Magnetization Transfer Imaging of Diffuse Axonal Injury Following Experimental Brain Injury in the Pig: Characterization by Magnetization Transfer Ratio with Histopathologic Correlation

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Abstract
Our goal was to evaluate the use of the magnetization transfer ratio (MTR) in the detection of diffuse axonal injury (DAI) resulting from traumatic brain injury in a swine model. DAI was created by applying a nonimpact, coronal plane, rotational acceleration to the heads of miniature swine (n = 4). GE imaging was performed with and without off-resonance MT saturation. Histologic correlation of axonal injury with MRI was performed 7 days postinjury. Thirty-one subcortical white matter regions and 10 deep white matter regions were selected for the direct comparison of histologic data and MTR measurements. Nineteen of 41 examined locations exhibited histologic evidence of axonal injury. The mean MTR in regions with axonal damage was significantly less than in regions without axonal damage. These changes were observed both in regions demonstrating high signal intensity on T2-weighted images (T2WI) (p <0.0001, n = 6) and in regions with no signal intensity change on T2WI (p < 0.05, n = 13). These results suggest that the measurement of MTR may have the potential for evaluation axonal damage in DAI following traumatic brain injury even when conventional T2WI does not demonstrate the lesion.