Image quality assessment of pixellated systems

The recent development of pixellated solid-state detectors for SPECT provides new opportunities for better image quality when the impact of energy resolution, spatial response and reconstruction technique is combined. In this investigation we assess the image quality of cadmium zinc telluride (CZT) based solid-state detector SPECT systems by use of Monte Carlo simulation, implemented in GEANT 4. Images are evaluated assuming different spatial and energy resolution, reconstruction algorithms and filtering. Phantoms for NEMA resolution and efficiency measurements, test phantoms for noise properties, and the Jaszczak phantom are used for this study. Monte Carlo results have found to be consistent with measured data and with analytical results. Jaszczak phantom simulations show that the better spatial resolution of pixellated detectors enables better lesion detectability compared to NaI(Tl) detectors. A hypothetical value of DeltaE=3% gives better contrast than the typical DeltaE=9.5% of an Anger camera. On the other hand, there is hardly any difference when energy resolution is improved from DeltaE=5% to DeltaE=3% for a CZT detector. Reconstruction shows a strong influence on SPECT image quality. Appropriate filters in the back-projection, and statistical reconstruction give better small lesion detectability and higher contrast-to-noise ratio, though peak-to-valley ratios and spatial resolution are reduced