Multiple sclerosis: Magnetization transfer MR imaging of white matter before lesion appearance on T2-weighted images

PURPOSE: To determine the evolution of magnetization transfer (MT) in white matter regions before and after plaque development in patients with multip le sclerosis (MS). MATERIALS AND METHODS: In a 5-year longitudinal evaluation, 30 patients wit h MS underwent conventional magnetic resonance (MR) imaging, MT MR imaging, and clinical assessment. Cross-sectional data in 12 healthy subjects were also collected. Semiautomated lesion classification with use of T2-weighted MR images was used to measure the time course of the MT ratio (calculated with MR data acquired without and with MT saturation) in every voxel and to help analyze the relationship with the status of lesions depicted on T2-we ighted images. RESULTS: There was a significant (P < .001) temporal decline in lesion MT r atio after lesion appearance on T2-weighted images. A significant (P < .001 ) progressive decline in MT ratio was also present in voxels that later bec ame lesions, prior to initial detection on T2-weighted images. Even 11/2 ye ars prior to lesion appearance, the MT ratio (33.3%) in regions destined to become such lesions was significantly (P < .001) lower than that in both w hite matter in healthy subjects (41.3%) and other normal-appearing white ma tter in patients with MS (38.1%). CONCLUSION: The MT ratio reveals progressive focal abnormalities in MS that antedate by up to 2 years the appearance of lesions on T2-weighted MR imag es.