Hepatobiliary kinetics of technetium-99m-IDA analogs: quantification by linear systems theory

A compartmental model describing the extraction and disposition of 99mTc-acetanilidoiminodiacetic acid (IDA) compounds by the liver has been applied to 5 adult patients admitted for cholecystitis investigations and 29 jaundiced infants the majority of whom were clinically differentiable into neonatal hepatitic and biliary atretic groups.

In each case kinetic rate constants were calculated to describe hepatocyte extraction of 99mTc-IDA structural analogs from blood pool (k21) and subsequent elimination (k3) of this compound into biliary tract. Also modeled was the reverse-binding constant (k12) describing the return of such radiotracer to the systemic circulation and the blood fraction (f) which accounted for the composite vasculature forming a matrix in the liver.

It was shown that these indices could be used to determine accurate compartmental mean residence times (MRT(c)s) for each patient by correlation with values obtained by deconvolutional analysis and independent measurement of leading edge parenchymal transit times. For the adult patients the following indices, typical of good hepatocyte function, were derived: k21 = 0.933 +/- 0.488 min-1, k12 = 0.0277 +/- 0.0340 min-1, k3 = 0.1610 +/- 0.0531 min-1, f = 0.3519 +/- 0.3048 and MRTc = 11.19 +/- 3.13 min. Analysis of the pediatric group revealed no significant differences in their respective MRT(c)s. However, significant differences in the extraction (p < 0.01) and excretion (p < 0.001) coefficients were prominent.

This method can be applied to provide accurate and meaningful intercompartmental rate parameters and MRT(c)s for adults, nonobstructed and obstructed infants.