3D photon impact determination in monolithic based PET detectors using FPGA processing

This work shows the implementation of novel methods to accurately determine the gamma ray impact position within monolithic scintillation crystals in PET systems. These methods have been implemented in an FPGA (Kintex 7) installed on each ADC board of the data acquisition system (DAQ) of the brain PET insert named MindView to provide the 511 keV photon impinging coordinates in real time. Two different methods have been compared: the commonly used Center of Gravity (CoG) approach and an alternative method named RTP (Raise To the Power) in combination with an estimation of the gamma photons DOI (depth of interaction). The DOI is estimated through the ratio of the energy to the peak maximum intensity of each light distribution. Despite CoG has been implemented with DSPs, performance has been improved with the RTP approach LUT-based, reducing the processing time from 1μ to 640 ns. The achieved time performance including the current development has been measured to be around 640 ns, ensuring the processing of all detected events at high data rates. The obtained results using the FPGA implementation have been compared to data processed off-line after directly transferred the whole raw data to a PC workstation. Here, we compared detector image quality in terms of spatial resolution and DOI capabilities without observing any difference.