates manual assembly during small-batch production, reducing mold costs. The one-piece molding process can improve consistency during large-scale production, which is also beneficial to improving economy. The circular boss is combined with the sealing ring to form a radial seal, which facilitates the assembly of the end cover and the cylinder opening while preventing water leakage between the cylinder and the end cover.

[0081] Specifically, if Figure 3-Figure 6 As shown, a U-shaped groove is provided at the bottom of the end cover, and the U-shaped opening is arranged downward. A universal wheel 8 is provided in the U-shaped groove. A mounting screw hole is provided on the top wall of the U-shaped groove. The upper end of the universal wheel 8 has a screw and is threadedly connected to the mounting screw hole. The roller of the universal wheel 8 extends to the bottom of the opening of the U-shaped groove, and cooperates with the arrangement of the strip hole 7 to facilitate the staff to drag the component to the designated position of the CT channel.

[0082] The universal wheel 8 supports 360° steering, and combined with the drag force of the strip hole 7, the phantom can easily achieve linear or steering movement in the CT channel. The friction is lower than that of the traditional sliding bottom surface, and the threaded connection method is convenient for installation.

[0083] In actual implementation, the number of nonlinear motifs is two, namely the first nonlinear motif and the second nonlinear motif;

[0084] like Figure 1-Figure 7 As shown, the first nonlinear die body includes a first cylinder 1 and a first end cap 3 installed at the openings at both ends of the first cylinder 1. The second nonlinear die body includes a second cylinder 2 and a second end cap 4 installed at the openings at both ends of the second cylinder 2. The upper ends of the first end cap 3 and the second end cap 4 are each provided with a strip hole 7. The four corners of the first end cap 3, the second end cap 4, and the fixing plate 9 are each provided with a connecting hole. The first end cap 3 and the second end cap 4 are respectively connected and locked to the adjacent end cap or the fixing plate 9 via fasteners 5.

[0085] Specifically, the diameters of the first cylinder 1 and the second cylinder 2 are unequal: 120-170 mm, and 200-300 mm, respectively. The design covers both wide and narrow diameters. Through serial scanning, attenuation characteristics can be acquired under different thickness conditions. The symmetrical distribution of the strip holes 7 on the end caps allows the phantom to be dragged from either end, accommodating the bidirectional passage requirements of the CT channel.

[0086] Specifically, if Figure 13 As shown, the opposing surfaces of the two first end covers 3 are each provided with a first boss 14, the outer diameter of the first boss 14 is adapted to the inner diameter of the opening of the first cylinder 1, and the two are fixed by bonding and sealed with a sealing ring after being plugged in. One of the first end covers 3 is also provided with a first water injection port 15 that penetrates therethrough, and one end opening of the first water injection port 15 is communicated with the inner cavity of the first cylinder 1, and the other end of the first water injection port 15 is sealed by a sealing plug 6;

[0087] like Figure 14 As shown, the opposing surfaces of the two second end covers 4 each have a second boss 16, the outer diameter of the second boss 16 is adapted to the inner diameter of the opening of the second cylinder 2, and the two are plugged in and fixed by bonding and sealed with a sealing ring. One of the second end covers 4 is also provided with a penetrating second water injection port 17, one end opening of the second water injection port 17 is connected to the inner cavity of the second cylinder 2, and the other end of the second water injection port 17 is sealed by a sealing plug 6.

[0088] Furthermore, three specific embodiments are provided below, including a combination of two or three of the first nonlinear motif, the second nonlinear motif, and the Pin motif, as follows:

[0089] Example 1

[0090] like Figure 1 and Figure 2 The combined structure of the first and second nonlinear phantoms shown in the figure has a first cylinder 1 and a second cylinder 2 adjacent to each other, and a first end cap 3 and an adjacent second end cap 4 are locked together by a fastener 5. During use, the composite calibration phantom assembly is pushed into the security inspection CT channel, and the position of the phantom is moved through the maintenance window on the channel. After scanning the first and second nonlinear phantoms in sequence, the calibration in maintenance mode is completed;

[0091] Example 2

[0092] like Figure 3 As shown, a Pin phantom is added to the first embodiment. The fixing plate 9 of the Pin phantom is fastened to the first end cap 3 on the free end of the first nonlinear phantom by a fastener 5. When in use, the composite correction phantom assembly is pushed into the security inspection CT channel, and the position of the phantom is moved through the inspection window on the channel. After scanning the Pin phantom, the first nonlinear phantom, and the second nonlinear phantom in sequence, the calibration in the factory mode is completed.

[0093] Example 3

[0094] like Figure 4 As shown, a Pin phantom is added to the first embodiment. The fixing plate 9 of the Pin phantom is fastened to the second end cap 4 on the free end of the second nonlinear phantom by a fastener 5. When in use, the composite correction phantom assembly is pushed into the security inspection CT channel, and the position of the phantom is moved through the inspection window on the channel. After scanning the Pin phantom, the second nonlinear phantom, and the first nonlinear phantom in sequence, calibration in factory mode is completed.

