Quantitative T2-mapping magnetic resonance imaging for assessment of muscle motor unit recruitment patterns

Introduction In this study, we aimed to determine whether muscle transverse relaxation time (T-2) magnetic resonance (MR) mapping results correlate with motor unit loss, as defined by motor unit recruitment patterns on electromyography (EMG). Methods EMG and 3-Tesla MRI exams were acquired no more than 31 days apart in subjects referred for peripheral nerve MRI. Two musculoskeletal radiologists qualitatively graded T-2-weighted, fat-suppressed sequences for severity of muscle edema-like patterns and manually placed regions of interest within muscles to obtain T-2 values from T-2-mapping sequences. Concordance was calculated between qualitative and quantitative MR grades and EMG recruitment categories (none, discrete, decreased) as well as interobserver agreement for both MR grades. Results Thirty-four muscles (21 abnormal, 13 control) were assessed in 13 subjects (5 females and 8 males; mean age, 46 years) with 14 EMG-MRI pairs. T-2-relaxation times were significantly (P < .001) increased in all EMG recruitment categories compared with control muscles. T-2 differences were not significant between EMG grades of motor unit recruitment (P = .151-.702). T-2 and EMG score concordance was acceptable (Harrell & apos;s concordance index [c index]: rater A, 0.71; 95% confidence interval [CI], 0.51-0.87; rater B, 0.77; 95% CI, 0.57-0.91). Qualitative MRI and EMG score concordance was poor to acceptable (c index: rater A, 0.60; 95% CI, 0.50-0.79; rater B, 0.72; 95% CI, 0.55-0.89). T-2 values had moderate-to-substantial ability to distinguish between absent vs incomplete (ie, decreased or discrete) motor unit recruitment (c index: rater A, 0.78; 95% CI, 0.50-1.00; rater B, 0.86; 95% CI, 0.57-1.00). Discussion Quantitative T-2 MR muscle mapping is a promising tool for noninvasive evaluation of the degree of motor unit recruitment loss.