Ventilation-perfusion lung imaging and selective pulmonary angiography in dogs with experimental pulmonary embolism.

To determine the accuracy and limitations of Xe-133 ventilation and Tc-99m perfusion lung images (V-P images) in detecting pulmonary emboli (PE), these studies were performed in 23 dogs after experimental production of PE by a modified Wessler technique. Fourteen of the animals also underwent selective pulmonary angiography. Xenon-133 abnormalities were seen immediately after embolization in two of the 23 animals (8.7%). Perfusion images revealed the location of 83% of emboli that completely obstructed pulmonary vessels, but only 26% of those that partially obstructed flow. Defects were seen with 97% of emboli that completely occluded vessels larger than 2.0 mm in diameter, but in only 66% of those occluding smaller vessels. Oblique perfusion images provided the only evidence of the perfusion defect associated with five of 88 (5.7%) angiographically proven emboli. V-P imaging is a sensitive technique for detecting PE unless the emboli lodge in very small vessels or incompletely obstruct a vessel. Xenon-133 abnormalities occur infrequently following PE, and should not be a common cause for a false-negative V-P match in clinical practice.