Magnetic levitation assisted support CT scan bed and control method thereof

Abstract

This invention discloses a magnetically levitated assisted CT scanning bed and its control method, including a CT gantry, scanning aperture, bed board, and array-type magnetic field generating unit. Rack magnetic field feedback unit, The position sensing and feedback system, as well as the emergency locking and safety mechanism, are described, with the array-type magnetic field generating unit embedded within the bed board; rack magnetic field The feedback unit is installed on the inner wall of the scanning port of the CT gantry. The position is directly opposite the magnetic field unit of the bed plate; the position sensing and feedback system includes sensors mounted on the inner wall of the frame, a controller for control, and a power driver that works in conjunction with the controller. This invention utilizes non-contact magnetic force as an intermediate supporting force. The magnetic field medium is completely transparent to X-rays, with no mechanical friction or abrasive particles. Within the scanning field of view, a controllable, uniformly upward Lorentz force or Maxwell stress is applied to the bed plate to counteract gravitational deformation.

Description

Technical Field

[0001] This invention belongs to the field of computed tomography (CT) technology, specifically a magnetically levitated assisted CT scanning bed and its control method. Background Technology

[0002] During CT scans, the scanning bed uses a cantilever structure to support the patient and extends horizontally into the scanning gantry. Existing thin carbon fiber bed boards inevitably sag under the patient's weight (flexural deformation). This deformation leads to the following three incompatible technical challenges: 1. Image artifacts: During the scanning process, the bed board may vibrate slightly due to load changes and inertia, resulting in motion artifacts in the reconstructed image and affecting low-contrast resolution.

[0003] 2. Positioning deviation: Bed sag causes the patient's actual scanning center to deviate from the gantry isocenter (ISOCenter). Especially in radiotherapy positioning or PET / CT attenuation correction, geometric deviation directly affects diagnostic accuracy and dose distribution in the treatment plan.

[0004] 3. Radiation Dose Paradox: To reduce deformation, conventional solutions include increasing the thickness of the bed board or using high-modulus composite materials. However, this significantly increases the attenuation path of X-rays. According to the beam hardening effect, the thicker the bed board, the higher the surface incident dose received by the patient, and the lower the image quality. How to solve the support stiffness problem without increasing the bed board thickness (or even thinning it) is a key technical bottleneck in reducing patient radiation dose.

[0005] Based on a review of existing technologies, the current technical approaches to solving scanning bed deformation can be mainly divided into three categories: "mechanical structure compensation", "physical pre-deformation", and "software post-correction".

[0006] 1. Best background technology: Mechanical two-end support solution Citation 1: CN21260408U - A CT Scanning Bed Mechanism Based on a Moving Gantry This design changes the traditional cantilever structure with one end fixed, using guide rails on the base to move the CT gantry, while the bed board is supported at both ends by two lifting mechanisms. Advantages: This design fundamentally solves the stress problem of the cantilever beam, resulting in minimal sagging deformation. Disadvantages: ① This design requires moving a CT gantry weighing several tons, demanding extremely high precision in the foundation and guide rails, significantly increasing costs; ② The bed board runs through the gantry, and the supports at both ends limit the rapid evacuation of the examination bed in emergencies; ③ It still relies on contact support, posing risks of mechanical wear and vibration transmission.

[0007] 2. Physical pre-deformation / aerodynamic compensation scheme Citation 2: CN102551785A - "A bed board and a bed including the bed board and a CT device" This design incorporates an inflatable air cushion within the bed frame shell, adjusting its height to compensate for patient position. Advantages: Adjustable height and tilt angle. Disadvantages: ① The air cushion compensates for the overall height, failing to suppress continuous deflection along the bed's length; ② The pneumatic system has a slow response time, unable to suppress high-frequency micro-vibrations during scanning; ③ The air cushion material's uneven density introduces additional X-ray attenuation artifacts.

[0008] 3. Structural pre-deformation compensation Citation 3: CN103126713A - "A scanning bed and a CT or PET system including the scanning bed" This solution uses a pre-deformed bed board, with the pre-deformation direction opposite to the load-bearing deformation direction. Advantages: passive compensation, low cost. Disadvantages: ① The pre-deformation amount is fixed, allowing precise compensation only for a specific load (e.g., a standard weight of 75kg), leading to overcompensation or undercompensation for obese or underweight patients; ② It cannot solve the problem of variable stiffness; the deflection curve of the bed board differs depending on its extension length, and the fixed pre-deformation cannot adapt adaptively.

