Intended for use in a pathology laboratory, the apparatus includes a multi-segment crystal array over which is positioned a platform supported receiving region with a pattern carrying indicia emulating and in registry with the pattern of the crystal array segments. The tissue carrying a radiolabeled locator is positioned on the receiving region and the photon emission count values for each segment are compiled and displayed at a computer monitor or as a print-out in conjunction with crystal segment identification. Observation of the count values by a pathologist then shows the location over a segment of highest count value at which locator is more likely to be concentrated. Sectioning then is carried out at that location.