CHARACTERIZATION OF MULTIPLE-SCLEROSIS PLAQUES WITH T1-WEIGHTED MR AND QUANTITATIVE MAGNETIZATION-TRANSFER

PURPOSE: To investigate the relationship between the appearance of mul tiple sclerosis lesions identified on unenhanced T1-weighted images an d their corresponding magnetization transfer ratios. METHODS: A total of 119 white matter lesions seen on T2-weighted images in 17 patients with multiple sclerosis were evaluated. Axial T1-weighted images were used to classify the lesions as isointense to white matter (10 lesions ), hypointense to white matter but hyperintense to gray matter (44 les ions), hypointense to gray matter (59 lesions), and relatively isointe nse to cerebrospinal fluid (6 lesions). The magnetization transfer rat io of each lesion was calculated, and an average magnetization transfe r ratio for each subcategory was determined. RESULTS: The magnetizatio n transfer ratio values became progressively lower with increasing hyp ointensity of lesions on T1-weighted images. The average magnetization transfer ratio for lesions isointense to white matter, hypointense to white matter but hyperintense to gray matter, hypointense to gray mat ter, and relatively isointense to cerebrospinal fluid was 34.90 +/- 2. 67 (mean +/- SD), 30.93 +/- 3.57, 27.27 +/- 3.56, and 23.62 +/- 2.83, respectively. All groups were significantly different from each other. CONCLUSION: Lesions isointense to white matter exhibited higher magne tization transfer ratio values than lesions that were hypointense. The se findings are consistent with relative preservation of the myelin st ructure in the former, perhaps indicating that these lesions are predo minantly inflammatory (edematous) in nature. The proportionately lower magnetization transfer ratio values of lesions that appear progressiv ely more hypointense on T1-weighted images may reflect varying degrees of demyelination, with increasing lesion hypointensity corresponding to more breakdown in the macromolecular structure. These results sugge st that T1-weighted images may be useful in characterizing the underly ing pathologic substrate in multiple sclerosis plaques.