Quantification of Volumetric Changes of Brain in Neurodegenerative Diseases Using Magnetic Resonance Imaging and Stereology

Abstract

In this chapter, we review the different magnetic resonance imaging (MRI)-based methods used to quantify whole and subcortical brain structures volume, and discuss the relevance of the brain atrophy in different neurodegenerative disseases. Although there are a lot of studies for multiple sclerosis (MS) and dementia of Alzheimer’s type (AD) for the brain atrophy using different methods, the optimal method for quantifying atrophy has not been established to date. In recent years, computed tomography (CT) scanning has been replaced with MRI scanning due to its enhanced soft-tissue resolution, especially for cerebrospinal fluid (CSF)-filled spaces, such as ventricular enlargement in patients with AD. Thus, a transition has occurred from CT to MRI in longitudinal studies investigating the human brain. As a result of development of new neuroimaging methods in clinical practice, volumetric methods started to be more sophisticated depending on various imaging methods (Lim et al., 2000). There are numerous reasons for the aforementioned transition; first of all, unlike CT, MRI has no inherent radiation effect, and secondly, CT underestimates cortical sulcal volume relative to MRI due to poorer resolution and spectral shift artifact on CT (Lim et al., 2000). Due to higher contrast resolution, MRI can better characterize the brain morphology including the size, tissue composition such as gray (or grey) matter and white matter, and shape of different cortical or subcortical neuroanatomic structures (Lim et al., 2000). Nowadays, it is possible to use MRI to visualize and quantify the directional coherence of white matter fibers, called diffusion tensor imaging (DTI), for investigation of connectivity and disconnectivity between different brain regions (Basser et al., 1994). Additionally, MRI equipments are also used to provide functional brain responses with functional MRI (fMRI) and perfusion MRI as in some nuclear medicine neuroimaging methods such as positron emission tomography (PET) and single photon emission computed tomography (SPECT). These methods can provide pathognomonic data of certain structural lesions in AD, as they can demonstrate neuronal activity or receptor characteristics (Small, 2002). High field MRI