Purpose: Subcortical white matter is known to be relatively unaffected by amyloid deposition in Alzheimer's disease (AD). We investigated the use of subcortical white matter as a reference region to quantify [(18)F]FDDNP binding in the human brain.
Methods: Dynamic [(18)F]FDDNP PET studies were performed on 7 control subjects and 12 AD patients. Population efflux rate constants (k(')(2)) from subcortical white matter (centrum semiovale) and cerebellar cortex were derived by a simplified reference tissue modeling approach incorporating physiological constraints. Regional distribution volume ratio (DVR) estimates were derived using Logan and simplified reference tissue approaches, with either subcortical white matter or cerebellum as reference input. Discriminant analysis with cross-validation was performed to classify control subjects and AD patients.
Results: The population estimates of k(')(2) in subcortical white matter did not differ significantly between control subjects and AD patients but the variability of individual estimates of k(')(2) determined in white matter was lower than that in cerebellum. Logan DVR showed dependence on the efflux rate constant in white matter. The DVR estimates in the frontal, parietal, posterior cingulate, and temporal cortices were significantly higher in the AD group (p<0.01). Incorporating all these regional DVR estimates as predictor variables in discriminant analysis yielded accurate classification of control subjects and AD patients with high sensitivity and specificity, and the results agreed well with those using the cerebellum as the reference region.
Conclusion: Subcortical white matter can be used as a reference region for quantitative analysis of [(18)F]FDDNP with the Logan method which allows more accurate and less biased binding estimates, but a population efflux rate constant has to be determined a priori.