ESTIMATION OF RELATIVE REGIONAL NEURORECEPTOR CONCENTRATION BY PET ORSPECT - THEORETICAL COMPARISONS OF USING A SINGLE LATE IMAGE OR A LATE PLUS EARLY IMAGE

The potential for using a single SPECT or PET image to estimate quanti tatively the relative regional neuroreceptor concentration was previou sly analyzed both theoretically and experimentally. The success of thi s approach depends upon acquiring the image at a time when changes in the regional radioactivity localization are much more sensitive to cha nges in the regional receptor concentration than to changes in deliver y. Using the binding of [C-11]carfentanil to the opiate receptor as a model, we have applied a computer simulation approach to determine the joint and marginal probability distributions for the ipsilateral/cont raleteral ratio of receptor concentrations and delivery. We have studi ed the effect, upon the probability distributions, of 1) the values of the sensitivities to receptor and delivery, 2) the selection of a par ticular operational procedure for interpreting the observed ipsilatera l and contralateral radioactivity localizations, and 3) the inclusion of radioactivity localizations at an early time point in addition to t hose at the later time point. We have found that the probability distr ibutions depend upon the sensitivities for both delivery and receptor. Incorporation of data at an early time point results in a significant sharpening of the probability distributions. There is an insignifican t effect of subtraction of the radioactivity localization in a control region.