99mTc imaging performance of the C-SPRINT Compton camera

C-SPRINT is an electronically-collimated imaging system that has been built using pixelated, low-noise, position-sensitive Si as the first detector, and a NaI scintillation detector ring as the second detector. The system consists of a single 4.5×1.5×0.03 cm ³ Si pad detector module with ~2 keV energy resolution centered at the front face of a 50 cm diameter, 12 cm long sodium iodide detector annulus. System sensitivity measurements using ^99mTc show an absolute efficiency of 1.8×10^-7. This value is an order of magnitude lower than predicted due to the combination of worse than expected silicon detector triggering performance, timing resolution issues, and system dead time effects. Spatial resolution measurements are within 10% of analytical predictions. Measured resolution for the ^99mTc point source is 15 mm FWHM. Images obtained were compared with measurements using a clinically-available mechanically collimated Anger camera. A resolution-variance study shows that the C-SPRINT camera performance on a per-detected photon basis is worse than the Anger camera for ^99mTc, but is similar for ¹³¹I, as predicted by theory. Gains in raw system sensitivity of a Compton camera similar in design to C-SPRINT can potentially lead to substantial improvements in noise-equivalent performance of electronically-collimated cameras over mechanical systems