Background Computed tomographic pulmonary angiography (CTA) combined with computed tomographic venography (CTV) of the lower extremities has been shown to have a higher diagnostic sensitivity than does CTA alone in patients with suspected pulmonary embolism. Most published studies of CTV following CTA have used 130 to 150 mL of nonionic intravenous contrast, the standard dose of contrast used with single detector CT scanning. The amount of intravenous contrast used for multidetector CT scanners is usually 100 mL or less. The objective of this study is to determine if 100 mL of intravenous contrast provides adequate opacification of the pelvic and lower extremity veins.
Methods Venous phase images were acquired in patients undergoing CTA for pulmonary embolism using a 16-row multidetector CT scanner. Three 5 mm single axial CT slices were taken: one at the level of the anterior inferior iliac spine, one at the level of the midfemoral heads, and one 5 cm below the lesser trochanter. Images were obtained 21/2 minutes after completion of the pulmonary angiogram. Hounsfield units (HU) were measured of the external iliac vein, common femoral vein, and superficial femoral vein and compared to the adjacent artery.
Results Preliminary data from 9 patients and 50 vein cross sections show an opacification average of 89.39 HU with a standard deviation of 19.5 HU. External iliac veins show an average of 93.13 HU with a standard deviation of 20.03 HU. Common femoral veins show an average of 89.82 HU with a standard deviation of 19.21 HU. Superficial femoral veins show an average of 85.16 HU with a standard deviation of 19.72 HU. The patient's average creatinine was 0.87, and the average weight was 91.25 kg.
Conclusions In patients with suspected pulmonary embolism, 100 mL of intravenous contrast appears to provide adequate opacification of the pelvic and lower extremity veins. Veins measuring 60 HU are considered adequately opacified. This suggests that using the current dose of contrast will permit concurrent testing for venous thrombosis and pulmonary embolism using multidetector CTA-CTV, but additional testing is necessary to compare weights and creatinine clearances and their effect on venous opacification.
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