Initial characterization of the Siemens E.CAM/sup +/: a dual-detector camera with coincidence imaging capability

Abstract

This study characterizes the performance of the new E.CAM/sup +/ dual-gamma camera imaging system with coincidence imaging capability. This device utilizes 20.25/spl times/14.75/spl times/5/8 thick NaI[Tl] scintillators and slat collimators for coincidence imaging. The intrinsic spatial resolution, scatter fraction, sensitivity, count-rate capability, energy resolution and clinical image quality are evaluated. Transaxial resolution is 4.9 mm at center and does not change significantly in the radial direction and degrades to 11.4 mm tangential at source position of 20 cm for maximum detector separation of 56.8 cm. Axial resolution degrades from 4.9 mm at center to 12.2 mm at R=20 cm. Similar resolutions were measured at smaller detector separations. Scatter fraction (NEMA NU-2) was measured as 11.7%, 14.8% and 16.1% for 20%, 30% and 30%+Compton energy windows. System sensitivity, in units of cps/[/spl mu/Ci/mL] was measured as 8102, 8772 and 9740 for a 20%, 30% and 30%+Compton energy windows with a 20 cm diameter cylindrical water phantom at an activity concentration of 46 nCi/mL. Dead time losses in this phantom of 50% occur at a radioactivity concentration of 0.16 /spl mu/Ci/mL with a corresponding trues count rate of 911 cps. The true coincidence count rate peaks at 966, 1129 and 1364 cps at activity concentration of 0.24, 0.27 and 0.30 /spl mu/Ci/mL for 20%, 30% and 30%+Compton energy windows, respectively. Noise-equivalent count rate (NEC) shows a peak rate of 762, 820 and 851 cps at activity concentrations of 0.20, 0.21 and 0.19 /spl mu/Ci/mL with 20%, 30% and 30%+Compton energy windows, respectively. The system percent energy resolution degrades from 7.1% at low dead time to approximately 10% at 85% dead time. The peak center shift is less than 3% over the same dead time range. The results show that this dual-headed NaI[T1]-based gamma camera will be suitable for FDG imaging in oncologic applications with superior energy resolution but inferior sensitivity as compared to traditional cylindrical PET tomographs. Further study is required to determine optimal imaging parameters for the E.CAM/sup +/.