Magnetization transfer imaging and proton MR spectroscopy in the evaluation of axonal injury: Correlation with clinical outcome after traumatic braininjury

BACKGROUND AND PURPOSE: Current imaging does not permit quantification of n eural injury after traumatic brain injury (TBI) and therefore limits both t he development of new treatments and the appropriate counseling of patients concerning prognosis. We evaluated the utility of magnetization transfer r atio (MTR) and proton MR spectroscopy in identifying patients with neuronal injury after TBI. METHODS: Thirty patients with TBI (21-77 years old; mean age, 42 years; adm ission Glasgow Coma Scale (GOS) scores 3-15; mean score, 11) were studied o n a 1.5-T system with magnetization transfer imaging and MR spectroscopy of the splenium, Magnetization transfer imaging was also performed in the bra in stem in all patients, and other areas of the brain were sampled in one p atient. The splenium of the corpus callosum and brain stem were studied bec ause these are often affected by diffuse axonal injury. Scans were obtained 2 to 1129 days after injury (median, 41 days). MTR was considered abnormal if it was more than 2 SD below normal. Proton MR spectroscopy was used to calculate the N-acetylaspartate (NAA)/creatine (Cr) ratio, GOS was determin ed at least 3 months after injury. RESULTS: In 10 patients with a GOS of 1 to 4, the mean NAA/Cr was 1.24 =/- 0.28; two of these patients had abnormal MTR in normal-appearing white matt er (NAWM). In 20 patients with a GOS of 5, the mean NAA/Cr was 1.53 +/- 0.3 7 (P <.05); four of these patients had abnormal MTR in NAWM, MTR abnormalit ies in NAWM were Identified in six patients, but these changes did not corr elate with GOS or MR spectroscopy changes. CONCLUSION: MTR and MR spectroscopy can quantify damage after TBI, and NAA levels may be a sensitive indicator of the neuronal damage that results in a worse clinical outcome.