[0095] It should be noted that the above embodiments are merely examples, and the composite calibration phantom assembly can be connected to other types of calibration phantoms through the connection holes so as to complete all calibration items in a single pass scan.

[0096] like Figure 20-23 As shown, in actual use, the composite calibration phantom assembly is pushed from the inlet channel 18 to the outlet channel 19, and the test segments of each phantom sequentially pass through the suspended section between the inlet channel 18 and the outlet channel 19. The X-ray source 20 above the suspended section emits an X-ray beam, which is detected by the detector 21 below. The Pin phantom, the first nonlinear phantom, and the second nonlinear phantom are detected in sequence.

[0097] Since the phantom will be partially suspended during testing, the width of each phantom testing section needs to be designed to ensure that when the center of gravity is in the suspended section, the rollers under the end covers on both sides of the center of gravity fall into the inlet channel 18 and the outlet channel 19, thereby stably supporting the composite phantom. The specific design is as follows:

[0098] 1. The widths of the Pin phantom, the first nonlinear phantom, and the second nonlinear phantom are similar and all larger than the width of the suspended section to ensure that each phantom detection section covers the suspended channel section. The combined design allows the center of gravity to fall on the second nonlinear phantom, and the center of gravity is close to or on the end cap.

[0099] The width of each model body is greater than the sum of the width of the suspended section and the distance of the center of gravity from the end cover, so as to ensure that the center of gravity is supported at the front and rear when passing through the suspended section. That is, the front universal wheel 8 of the first nonlinear model body always falls on the outlet channel 19, and the rear universal wheel 8 of the second nonlinear model body always falls on the inlet channel 18. When the center of gravity enters the outlet channel 19, although the outer universal wheel 8 of the second nonlinear model body is suspended, the center of gravity is already in the outlet channel 19, which can ensure that there is no risk of the water model overturning.

[0100] The suspended section originally had a bridge detection channel, but this section of the channel needed to be removed during calibration to avoid radiation absorption by the channel and affecting the calibration accuracy. The order of the first and second nonlinear phantoms can be swapped without affecting the support effect.

[0101] In summary, the Pin phantom in the composite correction phantom serves as a reference object with known geometric features and its theoretical CT image data is known. After being scanned by CT, the actual image data of the Pin phantom can be obtained. By comparing and analyzing the deviation between the actual trajectory and the theoretical trajectory, the position deviation data of the radiation source and detector can be obtained, thereby providing the direction and value for the radiation source adjustment and generating a detector position correction data table to obtain a more accurate CT system geometry, laying the foundation for the subsequent accurate reconstruction of CT three-dimensional images.

[0102] The first and second nonlinear phantoms in the composite correction phantom have known geometric structures and material properties, and the attenuation characteristics of pure water inside the cylinder are known, as well as their ideal CT image data. They are placed at several specific locations. After a CT scan, actual data is obtained and compared with theoretical data to calculate deviation values. A correction table is then constructed to eliminate cupping artifacts in CT images caused by water hardening.

[0103] The composite calibration phantom assembly assembles three sets of sub-phantoms into a single unit, reducing the number of phantom replacements and disassemblies. The relative positions of the three phantoms are known and specific, eliminating the need for repeated phantom replacement and position adjustment. Scans of the three phantoms can be completed sequentially. Furthermore, the three sets of sub-phantoms are designed to be detachably connected, making it easy to replace pure water in the first and second nonlinear phantoms and to disassemble and transport them.

[0104] The end cap design of the composite calibration phantom assembly can support the cylinder and the pure water inside it at both ends. Compared with the cantilever support method of general water phantoms, this support method is more stable and does not require counterweights, reducing the weight of the phantom and facilitating operation.

[0105] For operators, the total weight of the composite correction phantom assembly is large, and it needs to be dragged to a specific position in the CT channel. The universal wheels at the bottom of the composite correction phantom assembly make it easy to drag it to a specific position, and the long holes on the front and rear covers make it easy for people to grab and drag it.

[0106] The following is an explanation of the principles of this application and experimental images:

[0107] 1) Pin Motif Description

[0108] Function: used to calculate the position deviation of the ray source and the detector;

[0109] Principle of use: Pin phantom is used as a reference object with known geometric features, forming a predictable trajectory on the scanning chord diagram, such as Figure 15 As shown in the figure, based on the deviation between the actual trajectory and the ideal trajectory, the deviation of the ray source position and the detector position can be calculated. After obtaining the deviation, the ray source position can be fine-tuned and a correction table can be generated to correct the actual detector position to obtain a more accurate CT system geometry, laying the foundation for subsequent accurate reconstruction.

