JACK SIMON, MD, PhD: MRI has been used for a long time now in the diagnosis of MS to exclude other diagnoses. So that's a differential diagnosis utilization.

But more recently, it's become important in the early diagnosis of MS. For example, a patient presenting with a first clinical attack would now have an MRI to look for characteristic lesions. And if they have a characteristic lesion, then they're certainly more likely to have MS, and we can use this as a predictor of the likelihood of a second attack. Or we can use it now it now to follow for additional lesions, by MRI, that would indicate the patient has MS.

BRIAN APATOFF, MD, PhD: MRI is very helpful in assessing disease activity that's not going to be overtly apparent to either the patient or the clinician. Patients that come in with actual clinical relapses: blurred vision, weak leg are actually going to be having several bouts of disease activity radiographically apparent on MRI, but not really necessarily apparent to the patient or the doctor.

So the MRI is a very helpful way of assessing, as they would call it -- silent disease activity, where you might be having an increasing burden of demyelination which isn't going to necessarily registered by actual relapses.

JACK SIMON, MD, PhD: Turns out that most of the pathology in MS in the brain and spinal cord is subclinical. In other words, events are occurring over time, demyelinating events, events related to axonal injury or transection -- which don't show up clinically. So for example, if you count new lesions by MRI, you may see anywhere from 5 to 10 or sometimes 100 new lesions develop, and yet the patient may have no clinical signs or symptoms that develop. A neurologist may be unaware of the change in findings as well.