The brain MRI is the most sensitive test for detecting structural evidence of MS-related disease activity. The MRI scan can also discriminate new or old lesions, and thus provides a measure of disease activity. Each column contains three identical MRI slices obtained the same day with different image sequences. The three sets of images were made one month apart. In the third month, the gadolinium enhancement has almost disappeared, but the T2-weighted hyperintensity indicative of an MS plaque persists.
Evoked responses are changes in electrical conductivity in the central nervous system.
These responses can be evoked by stimulating a nerve and measuring the brain's response to the stimulation. The response is measured by electrodes applied to the scalp. Visual evoked responses are obtained by stimulating the eye with a checkerboard pattern of light that is projected on a television monitor. Brain stem auditory evoked responses are produced by clicking noises applied through earphones. Somatosensory responses are evoked by electrically stimulating nerves in the hands or feet.