Proton MR spectroscopy provides a method for indicating axonal viability after traumatic brain injury. Proton MRS can readily detect levels of N-acetyl aspartate, a chemical synthesized exclusively in neurons and axons. Diffuse brain injury selectively injures white matter tracts because of the high inertial strain created as a result of rotational acceleration and deceleration. Proton MRS may be beneficial in evaluating traumatic brain injured patients, in vivo, for diffuse injury. This work focused upon determining the spectroscopic profile of the splenium in normal and traumatic brain injured patients. The corpus callosum, especially the splenium, is a vulnerable site for shearing forces producing DAI. The findings from our investigation was that NAA/Cr in the normal splenium is elevated compared to normal lobar white matter. The spectroscopic profile of the splenium is distinct from that of lobar white matter. Examination of thirty five cases of traumatic brain inju ry show a population with a significantly lower NAA/Cr in the splenium compared to normal control subjects. Twenty four of the thirty five cases showed lowered NAA/Cr compared to the mean NAA/Cr found in control subjects. Eleven cases with low NAA/Cr in the splenium had unremarkable or normal MRI examinations. All eleven cases suffered neurotrauma sequelae sufficient to require outpatient rehabilitation treatment. Declines in NAA/Cr of the splenium may be a marker for widespread diffuse injury. A proton MR spectroscopy examination may be of particular use for patients with mild brain injury having unexplained neurologic and cognitive deficits. The depletion of NAA upon neuronal and axonal shearing may be responsible for these deficits. Proton MR spectroscopy may prove a useful tool for determining this type of injury. Future efforts are focused upon utilizing multislice chemical shift imaging (CSI) techniques to examine regional NAA levels.
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