Simply speaking, they are looking for the right size, shape and location.

A more technical description and comparison of demyelinating brain lesions (from the second link below), is:

"MS plaques are hyperintense on T2-weighted and FLAIR images and hypointense on T1-weighted scans. Specific signal intensities of MS lesions will vary depending on the magnetic field strength, the pulse sequence parameters, and partial volume effects. Occasionally, acute plaques may have a thin rim of relative T2 hypointensity or T1 hyperintensity. The T1 hyperintensity is attributed to free radicals, lipid-laden macrophages, and protein accumulations.

MS plaques are usually discrete foci with well-defined margins. Most are small and irregular, but larger lesions can coalesce to form a confluent pattern. Multiple focal periventricular lesions can give a "lumpy-bumpy" appearance to the ventricular margins. As a result of their perivenular distribution, many periventricular plaques have an ovoid configuration, with their long axis oriented transversely on an axial scan. The ovoid lesion is the imaging correlate of "Dawson's finger." In general, MS plaques have a homogeneous texture without evidence of cystic or necrotic components. Hemorrhage is not a feature of MS lesions. Edema and mass effect are also uncommon.

The periventricular white matter is a favorite site for MS plaques, particularly along the lateral aspects of the atria and occipital horns. The corpus callosum, corona radiata, internal capsule, visual pathways, and centrum semiovale are also commonly involved. When more than a few lesions are present, symmetric involvement of the cerebral hemispheres seems to be the rule. Any structures that contain myelin can harbor MS plaques, including the brain stem, spinal cord, subcortical U-fibers, and even within the gray matter of the cerebral cortex and basal ganglia. A distinctive site in the brain stem is the ventrolateral aspect of the pons at the fifth nerve root entry zone."

All three of these links provide more information . . . but it probably suffices to say "size, shape, location":

There are many causes of lesions (which is just a medical term for "damage"), but if you have them, what are they saying yours are from?

Cherie

Cherie