Abstract: A single photon emission computed tomography system produces multiple tomographic images of the type representing a three-dimensional distribution of a photon-emitting radioisotope. The system has a base including a patient support for supporting a patient such that a portion of the patient is located in a field of view. A longitudinal axis is defined through the field of view. A generally arcuate detector assembly is adjacent the field of view. The detector assembly extends generally arcuately at least partially about the field of view between a pair of ends. The ends are spaced apart so as to define an entry opening to the field of view. The detector assembly includes a plurality of photon-responsive detectors arranged along the arcuate detector assembly, with each detector being operable to detect if a photon strikes the detector. A generally arcuate photon-blocking member is positioned between the field of view and the detectors.