Spectroscopic and imaging capabilities of a pixellated photon counting system

We are studying the performance of various thickness GaAs pixel detectors b ump-bonded to a dedicated photon counting chip (PCC) for medical imaging ap plications in different energy ranges. In this work we present the experime ntal results obtained with a 600 mum thick pixel matrix (64 x 64 square pix els, 170 mum side) in the 60-140 keV energy range to evaluate the possible use of such a system in the nuclear medicine field. In particular, we have measured the spectroscopic properties of the detector (charge collection ef ficiency, energy resolution and detection efficiency) and evaluated the dis crimination capability of the electronics. Then we have measured the imagin g properties of the whole system in terms of Point Spread Function and usin g a home made thyroid phantom. We present also a comparison with a traditio nal gamma camera and an evaluation, made by both experimental measurements and software simulations, of the imaging characteristics related to the use of a collimation system. (C) 2001 Elsevier Science B.V. All rights reserve d.