The Importance of a Valid Reference Region for Intensity Normalization of Perfusion MR Studies in Early Alzheimer's Disease

摘要

Magnetic resonance imaging (MRI) of perfusion could represent a powerful tool in the characterization and tracking of Alzheimer's disease (AD). Brain perfusion presents a large physiological variability across subjects due to biological factors that make it difficult the detection of perfusion abnormalities in comparative analysis; this fact makes necessary a step of intensity normalization of perfusion images. The cerebellum is the most commonly used reference region in perfusion studies in AD patients using nuclear medicine techniques, since it has been reported to provide unbiased estimations. This knowledge has been directly extrapolated to perfusion studies with MRI, but no reports evaluate the consequences of using different normalization regions in MRI studies, and the cerebellum has not been yet confirmed as an optimal reference region. The purpose of this study, is to address the effect of using three reference regions, cerebellum, whole-brain white matter, and whole-brain cortical gray matter in the normalization of cerebral blood flow (CBF) parametric maps, based on a comparative analysis between patients with stable mild cognitive impairment (MCI), patients with AD, and healthy controls. Our results suggest that normalization by whole-brain cortical gray matter enables a more sensitive detection of perfusion abnormalities in AD. The cerebellum, therefore, is not the best reference region in MRI studies of early stages of AD.