Geometry optimization of electrically floating PET inserts for improved RF penetration for a 3 T MRI system

Area of Science:

• Medical Imaging Physics
• Radiological Sciences
• Biomedical Engineering

Background:

• Simultaneous PET-MRI requires effective radio frequency (RF) transmission through shielded PET inserts.
• Floating PET inserts with Faraday cages face challenges due to RF shielding blocking the MRI transmit field.
• Optimizing PET insert geometry is crucial for maintaining RF field integrity within the imaging region.

Purpose of the Study:

• To investigate the impact of geometric parameters on RF penetrability in shielded PET inserts.
• To optimize PET insert design for improved RF field transmission in PET-MRI systems.
• To determine design guidelines for RF-penetrable PET inserts.

Main Methods:

• Developed and tested 21 prototype cylindrical full-ring PET inserts with varying shield box dimensions and gaps.
• Studied different PET ring configurations: long-ring, short-ring, and two-ring inserts.
• Evaluated RF transmit (B1) fields and image signal-to-noise ratios using a homogeneous phantom in a 3T MRI system.

Main Results:

• A 3mm inter-box gap demonstrated acceptable RF field penetration for PET imaging.
• Multiple short-ring inserts with 5mm and 10mm ring-gaps showed enhanced RF field penetration.
• Rectangular shield boxes outperformed trapezoidal ones, and larger shield box heights reduced required RF power.

Conclusions:

• Geometric design of RF-shielded PET inserts critically influences RF penetrability.
• Proper selection of inter-box gaps, ring configurations, and shield box dimensions enables MRI-like RF field penetration.
• This research provides guidance for designing effective RF-penetrable PET inserts for integrated PET-MRI.