Abstract: A device and method for determining the x- and y-positions, as well as the depth of interaction, of an interaction between a gamma ray and a scintillation crystal. In one embodiment, a first and a second sensor array are disposed on opposite sides of a scintillation crystal which is subjected in incident gamma radiation resulting in the release of photons. The first sensor array provides a measurement of the x- and y-positions of the interaction while the second sensor array provides a measurement of the depth-of-interaction. In one embodiment, the first sensor array is a photomultiplier array and the second sensor array is an array of wavelength-shifting fibers.