Distribution volume as an alternative to the binding potential for sigma1 receptor imaging.

The applicability of total distribution volume (DV(t)) as an alternative to binding potential (BP) was investigated for neuroreceptor mapping by positron emission tomography (PET). BP is defined as a representative quantity of receptor density. However, for making parametric images of BP, a reference region where an aimed receptor has a very low density is assumed to exist in a target region such as the brain. Thus, if the kinetics of a radioligand for target receptors does not permit an appropriate reference region, BP imaging is unattainable. In this study, [(11)C]SA4503 PET is taken to be considered which has a high affinity to the sigma(1) receptors. Through a clinical investigation using wide ranges of physiological situations, ages, sex, diseases, and selective drug-loading conditions, DV(t) has a good linear relationship with BP, and the images can be used as a spatial distribution of sigma(1) density.