In vivo measurement of receptor density and affinity: comparison of the routine sequential method with a nonsequential method in studies of dopamine D2 receptors with [11C]raclopride.

Positron emission tomography with the dopamine D(2/3) receptor ligand raclopride was used to compare sequential (studies on 1 day) and nonsequential (different days) approaches to in vivo measurement of the density and affinity of receptors. The choice of temporal sequence of radiotracer injection over a range of specific activities might result in bias because of diverse factors. A strong concordance is reported between the outcomes of the sequential and nonsequential methods. This suggests that the characteristics of the dopamine D(2/3) receptors are relatively stable within physiologic boundaries and can be reproducibly and reliably measured in stable conditions.