In vivo measurements of the cerebral vascular compliance may have a significant impact on our ability to characterize and quantify changes that occur in the brain following an insult. In particular, these measurements may become important in the diagnosis of Mild Traumatic Brain Injury (MTBI).
MTBI, or post-concussive syndrome, is a significant epidemiological problem. In 1995, more than 1.74 million people in the U.S. alone experienced a mild TBI that resulted in a physician visit or temporary disability of at least 1 day. Many MTBI patients suffer long-term cognitive dysfunction, such as memory and thinking problems, headaches, depression, and anxiety. Histological studies with scanning electron microscopy (SEM) in animal models of MTBI have documented diffuse morphological changes in the wall of cerebral micro vessels following MTBI. However, current state of the art anatomical imaging with Magnetic Resonance Imaging (MRI) or Computerized X-ray Tomography (CT) is lacking in spatial resolution and sensitivity needed to depict these changes. Unlike static anatomical imaging, dynamic MRI of the cerebral blood flow may provide an indirect evidence for the occurrence of these morphological changes through their affect on the overall cerebral vascular compliance.
The proposed project aims to test the hypothesis that morphological changes occurring in the cerebral microvasculature of humans who had experienced MTBI will result with decreased mechanical compliance of the cerebral vasculature. The morphological changes, which include increase in the number of microvilla and thickening of the endothelial cell membrane mainly in the arterioles, capillaries, and venules, will reduce the elasticity of these vessels and therefore reducing the overall cerebral vasculature. Reduced vascular compliance, in turn, will result in altered pulsatile blood flow dynamics compared to flow dynamics in subjects with normal cerebral compliance.
A group of 20 subjects who had experienced MTBI with a persistence of cognitive dysfunction documented by neuropsychological assessment and an age-matched control group will undergo an MRI study. The study protocol includes anatomical imaging with T2-weighted MRI scan, functional imaging with single shot echo-planer scans for mapping brain activation during a simple motor task (finger tapping), and dynamic imaging of the arterial and venous blood flow pulsatility during the cardiac cycle with a motion-sensitive cine phase-contrast MRI technique. Cerebral compliance is derived from the relationship of the flow dynamics (pulsatility) of the total arterial inflow and venous outflow into and from the brain, e.g., the input and output of the cerebral vasculature. A statistically significant difference between compliance values measured in these two groups will confirm the hypothesis.