Ineffective disease control in multiple sclerosis leads to permanent disability, and biomarkers for early detection of inadequate treatment response are needed. The potential of the patlak derived influx constant (Ki) as a biomarker was investigated in fifteen relapsing-remitting multiple sclerosis patients undergoing alemtuzumab treatment. The subjects underwent dynamic contrast enhanced MRI and 3DT1-weighted scans to assess Ki in grey and white matter before and after treatment. The treatment associated change in Ki in grey matter predicted disease activity within two years. Treatment associated changes in Ki may be used as a biomarker of treatment efficacy.