525 The Neuroradiology Journal 22: 525-533, 2009 www.centauro.it SUMMARY – Alzheimer's Disease (AD) is a progressive neurodegenerative disease associated with memory loss and gradual behavioral, functional and cognitive impairment. Conventional imaging studies, such as magnetic resonance or computed tomography have played a secondary role in AD diagnosis: While other causes of memory loss and cognitive deficit can be evaluated by these imag- ing methods, AD structural changes are not detected until very late in the course of the disease. Recent and more precise techniques have been developed to detect subtle changes not visualized with those imaging methods. This article presents a review of the neuroimaging techniques used as a diagnostic aid for AD. Neuroimaging Studies in Alzheimer's Disease A Review H. CUELLAR*, P. GÓMEZ-RAMOS**, R. RIASCOS***, L. DE ALBA* * Department of Radiology, “José E. González” University Hospital, Universidad Autónoma de Nuevo León; Monterrey, México ** Department of Anatomy, Histology and Neurosciences, Faculty of Medicine, Universidad Autónoma de Madrid; Madrid, Spain *** Department of Radiology, The University of Texas Medical Branch; Galveston, TX, USA Key words: Alzheimer’s disease, dementia, cognitive decline, neuroimaging Introduction Alzheimer's Disease (AD) is a progressive neurodegenerative disease associated with memory loss and gradual behavioral, functional and cognitive impairment 1 . AD is characterized by a reduction in the number of parietal and temporal cortical neurons and the presence of senile plaques (SP) and neurofibrillar tangles (NFT). To date, a 100% feasible clinical diagno- sis has not been achieved, hence the AD diagno- sis belongs to the anatomopathologic field, and requires the presence of neurofibrillar tangles in the brain 2 . Generally, patients with a clinical diagnosis show extracellular β-amyloid depos- its and intraneuronal neurofibrillar changes 2 . Conventional neuroimaging techniques such as magnetic resonance (MR) or computed tomogra- phy (CT) have played a secondary role in AD di- agnosis: While other causes of memory loss and cognitive deficit can be evaluated by these im- aging methods, AD structural changes are not detected until very late in the course of the dis- ease. Recent and more precise techniques have been developed to detect subtle changes not vis- ualized by imaging methods. Other functional imaging modalities that disclose the physiologic changes occurring in the brain also have the po- tential of identifying early pathologic changes. We present a review of the neuroimaging tech- niques used as a diagnostic aid for AD. Computed Tomography Due to its low sensitivity and specificity for AD diagnosis, CT is mainly used to rule out other causes of dementia, such as vascular dementia, normotensive hydrocephalus, an in- tracranial mass, or when the MR is contrain- dicated. For best data achievement, the scan- ner must be acquired with thin slices parallel to the hippocampal long axis, the helicoidal images allow a coronal reconstruction and a better medial temporal lobe visualization as a result. In AD, enlargement of lateral ventri- cles and subarachnoid space, particularly the temporal horn secondary to atrophy, can be observed (figure 1). Hippocampal density de- crease, secondary to enlargement of choroid and hippocampal fissures, has shown a greater sensitivity (82%) in identifying AD patients or differentiating them from normal control pa- tients 4 . CT is less accurate in detecting early signs of neurodegenerative dementia so that MR is preferred whenever possible.