[0009] 4. Software post-calibration scheme Citation 4: CN117204871A - Medical Imaging Methods, Equipment and Multimodal Medical Imaging Methods This method uses CT data to obtain patient weight distribution information, matches it with a deformation space function, and corrects the PET images. Advantages: No hardware modifications are involved. Disadvantages: ① This is passive compensation, which can only correct pixel coordinates in image reconstruction and cannot correct the geometric position during the scanning process (i.e., whether the bed and patient are actually in a submerged state). It is ineffective for puncture biopsies and radiotherapy guidance that require real-time physical positioning; ② The correction model relies on prior data and has poor robustness to specific body types.

[0010] Conclusion: Existing technologies cannot achieve non-contact, adaptive, and high-bandwidth real-time physical support while maintaining an ultra-thin and low-attenuation CT bed. As a "virtual medium" that completely penetrates X-rays, there are currently no publicly reported applications of magnetic fields in the dynamic deformation control of CT bed panels. Summary of the Invention

[0011] In order to address the defects and shortcomings mentioned in the prior art, this invention provides a magnetically levitated assisted CT scanning bed and its control method that utilizes non-contact magnetic field force as an intermediate support force, the magnetic field force medium is completely transparent to X-rays, has no mechanical friction, and no wear particles, and applies a controllable, uniformly upward Lorentz force or Maxwell stress to the bed board within the scanning field of view to counteract gravitational deformation.

[0012] To achieve the above objectives, the present invention provides the following technical solution: a magnetically levitated assisted CT scanning bed, comprising a CT gantry, scanning aperture, bed board, and array-type magnetic field generating unit. Rack magnetic field feedback unit, The position sensing and feedback system, as well as the emergency locking and safety mechanism, are described, with the array-type magnetic field generating unit embedded within the bed board; rack magnetic field feedback unit Mounted on the inner wall of the scanning port of the CT gantry The position is directly opposite the magnetic field unit of the bed board; the position sensing and feedback system includes a sensor installed on the inner wall of the frame, a controller for control, and a power driver that works in conjunction with the controller.

[0013] Preferably, the array-type magnetic field generating unit is Permanent magnet passive Array-type magnetic field generating unit, Embedded N52H High-grade neodymium iron boron permanent magnets, with magnetic poles pointing vertically upwards and arranged in a rectangular grid array. .

[0014] Preferably, the bed board is a thin composite bed board, which adopts a carbon fiber thin shell structure with a thickness of ≤12mm, and an array of magnetic field generating units are embedded inside along the Z-axis direction.

[0015] Preferably, the bed board comprises an upper carbon fiber skin, a middle foam core, and a lower carbon fiber skin; permanent magnet It is completely embedded in the foam core layer, and the surface of the permanent magnet is flush with the inner surface of the upper and lower skin layers.

[0016] Preferably, the array-type magnetic field generating unit is Electromagnetic active Array-type magnetic field generating unit, Embedded flat Type Printed Circuit Board (PCB) Line circle or A wound air coil generates a controllable magnetic field when direct current is applied.

[0017] Preferably, the The rack magnetic field feedback unit includes: Excitation array: high permeability manganese-zinc ferrite core or ultra-thin silicon steel sheet laminated core, with Litz wire used for winding to reduce eddy currents; Drive circuit: Multi-channel independent adjustable constant current source, response frequency ≥1kHz.

[0018] Preferably, the sensor is a laser displacement sensor or an eddy current sensor, which monitors the Z-axis displacement of specific feature points on the upper surface of the bed board in real time.

[0019] Preferably, the controller is a PID controller based on FPGA or DSP, which calculates the required current value of each electromagnetic unit according to the displacement deviation.

