HEPATIC ENHANCEMENT DURING HELICAL CT - A COMPARISON OF MODERATE RATEUNIPHASIC AND BIPHASIC CONTRAST INJECTION PROTOCOLS

OBJECTIVE. The purpose of this study was to compare the degree and tim ing of peak hepatic enhancement, optimal scanning intervals, and optim al delay times of moderate-rate uniphasic and biphasic contrast materi al injection protocols for hepatic helical CT. MATERIALS AND METHODS. One hundred fifty patients were randomized into three injection protoc ols, receiving 42.3 g iodine (150 ml iothalamate meglumine) delivered using 3 ml/sec uniphasic, 2 ml/sec uniphasic, or biphasic (3 ml/sec [5 0 ml], 1 ml/sec [100 ml]) technique. Statistically fitted aortic and h epatic enhancement curves were generated from dynamic incremental CT d ata for each patient. Protocols were compared by maximum hepatic enhan cement, and contrast enhancement indices were modeled for a 38-sec hel ical acquisition. RESULTS. The 3 ml/sec and 2 ml/sec uniphasic protoco ls produced higher peak hepatic enhancement (64 +/- 15 H and 62 +/- 15 H [mean +/- 1 SD]) than the 3 ml/sec biphasic protocol (52 +/- 10 H; p < .001). Contrast enhancement indices for the 3 ml/sec uniphasic and 2 ml/sec uniphasic protocols (385 +/- 398 H/sec and 397 +/- 412 H/sec ) were significantly greater than the index for the 3 ml/sec biphasic protocol (123 +/- 194 H/sec; p < .0001) at a 50-H threshold, Optimal s can delay times were 50 +/- 8, 75 +/- 7, and 119 +/- 8 sec, respective ly, for the 3 ml/sec uniphasic, 2 mllsec uniphasic, and 3 ml/sec bipha sic techniques. CONCLUSION. The moderate-rate uniphasic injections stu died provided greater hepatic enhancement throughout the helical acqui sition without requiring the prohibitively long delay time necessitate d by the moderate-rate biphasic injection. These findings differ from prior results that showed that a uniphasic injection may provide compa rable levels of hepatic enhancement when compared with a high-flow-rat e biphasic injection.