TSPO and Alzheimer disease: To overcome regional heterogeneity of neuropathology distribution in AD [34], we applied a two-dimensional microglia response index to categorize the TSPO-PET signal into Aβ-plaque associated and Aβ-plaque-independent components of microglial activation by use of a multi-regional correlation analysis between TSPO-PET and Aβ-PET of the parcellated brain.