Gradient transparent RF housing for simultaneous PET/MRI using carbon fiber composites

The construction of a simultaneous PET/MRI scanner affords careful design to avoid disadvantageous interference between both imaging modalities. In this work we focus on the housing of the PET detector. The primary function of the housing is to encapsulate and shield the detector electronics and it should provide a reliable mechanical support. High conductive materials, e.g. copper, show excellent radio frequency (RF) shielding properties, but have negative impact on the MRI image quality due to induced eddy currents. Carbon fiber composites are less conductive for low frequencies and thus minimize MRI gradient induced eddy currents. Nevertheless they show good RF shielding properties for higher frequencies. Furthermore, carbon fibers have excellent mechanical properties and are highly gamma transparent, which make them a very interesting material for the construction of MRI compatible housings for PET detectors. We developed a housing based on a thin carbon fiber laminate shell, which encloses the PET electronics and combines electrical and mechanical properties as well. First prototypes have shown excellent eddy current performance, good RF shielding properties and superior mechanical robustness. Our method allows to produce custom shaped housings which can be easily replaced to evaluate different material compositions. The presented housing is used to build up the Hyperion II^D scanner, a preclinical simultaneous PET/MRI insert based on digital SiPM technology for rodent studies.