MODEL RELEASED. Doctor positioning a patient to undergo a gamma camera scan, a diagnostic technique that uses mildy radioactive tracers to detect sites of disease at an early stage. The radioisotope used (the majority of scans use technetium-99m) is linked to a tracer substance that becomes concentrated in the organ under investigation, following its injection into the blood circulation. Gamma rays pass through the body & are detected by the gamma camera (right) that provides a map (a scintigram) of activity in the organ, where healthy & abnormal tissues absorb the tracer at a different rate. Models: Dr Mike Keir & Gwennie