Magnetization Transfer Imaging of Spinal Cord Trauma after Whiplash Injury

Hoggarth, Mark Andrew

doi:https://doi.org/10.21985/n2-kkse-y049

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Magnetization Transfer Imaging of Spinal Cord Trauma after Whiplash Injury

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The mechanism underlying chronic pain and disability in those with chronic whiplash associated disorders (WAD) is poorly understood. Of the four million people who will seek medical care each year for neck injuries sustained during a motor vehicle collision (MVC), a quarter will develop chronic moderate to severe WAD. Disparate signs and symptoms, including changes in muscle composition, along with widespread hypersensitivity, and motor and sensory disturbances, all feature in those with WAD. The work described in this dissertation centers on an MRI technique, magnetization transfer (MT) imaging, that characterizes subtle changes in neural substrate, and may help identify spinal cord lesions in those with poor recovery. MT ratio (MTR) analysis is a technique that indirectly measures bound macromolecular water and has been shown to be sensitive to white matter demyelination in survivors of spinal cord injury. The initial aim of my work observed increased heterogeneity in regional MTR of those with long standing WAD that was not present in those who recover from an MVC. The magnetization transfer ratio homogeneity (MTRh) index was created to quantify this observation. I then characterized the repeatability and reliability of MTRh methods in a larger cohort of subjects exposed to an MVC, utilizing the spinal cord toolbox (SCT) software package for tract-specific analyses. Group differences were not observed in MTRh measures taken 9 months apart and no systematic bias was found, however subject-level repeatability was moderate for MTRh measures and poor for MTR. MTRh was then utilized for group-level comparisons between a cohort of participants electing recovery, mild continuing symptoms, or moderate to severe pain and disability using the Neck Disability Index, one year after an MVC. Significantly greater heterogeneity was found in the spinal cord white matter of those with moderate to severe WAD when compared to the other groups. Furthermore, these findings were driven by female participants, supporting widely reported clinical observations of worse outcome for females compared to males. Taken as a whole, the results from this dissertation support the need for further imaging workup in a select number of people with WAD who present with complex signs and symptoms that are otherwise unexplained. For those suffering, a diagnosis of a neural insult could lead to increased treatment options, improved prognosis, and better clinical outcome.

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