Improved tissue characterization in adrenoleukodystrophy using magnetization transfer imaging.

Abstract

We performed this study to evaluate the usefulness of magnetization transfer (MT) imaging techniques and magnetization transfer ratio (MTR) measurements in assessing patients with adrenoleukodystrophy (ALD). Twelve patients who encompassed the range of ALD phenotypes were evaluated prospectively with MR and MT imaging (including digital subtraction images). The MT images and spin-echo MR images were compared by two staff neuroradiologists and a staff neurologist for extent of disease, different zones of involvement, and the presence of enhancement. MTR measurements were obtained from affected and unaffected regions of the brain. Eight of the 12 patients exhibited gadolinium enhancement. In seven of these patients, the MT subtraction images showed two zones of abnormal signal within the affected white matter. Their MTR measurements were classified as zone 1 (mean MTR, 35%; SD, 6%) and zone 2 (mean MTR, 20%; SD, 6%). Three of the other patients showed a single zone of involvement corresponding to the affected white matter on the standard spin-echo MR images. Their MTR measurements were similar to that of zone 1. The remaining two patients had no demonstrable signal abnormalities on any of the images. We noted no difference in any of the 12 subjects in the extent of white matter involvement on any of the imaging techniques. The MTR measurements in the unaffected white matter (mean MTR, 46%; SD, 5%) approximated established MTRs in white matter of normal volunteers. MT imaging and MTR measurements are helpful clinical techniques that may improve the evaluation of patients with ALD, particularly in the proposed ability of these techniques to divide the affected white matter into different zones that correspond to specific pathologic areas. These techniques can help the understanding of pathogenetic mechanisms and the evaluation of therapies.