The evolution of multiple sclerosis lesions on serial MR

PURPOSE: To characterize temporal changes in signal intensity patterns of multiple sclerosis lesions on serial MR. METHODS: T1-, T2-, proton density-, and contrast-enhanced T1-weighted MR was performed on five patients with relapsing-remitting multiple sclerosis at least 22 times in the course of 1 year. RESULTS: Forty-three enhancing lesions and 1 new lesion that never showed enhancement were detected and followed for periods ranging from approximately 4 weeks to 1 year (total of 702 time points). At first detection the center of new lesions was brighter than the periphery (20 of 24 new lesions on proton density-weighted and 19 of 23 new lesions on contrast-enhanced images). On contrast-enhanced images, ring hyperintensity was predominant at time points later than 29 days. As lesions aged, a residual rim of "nonenhancing" hyperintensity often was noted on contrast-enhanced images. Some older lesions (> 1 year) showed similar appearance on unenhanced T1-weighted images. On proton density-weighted images ring hyperintensity was most frequent 2 to 4 months after lesion detection. The estimated average duration of gadopentetate dimeglumine enhancement was 1 to 2 months. CONCLUSIONS: A lesion evolution pattern relevant to MR was inferred. We believe that specific information about the histopathologic evolution of a lesion may be extracted not only from contrast-enhanced but also from nonenhanced serial MR. Assessment of drugs targeting specific phases of lesion evolution could benefit from quantitative pattern analysis of routine MR images.