Estimation of relative regional neuroreceptor concentration by PET or SPECT: a single late image compared with a late plus early image

The potential for using a single SPECT (single photon emission computed tomography) or PET (positron emission tomography) image to estimate quantitatively the relative regional neuroreceptor concentration was previously analyzed theoretically. The success of this approach depends on acquiring the image at a time when changes in the regional radioactivity localization are much more sensitive to changes in receptor concentration than to changes in delivery. In the present work, the authors have applied a computer simulation approach to determine the joint and marginal probability distributions for the ipsilateral/contralateral ratio of receptor concentrations and delivery. They have studied the effect on the probability distributions, of the values of the sensitivities to receptor and delivery, and the inclusion of radioactivity localizations at an early time point in addition to those at the later time point. The probability distributions depend on the sensitivities to both delivery and receptor. Incorporation of data an early time point results in a significant sharpening of the probability distributions