Application of delayed contrast extravasation MRI for depicting subtle blood-brain barrier disruption in a traumatic brain injury model

The blood-brain barrier (BBB) is composed of brain microvasculature that provides selective transport of solutes from the systemic circulation into the central nervous system to protect the brain and spinal microenvironment. Damage to the BBB in the acute phase following traumatic brain injury (TBI) is recognized as a major underlying mechanism leading to secondary long-term damage. However, due to the lack of technological ability to detect subtle BBB disruption (BBBd) in the chronic phase, the presence of chronic BBBd is disputable. Thus, the dynamics and course of long-term BBBd post-TBI remains elusive.30 C57BL/6 male mice subjected to TBI using our weight drop closed head injury model and 19 naïve controls were scanned by MRI up to 540 days following injury. BBB maps were calculated from delayed contrast extravasation MRI (DCM) with high spatial resolution and high sensitivity to subtle BBBd, enabling depiction and quantification of BBB permeability. At each time point 2-6 animals were sacrificed and their brains were extracted, sectioned, and stained for BBB biomarkers including: blood microvessel coverage by astrocyte using GFAP, AQP4, ZO-1 gaps and IgG leakage.we found that DCM provided depiction of subtle yet significant BBBd up to 1.5 years following TBI, with significantly higher sensitivity than standard contrast-enhanced T1-weighted and T2-weighted MRI (BBBd volumes main effect DCM/T1/T2 p<0.0001 F(2,70)=107.3, time point p<0.0001 F(2,133, 18.66)=23.53). In 33% of the cases, both in the acute and chronic stages, there was no detectable enhancement on standard T1-MRI, nor detectable hyper-intensities on T2-MRI, whereas DCM showed significant BBBd volumes. BBBd values of TBI mice at the chronic stage were fonud significantly higher compered to age matched naïve animals at 30,60 and 540 days. The calculated BBB maps were histologically validated by determining significant correlation between the calculated levels of disruption and a diverse set of histopathological parameters obtained from different brain regions, presenting different components of the BBB.Cumulative evidence from recent years points to BBBd as a central component of the pathophysiology of TBI. Therefore, it is expected that routine use of highly sensitive non-invasive techniques to measure BBBd, such as DCM with advanced analysis methods, may enhance our understanding of the changes in BBB function following TBI. Application of the DCM technology to other CNS disorders, as well as to normal aging, may shed light on the involvement of chronic subtle BBBd in these conditions.