Dynamic MR of Muscle Contraction During Electrical Muscle Stimulation: Potential Application to the Evaluation of Neuromuscular Diseases

Abstract

Thanks to the rapid evolution of therapeutic strategies for muscular and neuromuscular diseases, the identification of quantitative biomarkers for disease identification and monitoring has become crucial. Magnetic resonance imaging (MRI) has been playing an important role by noninvasively assessing structural and functional muscular changes. This exploratory study investigated the potential of dynamic MRI during neuromuscular electrical stimulation (NMES) to detect differences between healthy controls (HCs) and patients with metabolic and myotonic myopathies. The study included 14 HCs and 10 patients with confirmed muscular diseases. All individuals were scanned with 3 T MRI with a protocol that included a multi-echo gradient echo sequence for fat fraction quantification, multi-echo spin-echo for water T2 relaxation time calculation, and 3D phase contrast sequences during NMES. The strain tensor, buildup, and release rates were calculated from velocity datasets. Results showed that strain and strain buildup rate were reduced in the soleus muscle of patients compared to HCs, suggesting these parameters could serve as biomarkers of muscle dysfunction. Notably, there were no significant differences in fat fraction or water T2 measurements between patients and HCs, indicating that the observed changes reflect alterations in muscle contractile properties that are not reflected by structural changes. The findings provide preliminary evidence that dynamic muscle MRI during NMES can detect abnormalities in muscle contraction in patients with myotonia and metabolic myopathies, warranting further research with larger, more homogeneous patient cohorts.

Keywords: dynamic MRI; muscle; neuromuscular diseases; neuromuscular electrical stimulation.

FIGURE 1

Fat fraction (left) and water T2 (right) values for each ROI in patients (P) and healthy volunteers (V). Outliers outside the limits of the plot are represented by an arrow and corresponding values.

FIGURE 2

Strain (left), buildup rate (center), and release rate (right) for each ROI in patients (P) and healthy volunteers (V). Outliers outside the limits of the plot are represented by an arrow and corresponding values.

FIGURE 3

Three‐dimensional visualization of the map of the first strain eigenvector in the soleus muscle of a patient (left) and a healthy volunteer (right). A clear area of activation can be seen (marked by the red arrow) in the volunteer dataset, whereas the strain in the patient is generally lower and less localized.

FIGURE 4

Odds ratios of the considered variables across the three ROIs with 95% confidence interval. An odds ratio of 1 means that an increase in the considered variable has no influence on the likelihood that the subject belongs to the “patient” or “healthy control” group. A higher odds ratio means that an increase in the variable increases the likelihood for the subject to be a patient, and vice versa for odds ratios lower than 1.

FIGURE 5

Plots of the strain vs. the fat fraction (left) and water T2 (right), for all subject types and muscle ROIs. The correlation between the variables is negligible. Outliers outside the limits of the plot are represented by an arrow and corresponding values.