[0020] A control method for a magnetically levitated assisted CT scanning bed, characterized by the following steps: Step 1: When the thin bed board supports the patient and extends into the scanning hole of the gantry, the bed board initially sags with a displacement deviation > 0. Step 2: Status Awareness: The position sensor collects the actual height signal of the lower surface of the bed board in real time and sends it to the central controller; Step 3: Force field calculation: The controller calculates the distribution of the support force density required to counteract deformation in the Z-axis direction based on the preset bed stiffness matrix and real-time load distribution. Step 4: Magnetic actuation: The controller drives the electromagnetic array located on the frame to generate a magnetic field with the same polarity as the permanent magnets in the bed board, i.e., NN opposite each other. According to the principle that like poles of magnetic fields repel each other, a vertically upward repulsive force is generated. Step 5: Closed-loop stabilization: The repulsive force lifts the bed board upwards until the displacement sensor feedback value approaches the preset isocenter height threshold. The system maintains dynamic force-position balance, achieving a "zero stiffness" flight state.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. Non-contact: The magnetic field medium is completely transparent to X-rays, with no mechanical friction and no abrasive particles; 2. Localized support: The magnetic force acts only on the narrow annular area covered by the gantry (i.e., the location of the scan slice), rather than supporting the entire CT bed. Since CT scans are performed layer by layer, it is only necessary to ensure the accurate positioning of the CT bed for the current scan slice. 3. Radiation dose optimization: Due to the elimination of the physical thickening design, the bed board attenuation equivalent can be reduced to below 0.8 mmAleq. According to the CTDIvol dose formula, the patient's surface incident dose can be reduced by 15%-20%. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a cross-sectional view of the bed board in this invention; Figure 3 This is a block diagram illustrating the magnetic field force control principle of the present invention; Figure 4 A diagram of a second-order vibration system consisting of a bed board and a patient; Figure 5 This is a finite element simulation stress / magnetic coupling cloud diagram for this invention; Figure 6 This is a comparative experimental curve showing the invention and a traditional carbon fiber bed board; In the diagram: 101, CT gantry; 102, scanning port; 103, bed board; 104, array-type magnetic field generating unit; 105. rack magnet Field feedback unit ; 106. Laser displacement sensor; 107. Controller; 108. Power driver; 201. Upper carbon fiber skin; 202. Middle foam core; 203. Lower carbon fiber skin; 204. Permanent magnet. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0024] like Figure 1 and 2 As shown, a magnetically levitated assisted CT scanning bed includes a CT gantry 101, a scanning port 102, a bed board 103, and an array-type magnetic field generating unit 104. rack magnetic field feedback unit 105 、 The position sensing and feedback system, as well as the emergency locking and safety mechanism, are described, with the array-type magnetic field generating unit embedded within the bed board 103. The gantry magnetic field feedback unit is installed in the CT scanner. Inner wall of the scanning hole of the rack The position is directly opposite the magnetic field unit of the bed board 103; the position sensing and feedback system includes a sensor installed on the inner wall of the frame, a controller 107 for control, and a power driver 108 that works in conjunction with the controller.

[0025] The array-type magnetic field generating unit 104 is Permanent magnet passive Array-type magnetic field generating unit, Embedded N52H-grade neodymium Iron boron permanent magnets, with magnetic poles pointing vertically upwards, arranged in a rectangular grid array. .

[0026] The bed board 103 is a thin composite bed board, which adopts a carbon fiber thin shell structure with a thickness of ≤12mm, and an array of magnetic field generating units are embedded inside along the Z-axis direction.

[0027] The bed board 103 includes an upper carbon fiber skin 201, a middle foam core 202 and a lower carbon fiber skin 203. permanent magnet 204 is completely embedded in the foam core layer, and the surface of the permanent magnet 204 is flush with the inner surfaces of the upper and lower skin layers.

[0028] The rack magnetic field feedback unit 105 include: Excitation array: high permeability manganese-zinc ferrite core or ultra-thin silicon steel sheet laminated core, with Litz wire used for winding to reduce eddy currents; Drive circuit: Multi-channel independent adjustable constant current source, response frequency ≥1kHz.

[0029] The sensor uses a laser displacement sensor 106 or an eddy current sensor to monitor the Z-axis displacement of specific feature points on the upper surface of the bed board in real time.

[0030] The controller 107 adopts a PID controller based on FPGA or DSP to calculate the required current value of each electromagnetic unit according to the displacement deviation.

[0031] The second-order vibration system model of the bed board and patient constituted by the present invention is as follows: Figure 4 As shown, its magnetic force control principle is as follows: Figure 3 As shown: The system first receives the input (preset bed height R) and simultaneously collects the feedback (actual bed height Y). By comparing the input and feedback, the deviation E is obtained.

[0032] The deviation E is fed into the PID controller algorithm for processing. The signal output by the controller passes through the PWM drive module, which in turn controls the electromagnet current I.

