A normal 1.5 Tesla MRI will not show the finest damage from a concussion but it can show larger issues. With the prevalence of 3 T MRI's and above, more detail is available. When they combine the information from a non-contrast and with contrast MRI, they can image things that are not imageable otherwise.

A normal MRI differentiates tissue by its water content. The contrast material must have a different magnetic resonance from water.