Abstract: A diagnostic device, composition and method of diagnosing airway dysfunction in a patient, the apparatus and method require the subjecting of a pharmaceutical acceptable radionuclide, that is the composition, to an elevated temperature in an enclosed spaced to produce an inhalable gas-light product containing the vapour of the radionuclide in the space, delivery of the inhalable gas from the space is governed with the inhalable gas being inhaled by a patient to enable a film to be located adjacent the airways enabling mapping of the deposition of the radionuclide in the airways of the patient's lungs.