Myelin Water Imaging of Nerve Recovery in Rehabilitating Stroke Patients

Abstract

Background: Myelin water imaging (MWI) using MRI has been introduced as a method to quantify the integrity of myelin in vivo. However, the investigation of its potential to probe myelin changes has been limited.

Purpose: To determine the myelin change using MWI in the corticospinal tract (CST) during the rehabilitation of stroke patients.

Study type: Longitudinal.

Population: A total of 24 stroke patients within 6 months from the onset (64.3 ± 16.1 years, 14 women, 10 men) and 10 healthy volunteers (27.0 ± 2.2 years, 2 women, 8 men).

Field strength/sequence: Three-dimensional multiecho gradient echo sequence and diffusion-weighted echoplanar imaging sequence at 3 T.

Assessment: The changes of myelin water fraction (MWF) and fractional anisotropy (FA) during rehabilitation were analyzed in the CST and other regions using tractography software and region of interest drawings by the radiologist.

Statistical tests: A paired t-test was performed to investigate the change of MRI metrics during rehabilitation. In addition, an independent two-sample t-test was performed to investigate the effects of different rehabilitation protocols. A P-value <0.05 was considered significant.

Results: In the CST, MWF significantly changed from 5.83 ± 0.91% to 6.23 ± 0.97% after rehabilitation while changes of FA (0.442 ± 0.038 to 0.443 ± 0.035) were not significant (P = 0.656). The rate of change in MWF and FA, which were 6.69% and 0.439% respectively, were significantly different. Other regions did not show significant changes (range of MWF change: -3.44% to -1.61%, range of FA change: -1.39% to 0.79%, and range of P-value: 0.144-0.761). Further analysis showed that those with additional robot-assisted rehabilitation had a significantly larger MWF change than those with conventional rehabilitation only (rate of change: 11.2% vs. 3.2%).

Data conclusion: The feasibility of using MWI to monitor myelin content was demonstrated by showing the MWF changes during rehabilitation.

Level of evidence: 2 TECHNICAL EFFICACY STAGE: 2.

Keywords: brain plasticity; corticospinal tract; myelin water imaging; rehabilitation; stroke.