Imaging in multiple sclerosis

Multiple sclerosis (MS) is a common central nervous system (CNS) disease characterised pathologically by the development of multifocal inflammatory demyelinating white matter lesions. Magnetic resonance imaging (MRI) is the gold standard imaging technique for the identification of demyelinating lesions which can be used to support a clinical diagnosis of MS, and MS can now be diagnosed in some patients after a clinically isolated syndrome (CIS) using new MRI diagnostic criteria. Clinical trials of disease modifying treatments include MRI outcome measures of disease activity. The use of MR techniques to study the evolution of MS pathology in vivo is an important tool for obtaining better insights into pathophysiological mechanisms underlying the clinical course. This article will concentrate on the practical application of MRI in the management of MS. MR images are said to have contrast if there are differing areas of signal intensity. The contrast can be controlled to a certain extent by the parameters used and can produce images which contain differing levels of contrast depending on tissue content. For example, fat and water produce different image contrast. Images can be weighted towards particular contrast mechanisms. In T1 weighted images, fat is bright and cerebrospinal fluid (CSF) is dark; with T2 weighting, fat is dark and CSF is bright. Proton density (PD) weighting produces image contrast on the basis of the PD of the tissue. Such weighting of images has been exploited to identify inflammatory demyelinating lesions at different stages in their evolution.1 ### T2 and PD weighted imaging T2 weighted imaging identifies MS lesions as high signal foci against the low signal background of white matter. However, periventricular lesions are often indistinguishable from the adjacent CSF which is also of high signal with T2 weighting. Contrast from the lesion can be improved here by using PD weighting because of the lower CSF signal with …