Was it a "closed" MRI? Those are usually more accurate than the "open" version -- in other words, were you fully enclosed by the MRI machine?
If there are lesions (which is what I'm assuming you mean by "scar tissue") there, they usually can be seen. The "contrast" will make "active" lesions appear brighter; if you're in the middle of a relapse, or exacerbation, the lesions will appear brighter.
Sometimes, though, two different doctors, looking at the same MRI, will come up with differing views on what they're seeing, if the lesions are small, or not in areas typical for MS. So not having lesions on an MRI does not necessarily mean you don't have...or have...MS. A doctor has to take into account the clinical signs, symptoms, his experience, eliminating everything else that might be causing your symptoms, and then the results of the MRI, before making a diagnosis.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....