The investigators will image a cohort of persons with relapsing remitting multiple sclerosis (pwRRMS) using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and selective inversion recovery quantitative magnetization transfer imaging (SIR-qMT). pwRRMS will be imaged at baseline and at month-3 and month-12, after starting treatment with natalizumab. Changes in ktrans, a measure of BBB permeability derived from DCE-MRI, and in pool saturation ratio (PSR) a measure of myelin integrity derived from SIR-qMT will be computed to assess the ability of natalizumab to fully restore BBB integrity.~As a corollary aim, the investigators will assess changes in quality of life (QoL) measurements and the relation between those measurements and those derived from the above detailed quantitative MRI methods. QoL will be measured using the Visual Analogue Scale. This questionnaire entails 13 questions regarding the perceived effect of Tysabri, but also level of pain, fatigue, anxiety, depression before and during treatment with natalizumab. The answer to each question is rated on a color-coded bar the range of which is between 0 to 100.
In this study the investigators will assess the ability of Natalizumab, a medication given to treat multiple sclerosis (MS), to restore blood brain barrier integrity and repair subtle leakages of the blood brain barrier (BBB).