Is an MRI of brain without contrast sufficient enough to dx. late onset MS, or is contrast needed?

I also had a spinal tap......negative, but I have read that one can still have MS with a negative spinal tap.

My doc said "You do not have MS." How can he say that if these tests are not concrete tests for MS???!!

I wish I could believe him, but how can I?

What is the deciding factor?
Confusion keeps creeping in......