Fast maximum likelihood positioning for a staggered layer scintillation PET detector

Objective.In this study, we propose a fast implementation of a maximum likelihood positioning (MLP) algorithm to estimate the energy and identify the active scintillator pixel in staggered layer scintillation detectors for positron emission tomograph (PET).Approach.High processing speed of the MLP algorithm was achieved by developing an iteration-free implementation paired with additional computational optimizations. Further, the MLP was implemented for a staggered layer design with pixelated scintillators which enables the determination of the gamma's depth of interaction. The pixelation of the scintillator facilitates an iteration-free formulation of the MLP algorithm. The efficacy of the algorithm optimization was tested on a scintillation detector block designed for an ultra-high field BrainPET 7 T, comprising three scintillator pixel layers. Calibration measurements, in combination with an automated calibration script, were used to obtain the expected counts of scintillation photons required in the MLP algorithm.Main results.Using single-instruction-multiple-data parallelization, multi-threading and optimized cache lines, a maximum processing speed of approximately 22.5 million singles per second was achieved on a platform with four Intel Xeon Platinum 8168 CPUs and 60 threads, encompassing all required processing steps. The automatic calibration failed for 1-15 individual scintillator pixels in approximately 10% of the 120 scintillation detector blocks, necessitating manual correction. After applying the energy correction to the positioned single events, an energy resolution ofΔE=12%±2%FWHMwas obtained for the entire scintillation block.Significance.The obtained energy resolution is very close to the energy resolutions measured for the individual scintillator pixels, proving that the MLP accurately identifies the scintillating pixel and that the energy correction method effectively compensates for the light collection variations of the SiPM array. The presented method is not limited to PET and can be used as fast positioning and energy determination method with scintillation detectors for PET, SPECT and gamma cameras.