Assessment of a Technology that permits individualized scan delays on helical hepatic CT: A technique to improve efficiency in use of contrast material

OBJECTIVE. We performed this study to assess the usefulness of a computer automated scan technology (CAST) for individualizing scan delay during helical CT to improve the efficiency of hepatic enhancement. SUBJECTS AND METHODS. We prospectively evaluated 183 patients who were randomized into five groups. Control patients received 100 or 150 ml of contrast material (320 mg I/ml) with a 60-sec delay between contrast injection at 3 ml/sec and scanning. CAST patients received 100, 125, or 150 mi. In our latter groups we used an hepatic enhancement threshold of 50 H over baseline to determine the optimum delay between contrast injection and scanning. For the intergroup comparisons, we measured the liver on baseline and enhanced helical CT scans at the upper, mid, and lower levels of the liver. RESULTS. The mean enhancement in patients who received 150 mi of contrast material was 70.7 +/- 19.4 H for the control group and 81.0 +/- 17.5 H for the CAST group (p < .05). Hepatic enhancement above 50 H was achieved in 84% of the control subjects compared with 100% of CAST subjects; more than 60 H hepatic enhancement was achieved in 73% of control subjects and in 89% of CAST subjects. The use of CAST software with 125-ml contrast doses provided enhancement equivalent to that of control subjects who received 150 mi of contrast material (mean enhancement in CAST subjects, 70.3 +/- 15.4 H). Enhancement above 50 H was reached in 98% of CAST and 84% of control patients, With 100 ml of contrast material, 24% of patients failed to initiate CAST, resulting in enhancement similar to control patients (CAST, 54.2 +/- 11.4 H; controls, 56.9 +/- 15.2 H). CONCLUSION. Using a contrast dose of 150 mi, CAST provided significantly increased hepatic enhancement than that achieved in control subjects with less variability, For equivalent hepatic enhancement, contrast doses could be decreased by 25 mi using CAST technology because it provides individualized scan delays.