Magnetic resonance imaging (MRI) is considered the best test to help diagnose multiple sclerosis (MS). However, 5% of people with MS do not have abnormalities detected on MRI; thus, a "negative" scan does not completely rule out MS. In addition, some common changes of aging may look like MS on a MRI. Although they aren't widely needed, people with MS may get repeat scans to determine the status of their disease and how well their medications are working.