[0110] 2) Nonlinear model description

[0111] Function: Used to eliminate inaccurate CT values ​​caused by beam hardening;

[0112] Principle of use: Taking pure water in a phantom as an example, two nonlinear phantoms are used as reference objects with known geometric structures and material properties, and the attenuation characteristics of pure water are known. By placing them at different eccentric positions for scanning, the obtained phantom scanning data covers different detector ranges, such as Figure 16 and Figure 17 As shown in Figure 3, by joint analysis with the ideal pure water phantom data, the difference between the ideal and actual values ​​is obtained, so a correction table can be constructed to eliminate the cupping artifact caused by water hardening;

[0113] like Figure 18 The image shown is a correction table generated using nonlinear phantom calibration. When applied to the reconstruction, it can be seen that the CT values ​​of the water areas at different locations are uniform;

[0114] like Figure 19The image shown is the correction table generated without using a nonlinear phantom calibration. The resulting reconstruction of the pure water phantom shows that the CT value of the water in the center is significantly lower than that at the edge, and the grayscale curve exhibits a distinct cup-shaped curvature, which is caused by beam hardening. This demonstrates that the nonlinear phantom is effective in eliminating beam hardening.

[0115] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A composite correction phantom assembly for security CT, comprising a plurality of nonlinear phantoms, characterized in that: The nonlinear model comprises a cylinder and end caps located at both ends of the cylinder, one of the end caps is provided with a water inlet for injecting pure water into the cylinder, and the water inlet is sealed by a sealing plug (6); A plurality of nonlinear mold bodies are connected in series to form a composite mold body, wherein the cylinder diameters of two adjacent nonlinear mold bodies are different and the end covers are locked by fasteners (5); It also includes a Pin mold body mounted on an end cover on one side of the composite mold body, the Pin mold body including a fixing plate (9) and a test rod (10), the fixing plate (9) is fixed to the end cover via a fastener (5), and the test rod (10) is perpendicular to the outer side surface of the fixing plate (9) and is threadedly connected to the fixing plate (9); The end cover and the fixing plate (9) are both rectangular plates and are provided with connecting holes at four corners. The fasteners (5) are bolt fasteners and pass through the connecting holes and are locked by nuts. The composite phantom includes two nonlinear phantoms, which are respectively configured as a first nonlinear phantom and a second nonlinear phantom. The center of gravity of the composite phantom is located on the second nonlinear phantom. The detection segment widths of the Pin phantom, the first nonlinear phantom, and the second nonlinear phantom are all greater than the width of the suspended segment of the detection channel. The width of each mold body is greater than the sum of the width of the suspended section and the distance of the center of gravity from the end cover, so as to ensure that when the center of gravity passes through the suspended section, there is support at the front and back, so that the front side of the first nonlinear mold body always falls in the outlet channel (19), and the rear side of the second nonlinear mold body always falls in the inlet channel (18). When the center of gravity enters the outlet channel (19), the outer side of the second nonlinear mold body is suspended in the air, and the center of gravity is in the outlet channel (19), ensuring that the water model does not overturn.

2. The composite correction phantom assembly for security CT according to claim 1, characterized in that: The test rod (10) comprises a test section (101) and a connecting section (102) arranged at one end of the test section (101); a docking hole (11) is provided on the outer side of the fixing plate (9); and the connecting section (102) is threadedly connected to the fixing plate (9) through the docking hole (11).

3. The composite correction phantom assembly for security CT according to claim 1, characterized in that: The cylinder, the end cover, the sealing plug (6) and the fixing plate (9) are all made of low-density and high-radiation transmittance materials.

4. The composite correction phantom assembly for security CT according to claim 1, characterized in that: The upper ends of the end cover and the fixing plate (9) are both provided with strip-shaped holes (7).

5. The composite correction phantom assembly for security CT according to claim 1, characterized in that: The connecting hole comprises a first connecting hole (12) and a second connecting hole (13) which are opened on the upper end of the fixing plate (9) or the end cover and are separately provided. The first connecting hole (12) is a stepped through hole with a circular countersunk head, and the second connecting hole (13) is a stepped through hole with a square countersunk head. The screw end of the fastener (5) passes through the first connecting hole (12) and extends into the second connecting hole (13). The nut is snap-fitted and assembled in the second connecting hole (13) and is threadedly connected to the screw end of the fastener (5).

6. The composite correction phantom assembly for security CT according to claim 1, characterized in that: The first connecting hole (12) includes a first countersunk hole (121) and a first through hole (122) that are interconnected, and the second connecting hole (13) includes a second countersunk hole (131) and a second through hole (132) that are interconnected. The bolt head of the fastener (5) is arranged in the first countersunk hole (121), and the nut is snap-fitted into the second countersunk hole (131).

7. The composite correction phantom assembly for security CT according to claim 1, characterized in that: The inner wall of the water injection port has an internal thread, and the sealing plug (6) includes a head (61) and a threaded column (62). The free end of the threaded column (62) is threadedly connected to the water injection port and sealed by a sealing ring.

8. The composite correction phantom assembly for security CT according to claim 1, characterized in that: The cylinder and the end cover are integrally formed or assembled separately; When the cylinder and the end cover are assembled separately, one side of the end cover has a circular boss that matches the inner diameter of the cylinder opening. The end cover is fixed and sealed with the cylinder opening through the circular boss.

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