[A study of acquisition time using compartment analysis with 99mTc-GSA liver scintigraphy]

99mTc-galactosyl human serum albumin (99mTc-GSA) is a newly developed receptor-binding agent specific for the asialoglycoprotein receptor, which resides exclusively on the plasma membrane of mammalian hepatocytes. Liver scintigraphy using 99mTc-GSA was performed on 13 patients with liver disease. Dynamic data were obtained by gamma camera during 40 min after the intravenous injection of 3 mg (185 MBq) of 99mTc-GSA. Heart and liver time activity curves with acquisition times of 40,30 and 20 min were created, and two different compartment analyses were examined. One was a nonlinear five-compartment model adopting the Michaelis-Menten type for the transfer of 99mTc-GSA from hepatic blood to receptor, and the other was a linear five-compartment model assuming a linear rate constant (P(2)*) for the transfer of 99mTc-GSA. The maximum removal rate obtained by the nonlinear model, P(2), was found to be independent of the change in acquisition time, while the maximum removal rate obtained by the linear model, P(2)*.Km, which was given by the product of P(2)* and the Michaelis constant Km, increased with shortening acquisition times from 40 to 20 min. For both models, the liver blood flow rate decreased with shortening acquisition time. The maximum removal rate and liver blood flow rate obtained by the linear model were significantly correlated with those obtained by the nonlinear model. It was concluded that linear model with an acquisition time of 20 min was applicable to liver scintigraphy with 99mTc-GSA.