SATURATION ANALYSIS IN PET - ANALYSIS OF ERRORS DUE TO IMPERFECT REFERENCE REGIONS

In the determination of specific binding in receptor binding technique s in vitro as well as in vivo, determination of the nonspecific bindin g as well as the free component is of crucial importance. If a low pro portion of specific binding is included when determining the nonspecif ic binding, relatively large errors may be obtained. In the present st udy, benzodiazepine (BZ) receptor binding in the human brain was deter mined in vivo using position emission tomography (PET) by applying a s aturation procedure using [C-11]flumazenil as an example of this probl em. Analysis of the errors in B-max and K-D obtained using Scatchard a nalysis in PET was performed using a priori information from in vitro [H-3]flumazenil binding in the pens, used normally as a reference regi on in BZ receptor binding studies. Even if the density of BZ receptors in the reference region pens is only 2% compared to that in the front al cortex, this small proportion of specific binding sites will result in a 10% error in the P-max and K-D values. Simulation of a number of Scatchard plots was performed at varying ratios between the nonspecif ic and the specific binding.