Comparison of iodixanol with iohexol for delayed pelvic venous opacification: A preliminary study of potential use for CT venography

OBJECTIVE. The goal of this prospective randomized study was to determine whether isosmolar contrast material offers an advantage over low-osmolar contrast material for delayed venous opacification in CT venography. SUBJECTS AND METHODS. We prospectively enrolled 200 adult outpatients. Patients were randomized to receive either the low-osmolar (hyperosmolar to blood) nonionic contrast medium, iohexol, or the nonionic isosmolar contrast medium, iodixanol. Images were obtained before contrast administration and 180 sec after contrast administration through the pelvis at the level of the external iliac vessels. Opacification of the external iliac vessels was assessed both objectively and subjectively. RESULTS. The arterial and venous densities before contrast administration were approximately 45 H for both groups. On delayed images obtained after contrast administration, the mean venous density was 95.2 H for iohexol and 101.4 H for iodixanol. Changes in venous density due to administration of iohexol and iodixanol were 49.8 and 56.1 H, respectively. This 12.5% difference was highly significant (p = 0.002). Sixty-six percent of the images in the iodixanol group were rated either 4 (good) or 5 (excellent), whereas only 36% of the iohexol group achieved a similar rating on our subjective rating scale. This difference was statistically significant (χ² = 16.4, p < 0.001, df = 1). CONCLUSION. Our study shows that isosmolar contrast material provides significant improvement in delayed opacification of the external iliac vessels in comparison with conventional low-osmolar contrast medium (hyperosmolar to blood).