Quantitative hepatobiliary scintigraphy aids in the diagnosis of hepatic disease. Two scintigraphic parameters that have great value in discriminating between hepatocellular and biliary disease are hepatic extraction fraction (HEF), which is a measure of the hepatic extraction efficiency (HEE), and hepatic excretion rate. It is generally accepted that hepatic extraction fraction is normally 100%, but a review of the literature provided little information on the actual HEF of 99mTc-mebrofenin.
Methods: We determined the HEE of 99mTc-mebrofenin in nine normal dogs after direct injection into the afferent hepatic vasculature using a two-compartment model. The forward and reverse rate constants for the two-compartment model were solved by a simple graphic approach and a more complex numerical approach using a nonlinear least squares algorthm. The HEEs were determined using both methods.
Results: The HEE for the graphic and numerical methods of analysis were not significantly different and were calculated to be 92.2 +/- 4.75% (mean +/- s.d.) and 91.2 +/- 4.44% (mean +/- s.d.) by each method, respectively. The half-time clearance of 99mTc-mebrofenin was 19.10 +/- 4.86 min (mean +/- s.d.).
Conclusion: This study validates the assumption that the normal HEE of 99mTc-mebrofenin is nearly 100%, barring species differences.