C-SPRINT - A PROTOTYPE COMPTON CAMERA SYSTEM FOR LOW-ENERGY GAMMA-RAYIMAGING

An electronically-collimated imaging system is being built using pixel lated, low-noise, position-sensitive silicon as the first detector, an d a sodium iodide scintillation detector ring as the second detector. The system consists of a single 3x3x0.1 cm(3) silicon pad detector mod ule with 1 keV energy resolution centered at the front face of a 50 cm diameter, 10 cm long NaI detector annulus. Custom acquisition and tim ing electronics have been manufactured to minimize system dead time. M onte Carlo modeling is used to predict system sensitivity and position resolution. Simulations using the existing setup show angular uncerta inties of 4.1 degrees and 2.2 degrees FWHM for Tc-99m and I-131 point sources, respectively (7.2 mm and 3.8 mm at 10 cm). Sensitivity can be improved by more than a factor of a hundred over the existing setup b y stacking five 1 mm thick 9x9 cm(2) silicon arrays and redesigning th e second detector geometry to accept a wider range of scattering angle s. Lower bound calculations show that our electronically-collimated ca mera system challenges current mechanically-collimated systems for bot h Tc-99m and I-131 despite the deleterious effects of Doppler broadeni ng. Preliminary measurements show a timing resolution of 41 ns FWHM be tween the silicon detector and a single SPRINT module.