ABSTRACT
Magnetic resonance imaging is a sensitive tool for measuring various aspects of multiple sclerosis (MS) pathology in vivo. Lesions on T2-weighted and contrast-enhanced T1weighted magnetic resonance imaging (MRI) scans are used routinely as indicators of disease activity for diagnosis and in clinical trials of immunomodulatory agents. However, contrast-enhancing lesions and T2 lesions reflect pathologic processes that are potentially reversible and that indicate variable amounts of tissue injury (see chapters 6 and 8). Furthermore, lesion measurements fluctuate over time and do not account for diffuse pathology in the normal-appearing white matter (NAWM). These factors limit the usefulness of conventional lesion measurements. New MRI measures are sought as more reliable markers of MS disease progression (see chapters 7, 10 and 11). One straightforward approach is the estimation of atrophy of central nervous system (CNS) structures. In contrast to lesions, atrophy reflects the end result of irreversible and severely damaging pathologic processes caused by MS. Axonal damage and loss, chronic demyelination, and gliosis result in a reduction in CNS parenchymal tissue volume and a corresponding expansion of cerebrospinal fluid spaces. These gross morphologic changes can be accurately quantified using standard MRI acquisitions and various computer-aided image analysis approaches, even in the early stage of disease. The recent focus on axonal damage as a significant component of MS pathology and a major cause of progressive disability has led to widespread interest in the measurement of atrophy in MS patients. CNS atrophy is now widely regarded as an objective measure of global disease burden and an indirect measure of disease severity in MS.
