The blood brain barrier is not a membrane, like the meninges (dura, pia, arach, etc) It is the way that molecules are "filtered" by the endothelium before going out of the bloodstream. I would Guess you can use contrast that would normally not cross the barrier to judge its permeability
Thank you for this concise explanation. I feel like every time the term BBB comes up nobody really knows how it works and I've never taken the time to research
