Scintigraphic Detection of Pulmonary Emboli by Serial Positron Imaging of Inhaled15O-Labeled Carbon Dioxide

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Abstract
Inhaled radioactive carbon dioxide is retained in pulmonary blood distal to embolic obstruction and appears as an area of increased radioactivity that delineates the site and magnitude of the affected zone. The scintigraphic detection of pulmonary emboli by serial imaging of inhaled carbon dioxide labeled with cyclotron-produced 15O2 was evaluated in 27 patients undergoing conventional pulmonary ventilation/perfusion imaging and pulmonary arteriography. Fifteen patients proved to have pulmonary emboli on arteriography. Sensitivity (87 per cent) and specificity (92 per cent) rates for inhalation imaging were superior to those of conventional ventilation/perfusion imaging (P15O2 activity was markedly delayed over embolized pulmonary segments (mean half time of 47.0±11.1 seconds [S.E.M.]) in comparison to normal segments (mean of 3.6±0.08 seconds; P<0.001). Pulmonary imaging by this method provides an approach to the detection of pulmonary emboli that is relatively sensitive and specific and permits analysis of persisting perfusion in embolized pulmonary segments. A major practical limitation, however, is the necessity of a nearby cyclotron. (N Engl J Med 299:279–284, 1978)