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Multiple Sclerosis Role of Contrast-enhanced Magnetic Resonance Imaging in Multiple Sclerosis Àlex Rovira 1 and Cristina Auger 2 1. Head of Neuroradiology Section and Magnetic Resonance Unit, Department of Radiology and Associate Professor of Radiology, Universitat Autònoma de Barcelona, Vall d'Hebron University Hospital; 2. Neuroradiology Clinical Coordinator, MR Unit, Department of Radiology, Vall d'Hebron University Hospital, Barcelona, Spain Abstract Magnetic resonance imaging (MRI) is an important diagnostic tool in different central nervous system (CNS) disorders including brain cancer and cerebrovascular, inflammatory and neurodegenerative diseases. The most commonly used MRI contrast agents are gadolinium-based compounds that have been successfully employed in combination with T1-weighted sequences to detect and monitor focal disease-related abnormalities. These gadolinium-based contrast agents facilitate the visualisation of areas of blood brain barrier disruption, show good performance in diagnostic procedures and present a favourable safety profile. In multiple sclerosis (MS), conventional MRI, including T2-weighted and gadolinium-enhanced T1-weighted sequences, is pivotal to diagnose and to monitor disease activity and progression. Advanced magnetic resonance (MR) techniques and new contrast agents are currently being developed to improve the ability to identify CNS structural and functional abnormalities in MS, which may better correlate with and predict the clinical course of the disease. Keywords Magnetic resonance imaging (MRI), gadolinium-based contrast agents, multiple sclerosis (MS) Disclosure: Àlex Rovira serves on scientific advisory boards for NeuroTEC, Bayer-Schering Pharma and BTG International Ltd. and on the editorial board of the American Journal of Neuroradiology and Neuroradiology. He has received speaker honoraria from Bayer-Schering Pharma, Sanofi-Aventis, Bracco, Merck-Serono, Teva Pharmaceutical Industries Ltd. and Biogen Idec, receives research support from Bayer-Schering Pharma and serves as a consultant for Novartis. Cristina Auger has received speaker honoraria from Merck-Serono and Novartis. Acknowledgement: Editorial assistance was provided by Touch Briefings and funded by Bayer. Received: 3 September 2012 Accepted: 12 September 2012 Citation: European Neurological Review, 2012;7(3):181–8 Correspondence: Àlex Rovira, Magnetic Resonance Unit (IDI), Department of Radiology, Vall d’Hebron University Hospital (Soterrani-1), Passeig Vall d'Hebron 119–129, 08035 Barcelona, Spain. E: alex.rovira@idi-cat.org Support: The publication of this article was funded by Bayer. The views and opinions expressed are those of the authors and not necessarily those of Bayer. Magnetic Resonance Imaging in Multiple Sclerosis Since its introduction to medical practice in the 1980s, magnetic resonance imaging (MRI) has become an indispensable imaging technique. It exploits differences in relaxation times (T1 and T2) between nuclei that have an odd number of nucleons (protons and neutrons) – usually hydrogen protons from water molecules present in bodily tissues. When these nuclei are subjected to a homogeneous magnetic field and stimulated by radiofrequency pulses they return to an equilibrium state at different relaxation rates generating variable resonance signals. Differences between water-containing tissues affect the relaxation rates and allow the generation of an image revealing structural differences within these tissues. Initially used for chemical and physical analyses, it rapidly evolved into a fundamental medical imaging procedure that revealed to be particularly useful in the detection of lesions of the central nervous system (CNS). 1 This high-resolution technique allows detection of focal and diffuse abnormalities in the white and grey matter and has become an established tool in the diagnosis of multiple sclerosis (MS) at clinical centres worldwide. It has also proved valuable in monitoring disease activity and progression, and treatment response in the research setting. 2 © TOUCH BRIEFINGS 2012 Gadolinium-based compounds markedly decrease the T1 relaxation time of adjacent mobile water protons. As a result, after intravenous gadolinium administration, there is a locally increased signal on T1-weighted images from CNS tissues where, normally, there is no blood brain barrier (e.g., the circumventricular organs, meninges and choroid plexus) or where it is abnormally compromised or even absent. This occurs in many types of tumoural, inflammatory and infective lesions. Longitudinal and cross-sectional magnetic resonance (MR) studies have shown that contrast-enhancement occurs in almost all new MS plaques in patients with relapsing-remitting MS (RRMS) or secondary progressive MS (SPMS). This enhancement correlates with altered blood brain barrier permeability in the setting of acute perivascular inflammation, discriminating acute active from chronic inactive lesions (see Figure 1). The gadolinium enhancement varies in size and shape, and usually lasts from a few days to weeks with an average duration of three weeks. New contrast-enhancing lesions are nearly always associated with a hyperintense lesion in the same location on T2-weighted images. The extent of these new T2 lesions usually contract over time (three–five months) and their intensity is reduced as oedema resolves and some tissue repair occurs, leaving 181