Functional and Structural MR Imaging in Neuropsychiatric Disorders, Part 1: Imaging Techniques and Their Application in Mild Cognitive Impairment and Alzheimer Disease

Abstract

SUMMARY:During the past decade, the application of advanced MR imaging techniques in neuropsychiatric disorders has seen a rapid increase. Disease-specific alterations in brain function can be assessed by fMRI. Structural GM and WM properties are increasingly investigated by DTI and voxel-based approaches like VBM. These methods provide neurobiologic correlates for brain architecture and function, evaluation tools for therapeutic approaches, and potential early markers for diagnosis. The aim of this review was to provide insight into the principles of functional and structural imaging and to delineate major findings in MCI, AD (Part 1), autism, and schizophrenia (Part 2), which are common psychiatric disorders covering different stages of the life span. Part 2 will conclude by summarizing current applications, limitations, and future prospects in the field of MR imagingϪbased neuroimaging.ABBREVIATIONS ACC ϭ anterior cingulate cortex; AD ϭ Alzheimer disease; ASD ϭ autism spectrum disorders; BOLD ϭ blood oxygen level-dependent; DMN ϭ default mode network; EEG ϭ electroencephalography; FA ϭ fractional anisotropy; GM ϭ gray matter; ICA ϭ independent component analysis; MCI ϭ mild cognitive impairment; MD ϭ mean diffusivity; PCC ϭ posterior cingulate cortex; rsfMRI ϭ resting-state fMRI; VBM ϭ voxel-based morphometry T he past years have seen significant advances in the areas of functional and structural neuroimaging, particularly in their application to the field of neuropsychiatric disorders.MR imagingϪbased methods such as fMRI, DTI, and VBM provide neurobiologic correlates of neuropsychiatric disorders in vivo and potential early markers of disease for improved diagnosis. However, we still need to tune the available neuroimaging markers to provide an individually applicable marker of disease to predict the risk of an asymptomatic or oligosymptomatic subject developing a specific neuropsychiatric disease. This is most relevant for the design and conduction of future primary or secondary prevention trials of neurodegenerative disorders such as AD or genetically determined disorders, the course of which can be dramatically improved through early intervention, such as schizophrenia or ASD. To date the clinical application of MR imaging in neuropsychiatric diseases is mostly limited to the exclusion of macroscopic abnormalities. In this review, we discuss the methodologic basis and the scope and limitations of functional and structural MR imaging techniques and summarize major findings gained by applying these techniques to AD, schizophrenia, and ASD. Brain Function as Assessed by fMRIClassic task-dependent fMRI paradigms use the change in BOLD signal intensity evoked by the performance of a specific task in the scanner. The increase of BOLD signal intensity is an indirect measure of activation of a distinct brain region. 1 rsfMRI is a novel approach in which the patient does not perform a task but lies quietly in the scanner. It allows the detection of functional resting-state connectivity of brain networks. Function...

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