[Dose estimation of Tc-99m-DTPA-galactosyl-human serum albumin (Tc-99m-GSA) in the blood with nonlinear regression method].

Tc-99m-DTPA-galactosyl-human serum albumin (Tc-99m-GSA) was applied as an agent for receptor-binding hepatic scintigraphy. A single dose of 3-10 mg/185 MBq (5 mCi) Tc-99m-GSA per body was administered in four healthy volunteers and three patients. Time-activity curves for 60 (40) min after injection were obtained from the regions-of-interest over the heart and lung (back-ground). Exponential regression curve was generated from the heart curve during 2-60 (40) min after background subtraction with nonlinear least squares method. Regression curve was well fitted to the heart curve and a significant correlation coefficient of 0.997 +/- 0.003 was obtained between these two curves. Absolute dose of GSA in the blood was decided on the assumption that extrapolated value of regression curve at time 0 represented the total injected dose. The absolute dose differences between sample blood and regression curve were 1.4-4.3% (mean). Nonlinear regression analysis is useful for estimating quantitative dose of GSA in blood without any blood samples.