Prototype Parallel Readout System for Position Sensitive PMT Based Gamma Ray Imaging Systems

A parallel prototype readout system that allows digitization and acquisition of 64 or more anode signals from a position sensitive photomultiplier tube (PSPMT) was developed for a miniature hand-held gamma camera. This acquisition system was developed to study the benefits of a digital readout system compared to charge multiplexed techniques such as resistive division. The system was developed using CAMAC instrumentation standard and controlled via a Macintosh Computer. Four 16-channel charge-to-digital conversion (QDC) CAMAC modules were used to digitize individual anode signals from the PSPMT. To maximize the data transfer rate, a list processor module was also added in the system. For acquisition and processing of the digitized data, we used Kmax software from SPARROW. The system provided 99.9% spatial linearity when inter-anode gain correction was applied to list-mode data. Much improved scintillation crystal separation in a flood histogram with 16:1 peak to valley ratio, and higher edge sensitivity was obtained compared to resistive charge multiplexing readout