First coincidences in pre-clinical Compton camera prototype for medical imaging

LEPSICompton collimated imaging may improve the detection of gamma rays emitted by radioisotopes used in single photon emission computed tomography (SPECT). We present a crude prototype consisting of a single 500 $\mu$m thick, 256 pad silicon detector with pad size of 1.4$\times$1.4 mm$^2$, combined with a 15$\times15\times$1 cm$^3$ NaI scintillator crystal coupled to a set of 20 photo multipliers. Emphasis is placed on the performance of the silicon detector and the associated read-out electronics, which has so far proved to be the most challenging part of the set-up. Results were obtained using the VATAGP3, 128 channel low-noise self-triggering ASIC as the silicon detector's front-end. The noise distribution ($\sigma$) of the spectroscopic outputs gave an equivalent noise charge (ENC) with a mean value of left angle =137 e with a spread of 10 e, corresponding to an energy resolution of 1.15 keV FWHM for the scattered electron energy. Threshold settings above 8.2 keV were required for stable operation of the trigger. Coincident Compton scatter events in both modules were observed for photons emitted by $^{57}$Co source with principal gamma ray energies of 122 and 136 keV