Resolution rates of pulmonary embolism assessed by serial positron imaging with inhaled O-15-labeled carbon dioxide.

Embolic obstruction of pulmonary blood flow results in delayed regional clearance of inhaled C15O2. Focally retained C15O2 appears as zones of increased O-15 activity on serial positron scintigrams, which show the locations of occluded pulmonary segments. Inhalation of C15O2, with serial imaging by a multicrystal positron camera, was used to locate and assess the magnitude of occluded pulmonary segments in eight patients with arteriographically documented pulmonary emboli. The imaging with C15O2 inhalation was repeated after 1 wk of i.v. heparin therapy to evaluate the ability of this technique to determine resolution rates of pulmonary emboli during anticoagulant therapy. In all patients, zones of increased C15O2 activity corresponded with sites of emboli identified arteriographically. After 1 wk of continuous heparin therapy, zones of focally retained C15O2 were totally resolved in three patients, diminished in four, and unchanged in one. The regional pulmonary clearance rate of C15O2 was delayed over embolized pulmonary segments in all patients (men clearance half-time = 42.2 sec +/- 11.2 s.e.m.) and improved after heparin therapy (13.9 +/- 3.9 sec; p less than 0.05). Serial C15O2 inhalation imaging is a rapid noninvasive radionuclide technique for detection of pulmonary emboli. It can be repeated at frequent intervals to assess the resolution of emboli during anticoagulant therapy.