PET/MR Gradient Distortion Correction via RF Probes
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Solution Overview
Problem
Integrating a PET imaging device into an MRI scanner is challenging due to induced eddy currents that cause non-linear gradient magnetic field distortions, block RF excitation pulses, and create magnetic field inhomogeneities, leading to image defects such as ghosting, blurring, and distortions.
Innovation Solution
A combined PET/MR system with a PET detector module and RF probes to measure magnetic field strength, a gradient magnetic field distortion correction system to determine and correct distortions, and an MR reconstruction system to produce corrected image representations, along with RF shielding for PET detector units to minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a PET detector module is introduced into the bore of an MRI apparatus, then combined PET/MR imaging capability is achieved, but induced eddy currents cause non-linear gradient magnetic field distortions and image defects
Solution Approach 1:
The system performs preliminary measurement of the PET detector module's geometric characteristics and material properties before imaging. Distortion correction maps are pre-calculated based on these measurements, allowing the MRI system to compensate for eddy current effects before actual imaging begins, thus maintaining gradient field linearity while enabling combined PET/MR capability
Solution Approach 2:
The system incorporates feedback mechanisms where the PET detector module's presence and effects are continuously monitored during imaging. Real-time distortion correction is applied based on measured geometric characteristics and material properties, adjusting gradient fields to compensate for eddy currents and maintain imaging precision
2Adaptability or versatility
If a PET detector module is introduced into the bore of an MRI apparatus, then combined PET/MR imaging capability is achieved, but the PET detector blocks RF excitation pulses and resonance signals
Solution Approach 1:
The PET detector module is segmented into multiple sub-detectors with individual RF shielding. This segmentation allows the system to isolate RF interference at the detector level while maintaining overall imaging capability. Each sub-detector can be independently shielded, enabling combined PET/MR imaging without complete blockage of RF pulses
Solution Approach 2:
RF shielding structures act as intermediaries between the PET detector module and the MRI RF system. These shields block direct RF interaction while allowing the PET detector to function, thus resolving the conflict between combined imaging capability and RF signal transmission
3Adaptability or versatility
If a PET detector module is introduced into the bore of an MRI apparatus, then combined PET/MR imaging capability is achieved, but magnetic field inhomogeneities cause signal loss due to dephasing
Solution Approach 1:
The system performs preliminary characterization of the PET detector module's magnetic susceptibility properties before imaging. Distortion correction maps are pre-calculated based on these properties, allowing the MRI system to compensate for magnetic field inhomogeneities before imaging begins, thus maintaining signal accuracy while enabling combined PET/MR capability
Solution Approach 2:
The system incorporates feedback mechanisms where magnetic field inhomogeneities are continuously monitored during imaging. Real-time correction is applied based on measured geometric characteristics and material properties, adjusting gradient fields to compensate for dephasing and maintain signal precision
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
The system effectively compensates for gradient and B0 field distortions, reducing image artifacts and allowing for accurate combined PET/MR imaging without repeated calibration cycles.
Implementation Method 1
a main field magnet which generates a stationary magnetic field through the examination region
Implementation Method 2
a gradient magnetic field system which applies magnetic field gradients across the examination region
Implementation Method 3
an RF system that applies RF excitation pulses to excite resonance in a subject/volume of interest in the examination region
Implementation Method 4
A PET detector module is permanently or removably fixed in the examination region to detect radiation from radiopharmaceuticals injected in the subject/volume of interest
Implementation Method 5
A plurality of RF probes which measure magnetic field strength are mounted in the examination region in a fixed relationship to the PET detector module
Implementation Method 6
A gradient magnetic field distortion correction system determines distortions in the gradient magnetic fields and corrects the magnetic resonance signals in accordance with the determined distortion
Implementation Method 7
A magnetic resonance reconstruction system reconstructs the corrected magnetic resonance signals into an image representation
Data Source
AI summary
A combined PET/MR system includes an MR subsystem including a main field magnet (14) which generates a stationary magnetic field through an examination region (16), a gradient magnetic field system (18, 20, 22, 24) which applies magnetic field gradients across the examination region, and an RF system (26, 28, 32, 34, 36, 38) that applies RF excitation pulses to excite resonance in a subject in the examination region and receive magnetic resonance signals from the subject. A PET detector module (70) which is permanently or removably fixed in the examination region (16) to detect radiation from radiopharmaceuticals injected into the subject causes distortions in the magnetic field gradients. A plurality of probes (90) which are mounted in a fixed relationship to the PET detector module (70) measure magnetic field strength. A gradient magnetic field distortion correction system (110) determines distortions caused in the gradient magnetic fields and corrects the magnetic resonance signals accordingly. The PET detector module includes a plurality of RF shielded detector units (132) which are mounted in a circumferentially spaced relationship with a gap (136) there between through which RF excitation pulses and magnetic resonance signals pass.