A Compton camera has two detectors which each sense the location, energy and time of photon collisions. Compton events are detected in which a photon emanating from the subject collides with one detector at energy (E.sub.1) and then the second detector at (E.sub.2), both energies E.sub.1 and E.sub.2 are measured and used in conjunction with an initial photon energy E.sub.0 to increase the resolution of the camera.