Dynamic incremental CT: Effect of volume and concentration of contrast material and patient weight on hepatic enhancement

PURPOSE: To develop an individualized approach to the intravenous administration of contrast material for hepatic computed tomography (CT). MATERIALS AND METHODS: Two hundred patients were randomized into eight protocols. Each group received different volumes and concentrations of contrast material. For each protocol, maximum hepatic enhancement (MHE) was calculated, with an adjustment for iodine dose and patient weight. The contrast enhancement index (CEI) and optimum scanning interval were calculated for hepatic enhancement thresholds of 10-60 HU. RESULTS: The MHE calculated as a function of patient weight was 96 HU ± 19 per gram of iodine per kilogram of body weight. CEIs obtained with a contrast material concentration of 240 mg of iodine per milliliter were inferior to those obtained with a concentration of 320 or 350 mg I/mL. At low enhancement thresholds, the volume of contrast material had a more important effect than the concentration on CEI and optimum scanning interval; at high thresholds, concentration had a more important effect. CONCLUSION: For a patient of known weight, one can calculate the iodine dose needed to provide a desired level of hepatic enhancement. Use of a contrast material with a concentration of 240 mg I/mL is not recommended for dynamic incremental hepatic CT, except in small patients (eg, those weighing less than 73 kg).