To assess the degree of the venous enhancement and to determine the incidence of deep venous thrombosis in patients who were clinically suspected of pulmonary embolism by lower limbs venography after CT pulmonary angiography in a 16-slice spiral computed tomography (CT) scanner (Siemens Medical Systems, Germany). The accuracy of CT venography was evaluated compared with Color Doppler Ultrasound Imaging.

Venous phase imaging were acquired on 16 slices spiral computed tomography from the diaphragm to the upper calves 170sec after completion of CT pulmonary angiography (120ml of ultravist or omnipaque 300 injected by two phase: the first, 50ml at a rate of 4ml/s, the second, 70ml at a rate 2ml/s ) in 84 patients. The CT values of the venous enhancement from inferior venae cava to popliteal vein were recorded. Color Doppler sonography of the limbs was done in 70 patients within 3 days by one doctor who was unaware of the CT findings. Results of CT venography were compared with the results of Color Doppler sonography.

The enhancement of superior femoral vein with CT values ranged from the highest of 100±19HU and the lowest is 60.1HU. 17 patients (24.3%) had deep venous thrombosis on CT with the density of 39±13HU, 15 patients among those had pulmonary embolism simultaneously. Undetermined diagnosis was made in 5 examinations（6.5%） because of nonuniform enhancement. 7 locations in 4 patients were negative on CT venography but positive on sonography with mural thrombus diagnosed at 5 locations. The sensitivity, specificity and accuracy of CT venography compared with sonography were 90.48%,100%, 97.22% respectively, but decreased to 86.36%, 92.73%, 90.91% respectively if undetermined cases contained. The sensitivity, specificity and accuracy of CT venography were 85.71%, 99.79, 99.11% respectively according to the locations of thrombus. In addition, the CT venography also showed thrombosis of inferior venae cava filter and iliac veins in 7 patients.

Multiple-slice spiral CT is a very accurate method in the diagnosis of acute deep venous thrombosis as well as thrombosis in inferior venae cava and iliac veins.