Kinetic sensitivity of a receptor-binding radiopharmaceutical: technetium-99m galactosyl-neoglycoalbumin.

Kinetic sensitivity is the ability of a physiochemical parameter to alter the time-activity curve of a radiotracer. The kinetic sensitivity of liver and blood time-activity data resulting from a single bolus injection of [99mTc]galactosyl-neoglycoalbumin [( Tc]NGA) into healthy pigs was examined. Three parameters, hepatic plasma flow scaled as flow per plasma volume, ligand-receptor affinity, and total receptor concentration, were tested using [Tc]NGA injections of various molar doses and affinities. Simultaneous measurements of plasma volume (iodine-125 human serum albumin dilution), and hepatic plasma flow (indocyanine green extraction) were performed during 12 [Tc]NGA studies. Paired data sets demonstrated differences (P(chi v2) less than 0.01) in liver and blood time-activity curves in response to changes in each of the tested parameters. We conclude that the [Tc]NGA radiopharmacokinetic system is therefore sensitive to hepatic plasma flow, ligand-receptor affinity, and receptor concentration. In vivo demonstration of kinetic sensitivity permits delineation of the physiologic parameters that determine the biodistribution of a radiopharmaceutical. This delineation is a prerequisite to a valid analytic assessment of receptor biochemistry via kinetic modeling.