A Spartan3e based low-cost system for gamma-ray detection in small SPECT or PET systems

The development and assessment of a readout system based on Field Programmable Gate Array (FPGA) for dedicated nuclear medicine cameras is presented. We have used Xilinx Spartan3e, which is one of the simplest FPGA evaluation boards. The aim of this work is to offer a simple, opensource data acquisition tool, which provides accurate results for nuclear imaging applications.. The system has been evaluated using three different experimental setups: Pulses from two position-sensitive photomultipliers (PSPMTs) and a Silicon Photomultiplier (SiPM), were recorded, using ^99mTc and ¹¹¹In point sources. Spartan3e FPGA has a dual channel, 14-bit analog to digital converter with a sampling rate of 1.5Msps per channel. The tool was designed using Xilinx´s Embedded Development Kit and was based in Xilinx´s Microblaze soft-core processor. PSPMT anode signals spectra of single position and SiPM energy spectra were compared with those obtained with a reference multiparameter based data acquisition system using nuclear instrumentation modules modules. A number of tests were carried out to assess different algorithms for pulse maximum estimation and Gaussian fitting provided optimal results. The results have shown that the FPGA data acquisition system i) provides accurate digitization of the PSPMTs anode signals in various conditions and ii) gives similar energy spectra when SiPMs are used.