A comparison of magnetization transfer ratio, magnetization transfer rate,and the native relaxation time of water protons related to relapsing-remitting multiple sclerosis

BACKGROUND AND PURPOSE: Magnetization transfer (MT) imaging and measurement s of the magnetization transfer ratio (MTR) have extended our capability to depict and characterize pathologic changes associated with multiple sclero sis (MS). We wanted to investigate whether the analysis of other MT paramet ers, such as magnetization transfer rate (k(for)) and relative measure of w ater content (T1(free)), adds insight into MS-related tissue changes. METHODS: Quantitative MT imaging by use of phase acquisition of composite e choes was performed in nine patients with clinically definite relapsing-rem itting MS and eight healthy control subjects on a 1.5-T MR system. We analy zed a total of 360 regions of interest and compared control white matter wi th various types of lesions and normal-appearing white matter in MS. RESULTS: We found a strong correlation between the MTR and k(for), but this relation was non-linear. A slight but significant reduction of the MTR in normal-appearing white matter of patients with MS was attributable to a red uced transfer rate only, whereas a lower MTR was associated with both a red uction of k(for) and an increase of T1(free) in regions of dirty white matt er. Moreover, areas such as edema and T1-isointense lesions had a similar M TR but could be differentiated on the basis of T1(free). CONCLUSION: Estimates of k(for) and T1(free) appear to complement MTR measu rements for the understanding of MT changes that occur with different types of MS abnormalities in the brain.