Udkas is right. Contrast, while desirable, isn't crucial. Much more important is the strength of the magnet (1.5 T minimum, 3T preferable), and that the MS protocol is used. That means intervals of 3 mm between images, so as not to miss tiny lesions (if at all possible).
Also important is the software used in conjunction with the magnet. If it is good, then an MRI done without contrast, using MS protocol, should show what's going on in the brain's white matter.