QUANTITATION OF BENZODIAZEPINE RECEPTORS IN HUMAN BRAIN USING THE PARTIAL SATURATION METHOD

The in vivo quantification of the benzodiazepine receptor concentratio n in humans using PET and flumazenil (FMZ) is usually based on Scatcha rd analysis when the goal is to avoid blood sampling. The experimental protocols, however, include several (at least two) experiments with v arious specific activities in the same subject to obtain a range of bo und ligand concentrations. Methods: We propose the partial saturation method, which is based on a natural decrease in bound ligand concentra tion after an FMZ injection with an average dose between a tracer dose and a saturation dose. An adequate range of bound ligand concentratio ns can thus be obtained from a single experiment. The free ligand conc entration is estimated from the PET measurement in the pens after corr ection for the effect of the small receptor site concentration in this reference region. Results: The receptor concentration and affinity es timates obtained with this approach in six regions of interest agree w ith previously published values obtained by using more complex approac hes. Receptor concentration appears to be insensitive to the uncertain ties with regard to the receptor site concentration in the pens. Concl usion: The partial saturation protocol can be used to estimate both th e benzodiazepine receptor concentration and the FMZ affinity in routin e examinations in adults (or even in children) using a single 40-min e xperiment without blood sampling.