Radiology: 7T MRI sheds new light on MS lesions

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Combined analysis of 7T R2* and phase data could improve characterization of multiple sclerosis (MS) lesions, according to a study published in the January issue of Radiology.

Previous research revealed strong contrast in magnitude and phase images of susceptibility- (or T2*) weighted MR studies. The current study was designed to clarify the mechanism of contrast for MS lesions at susceptibility-weighted exams, and also to assess via histologic analysis the role of iron and myelin in generating this contrast, according to Bing Yao, PhD, of the advanced MRI section at the National Institutes of Health in Bethesda, Md., and colleagues.

The study population was comprised of 12 men and 12 women with MS who underwent 7T MR and physical exam between January 2009 and December 2010.

After acquisition, images were reconstructed using a phase-sensitive noise-weighted channel combination and quantitative R2* and phase maps were generated. Lesions were identified and characterized according to five categories: hypointense, hyperintense, hypointense-rim, hyperintense-rim and isotense, according to the research team.

The study also included a postmortem analysis of the brain of a 70-year-old MS patient, which was analyzed at 7T MR and stained for myelin and ferritin.

Because of image artifacts, the researchers excluded three patients from the MR analysis. Of the remaining 21 patients, “[both] magnitude and phase images showed a varied appearance of MS lesions within and across patients,” wrote Yao and colleagues.

The R2* and phase data showed lesion details not visible with conventional MR exams. They revealed lesions with and without rim contrast, a phenomenon also demonstrated in the postmortem analysis. “The correlation between MR images and the iron and myelin stain suggests that the varying MR imaging phase and R2* contrast is due to varying levels of iron and myelin,” wrote Yao et al. Both analyses showed that regions with substantial R2* reduction had normal phase, which led to the observation that myelin and iron likely had different effects on R2* and phase contrasts.

Yao and colleagues concluded that the combination of both R2* and phase data could allow researchers to distinguish between changes in tissue myelin and iron associated with MS, which “combined with the increased spatial resolution and contrast available with high-field-strength MRI, may provide great help in characterizing the disease process underlying MS lesions.”