Quantitative analysis by digital computer of 99mTc-N-pyridoxyl-5-methyltryptophan (99mTc-PMT) hepatogram in diffuse parenchymal liver diseases.

99mTc-N-pyridoxyl-5-methyltryptophan (99mTc-PMT) hepatograms were analyzed to provide information about the liver and bile duct. Calculations were based on a four compartmental model and included corrections for blood, tissue, hepatic parenchymal and bile backgrounds. The time activity curves for 99mTc-PMT in the cardiac region were described as the sum of two exponential functions, while curves for the hepatic regions were described as the sum of three exponential components. The measured hepatograms were compared with simulations and good agreement between the two curves showed that the compartmental model adequately described the blood and bile activities in vivo. Hepatic excretion rate constants were 0.179 +/- 0.026 in three normal subjects, 0.102 +/- 0.012 in four patients with chronic hepatitis and 0.082 +/- 0.034 in six patients with liver cirrhosis. In the case of diffuse parenchymal liver disease, there were lower rate constants for the excretion from the liver to the bile ducts than in normals, and the relative distribution volumes were also larger than normal. Prior to the development of this compartmental model, no useful kinetic model had been found which could satisfactorily explain the time activity curves. Experience in human studies proves this method to be accurate in determining the rate constants for the hepatobiliary transport of 99mTc-PMT.