Optimal Scan Time of Dual-phase Spiral CT in Normal Rabbit Liver: Effect of Contrast Injection Rate

ABSTRACT

PURPOSE: To determine the effect of contrast injection rate on rabbit liver enhancement and the optimaltem-poral window for dual-phase spiral CT of rabbit liver at each injection rate. MATERIALS AND METHODS: Usingspiral CT, seven New Zealand White rabbits underwent dynamic scanning at one level of liver. Three protocols ofcontrast injection rates were employed, namely 0.3 ml/sec(group 1), 1ml/sec(group 2) and 2 ml/sec(group 3). During120 seconds of total scan time, the scan interval was 3 seconds. Densities of the aorta, liver and portal veinwere averaged in equivalent time. The different injection rate protocols were compared for peak enhancement/timeon a time density curve. RESULTS: Mean peak enhancement (HU) in equivalent time(secs) was 310/18(group 1),383/9(group 2) and 357/6(group 3) in the aorta ; 34/36, 40/36 and 41/30 in the liver ; and 135/36, 153/24 and170/21 in the portal vein. The temporal window during the arterial phase was 12-21 sec(group 1), 6-12 sec(group2), and 6-12 sec(group 3). The temporal window during the portal phase was from 30 sec(0.3ml/sec), 21sec(1ml/sec)and 21 sec(2 ml/sec). CONCLUSION: During dual-phase spiral CT, the temporal window for liver scanningshould be determined according to each contrast injection rate. A slow contrast injection rate prolongs thetemporal window during the arterial phase.