MR image quality and timing resolution of an analog SiPM based pre-clinical PET/MR insert

A pre-clinical PET insert for a clinical 3T MRI scanner has been developed to acquire PET images simultaneously with MRI data. We assessed the imaging performance of the MR scanner equipped with the PET insert by running spurious noise scans with the MR scanner and by measuring the image SNR with homogeneous standard MR phantoms of different sizes. Also the B1 field distribution map was measured. The noise scans on the MR scanner with the PET insert powered on showed that RF power is coupled from the PET insert into the MR acquisition system. With additional common mode blocking, the noise floor was raised by factor 1.6 when the PET insert was acquiring data compared to the case that it was switched off. MR image SNR was quantified as described in the corresponding NEMA standards publication. Without additional common mode blocking, image SNR is reduced by a factor between 1.5 and 2, depending on the size of the object. With additional common mode blocking, image SNR is reduced by a factor 1.3 only. The timing resolution of the PET scanner was also determined after twofold correction of the timestamps. Mean coincidence timing resolution is approximately 3 ns, the best observed coincidence timing resolution was approximately 2 ns and the worst observed coincidence timing resolution was approximately 6 ns.