Abstract: Although our study included only a small number of subjects with a variety of disease types, we believe that the fundamental relationship demonstrated between WC and MTR depends more on the underlying pathology than on the disease subtype. Although our study considered only the parameter MTR, it has been considered in several published studies as a specific measure of myelination (1-3). The purpose of our study was to show that MTR can be strongly influenced by tissue constituents other than myelin, and, therefore, it may not be justifiable to use MTR as a surrogate marker for myelin in research studies and clinical trials. Irene M. Vavasour PhD [email protected]*, Cornelia Laule PhD* , David K.B. Li MD*, Anthony L. Traboulsee MD , Alex L. MacKay DPhil* §, * Department of Radiology, University of British Columbia, Vancouver, Canada, Department of Pathology & Laboratory Medicine, University of British Columbia, Vancouver, Canada, Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada, § Department of Medicine (Neurology) and Multiple Sclerosis Clinic, University of British Columbia, Vancouver, Canada.