Characterization of white matter lesions in multiple sclerosis and traumatic brain injury as revealed by magnetization transfer contour plots

Abstract

Background and purpose: Magnetization transfer imaging provides information about the structural integrity of macromolecular substances, such as myelin. Our objective was to use this imaging technique and contour plotting to characterize and to define the extent of white matter lesions in multiple sclerosis and traumatic brain injury.

Methods: Magnetization transfer imaging was performed of 30 multiple sclerosis plaques and 10 traumatic white matter lesions. Magnetization transfer ratios (MTRs) were calculated for the lesions, for the normal- or abnormal-appearing surrounding white matter, and for remote normal-appearing white matter. MTR contour plots were constructed about these lesions.

Results: The contour plot appearance of MS plaques differed from that of traumatic white matter lesions. There was a gradual increase in MTR values at points at increasing distances from the center of the MS plaques; this was true for those lesions with and without surrounding T2 signal abnormality (halos). In contrast, there was an abrupt transition in MTR values between traumatic lesions and normal-appearing surrounding white matter. Additionally, the size of the MTR abnormality exceeded the size of the T2 signal abnormality for the MS plaques.

Conclusion: MTR contour plots permit characterization and border definition of white matter lesions. Analysis of the contour plots suggests that MS is a centrifugal process with the lowest MTR within the center of the lesion. In contrast, traumatic white matter injuries are discrete lesions with abrupt transitions between the abnormal lesion and normal brain.

fig 1.

A, Axial T2-weighted (3000/90/1) image in a patient with MS. Right periventricular lesion is poorly defined, with a halo of signal abnormality (arrow). In contrast, left periventricular lesion appears well circumscribed (arrowhead). B, Contour plot applied to magnetization transfer map. Regions in green delineate areas with MTR less than 0.39; those in blue delineate areas with MTR less than 0.35, and those in black depict areas with MTR less than 0.32. This contour map reveals that both periventricular lesions are actually poorly defined, with gradations of surrounding MTR abnormality. The center of the left periventricular lesion appears as a small focus surrounded by a black contour line (arrow). This is surrounded by a blue contour (arrowhead), which in turn is encompassed by a green contour (double arrowheads). In fact, the green contour line surrounds all of the periventricular white matter, confirming a diffuse abnormality of the magnetization transfer parameters of the white matter. C, Magnified view of contour plot applied to an MS plaque reveals fingerlike projections of abnormally low MTR values (arrowheads) extending into the white matter surrounding the lesion.

fig 2.

A, Axial T2-weighted (2500/90/1) image depicts a well-circumscribed nonhemorrhagic lesion in the splenium of the corpus callosum. There is also a small contusion in the right occipital cortex. B, Contour plot applied to magnetization transfer map. Region of MTR abnormality is also shown to be well circumscribed and does not exceed the boundaries of the signal abnormality seen on the T2-weighted image (arrow). Area encircled with green depicts region with MTR less than 0.39 (blue = 0.35; red = 0.32). The MTR associated with normal gray matter is lower than that associated with normal white matter. The blue and green contours seen in the cortex, the basal ganglia, and the thalami do not represent areas of abnormality.