We attempt to clarify those intravascular ultrasound (IVUS) findings indicative of fresh and chronic pulmonary thromboemboli (PTE). Method: We studied PTE in the acute and chronic phases in 14 clinical and 7 autopsy cases of IVUS imaging using
a 20 MHz mechanical transducer. Results: In the acute phase, large PTE attached to the proximal pulmonary artery were
depicted as echolucent masses with irregular echogenic surfaces protruding into the lumens, which the IVUS findings confirmed
in autopsy cases of acute PTE. Two subacute cases showed PTE that appeared as slightly echolucent crescent-shaped masses
with smooth echogenic surfaces that narrowed the lumens. Chronic recurrent PTE associated with pulmonary hypertension had
a highly echogenic crescent-shape with partial bulging of the vessel wall at the site of persistent thrombi. Similar highly echogenic
images of PTE were noted also in the autopsy cases of chronic PTE. Conclusion: IVUS can be used to distinguish between acute
and chronic PTE.