Solid State PET Detectors in MRI Bore
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Solution Overview
Problem
The integration of PET and MRI scanners is hindered by the adverse effects of MRI magnetic fields on PET scanner components, leading to low signal-to-noise ratio and image noise in PET images due to limited radiopharmaceutical radioactivity and reconstruction processing noise, as well as spatial constraints in the MRI scanner bore.
Innovation Solution
The implementation of a PET/MR scanner with solid state radiation detectors and time-of-flight PET processing, which detects gamma rays using silicon photomultipliers and reconstructs images using TOF-PET and MRI reconstruction processing, while a cooling system is used to manage heat and vibrations, and coincidence processing determines lines of response for improved image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PET scanner hardware is incorporated into the high magnetic field environment of an MRI scanner, then integration of PET and MRI functions is achieved, but PMTs are adversely affected by magnetic fields making direct incorporation problematic
Solution Approach 1:
The patent extracts the PET detection function from the traditional PMT-based system and implements it using solid state radiation detectors that are insensitive to magnetic fields. This allows the PET functionality to be taken out of the magnetic field environment, resolving the compatibility issue between PET detectors and MRI magnetic fields.
Solution Approach 2:
The patent replaces the traditional PMT-based detection system with solid state radiation detectors. This substitution eliminates the magnetic field sensitivity issue because solid state detectors do not rely on the same magnetic field-dependent mechanisms as PMTs, enabling operation within the MRI magnetic field environment.
2Measurement precision
If higher density of radiation detectors is used to increase PET image resolution and count rate capability, then image quality improves, but smaller detectors have lower radiation count rates and higher noise
Solution Approach 1:
The patent changes the fundamental parameters of the radiation detectors by using solid state detectors with different detection mechanisms compared to traditional PMT-based detectors. This parameter change allows for higher detector density without the trade-off of reduced count rate capability, as solid state detectors can maintain high efficiency even in smaller formats.
3Measurement precision
If radiopharmaceutical radioactivity is increased to improve PET signal strength, then image quality improves, but patient exposure to radiation increases
Solution Approach 1:
The patent replaces the traditional PMT-based detection system with solid state radiation detectors that have different detection characteristics. This substitution enables improved signal detection efficiency, allowing for lower radiopharmaceutical doses while maintaining adequate image quality, thereby reducing patient radiation exposure.
4Power
If heat and vibrations from MR components are present, then MRI function is maintained, but image noise for PET systems increases
Solution Approach 1:
The patent extracts the PET detection function from the magnetic field environment and implements it using solid state detectors that are insensitive to magnetic fields and thermal vibrations. This allows the PET detection to be separated from the sources of heat and vibrations generated by MRI components, reducing thermal noise in PET images.
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 approach enables reduced-noise reconstruction of TOF-PET imaging data and generates high-resolution PET images, simplifying the construction of PET/MR scanners and improving image quality by localizing lines of response and reducing noise.
Implementation Method 1
solid state radiation detectors disposed in or on the scanner housing are arranged to detect gamma rays emitted from the imaging region
Implementation Method 2
Time-of-flight positron emission tomography (TOF-PET) processing is configured to determine localized lines of response based on (i) locations of substantially simultaneous gamma ray detections output by the solid state radiation detectors and (ii) a time interval between said substantially simultaneous gamma ray detections
Implementation Method 3
a cooling system is used to manage heat and vibrations
Data Source
AI summary
In a combined scanner, a main magnet (20) and magnetic field gradient coils (28) housed in or on a scanner housing (12, 18) acquires spatially encoded magnetic resonances in an imaging region (14). Solid state radiation detectors (50, 50′, 50″) disposed in or on the scanner housing are arranged to detect gamma rays emitted from the imaging region. Time-of-flight positron emission tomography (TOF-PET) processing (52, 54, 58, 60, 62) determines localized lines of response based on (i) locations of substantially simultaneous gamma ray detections output by the radiation detectors and (ii) a time interval between said substantially simultaneous gamma ray detections. TOF-PET reconstruction processing (64) reconstructs the localized lines of response to produce a TOF-PET image. Magnetic resonance imaging (MRI) reconstruction processing (44) reconstructs the acquired magnetic resonances to produce an MRI image.