Initial PET Performance Evaluation of a Preclinical Insert for PET/MRI\n with Digital SiPM Technology

Abstract

Hyperion-IID is a positron emission tomography (PET) insert which allows\nsimultaneous operation in a clinical magnetic resonance imaging (MRI) scanner.\nTo read out the scintillation light of the employed LYSO crystal arrays with a\npitch of 1 mm pitch and 12 mm in height, digital silicon photomultipliers (DPC\n3200-22, Philips Digital Photon Counting) (DPC) are used. The basic PET\nperformance in terms of energy resolution, coincidence resolution time (CRT)\nand sensitivity as a function of operating parameters, such as the operating\ntemperature, the applied overvoltage, activity and configuration parameters of\nthe DPCs, were evaluated on system level. The measured energy resolution did\nnot show a large dependency on the selected parameters and is in the range of\n12.4-12.9% for low activities and degrades to ~13.6% at activities of ~100 MBq.\nThe CRT strongly depends on the selected trigger scheme (trig) of the DPCs. We\nmeasured approximately 260 ps, 440 ps, 540 ps and 1300 ps for trig 1-4,\nrespectively. The trues sensitivity for a NEMA NU 4 mouse-sized scatter phantom\nwith a 70-mm-long tube of activity was dependent on the operating parameters\nand was determined to be 0.4-1.4% at low activities. The random fraction stayed\nbelow 5% at activities up to 100 MBq and the scatter fraction was evaluated as\n~6% for an energy window of 411-561 keV and ~16% for 250-625 keV. Furthermore,\nwe performed imaging experiments using a mouse-sized hot-rod phantom and a\nlarge rabbit-sized phantom. In 2D slices of the reconstructed mouse-sized\nhot-rod phantom ({\\O} = 28 mm), the rods were distinguishable from each other\ndown to a rod size of 0.8 mm. There was no benefit of the better CRT of trig 1\nover trig 3, where in the larger rabbit-sized phantom ({\\O} = 114 mm), we could\nshow a clear improvement of image quality using the time-of-flight information.\n