Magnetization transfer ratio histogram analysis of gray matter in relapsing-remitting multiple sclerosis

Abstract

Background and purpose: Gray matter may be affected by multiple sclerosis (MS), a white matter disease. Magnetization transfer ratio (MTR) is a sensitive and quantitative marker for structural abnormalities, and has been used frequently in the imaging of MS. In this study, we evaluated the amount of MTR of gray matter among patients with relapsing-remitting MS and healthy control subjects as well as the correlation between gray matter MTR abnormality and neurologic disability associated with relapsing-remitting MS.

Methods: We obtained fast spin-echo dual-echo and magnetization transfer (with and without MT saturation pulses) images from eighteen patients with relapsing-remitting MS and 18 age-matched healthy control subjects. Gray matter was segmented using a semiautomated system. Gray matter MTR histogram parameters, Kurtzke Expanded Disability Status Scale (EDSS), total T2 lesion volume, and gray matter volumes were obtained for statistical analysis.

Results: A significant difference was found in gray matter MTR between patients with relapsing-remitting MS and healthy subjects (mean and median). Gray matter MTR histogram normalized peak heights in patients inversely correlated with EDSS (r = -0.65, P =.01). There was also an inverse correlation between mean MTR of gray matter and total T2 lesion volume.

Conclusion: The MTR of gray matter significantly differed between patients with relapsing-remitting MS and healthy control subjects, suggesting that MS is a more diffuse disease affecting the whole brain, and neuronal damage accumulates in step with T2 lesion volume. Our finding of the relationship between gray matter MTR and EDSS indicates that measurement of gray matter abnormality may be a potentially useful tool for assessing clinical disability in MS.

fig 1.

Segmentation of gray matter results (right) and corresponding proton density– (left) and T2-weighted (middle) in control subjects (A) and patients (B). Note that the enlargement of the sulci attributable to brain atrophy could be seen on the T2-weighted image (B, middle) in MS patients, which might be due to the volume loss of white matter

fig 2.

The average gray matter MTR histograms between 18 relapsing-remitting MS patients (solid line) and 18 age-matched control subjects (dotted line). Note the whole body of the histogram was shifted to the left in MS patients, although the peak height is similar with healthy individuals

fig 3.

Regression analysis of relative frequency of gray matter MTR mode versus EDSS in relapsing-remitting MS patients. Dots are the relative frequencies of gray matter MTR mode (peak heights) for individual patients on EDSS. The line represents the predictive relative frequency of MTR mode with EDSS as a function. There was an inverse correlation (Spearman rank correlation, r = −0.65) between relative frequency of mode and EDSS

fig 4.

Regression analysis of gray matter MTR mean values versus total T2 lesion volume (mm³) in relapsing-remitting MS patients. Dots are the mean MTR values for individual patients. The line represents the predictive mean MTR with total T2 lesion volume as a function. There was an inverse correlation (Pearson correlation coefficient, r = −0.55) between mean MTR of gray matter and T2 lesion volume