There is a growing interest among nuclear and particle physicists for the application of the detection techniques used in subatomic physics to medical imaging. As well, the code used to simulate the response of these detectors to ionizing particles named GEANT can be applied to simulate medical imaging devices. GEANT allows a complete Monte-Carlo treatment of the attenuation by body parts and of the generation and tracking of optical photons from scintillation inside the crystal. The authors used GEANT to simulate a high resolution gamma camera for small animal imaging. Their study shows a significant correlation between the depth of a source in the body and the energy spectrum of the photons detected in the gamma-camera.