Volumetric method for evaluating magnetization transfer ratio of tissue categories: application to areas of white matter signal hyperintensity in the elderly.

An objective technique for analyzing magnetization transfer ratio of segmented tissues was used to evaluate differences between normal-appearing white matter and areas of white matter signal hyperintensity on T2-weighted magnetic resonance images in 23 healthy elderly subjects (mean age, 75 years). Segmented brain images (cerebrospinal fluid, gray matter, white matter, areas of white matter signal hyperintensity) computed from T1- and T2-weighted images were combined with magnetization-transfer-ratio images to produce magnetization-transfer-ratio histograms for each tissue. There was a significant 8.1% reduction in mean magnetization transfer ratio for areas of white matter signal hyperintensity compared with normal-appearing white matter (P < .001). The magnetization transfer ratio for all tissue categories was significantly negatively correlated with age (all, P < .05). This method of measuring magnetization transfer ratio was objective, independent of regional variations, and as reproducible as the segmentation procedure.