New shielding configurations for a simultaneous PET/MRI scanner at 7T

Area of Science:

• Medical Imaging
• Biophysics
• Materials Science

Background:

• Designing simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) systems presents challenges due to electromagnetic interference (EMI) between subsystems.
• Radio frequency (RF) interference and gradient-induced eddy currents can degrade the performance of either PET or MRI modalities.

Purpose of the Study:

• To identify and resolve sources of EMI in hybrid PET/MRI systems.
• To develop shielding strategies that do not compromise the performance of either PET or MRI subsystems.

Main Methods:

• Investigated carbon fiber composite as an RF shield at the Larmor frequency (300MHz).
• Assessed interference from low-frequency electromagnetic radiation (81kHz) from gradient amplifier power supplies.
• Implemented shielding techniques including carbon fiber tubes, copper foil, and common grounding to create an electrostatic cage for the PET detector.
• Analyzed gradient switching effects on PET detector count rates.

Main Results:

• Carbon fiber composite demonstrated effective RF shielding at 300MHz with negligible gradient eddy currents, also providing structural support.
• Interference from 81kHz radiation was reduced by using dual carbon fiber tubes with common grounding.
• Further reduction in interference was achieved by adding copper foil and establishing a common ground for the PET detector, forming an electrostatic cage.
• Gradient switching caused PET count losses, varying with detector location and switched gradient.

Conclusions:

• Carbon fiber composites are suitable for shielding PET/MRI systems against RF interference and eddy currents.
• Multi-component shielding strategies effectively mitigate low-frequency interference and improve PET detector performance in hybrid systems.
• Understanding gradient switching effects is crucial for optimizing PET detector placement and design in simultaneous PET/MRI systems.