PET performance evaluation of a pre-clinical SiPM based MR-compatible PET scanner

We have carried out a PET performance evaluation of an SiPM based scanner designed for fully simultaneous preclinical PET/MR studies. The PET scanner has an inner diameter of 20 cm with a crystal size of 1.3 by 1.3 by 10 mm. The crystals are read out using MR-compatible SiPMs to allow the PET scanner to be located within a Philips 3T Achieva MRI scanner. The spatial resolution of the system, measured using SSRB and 2D FBP is just under 2.4mm in the trans-axial and axial directions. The system sensitivity is 0.6% for a point source at the centre of the field of view. The true coincidence count rate shows no sign of saturating at 30 MBq, at which point the randoms fraction is 9%, and the scatter fraction for a rat sized object is approximately 23%. Artefact-free images of phantoms have been obtained using SSRB/FBP and iterative reconstructions. The current performance is limited because only one of three axial ring positions is currently populated with detectors, and limitations of the first-generation detector readout ASIC used in the system. The performance of the system as described is sufficient for imaging rat-sized animals and large organs within the mouse. We have demonstrated here the feasibility of using the system to investigate dynamic processes simultaneously in a mouse using PET and MR with a dual labeled PET/MR probe. Extrapolating from the current performance results we anticipate that population of all three detector rings and upgrading of the readout ASIC will result in an MR-compatible PET scanner with performance similar to that of state-of-the-art non-MR-compatible pre-clinical systems.