CT of deep venous thrombosis and pulmonary embolus: Does iso-osmolar contrast agent improve vascular opacification?

PURPOSE: To prospectively compare the vascular attenuation achieved with the iso-osmolar dimeric contrast agent iodixanol with that achieved with the nonionic monomeric contrast agent iohexol for computed tomographic (CT) venography after CT pulmonary angiography. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained, and 51 consecutive patients undergoing CT pulmonary angiography and CT venography were recruited. A 130-mL dose of iodixanol 320 was injected intravenously at a rate of 4 mL/sec and followed by injection of 50 mL of saline. CT venography was performed after 3.5 minutes. From prior studies, 51 patients of similar weight were picked as control subjects. They received a similar iodine load with iohexol 300 and were studied with a similar technique. Section thickness was 1.25 mm for pulmonary emboli and 5 mm for deep venous thrombosis. Test and control group characteristics (ie, sex, age, and weight) were not significantly different (P > .05). Additionally, in test patients who had undergone CT pulmonary angiography and CT venography during the two preceding years, current and previously obtained CT scans were compared (ie, paired studies). Regions of interest were measured in four pulmonary artery and four lower extremity vein locations by two independent observers. RESULTS: Iodixanol increased average attenuation by 7 HU (P < .05) in the lower extremities and decreased average attenuation by 42 HU (P < .05) in the pulmonary arteries. In the 11 paired studies, similar results were obtained. CONCLUSION: Iodixanol caused a modest but statistically significant improvement in venous attenuation and a decrease in arterial attenuation. The diagnostic importance of this small increase in venous attenuation is not clear.