Background: Chronic T(1) hypointense lesions in multiple sclerosis (MS) are areas of severe tissue destruction. The purpose of this study was to compare total water content (WC),myelin water content (MWC), magnetization transfer ratio (MTR), T(1) relaxation time (T(1)), mean T(2) relaxation time (GMT(2)) between stable MS lesions that are hypointense and isointense on T(1)-weighted images.
Methods: Six MS patients were scanned five times over one year. WC, MWC, MTR, T(1) and GMT(2) were calculated for 15 isointense and 15 hypointense chronically stable T(1) lesions, as well as contralateral normal appearing white matter (NAWM).
Results: All MR measurements from both iso- and hypointense stable lesion types were significantly different from NAWM. WC, T(1) and GMT(2) were significantly higher and MTR significantly lower in hypointense T(1) lesions compared to isointense lesions. MWC was not significantly different between iso- and hypointense lesions.
Conclusions: This work suggests that myelin loss occurs equally in both the chronic isointense and hypointense lesions but hypointense lesions are distinguished by increased extracellular water.