Development of a readout electronic for a Si-pixeldetector for application in a Compton camera

Compton cameras are very promising gamma-ray imaging systems, which have already found their application in astrophysics. Their use in nuclear medicine could offer higher sensitivity and better spatial resolution than existing mechanically-collimated gamma cameras, leading to a reduction of the radiation dose given to a patient. A Comp- ton camera consists basically of two detectors: a scatter detector, where Compton scatter- ing takes place, and a photoabsorber, where the scattered photons are absorbed. Silicon pixel detectors are the best choice for a scatter medium since they provide good position resolution, good energy resolution at room temperature and a relatively small Doppler broadening effect. Scintillation detectors are preferred for the use as a photoabsorber because of their greater stopping power. In the present work a low noise readout electronic for Si-pixeldetectors with 200µmà 200µm pixel size has been developed in CMOS technology. The electronic is self-triggering and delivers also a timestamp for the use in coincidences. Bonded to a Si-pixeldetector the readout circuit has been tested with gamma-ray sources; an electronic noise of about 49e − was obtained. A pixellated CsI detector read out by a Si PIN photodiode array has been studied as a photoabsorber.