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This chapter provides an overview of magnetic resonance imaging (MRI) methods. The focus on iron in Parkinson's disease (PD) imaging has remained an important topic and researchers have often utilized T2*, or its reciprocal R2*, in nigral imaging protocols. Some iron-sensitive methods have been recently developed. These include adiabatic T2ρ, magnetization transfer (MT) imaging, and susceptibility-weighted imaging (SWI). The authors have developed a novel rotating frame relaxation experiment called relaxation along a fictitious field (RAFF). There has been greater refinement with the utilization of methods that do not employ a-priori regions of interest (ROIs). One such method is voxel-based morphometry (VBM), in which there is standardization of data and then voxel-by-voxel comparison between group data to determine if there are differences in signal intensity. Diffusion tensor imaging (DTI) provides structural data based on the directionally restrained diffusion of water within fiber tracts.
Double inversion recovery (DIR) is an inversion recovery sequence which applies two consecutive inversion pulses leading to a simultaneous attenuation of the cerebrospinal fluid (CSF) and white matter which improves the contrast between gray and white matter. Quantitative magnetic resonance imaging (MRI) techniques are able to detect and to quantify primary and secondary gray matter abnormalities and provide further insights into disease progression and contribution of these changes to clinical outcome measures. Proton MR spectroscopy (1H-MRS) is frequently used for the evaluation of normal appearing brain tissue in multiple sclerosis (MS). Diffusion tensor imaging (DTI) assesses the random movement of water molecules within the brain tissue. Magnetization transfer (MT) imaging is based on a magnetization interaction between free water protons and protons bound to macromolecular structures. T1- and T2-relaxation time (RT) measurements allow the assessment and quantification of white matter and gray matter damage in various neurodegenerative and neuro-inflammatory diseases.
Structural imaging studies in major depression have identified volume alterations in prefrontal cortex, hippocampus, amygdala, and basal ganglia structures. This chapter reviews structural imaging findings in major depression focusing on magnetic resonance imaging (MRI) methodologies such as volumetric analysis, shape analysis, magnetization transfer (MT), and diffusion tensor imaging (DTI). White matter hyperintensities have been seen in periventricular, deep white matter and subcortical regions in association with major depression. More subtle white matter alterations have been detected with DTI and MT, suggestive of microstructural abnormalities, even in normal-appearing white matter. Another quantification technique measures the average diffusion of water in a voxel and can be expressed as the apparent diffusion coefficient (ADC). Several studies have used DTI to examine microstructural changes in white matter that appears normal using more conventional MRI techniques. The chapter explores the pathological and cognitive correlates, as well as the clinical significance of these structural findings.
This chapter describes brain abnormalities that can be observed on magnetic resonance imaging (MRI) in patients with vascular dementia (VaD). It presents an overview of MRI abnormalities indicative of cerebrovascular disease. Computed tomography (CT) is sufficient to rule out causes of cognitive decline other than VaD or neurodegenerative types of dementia. In addition, infarcts can be observed on CT, and small-vessel disease and atrophy are appreciable to some extent. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoaraiosis (CADASIL) is a hereditary form of VaD, presenting in young patients in the absence of vascular risk factors. On imaging, diffuse white matter hyperintensities involving the U-fibers are characteristically observed, mainly in the temporal, temporopolar, and frontal regions. Quantitative methods such as diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI) provide valuable new ways to assess the integrity of white matter in more detail.
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