C-SPRINT: A prototype Compton camera system for low energy gamma ray imaging

An electronically-collimated imaging system is being built using pixellated, low-noise, position-sensitive silicon as the first detector, and a sodium iodide scintillation detector ring as the second detector. The system consists of a single 3x3x0.1 cm(3) silicon pad detector module with 1 keV energy resolution centered at the front face of a 50 cm diameter, 10 cm long NaI detector annulus. Custom acquisition and timing electronics have been manufactured to minimize system dead time. Monte Carlo modeling is used to predict system sensitivity and position resolution. Simulations using the existing setup show angular uncertainties 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 by stacking five 1 mm thick 9x9 cm(2) silicon arrays and redesigning the second detector geometry to accept a wider range of scattering angles. Lower bound calculations show that our electronically-collimated camera system challenges current mechanically-collimated systems for both Tc-99m and I-131 despite the deleterious effects of Doppler broadening. Preliminary measurements show a timing resolution of 41 ns FWHM between the silicon detector and a single SPRINT module.