Transmission computed tomography, Tc-99m MAA scintigraphy, and plain chest radiography after experimentally produced acute pulmonary arterial occulusion in the dog.

We have occluded segmental and subsegmental pulmonary arteries in the dog with Swan-Ganz balloon catheters or i.v. injection of autologous clot, and have studied the chest with transmission computed tomography (TCT), Tc-99m-MAA gamma imaging, and plain radiographs. The arterial occlusions were between 1 and 5 hr old at the time of imaging. Radiographs revealed no lesions. Tc-99m MAA scanns revealed ten of 11 lesions. When a TCT image was made before i.v. injection of Renografin-60, two of 11 lesions were identified; after Renografin the score was four out of ten. The appearance of lesions on TCT was highly variable. Tc-99m-MAA gamma imaging, therefore, is far more accurate than TCT in the identification of small experimentally produced acute pulmonary arterial occlusions in the dog, and our study fails to suggest a secure place for TCT in the diagnosis of small, acute human pulmonary emboli. The commonly-held assumption that postembolic lung is oligemic is questioned.