Analysis of the early blood kinetics of Tc-99m-GSA and its verification: new one-compartment model and regression equation

Technetium-99m-galactosyl human serum albumin (Tc-99m-GSA) is a radiopharma ceutical that binds to asialoglycoprotein receptors in the hepatocyte membr ane; the level of Tc-99m-GSA accumulation in the liver correlates well with the parameters of hepatic function tests, We hypothesized that the early b lood kinetics of Tc-99m-GSA could be described by a simple one-compartment model expressed as an offset + a monoexponential function (y=y(o)+Ae(-alpha t)). The aims of this study were to assess the validity of this hypothesis using sequentially measured blood levels of 99mTc-GSA, which were approxima ted by a regression expression, and to analyse the regression equation. 99m Tc-GSA levels were measured in blood samples collected from 30 patients wit h liver disease. From sequential changes in radioactivity up to 30 min afte r injection, a regression equation expressed as an offset + a monoexponenti al function was calculated and evaluated by multiple correlation coefficien ts and absolute deviations (% error). The liver uptake rate 15 min after in jection of Tc-99m-GSA (liver uptake rate 15, UTR 15) was calculated from th e regression equation in each case. The respective relationships of this pa rameter to the coefficient [A] and gradient [alpha] were evaluated. In all cases, the measured values of radioactivity in blood samples could be fitte d to an offset + a monoexponential function. The validity of our hypothesis was supported by examining regression equations calculated from blood Tc-9 9m-GSA levels, Analysis of the regression equations suggested a potential f or a new index of hepatic functional reserve. ((C) 2001 Lippincott Williams & Wilkins).