Detection of pulmonary emboli by positron imaging of inhaled 15O-labeled carbon dioxide

A new radionuclide approach to the scintigraphic detection of pulmonary emboli is described. This method utilizes cyclotron-produced C15O2, administered by inhalation, for rapid labeling of pulmonary blood. Following clearance of oxygen-15 from the lungs by pulmonary blood flow, focal retention of activity results from stasis of blood distal to emboli. On serial positron imaging, focally retained activity delineates embolized pulmonary segments and identifies the location and extent of pulmonary emboli. In animal studies this positron scintigraphic method detected emboli as small as 2 mm in diameter. In patients with suspected pulmonary emboli, this approach appears to be both sensitive and specific. Clinically, C15O2 inhalation imaging is most useful for the detection of pulmonary emboli in patients with chronic lung disease or congestive heart failure. It is rapid and safe and can be easily repeated, with minimal radiation exposure, for determining resolution rates of emboli and for assessing residual blood flow distal to emboli.