PARP1 and Alzheimer disease: PET imaging of PARP1 could reveal the roles of PARP1 in the pathophysiological alterations in AD brains, such as excessive aggregation of misfolded Aβ, hyperphosphorylated tau proteins, neuroinflammation activation, cholinergic deficit, impaired glucose utilization and synaptic dysfunction, and facilitate the translation of PARP1 as a therapeutic target in AD.