Inter-Crystal Scatter Processing in NeuroEXPLORER Brain Imager

Advances in positron emission tomography instrumentation have pursued smaller detector sizes to achieve better spatial resolution and overall image quality. The inter-crystal scatter (ICS) hampers the positioning accuracy of gamma photon detection. NeuroEXPLORER aims to optimize scanner parameters for brain imaging by utilizing both time-of-flight (ToF) and depth-of-interaction (DoI) information. The heart of the detection block is 4 U-Shape crystals read out by 2×2 silicon photomultipliers (SiPM) which is called micro-block. While the ICS inside this block will degrade positioning, the event will be registered with energy close to photopeak interaction due to the light sharing. The scattered events between micro-blocks should be handled carefully to recover the parameters of the first interaction. Using Monte Carlo method, in this work we simulated the 6-ring scanner, where each ring has 20 modules and each module holds 12×12 micro-blocks. Small spherical sources were placed from the center to 15 cm off-center. Three scattered event processing methods (based on low energy, high energy and low DoI) were explored and the accuracy of assigning the event parameters is measured using the minimum distance of the source location to the Line-of-Response (LOR). Results show that without the ICS recovery, the scanner loses 43% of sensitivity, and the recovered counts do not degrade the positioning accuracy. The low DoI criteria proves to be a better option to identify the location of the scattered event.