Development of a gamma radiation imaging detector based on a GSO crystal scintillator and a position sensitive PMT

An imaging gamma detector was developed using a 5" diameter Hamamatsu R3292 position sensitive PMT and GSO crystal scintillator plates from Hitachi. Plate sizes from 4×4 cm to 8×8 cm and thickness from 1.25 mm to 2.5 mm were used to detect 28-35 keV photons from ¹²⁵I and 140 keV gamma\´s from ^99mTc. Several novel features of the detector were investigated including improvement of detector resolution by using anode wire sections and truncated center-of-gravity calculations. After the PSPMT\´s readout was optimized a resolution of about ~5 mm @ 140 keV was obtained using only fourteen (7x,7y) anode wire sections in lieu of the standard 28×28 individual crossed-wires. Due to good obtained overall energy resolution, efficient scatter rejection is expected by placing just one simple energy window on scintillation signals coming from the detector. Measurements were made with point and linear sources as well as thyroid and compressed breast phantoms with simulated lesions. The phantoms contained appropriate concentrations of ^99mTc emitting 140 keV gamma radiation. The detector combines good performance with small size and economical makeup. After additional phantom tests and software improvement we are planning to use it first as a small field-of-view small animal gamma imager