Estimation of fractional liver uptake and blood retention of 99mTc-DTPA-galactosyl human serum albumin: an application of a simple graphical method to dynamic SPECT

Abstract

Running Title: Estimation of Tc-99m GSA liver uptake Key words: Tc-99m galactosyl human serum albumin, liver uptake, hepatic function 1 SummaryThe objective of this study was to investigate clinical utility of a graphical method for estimating liver uptake and blood retention of Tc-99m-DTPA-galactosyl human serum albumin (Tc-99m GSA) using dynamic SPECT data. Under the following two assumptions on the kinetics of Tc-99m GSA: 1) Tc-99m-GSA distributes only between blood and liver; 2) no Tc-99m-GSA metabolism during observation period, a plot of liver counts versus cardiac blood pool counts should be theoretically on a straight line.From the slope and y-intercept of a regression line, coefficients for converting count-based liver and blood pool data to % injected dose (%ID) can be calculated. The applicability of this method was tested on dynamic SPECT data from 30 patients with liver dysfunction. To validate this method, plasma concentrations (%ID/ml plasma) at 6, 15 and 30 minutes after the injection were estimated by this method and compared with the measured ones. To investigate clinical significance of % liver uptake, % liver uptake obtained by this method was compared with the results of conventional liver function tests including serum albumin, hepaplastin test, prothrombin time and indocyanine green clearance. In every data set, a plot of liver counts to cardiac blood pool counts was fitted well by a straight line (p<0.00001). Estimated plasma concentrations by this method showed good correlations with the measured ones at 6, 15 and 30 min after the injection (r=0. 748, 0.838, 0.875, respectively, p<0.0001). The liver uptake determined by this method showed good correlations with the results of conventional hepatic function tests (p<0.002). The graphical method could provide accurate estimate of %ID of Tc-99m GSA in the blood without blood sampling. The liver uptake determined by this method could be a simple but useful quantitative indicator of hepatic function.2

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