<qa>  What is the correlation between in vivo and postmortem measures?Outcome measures include data derived from magnetic resonance imaging MRI of the brain and spinal cord, optical coherence tomography OCT of the retinas, clinical examination, and disability scales; radiological and pathological examination of CNS tissue; and the correlation between in vivo and postmortem measures. Particular attention will be paid to the extent to which longitudinal in vivo changes predict postmortem findings. 