[en] A Monte-Carlo photon transport code to simulate scintigraphy is developed. The scintigraphy consists of injecting a patient with a radioactive tracer (Tc, a 140 keV photon emitter) attached to a biologically active molecule. Complicated physical phenomena, photon interactions, occurring in between the radioactive source emission and the detection of the photon on the gamma-camera, require an accurate description. All these phenomena are very sensitive to the characteristics of human tissues and we had to use segmented computerized tomography slices. A preliminary theoretical study of the physical characteristics (rather badly known) of the biological tissues resulted in a two family classification: soft and bone tissues. By devising a Monte-Carlo simulator a systematic investigation was carried out concerning the relative weight of different types of interaction taking place in the traversed tissue. The importance of bone tissues was evidenced in comparison with the soft tissues, as well as the instability of these phenomena as a function of the patient morphology. These information are crucial in the elaboration and validation of correction techniques applied to the diagnosis images of clinical examinations