n. a radioactive gas that is the shortest-lived isotope in medical use (half-life 13 seconds). It can be used to investigate the *ventilation of the lungs. The patient breathes a small quantity of the gas, the arrival of which in different parts of the lungs is recorded by means of a *gamma camera. This is often performed as part of *ventilation-perfusion scanning to look for pulmonary emboli (clots in the lungs). See also rubidium-81.
Health Encyclopedia