Ek T Tan1, Kenneth C Serrano2, Pravjit Bhatti3, Farhad Pishgar4, Alyssa M Vanderbeek1,5, Carlo J Milani6, Darryl B Sneag1. 1. Department of Radiology and Imaging, Hospital for Special Surgery, New York, 10021, New York, USA. 2. Renaissance School of Medicine at Stony Brook University, Stony Brook, 11794, New York, USA. 3. Georgetown University School of Medicine, Washington, 20007, District of Columbia, USA. 4. Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, 21205, Maryland, USA. 5. Biostatistics Core, Research Administration, Hospital for Special Surgery, New York, 10021, New York, USA. 6. Department of Physiatry, Hospital for Special Surgery, New York, 10021, New York, USA.
Abstract
BACKGROUND: Quantitative MRI (qMRI) metrics reflect microstructural skeletal muscle changes secondary to denervation and may correspond to conventional electromyography (EMG) assessments of motor unit recruitment (MUR) and denervation. HYPOTHESIS: Differences in quantitative T2 , diffusion-based apparent fiber diameter (AFD), and fat fraction (FF) exist between EMG grades, in patients with clinically suspected neuropathy of the brachial plexus. STUDY TYPE: Prospective. POPULATION: A total of 30 subjects (age = 37.5 ± 17.5, 21M/9F) with suspected brachial plexopathy. FIELD STRENGTH/SEQUENCE: 3-Tesla; qMRI using fast spin echo (T2 -mapping), multi-b-valued diffusion-weighted echo planar imaging (for AFD), and dual-echo Dixon gradient echo (FF-mapping) sequences. ASSESSMENT: qMRI values were compared against EMG grades (MUR and denervation). qMRI values (T2 , AFD, and FF) were obtained for five regional shoulder muscles. A 4-point scale was used for MUR/denervation severity. STATISTICAL TESTS: Linear mixed models and least-squares pairwise comparisons were used to evaluate qMRI differences between EMG grades. Predictive accuracy of EMG grades from qMRI was quantified by 10-fold cross-validated logistic models. A P value < 0.05 was considered statistically significant. RESULTS: Mean (95% confidence interval) qMRI for "full" MUR were T2 = 39.40 msec (35.72-43.08 msec), AFD = 78.35 μm (72.52-84.19 μm), and FF = 4.54% (2.11-6.97%). Significant T2 increases (+8.36 to +14.67 msec) and significant AFD decreases (-11.04 to -21.58 μm) were observed with all abnormal MUR grades as compared to "full" MUR. Significant changes in both T2 and AFD were observed with increased denervation (+9.59 to +15.04 msec, -16.25 to -18.66 μm). There were significant differences in FF between some MUR grades (-1.45 to +2.96%), but no significant changes were observed with denervation (P = 0.089-0.662). qMRI prediction of abnormal MUR or denervation was strong (mean accuracy = 0.841 and 0.810, respectively) but moderate at predicting individual grades (accuracy = 0.492 and 0.508, respectively). DATA CONCLUSION: Quantitative T2 and AFD differences were observed between EMG grades in assessing muscle denervation. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 1.
BACKGROUND: Quantitative MRI (qMRI) metrics reflect microstructural skeletal muscle changes secondary to denervation and may correspond to conventional electromyography (EMG) assessments of motor unit recruitment (MUR) and denervation. HYPOTHESIS: Differences in quantitative T2 , diffusion-based apparent fiber diameter (AFD), and fat fraction (FF) exist between EMG grades, in patients with clinically suspected neuropathy of the brachial plexus. STUDY TYPE: Prospective. POPULATION: A total of 30 subjects (age = 37.5 ± 17.5, 21M/9F) with suspected brachial plexopathy. FIELD STRENGTH/SEQUENCE: 3-Tesla; qMRI using fast spin echo (T2 -mapping), multi-b-valued diffusion-weighted echo planar imaging (for AFD), and dual-echo Dixon gradient echo (FF-mapping) sequences. ASSESSMENT: qMRI values were compared against EMG grades (MUR and denervation). qMRI values (T2 , AFD, and FF) were obtained for five regional shoulder muscles. A 4-point scale was used for MUR/denervation severity. STATISTICAL TESTS: Linear mixed models and least-squares pairwise comparisons were used to evaluate qMRI differences between EMG grades. Predictive accuracy of EMG grades from qMRI was quantified by 10-fold cross-validated logistic models. A P value < 0.05 was considered statistically significant. RESULTS: Mean (95% confidence interval) qMRI for "full" MUR were T2 = 39.40 msec (35.72-43.08 msec), AFD = 78.35 μm (72.52-84.19 μm), and FF = 4.54% (2.11-6.97%). Significant T2 increases (+8.36 to +14.67 msec) and significant AFD decreases (-11.04 to -21.58 μm) were observed with all abnormal MUR grades as compared to "full" MUR. Significant changes in both T2 and AFD were observed with increased denervation (+9.59 to +15.04 msec, -16.25 to -18.66 μm). There were significant differences in FF between some MUR grades (-1.45 to +2.96%), but no significant changes were observed with denervation (P = 0.089-0.662). qMRI prediction of abnormal MUR or denervation was strong (mean accuracy = 0.841 and 0.810, respectively) but moderate at predicting individual grades (accuracy = 0.492 and 0.508, respectively). DATA CONCLUSION: Quantitative T2 and AFD differences were observed between EMG grades in assessing muscle denervation. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 1.
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