FIG. 2.

Normalized histograms of T₁ (top) and T₂ (bottom) relaxation rates demonstrate the overlap of the MR characteristics of leukoencephalopathy and those of normal tissues in an image from a single patient. In general, both relaxation rates are lower for white matter than for gray matter; the relaxation rate of deep gray structures (i.e., putamen, caudate, and thalamus) is lower than that of cortical gray matter but higher than those of white matter. The T₁ relaxation rates of leukoencephalopathic tissue (bold line) lies directly between and completely overlaps those of white matter and deep gray matter. As would be expected, the T₂ relaxation rate of leukoencephalopathic tissue is, on average, higher than those of cortical gray matter and white matter.