Abstract: A source emitting gamma rays of discrete energy is imaged using a Compton type scattering camera. The source location of emitted gamma rays is determined from primary and secondary interaction positions and the energy deposited (.DELTA.E) when the gamma-ray Compton scatters mainly from a primary detector system. .DELTA.E is mainly determined by measuring the energy of the scattered gamma ray when it interacts in a secondary detector system and subtracting this value from a known energy value of the emitted gamma ray. Gamma rays that undergo only one Compton scatter interaction in the primary detector system are emphasized or preferred in the image reconstruction. The present invention optimizes the materials, geometrics, and electronics of the primary and secondary detector system so as to maximize the occurrence and acquisition of these preferred events while simultaneously maintaining close proximity of primary system to the photon source as well as high energy resolution in the secondary detector system.