Movable PET Detectors for MR Image Quality in PET-MRI
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Solution Overview
Problem
Conventional PET-MRI apparatuses face challenges in obtaining high-quality MR images due to the influence of PET detectors disposed within the magnetic field center, and the use of photomultiplier tubes is not feasible in strong radio frequency magnetic fields.
Innovation Solution
The PET-MRI apparatus employs Avalanche Photodiodes or Silicon Photomultipliers as detectors, and strategically positions them adjacent to the inner circumference of the bore to avoid the magnetic field center, using a moving mechanism to adjust their position based on imaging modes and incorporating a vibration damping mechanism to minimize interference and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PET detectors are disposed at the magnetic field center to optimize PET imaging, then PET detection precision is improved, but MR image quality deteriorates due to material influence
Solution Approach 1:
The patent employs a movable PET detector assembly that can dynamically adjust its position along the bore axis. The detector assembly includes a moving mechanism that allows it to be positioned at different locations, enabling optimization for either PET or MR imaging modes as needed
Solution Approach 2:
The imaging system is segmented into distinct functional zones: the PET detector assembly as a separate movable unit, the gradient coil, and the bore region. This segmentation allows independent optimization of each component's position and function, resolving the conflict between PET detection precision and MR image quality
2Measurement precision
If photomultiplier tubes are used as PET detectors, then detection sensitivity is improved, but they cannot function in strong radio frequency magnetic fields
Solution Approach 1:
The patent changes the fundamental parameter of the detector material from photomultiplier tubes (which are sensitive to magnetic fields) to magnetic field-insensitive detectors such as silicon photomultipliers (SiPM) or avalanche photodiodes (APD). This parameter change enables the detector to maintain high sensitivity while operating in the presence of strong radio frequency magnetic fields
Solution Approach 2:
The patent adopts solid-state detector materials (silicon-based detectors) that are more robust and less sensitive to magnetic field interference compared to photomultiplier tubes. These detectors can withstand the harsh electromagnetic environment of MRI systems without requiring special shielding or complex protection mechanisms
3Manufacturing precision
If PET detectors are positioned to avoid the magnetic field center to improve MR image quality, then MR image quality is improved, but PET detection precision deteriorates
Solution Approach 1:
The PET detector assembly is designed to be movable along the bore axis, allowing dynamic repositioning between different imaging modes. During MR imaging, the detector is positioned away from the magnetic field center to minimize interference, while during PET imaging, it is moved to the optimal detection position, thus resolving the precision-quality trade-off
Solution Approach 2:
The system performs preliminary positioning of the PET detector assembly based on the intended imaging mode before actual imaging begins. The controller pre-positions the detector at the appropriate location along the bore axis, ensuring optimal conditions are established before data acquisition starts
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration suppresses the deterioration of MR image quality, allows for simultaneous high-quality PET and MR imaging, and facilitates easy integration with conventional MRI systems by avoiding the magnetic field center and routing signals and power cables appropriately.
Implementation Method 1
PET detectors which detect gamma rays emitted from positron emitting radionuclides and output signals corresponding to the detected gamma rays
Implementation Method 2
a vibration damping mechanism which damps vibrations generated by the gradient coil 3 interposed therebetween
Data Source
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AI summary
In a PET (Positron Emission Tomography)-MRI (Magnetic Resonance Imaging) apparatus (100) of an embodiment, a magnet (1) that is a seamless structure generates a static magnetic field in a bore having a cylindrical shape. First detectors (13a, 33a) and second detectors (13b, 33b) are each formed in a ring shape and detect gamma rays emitted from positron emitting radionuclides injected into a subject. The first detectors (13a, 33a) and the second detectors (13b, 33b) are disposed with a space therebetween in an axial direction of the bore so as to interpose the magnetic field center of the static magnetic field therebetween.