[0033] Current I drives the electromagnet to generate a corresponding magnetic induction intensity B, which in turn generates a levitation force F as the final output of the system.

[0034] The entire process constitutes a typical closed-loop feedback control system, used to achieve precise control of the suspension height.

[0035] When levitation is not enabled, the stress / magnetic coupling in the finite element simulation is as follows: Figure 5 As shown in (a), the stress cloud diagram in the Z direction of the bed plate shows that the maximum deformation is located at the end of the cantilever. After enabling levitation, the stress / magnetic coupling in the finite element simulation is as follows: Figure 5 As shown in (b), local deformation in the scanned area is completely suppressed. Example 2

[0036] A high-precision diagnostic CT bed based on permanent magnet + electromagnetic hybrid excitation. 1. Design parameters: Bed board specifications: Length 2400mm, Width 480mm, Thickness 12mm. Made of T700 grade carbon fiber prepreg, autoclaved. Core material is PMI foam, density 75kg / m³.

[0037] Permanent magnet array: 20mm × 20mm × 3mm (thickness), N52H neodymium iron boron, surface magnetic induction intensity ≥1.45T. Embedded in a rectangular array with a 50mm spacing in the central area of ​​the bed board (covering the human torso). The magnets are sealed in a laser-welded titanium alloy enclosure to prevent oxidation.

[0038] The rack-mounted electromagnet array consists of 24 independent E-type electromagnets distributed in a 120° fan-shaped area along the circumference of the rack, with a maximum ampere-turns of 1200AT per group. The magnetic pole surfaces are covered with a 0.1mm polyimide insulating and wear-resistant layer.

[0039] 2. Control Implementation: Sensors: Two point laser displacement sensors with a sampling rate of 2kHz and a resolution of 1μm. Mounted at the 12 o'clock and 3 o'clock positions on the frame, they monitor the Y-axis displacement and roll angle displacement of the bed plate, respectively.

[0040] Control strategy: A combined feedforward and feedback control is adopted.

[0041] Feedforward: Based on the patient's registered weight, a baseline suspending current is preset to overcome static gravity.

[0042] Feedback: PID controller, proportional gain Kp=2.5, integral time Ti=0.01s, derivative time Td=0.002s. Output limiting prevents magnetic overshoot.

[0043] Safety logic: Redundancy between software and mechanical limits. If the magnetic levitation system loses power, the mechanical auxiliary support rollers will lower the bed board by 5mm to ensure patient safety.

[0044] 3. Experimental Results With a simulated load of 120kg, the bed board extends to 1300mm: Suspension not activated: Bed board end sag 18.7mm.

[0045] Enable suspension: The dynamic displacement of the bed plate in the scanning area (400-800mm from the end) is <±0.08mm.

[0046] Radiation dose test: Under 120kV and 300mA conditions, the CT value uniformity of the 12mm thick bed board of this scheme is better than that of the traditional 20mm bed board, and the dose at the center of the phantom is reduced by 18.6%. Example 3

[0047] A high-precision diagnostic CT bed with pure electromagnetic active levitation (suitable for ultra-high field MRI-CT multimodal). 1. Differentiated design: To avoid interference from permanent magnets on the uniformity of the MRI magnetic field, this embodiment removes the permanent magnets inside the bed board and adopts a completely electromagnetic repulsion mode.

[0048] Bed board side: Embedded helical hollow coils made of flexible copper clad laminate (FPC), only 0.8mm thick. When 10kHz AC current is applied, an alternating magnetic field is generated.

[0049] On the rack side: synchronous excitation is adopted, and dynamic repulsion or attraction is achieved through phase control (depending on the phase difference of 0° or 180°).

[0050] Advantages: The magnetic field can be turned off, there is no residual magnetism, and it is compatible with MRI.

[0051] Challenges: A high-power, high-frequency drive power supply is required, and the micro-thermal effect generated by eddy currents within the carbon fiber structure must be addressed.

[0052] 2. Implementation details: It employs the principle of double-side electromagnetic induction. The bed coil serves as the primary side, and the frame coil as the secondary side. When a high-frequency current is applied to the frame coil, the bed coil induces a current, and the two interact to generate a repulsive force. The magnitude of the levitation force can be controlled by adjusting the current amplitude of the frame coil.

