Dual-phase contrast in MDCT: Liver parenchymal enhancement in three split-bolus protocols : What are the consequences?

Objective: Split-bolus injection protocols are increasingly used in abdominal CT to combine certain enhancement phases in one acquisition. It is unclear in what extent liver parenchymal enhancement is affected by such a protocol design. The purpose of this study was to compare liver parenchymal enhancement in three split-bolus MDCT protocols used in our institution. The enhancement values were compared with a conventional single-phase CT abdomen and the portovenous phase of a 3-phase liver CT. Materials and methods: A retrospective analysis was performed on data obtained by a split-bolus CT intravenous pyelogram, a split-bolus CT Thorax (including liver) and a single-pass split-bolus trauma protocol. Enhancement values of the large vessels and the liver were compared with values found in a conventional CT Abdomen and the portovenous phase of a 3-phase liver CT. There were 25 cases evaluated for all mentioned protocols. Secondly, to determine the effect of the split-bolus protocols on lesion detection, liver-to-lesion contrast was compared in patients who underwent both a split-bolus CT and a CT abdomen or 3-phase liver CT. Results: Significant lower enhancement values of the liver parenchyma were found for the CT IVP protocol (68±22 HU) compared to the enhancement of the single-phase CT abdomen (108±20 HU, p<0.01) and the portovenous phase of a 3-phase Liver CT (111±28 HU, p<0.01). No difference was found between liver enhancement of the split-bolus CT thorax-liver (98±16 HU) and CT trauma protocol (92±16 HU) compared to the conventional single-phase CT abdomen and the portovenous phase of a 3F-liver CT. Liver-to-lesion contrast was measured in 56 patients. Difference in attenuation values between cysts and liver parenchyma was significantly lower in the CT IVP compared to the CT Abdomen/CT 3-phase Liver group (n = 30, 58±25 HU versus 88±19 HU, p<0.01), also liver-to-haemangioma contrast was inferior compared to the control group (n = 8, 5±9 HU versus 58±35 HU, p<0.05). In four patients liver-to-metastasis contrast was measured, we measured 58±22 HU in CT Abdomen/CT 3-phase Liver compared to 23±24 HU in the CT IVP (p=0.068). No significant differences were found when liver-to-lesion contrast was compared in patients who underwent both a split-bolus CT Thorax-liver and a CT Abdomen. Conclusion: The split-bolus CT Thorax-liver and the CT Trauma protocol provided sufficient enhancement of the liver. In the split-bolus CT IVP protocol the liver did not enhance enough for optimal assessment. Especially haemangiomas appeared isodense to the liver parenchyma.