Ventilation studies with krypton-81m.

Nuclear medicine offers well-established methods for regional lung function assessment in the preoperative evaluation of patients with lung disease. The perfusion study with Tc-99m macroaggregates is simple and can be performed without special precautions in radiation shielding. The ventilation study with Xe-133, however, requires more elaborate apparatus as well as special procedures to collect the exhaled radioactive rare gas. Nuclear medicine departments with access to short-lived radionuclides from a nearby cyclotron can use the krypton isotope Kr-81m. The physical half-life of Kr-81m is 13 s. Its gamma energy of 190 keV is optimal for gamma cameras. Kr-81m can be used as a medical isotope in spite of its short half-life. It can be eluted with a continuously flowing gas from the generator containing the mother nuclide Rb-81 which has half-life of 4.6 h. This short half-life not only simplifies radiation protection but allows repeated studies in different projections as well. Examples of comparative studies with Xe-133 and Kr-81m are presented. The importance of taking not only anterior and posterior pictures but also lateral oblique views is stressed.