Synthetic MRI Can Be Useful in Calculating Myelin Volume Fraction, MS Study Says

Synthetic magnetic resonance imaging (SyMRI) appears to be a valid option for quantifying myelin fraction in patients with multiple sclerosis (MS), according to a new study that compared the technology with other measurement approaches.

Myelin imaging can be an important clinical tool for tracking the prognosis of patients with MS and evaluating the effectiveness of therapy. But, as a team of investigators from Japan and France note in a study in the journal Cells, accurately assessing myelin can be an exceedingly difficult challenge.

“There is currently no recognized gold standard for myelin estimation, although myelin water fraction is one of the best validated and most commonly used quantitative measurements for noninvasive assessment of myelin content in the brain,” write the investigators, including corresponding author Shigeki Aoki, MD, Phd, of Juntendo University School of Medicine, in Tokyo.

Lately, however, a new technology has emerged that has the potential to improve the situation. SyMRI uses multislice, multiecho, and multidelay acquisition to simultaneously measure longitudinal T1 relaxation rate, transverse T2 relaxation rate, proton density, and local radiofrequency field B1. The latter measurement can help correct location variations in flip angle. The system is able to obtain full head coverage in about 6 minutes, Aoki and colleagues said.

“From these absolute parameters, it is possible to create any contrast-weighted image that is clinically useful, including T1-weighted (T1w) or T2-weighted (T2w) images, using SyMRI software,” the investigators say. “Using the same absolute parameters, SyMRI also allows myelin measurement.”

Knowing that it was feasible to measure myelin using SyMRI, Aoki and colleagues wanted to know whether such a measure was accurate compared to other existing measurement strategies.

To find out, they recruited 37 people with relapsing-remitting MS (RRMS). Sixteen were excluded because they did not have any plaque or only small plaques on the brain or because they had diffuse extensive white matter abnormalities. That left 21 patients included in the study.

The investigators then used 4 techniques to measure the white matter of the patients: SyMRI, magnetization transfer saturation (MTsat), T1-weighted images divided by T2-weighted images (T1w/T2w), and radial diffusivity (RD).

They found the results of SyRMI myelin volume fraction were comparable to the other techniques. “Moreover, it presented better sensitivity for detecting the difference between plaque or periplaque regions and [normal-appearing white matter],” they added, “which warrants further investigation for SyMRI myelin volume fraction to be useful for diagnosis and prognosis evaluation.”

Aoki and colleagues said there is still more research and still other factors to be considered. Each type of imaging has its own advantages and disadvantages.

Also, the authors did not compare SyMRI to myelin water imaging, one of the “best-validated techniques.”

“Further studies comparing SyMRIMVF and myelin water imaging in patients with MS should be conducted to analyze the association between these metrics,” Aoki and colleagues write.

The authors conclude by noting that while subregional analysis showed a weaker, but significant, correlation in myelin estimation, particularly for normal-appearing white matter, normal-appearing why matter SyMRI myelin volume fraction “was significantly associated with disease duration.” SyMRI myelin volume fraction “could therefore yield additional complementary information about microstructural tissue damage in patients with MS.”

Reference

Saccenti L, Hagiwara A, Andica C, et al. Myelin measurement using quantitative magnetic resonance imaging: A correlation study comparing various imaging techniques in patients with multiple sclerosis. Cells. 2020;9(2):393. doi:10.3390/cells9020393.