Background and purpose: Conventional MR imaging of multiple sclerosis (MS) provides relatively poor pathologic specificity, which has led to the investigation of more sophisticated MR techniques. The purpose of this study was to combine magnetization transfer (MT) imaging and proton MR spectroscopic imaging (MRSI) to evaluate the specific pathologic features of myelination and neuronal integrity in patients with MS and to determine the relationship between these measures within plaques.
Methods: We acquired conventional MR, MT, and proton MRSI data and evaluated clinical disability in 30 patients with MS, whose conditions were categorized as relapsing-remitting, primary progressive, or secondary progressive. The lesions were classified, using a semiautomated edge-following technique, on T2-weighted MR images, and an analysis of MT and proton MRSI data was conducted for lesion regions as well as for tissue that was categorized as normal.
Results: The MT ratio (MTR) of normal-appearing white matter in the patients with MS was significantly lower than in the healthy participants, whereas gray matter values were unchanged. MS lesions showed a large reduction in MTR, with old lesions exhibiting a lower MTR than new lesions. The average lesion MTR and the MR spectroscopic imaging-measured relative concentration of N-acetylaspartate, a marker of neuronal integrity, was positively correlated in patients with relapsing-remitting MS. This relationship was strengthened in regions containing new lesions.
Conclusion: The integrated use of MT and MR spectroscopic imaging provides a more complete description of the pathologic features of MS than does conventional MR imaging alone, and our data suggest that axonal damage occurs in step with new demyelination and is not a late feature of the disease.