Effects of detector sensitivity on image quality in multidetector SPECT

The common imaging practice of each detector on a multidetector SPECT imaging system to acquire only a fraction of the total number of projections in a 360° projection set introduces the possibility of imbalances in system response which can cause artifacts and changes in image quality. Here we evaluate the effect of variations in detector sensitivity caused by differences in the position of the photopeak window, window width, and different collimators on reconstructed image quality. Analytical simulations of cardiac phantom geometries and experimental measurements with Data Spectrum´s Cardiac and Deluxe SPECT phantoms on a three detector SPECT imaging system were used in the evaluation. The relative efficiency of one of three detectors was changed over a series of values between 100 and 0%, while the efficiency of the remaining two detectors was maintained at 100%. The results show that decreased activity and geometric distortions occur along directions perpendicular to the projections with altered sensitivity. The degree of distortion and decrease of activity depends on the geometry of the activity distribution and the reduction in sensitivity. The relative count ratios in the regions with decreased activity varied over a range of 1.0 to 0.59 as the detector sensitivity is decreased from 100 to 0% of the full energy window. Variations in detector sensitivity can degrade spatial resolution and uniformity and create artifacts in reconstructed tomographic slices