Position estimation using neural networks in semi-monolithic PET detectors

Abstract

<i>Objective</i>. The goal of this work is to experimentally compare the 3D spatial and energy resolution of a semi-monolithic detector suitable for total-body positron emission tomography (TB-PET) scanners using different surface crystal treatments and silicon photomultiplier (SiPM) models.<i>Approach</i>. An array of 1 × 8 lutetium yttrium oxyorthosilicate (LYSO) slabs of 25.8 × 3.1 × 20 mm³separated with Enhanced Specular Reflector (ESR) was coupled to an array of 8 × 8 SiPMs. Three different treatments for the crystal were evaluated: ESR + RR + B<i>,</i>with lateral faces black (B) painted and a retroreflector (RR) layer added to the top face; ESR +<i>RR</i>, with lateral faces covered with ESR and a RR layer on the top face and; All ESR, with lateral and top sides with ESR. Additionally, two SiPM array models from Hamamatsu Photonics belonging to the series S13361-3050AE-08 (S13) and S14161-3050AS-08 (S14) have been compared. Coincidence data was experimentally acquired using a²²Na point source, a pinhole collimator, a reference detector and moving the detector under study in 1 mm steps in the<i>x</i>- and<i>DOI</i>- directions. The spatial performance was evaluated by implementing a neural network (NN) technique for the impact position estimation in the<i>x</i>- (monolithic) and<i>DOI</i>directions.<i>Results</i>. Energy resolution values of 16 ± 1%, 11 ± 1%, 16 ± 1%, 15 ± 1%, and 13 ± 1% were obtained for the<i>S1</i><i>3-</i>ESR + B + RR,<i>S1</i><i>3-All</i>ESR,<i>S14-</i>ESR + B + RR,<i>S14-</i>ESR + RR<i>,</i>and<i>S14-</i>AllESR, respectively. Regarding positioning accuracy, mean average error of 1.1 ± 0.5, 1.3 ± 0.5 and 1.3 ± 0.5 were estimated for the<i>x</i>- direction and 1.7 ± 0.8, 2.0 ± 0.9 and 2.2 ± 1.0 for the<i>DOI</i>- direction, for the ESR + B + RR, ESR + RR and All ESR cases, respectively, regardless of the SiPM model.<i>Significance</i>. Overall, the obtained results show that the proposed semi-monolithic detectors are good candidates for building TB-PET scanners.