Thromboembolic disease detection at indirect CT venography versus CT pulmonary angiography

PURPOSE: To assess the incremental increase in thromboembolic disease detection at indirect computed tomographic (CT) venography versus CT pulmonary angiography and to determine the importance of scan interval for indirect CT venography on the basis of thrombus length. MATERIALS AND METHODS: Institutional review board approval was obtained, and informed consent was not required. The study included 1590 consecutive patients undergoing CT pulmonary angiography for the suspicion of pulmonary embolism. Two minutes after completion of pulmonary angiography, a contiguous indirect CT venography was performed from the iliac crest to the popliteal fossa. The presence of pulmonary embolism or deep venous thrombosis (DVT) was recorded for all patients. The lengths of all deep venous thrombi found in the first 378 consecutive patients were recorded. RESULTS: Pulmonary embolism was detected in 243 (15%) of 1590 patients at CT pulmonary angiography, and DVT was detected in 148 (9%) patients at indirect CT venography. Among 148 patients with DVT, pulmonary embolism was detected in 100 patients at CT pulmonary angiography. Thus, the addition of indirect CT venography to CT pulmonary angiography resulted in a 20% incremental increase in thromboembolic disease detection compared with that at CT pulmonary angiography alone (99% confidence interval: 17%, 23%). Among the 378 patients, DVT was present in 33 patients at indirect CT venography. Two (6%) of 33 patients had clots measuring 2 cm or less, six (18%) had clots measuring 3-4 cm, and 25 (76%) had clots measuring more than 4 cm in length. CONCLUSION: The addition of indirect CT venography to CT pulmonary angiography incrementally increases the detection rate of thromboembolic disease by 20%. Performance of indirect CT venography by using contiguous section intervals, with a section width of 1 cm, is recommended to accurately detect DVT. (C) RSNA, 2005.