OPTIMIZING CONTRAST ENHANCEMENT DURING HELICAL CT OF THE LIVER - A COMPARISON OF 2 BOLUS TRACKING TECHNIQUES

OBJECTIVE. The purpose of this study was to evaluate a recently develo ped hardware and software system for CT scanning that generates images in real time and switches to helical CT scanning by either a visual c ue or a region of interest (ROI) amplitude threshold. SUBJECTS AND MET HODS. We randomly and prospectively divided 120 abdominal CT examinati ons into three groups. Two groups received 75 ml of contrast agent at 1.5 ml/sec. Helical CT scanning began after visualization of the contr ast bolus arrival in the hepatic veins (visual cue triggering) (39 pat ients) or after reaching an ROI threshold (automated ROI threshold tri ggering) (39 patients). A third group served as a control group (42 pa tients) and received 150 ml of contrast agent at 1 ml/sec. Quality of hepatic enhancement was assessed objectively and subjectively. Compari sons were made after stratifying each group into three weight classes. RESULTS. Errors occurred in 12 (31%) of 39 examinations in the group with automated ROI threshold triggering. In that group, we found a sig nificantly (p <.04) lower mean hepatic enhancement in two of three wei ght categories, and a significantly (p <.04) lower mean subjective sca n quality in one of three weight categories, than we found in the grou p with visual cue triggering. CONCLUSION. Optimizing portal venous pha se helical CT of the liver after a low-volume bolus of contrast agent and an injection rate of 1.5 ml/sec is best achieved by initiating hel ical CT scanning after visualizing the contrast bolus arrival within t he liver rather than after reaching a preset attenuation threshold.