Low cost FPGA based data acquisition system for a gamma imaging probe

We present the development of a low cost field programmable gate arrays (FPGA) based data acquisition system for a gamma imaging probe proposed for sentinel lymph node (SLN) mapping. Radioguided surgery using a gamma probe is an established practice and has been widely introduced in SLN biopsies. For such applications, imaging systems require compact readout electronics and flexibility. Embedded systems implemented in the FPGA technology offer new possibilities in data acquisition for nuclear medicine imagers. FPGAs are inexpensive compared to application specific integrated circuits (ASICs), usually used for the readout electronics of dedicated gamma cameras and their size is rather small. In this study, cost effective analog to digital converters (ADCs) were used and signal processing algorithms were implemented in the FPGA to extract the energy and position information. The analog front-end electronics were carefully designed taking into account the low sampling rate of the ADCs. The reference gamma probe has a small field of view (2.5 cm x 2.5 cm) and is based on the R8900U-00-C12 position sensitive photomultiplier tube (PSPMT) coupled to a pixellated CsI(Na) scintillator with 1 mm x 1 mm x 5 mm crystal element size. Measurements were carried out using a general purpose collimator and Tc-99m sources emitted at 140 keV. Performance parameters for the imaging gamma probe were compared with those obtained when data were acquired using the standard NIM (Nuclear Instrumentation Modules) electronics and found to be in very good agreement, which demonstrates the efficiency of the proposed implementation