Combined CT venography and pulmonary angiography: How much venous enhancement is routinely obtained?

OBJECTIVE. Combined CT venography and helical pulmonary angiogaphy is a new diagnostic test that permits radiologists to check both the pulmonary arte ries for embolism and the deep veins of the abdomen, pelvis, and legs for t hrombosis in a single examination. The purpose of this study was to determi ne the degree of venous enhancement routinely obtained using this combined CT examination. MATERIALS AND METHODS. We identified all patients at a single institution w ho, during a 29-month period, had symptoms suggestive of pulmonary embolism and who underwent CT venography and helical pulmonary angiography. The exa minations were performed after the patients received a rapid (3-5 mL/sec) T V injection of 150 mt of nonionic contrast medium (240 mg I/mL), CT venogra phy: of the abdomen, pelvis, and lower extremities was performed as follows : Beginning 3 min after the start of contrast medium infusion for helical C T pulmonary angiography, 1-cm axial images obtained at 5-cm intervals were acquired from an area ranging from the diaphragm to the calves, Patients wh o had evidence of deep venous thrombosis on CT scans were excluded from fur ther analysis. The venous portions of the remaining 429 examinations were r etrospectively reviewed at a CT console or workstation by one of two radiol ogists, and Hounsfield unit measurements were recorded from the inferior ve na cava as well as from the right and left external or internal iliac, comm on femoral, superficial femoral. and popliteal veins. A single Hounsfield u nit measurement was obtained from the center of each vessel using a region of interest that was approximately half the diameter of the vessel. Mean Ho unsfield unit measurements were then calculated for these venous stations. RESULTS. Mean Hounsfield unit measurements at the inferior venn cava and at the right and left external or internal iliac veins were 97, 95, and 95 H, respectively. R lean measurements at the common femoral veins were 95 H fu r both the right and left; the mean measurements at the superficial femoral veins were 91 H for both the right and left, and those at the popliteal ve ins were 97 H for the right and 94 H for the left. CONCLUSION. CT venography of the abdomen, pelvis, and lower extremities beg un 3 min after the start of contrast medium infusion for helical CT pulmona ry angiography routinely produced high mean levels of venous enhancement.