A radiation imaging device suitable for SPECT or other nuclear imaging includes a detector (22) which receives radiation. A fan beam-slit collimator (20) is positioned adjacent a radiation receiving face (32) of the detector, intermediate the detector and a radiation source (12, 18). The collimator includes a plurality of slats (30) having a common focus. A body (44) adjacent the slats defines one or more elongate slits (46). The slit is arranged such that radiation passes through the slit and between the slats to the detector face. The body is at least substantially impermeable to the radiation. The fan beam-slit collimator (20) enables higher resolution or efficiency to be achieved from the detector.