A radiation detector that includes multiple adjacent modular detector segments. Each segment includes an array of scintillation crystal elements, a light guide arranged adjacent to the array of scintillation crystal elements, and reflectors arranged around a periphery of the segment so that light produced by a scintillation event in the segment is substantially confined to the segment. In one embodiment, each segment is coupled to multiple photosensors, each photosensor receiving light from at least one of the segments.