Krypton Kr 81m is radiolabeled noble gas suitable only for inhalation in diagnostic studies. Krypton Kr 81m used for Imaging ventilated regions of the lung, Combined with pulmonary perfusion scintigraphy for diagnosis of pulmonary embolism and other conditions. Krypton Kr 81m diffuses easily, passing through cell membranes and exchanging freely between blood and tissue. It is distributed in the lungs in a manner similar to air, thus representing the regions of the lung that are aerated. The gamma photons of krypton Kr 81m can then be employed to obtain counts per minute per lung or region of the lung, or to display their distribution as a scan.