Application of MRI-based partial-volume correction to the analysis of PET images of μ-opioid receptors using statistical parametric mapping

The accurate quantification of brain radioactivity concentration is limited by the spatial resolution of the PET scanner for structures smaller than 2-3 times the resolution. In the presence of enlarged cerebrospinal fluid spaces or regions of cortical neuronal loss, a significant underestimation of gray-matter radioactivity concentration due to the resulting partial-volume averaging can potentially occur. To recover the true radioactivity concentration from PET data, algorithms that use the high-resolution anatomic information provided by MRI have been developed. Their effect on PET quantification has been assessed using regions of interest and non-operator-dependent voxel-based analyses such as statistical parametric mapping (SPM), although the mechanisms that lead to an improvement in PET quantification after partial-volume correction (PVC), compared with no PVC, have not been addressed. Methods: We studied the influence of our previously described MRI-based PVC algorithm on SPM analysis of age effects on μ-opioid receptor (μ-OR) binding using ¹¹C- carfentanil PET in 14 healthy subjects (age range, 29-74 y). Results: μ-OR binding increased with age at a rate of about 0.9% per year in the left temporal cortex after PVC, consistent with the results obtained from human autoradiographic studies. Without PVC, no significant relationship with age was observed. PVC decreased mainly the residual variability of voxel μ-OR binding values around the age regression line. Conclusion: MRI-based PVC improves the sensitivity and accuracy of voxel-based statistical analysis of PET data.