A cost-effective field-programmable-gate-array-based pulse processor for biomedical imaging applications

Objective: This paper presents the design and evaluation of a cost-effective, high-spatial resolution, multichannel, field-programmable gate array (FPGA)-based readout system for Positron Emission Tomography (PET) detectors suitable for clinical and pre-clinical work in cancer and other diseases. A key challenge in PET imaging is the precise measurement of the time of arrival and energy of gamma photons originating from positron annihilation, along with the position of interaction within the detector. These parameters enhance image quality by improving coincidence detection, excluding Compton-scattered photons, and improving system spatial resolution. We developed a 16-channel readout system using single silicon photomultiplier (SiPM) element readout for efficient and precise energy, time, and position measurements. Each channel incorporates an FPGA-based sigma-delta analog-to-digital converter (Sigma Delta-ADC) and tapped delay line (TDL) based time-to-digital converter (TDC) for timing and energy estimation. Performance characterization of the system was performed through simulation, electronically generated waveform, and actual PET detector signals from three different single scintillation crystals of face dimensions 3 x 3 mm2 and depths of 5 and 20 mm coupled to a 3 x 3 mm2 SiPM. We also constructed and tested a modular PET detector with a 10x10 array of 1.2x1.2x14 mm3 LSO crystals coupled to a 4x4 SiPM array of 3 x 3 mm2 elements. Best energy resolution was 9.3% at the 511 KeV photopeak and best coincidence timing resolution (CTR) was 210 +/- 3.5 ps. Our system balances cost-effectiveness with performance and contributes to developments in PET signal acquisition and detector technology.