A contrast agent delivery nomogram for hepatic spiral CT

Purpose: A nomogram for hepatic spiral CT (SCT) was constructed based on randomization of patients into a prospective study using four different injection protocols. Its utility in a separate prospective randomized trial was subsequently evaluated in a new group of patients. Method: Thirty-nine patients randomized into four groups underwent SCT (Somatom-Plus S; 24 s exposure, 10 mm collimation, 10 mm/s) using 90 mi Omnipaque 240 (22 g I) at 2.5, 4, 5, or 6 ml/s. Peak and mean aortic and liver enhancement and time to peaks were measured and correlated with patients' age, weight, dose, rate, and contrast agent concentration, and a nomogram was constructed. In the validation experiment, 20 new patients were randomized to nomogram-guided and control groups for contrast dose administration during SCT. All patients underwent SCT (Somatom-Plus S; 32 s exposure, 10 mm collimation, 10 mm/s) using 90 mi Omnipaque 240 or 140 mi Hypaque 60 at 1.5-6 ml/s. Peak and mean aortic and liver enhancement and time to peaks were measured and correlated with patients' age, weight, dose, rate, and contrast agent concentration. Mean and peak aortic and hepatic enhancements were measured and rated by three blinded reviewers, Results: Peak hepatic enhancement occurred 32 s after termination of contrast bolus administration in all groups. Correlation between the predicted and actual enhancement was very good (r = 0.7-0.9). Ninety-eight percent of the nomogram-guided group had optimal timing and utilized 10% less contrast agent than the control group. Conclusion: The phenomenon of peak hepatic enhancement occurring 32 s after the termination of contrast bolus regardless of injection rate may be of use in a nomogram for optimal contrast delivery for hepatic SCT.