MRSI of the medial temporal lobe at 7 T in explosive blast mild traumatic brain injury.

PURPOSE

Up to 19% of veterans returning from the wars in Iraq and Afghanistan have a history of mild traumatic brain injury with 70% associated with blast exposure. Tragically, 20-50% of this group reports persistent symptoms, including memory loss. Unfortunately, routine clinical imaging is typically normal, making diagnosis and clinical management difficult. The goal of this work was to develop methods to acquire hippocampal MRSI at 7 T and evaluate their sensitivity to detect injury in veterans with mild traumatic brain injury.

METHODS

At 7 T, hippocampal MRSI measurements are limited by: (1) poor B(0) homogeneity; (2) insufficient B(1)(+) strength and homogeneity; and (3) chemical shift dispersion artifacts. To overcofme these limitations we: (1) used third degree B(0) shimming; (2) an inductively decoupled transceiver array with radiofrequency shimming; and (3) a volume localized single slice sequence using radiofrequency shimming-based outer volume suppression.

RESULTS

In 20 controls and 25 veterans with mild traumatic brain injury due to blast exposure with memory impairment, hippocampal N-acetyl aspartate to choline (P < 0.001) and N-acetyl aspartate to creatine (P < 0.001) were decreased in comparison to control subjects.

CONCLUSION

With the appropriate methods robust spectroscopic imaging of the hippocampus can be carried out at 7 T. MRSI at 7 T can detect hippocampal injury in veterans with mild traumatic brain injury.