Difference in Global Hepatic Enhancement Assessed by Dynamic CT in Normal Subjects and Patients with Hepatic Metastases

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Abstract
Our goal was to determine if there are differences in liver densitometry parameters using helical CT between normal subjects and subjects with liver metastases. One-hundred fifty subjects (64 with normal livers and 86 with CT-visible hepatic metastases) underwent dual phase helical scanning of the liver. Images were obtained in the “arterial” (early) and “venous” (late) phases of hepatic enhancement. Densitometry measurements were obtained from the liver (distinct from obvious lesions or vessels) and aorta at 25, 40, 75, and 90 s. Enhancement values at the same time points were calculated in 73 subjects in whom noncontrast images of the liver were available. A peak liver densitometry value was also determined. Several ratios were determined for each time point: the liver/aortic ratio (L/A), liver/liver peak ratio (L/P), liver enhancement/aortic enhancement ratio (LE/AE), and liver enhancement/liver peak enhancement ratio (LE/LPE). The degree of tumor burden in the hepatic metastatic group was assessed in each case. Values for L/A, L/P, LE/AE, and LE/LPE at 25 and 40 s were significantly (p < 0.05) higher in the liver metastases group than the normal liver group. Enhancement ratios were even more elevated in breast cancer, which can have hypervascular metastases. These CT parameters did not show significant differences when analyzed according to the degree of hepatic metastatic tumor burden. All densitometry parameters and ratios obtained at 75 and 90 s were not significantly different between the two groups. In the early phase of bolus intravenous contrast agent administration, the visually normal portion of the liver parenchyma in patients with hepatic metastases enhances to a greater degree than the liver in normal subjects. This may reflect generalized increased hepatic arterial flow in tumor-bearing livers and has the potential to increase the sensitivity of CT for detection of hepatic metastases.