For the past 10 years it has been believed, but not proved, that trauma and brain injury create, even in mild TBI, disruptions in the brain blood barrier (BBB). The brain blood barrier is a system of tight junctions around any and all blood vessels which enter into the brain or spinal column. This allows the CNS to have its own closed off system of immune response. The brain and spinal cord are aggravated by the presence of blood and so damaged BBB can allow both blood and other large molecules into the CNS where they do not belong. A newly developed type of MRI of the brain, called Dynamic Contrast Enhanced MR, is now available to attempt to quantify the extent of any BBB disruption. It has been shown to be a potentially useful tool to evaluate mild TBI in several recent studies.