Resolution and noise properties of 123I MIBG SPECT with collimator-detector response modeling

The effects of collimator-detector response (CDR) were studied for two clinical SPECT systems, the Siemens Symbia and GE Infinia, in terms of image resolution, noise properties, and activity estimation of ¹²³I-MIBG in the heart. For each camera, Monte Carlo simulations were used to create CDR models, which were incorporated into a rotation-based projector for 3D-OS-EM SPECT reconstruction. The CDR models were used to generate simulated projections to study the degrading effects of the various CDR components, as well as the efficacy of compensating these components. In simulated images contaminated by ¹²³I septal penetration and detector scatter, compensating the geometric response alone qualitatively restored image contrast, however, activity in the heart was significantly underestimated. The CDR models and the effect of CDR compensation were highly system-dependent. The contribution of detector scatter to activity underestimation was 8-10% for the Symbia and 18-20% for the Infinia, while the contribution of septal penetration was 30% for the Symbia and 5% for the Infinia. The simulation results were confirmed in SPECT measurements of a physical torso phantom on a Symbia SPECT/CT system. These results demonstrate that accurate activity estimation of cardiac ¹²³IMIBG SPECT may require CDR compensation of septal penetration and detector scatter.