[0053] 3. Effects: Under a 5mT ambient magnetic field, the system successfully achieved stable levitation of the simulated bed board, verifying the feasibility of magnetic levitation technology in the field of interconnection of imaging equipment. Example 4

[0054] The comparative experimental curves of this invention and traditional carbon fiber bed boards are as follows: Figure 6 As shown, (a) is the rising index curve of a traditional carbon fiber bed board, and (b) is the rising index curve of the present invention. The sag of the present invention is maintained within ±0.15mm in the full extension range.

[0055] The performance comparison between the present invention and the prior art is shown in the table below:

[0056] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A magnetic suspension assisted support CT scan bed, characterized by: It includes a CT gantry (101), scanning port (102), bed board (103), and array-type magnetic field generating unit (104). rack magnetic field feedback unit (105) 、 The position sensing and feedback system, as well as the emergency locking and safety mechanism, are provided, with the array-type magnetic field generating unit embedded within the bed board (103); rack magnetic field feedback unit Installed on the inner wall of the CT gantry scanning port The position is directly opposite the magnetic field unit of the bed board (103); the position sensing and feedback system includes a sensor installed on the inner wall of the frame, a controller (107) for control, and a power driver (108) that works with the controller.

2. The magnetic levitation assisted support CT scan bed according to claim 1, wherein: The array-type magnetic field generating unit (104) is Permanent magnet passive Array-type magnetic field generating unit, Embedded with N52H grade neodymium iron boron permanent magnets, with magnetic poles perpendicular to each other. Upwards, arranged in a rectangular grid array .

3. The magnetically levitated assisted CT scanning bed according to claim 1, characterized in that: The bed board (103) is a thin composite bed board with a carbon fiber thin shell structure with a thickness of ≤12mm and an array of magnetic field generating units embedded in the Z-axis direction.

4. The magnetic levitation assisted support CT scan bed according to claim 1, wherein: The bed board (103) includes an upper carbon fiber skin (201), a middle foam core (202) and a lower carbon fiber skin (203). permanent magnet (204) is completely embedded in the foam core layer, and the surface of the permanent magnet (204) is flush with the inner surface of the upper and lower skin layers.

5. The magnetic levitation assisted support CT scan bed according to claim 1, wherein: The array-type magnetic field generating unit (104) is Electromagnetic active Array-type magnetic field generating unit, Embedded flat printed circuit board (PCB) lines circle or Around A linear air-core coil generates a controllable magnetic field when direct current is applied.

6. A magnetically levitated assisted CT scanning bed according to claim 1, characterized in that: The rack magnetic field reverse Feed unit (105) include: Excitation array: high permeability manganese-zinc ferrite core or ultra-thin silicon steel sheet laminated core, with Litz wire used for winding to reduce eddy currents; Drive circuit: Multi-channel independent adjustable constant current source, response frequency ≥1kHz.

7. The magnetic levitation assisted support CT scan bed according to claim 1, wherein: The sensor is a laser displacement sensor (106) or an eddy current sensor, which monitors the Z-axis displacement of specific feature points on the upper surface of the bed board in real time.

8. A magnetically levitated assisted CT scanning bed according to claim 1, characterized in that: The controller (107) adopts a PID controller based on FPGA or DSP to calculate the required current value of each electromagnetic unit according to the displacement deviation.

9. A method of controlling a magnetic levitation-assisted support CT scan bed according to claim 1, characterized by: The steps are as follows: Step 1: When the thin bed board supports the patient and extends into the scanning hole of the gantry, the bed board initially sags with a displacement deviation > 0. Step 2: Status Awareness: The position sensor collects the actual height signal of the lower surface of the bed board in real time and sends it to the central controller; Step 3: Force field calculation: The controller calculates the distribution of the support force density required to counteract deformation in the Z-axis direction based on the preset bed stiffness matrix and real-time load distribution. Step 4: Magnetic actuation: The controller drives the electromagnetic array located on the frame to generate a magnetic field with the same polarity as the permanent magnets in the bed board, i.e., NN opposite each other. According to the principle that like poles of magnetic fields repel each other, a vertically upward repulsive force is generated. Step 5: Closed-loop stabilization: The repulsive force lifts the bed board upward until the feedback value from the displacement sensor approaches the preset isocenter height threshold. The system maintains dynamic force-position balance, achieving a "zero stiffness" flight state.

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