Arterial spin labeling MRI: an emerging biomarker for Alzheimer's disease and other neurodegenerative conditions

Purpose of review The search for biomarkers that detect and track disease progression in early Alzheimer's disease has been a major pursuit for two decades. Functional measures reflecting alterations of synaptic activity associated with neuronal dysfunction have displayed promise for following disease course in early stages. Although fluorodeoxyglucose positron emission tomography (FDG PET) and blood oxygen level-dependent functional MRI (BOLD fMRI) have been studied extensively for this purpose, this review will discuss the emergence and potential role of arterial spin labeling (ASL) MRI, which measures cerebral blood flow (CBF), in neurodegeneration. Recent findings Several recent studies have explored ASL MRI in early and prodromal Alzheimer's disease and have reported areas of hypoperfusion that overlap considerably with hypometabolism frequently reported with FDG PET. However, some studies have also noted increased regional CBF of patients with prodromal and early stage clinical Alzheimer's disease, which may have implications for pathophysiology and the role of compensatory responses to neurodegeneration. Additionally, a few recent studies have begun to use this modality to explore the role of cerebrovascular factors in cognitive decline and the relationship to Alzheimer's disease. Summary ASL MRI is just beginning to be applied more widely to various neurodegenerative conditions. Initial data suggest that this methodology may provide similar information to FDG PET, but with several advantages in the ease of acquisition and expense. Additional applications of this modality, including task-related studies and testing of pharmacological effects, are underexplored, but are potentially of significant value in understanding disease-related functional changes and treatment effects.