RF shielding materials for highly-integrated PET/MRI systems

Area of Science:

• Medical Imaging Physics
• Materials Science for Medical Devices
• Radio Frequency Engineering

Background:

• Simultaneous PET/MRI systems require novel radio frequency (RF) shielding solutions to mitigate interference.
• Conventional PET detector housings limit integration possibilities; excluding components like scintillators offers advantages but necessitates RF shielding interfaces.
• Selecting appropriate RF shielding materials is critical for maintaining both PET and MRI performance.

Purpose of the Study:

• To evaluate the shielding effectiveness (SE) and impact on positron emission tomography (PET) performance of various RF shielding materials.
• To assess the magnetic resonance imaging (MRI) compatibility of these materials by analyzing their effect on magnetic field homogeneity.
• To identify optimal RF shielding materials for integrated PET/MRI systems.

Main Methods:

• Examined 10 different RF shielding materials, including coated glasses, coated foils, and meshes.
• Measured shielding effectiveness (SE) at 100 and 300 MHz.
• Assessed PET performance by measuring photon attenuation (PA), energy resolution (dE/E), and coincidence resolving time (CRT).
• Evaluated MRI compatibility by analyzing the impact on B0 field homogeneity.

Main Results:

• Coated glasses and foils achieved SEs up to 25 dB at 300 MHz with low photon attenuation (<23%) and minimal impact on PET performance (dE/E, CRT) and B0 homogeneity.
• Meshes offered higher SEs (up to 56 dB) but resulted in significantly higher photon attenuation (>58%) and greater degradation of PET performance metrics.
• Coated foil HS 9400 demonstrated excellent performance with SE = 25 dB, PA = 22%, dE/E = 12%, and CRT = 274 ps, with no measurable impact on B0 homogeneity.

Conclusions:

• Coated foils and glasses are promising candidates for RF shielding interfaces in integrated PET/MRI systems due to their balance of shielding capability and minimal performance impact.
• Meshes provide superior shielding but their high photon attenuation and impact on PET performance limit their suitability for this application.
• The coated foil HS 9400 is recommended for PET/MRI integration concepts, offering a robust solution for effective RF shielding without compromising image quality or system compatibility.