[Dynamic study of the liver with helical scanning: determination of hepatic contrast enhancement in routine studies]

Helical CT makes possible imaging of the entire liver in as few as 20 seconds during a single breath hold. This method is thus superior to conventional dynamic CT. In this study, optimal late scanning time and optimal volume of contrast medium in the liver were determined with helical CT in routine studies. (1) Optimal late scanning time In 50 cases, CT images of the liver were obtained at various times following the administrations of contrast medium (1.4 ml/kg). Scanning was started at 60,90,120,150 and 180 seconds after injection. Enhancement of the liver and detection of hepatic and portal veins were best at 60 seconds, followed at 90 seconds. However, a scanning delay of 60 seconds still had an effect on the arterial phase. The optimal late scanning time was thus concluded to be at 90 seconds. (2) Optimal volume of contrast medium In 40 cases, CT images of the liver were obtained following the administration of various amounts of contrast medium (1.0 ml, 1.2 ml, 1.4 ml, 1.6 ml/kg) to determine the optimal volume. No significant difference was found between 1.6 ml/kg compared and 1.4 ml/kg of administered contrast medium. It is evident from the present data that a scanning delay of 90 seconds appears to be optimal and a contrast medium volume of 1.4 ml/kg (body weight) is best for conducting helical dynamic CT on the liver.