Optimizing liver contrast in helical liver CT: value of a real-time bolus-triggering technique.

Optimal liver enhancement during portal venous-phase helical CT is crucial in the detection of parenchymal liver lesions. In the prospective study reported here we investigated the effects of a real-time bolus-tracking system on mean and maximal liver enhancement. In 79 patients referred to us for abdominal CT we injected 120 ml of non-ionic contrast (300 mg I/ml) at a rate of 3 ml/s. After a nonintravenous contrast upper abdominal scan a portal venous phase was performed. In 39 patients (mean weight 72.6 +/- 18.7 kg, range 48-139 kg) real-time bolus tracking was performed using the CARE Bolus software (Siemens, Erlangen, Germany). The software performs repetitive low-dose test scans in a preselected region of interest and measures the Hounsfield attenuation and liver enhancement in real-time. After a critical threshold (we selected 31 HU) is surpassed, the software starts diagnostic spiral scanning. Our control consisted of 40 patients weighing 51-100 kg (mean 73.2 +/- 11.1 kg) who were scanned with a fixed, preselected start delay of 80 s. Mean hepatic enhancement was 54.0 +/- 9.9 HU (range 33.3-74 HU) in 37 automatically triggered patients, mean peak hepatic enhancement 64.6 +/- 12.6 HU (range 42.0-91.8 HU). In 2 patients of the study group scanning had to be started manually. In the control group with fixed delay mean enhancement was 48.3 +/- 9.2 HU (range 33.8-71.6 HU) and peak enhancement 55.5 +/- 9.7 HU (range 39.7-81.0 HU). Differences were significant (p < 0.05, Student's t-test). Real-time bolus tracking significantly increased mean hepatic enhancement and may improve portal venous hepatic CT scanning.