Optimization through Monte Carlo Simulations of a novel High-Resolution Brain-PET System based on Resistive Plate Chambers

Based on previous results obtained with a pre-clinical Positron Emission Tomography (PET) scanner for mice using Resistive Plate Chambers (RPCs) detectors, we believe that constructing a brain-dedicated PET based on RPCs, the HiRezBrainPET, may provide the very-high spatial resolution deemed helpful in brain imaging. Previous experimental studies with this small-animal RPC-PET system provided a spatial resolution of 0.4 mm Full Width at Half Maximum. The brain-dedicated scanner, very similar in shape to the previously proposed for Time-Of-Flight (TOF) Human full-body PET, will consist of 4 detection heads perfectly aligned, each having a stack of a given number of RPC detectors (4, 8, or 10 in the present work). Each detector will consist of 2 detection modules with five amplification gaps, each with its axial electrode, sharing a common transaxial and timing electrode. This work is part of the active development of a first fully functional prototype. It presents the initial studies performed by Monte Carlo simulations to find: 1) the thickness of the RPCs glass plates that maximize the detection efficiency, as well as the influence of the readout electrodes thickness on the detection efficiency; and 2) the loss of coincidence data by only performing coincidences between opposing heads, relative to that obtained if the coincidences were performed using all available heads. The results showed that for stacks of 4, 8, and 10 detectors, the glass plate thickness that maximizes the detection efficiency is equal to, respectively, ~308 µm, ~279 µm, and ~257 µm, with the corresponding detection efficiencies being 7.18%, 12.97%, and 15.47%. For the glass plates thicknesses commercially available – 280 µm, 330 µm, and 400 µm - the efficiencies obtained were, respectively: 7.10%, 7.15%, and 7.09% for a stack of 4 detectors, 12.97%, 12.80%, and 12.40% for a stack of 8 detectors, and 15.40%, 15.12% and 14.59% for a stack of 10 detectors. It was also found that the influence of the readout electrodes on the detection efficiency is negligible. Regarding the coincidences, almost all coincidences occur between opposing heads for sources placed at the scanner center. However, as the source is moved off-center in the transaxial plane, the number of coincidences between opposing heads decreases significantly, increasing the number of coincidences between adjacent heads. Thus, it is worth implementing a coincidence scheme that uses all detection heads instead of only opposing ones.