Optimum real-time reconstruction of Gamma events for high resolution Anger camera with the use of GPGPU

Aim of the HICAM project is to build a new, compact Gamma-ray imager with a submillimeter spatial resolution, based on the Anger Camera principle. The system is composed of a detection module with frontend ASICs, an acquisition board and a host PC, where real-time data processing and image reconstruction is implemented. The detector is based on an array of 100 Silicon Drift Detectors (SDDs) of 1 cm2 each in a 10 ×10 cm2 format, coupled to a single scintillator crystal. Position of the interaction with the crystal and energy of the incident radiation are obtained through the use of a MLE algorithm, that optimally exploits the information obtained from the detectors. Moreover it is possible to modify the algorithm in order to determine the depth of interaction of the Gamma photon inside the crystal. The MLE algorithm, on the other hand, requires a large amount of calculations per event. In order to process the events in real-time we have implemented the MLE algorithm on a GPGPU, obtaining a processing rate of 150000 events/second, considering a FOV of 512 ×512 ×10 points (calculation of the z coordinate is performed). In the paper we discuss the derivation of the algorithm, its performance for what concerns spatial resolution and distortion, and the speed of its implementation on the GPGPU.