Abstract:
A novel methodology for quantifying three-dimensional (3D) volumetric strain distribution within human skeletal muscle, specifically the tibialis anterior (TA), is introduced using cine Phase Contrast (CPC) MRI during passive ankle tension. Intramuscular pressure (IMP), a significant correlate of muscle tension, is known to exhibit non-uniform distribution within muscle, influenced by factors such as muscle geometry, size, architecture, and boundary conditions. Understanding this non-uniformity is crucial for clinical applications, and 3D volumetric strain, as a measure of tissue deformation and changes in fluid mass to volume ratio, is hypothesized to be a strong correlate of IMP. The presented method involves generating a 3D hexahedral mesh of the TA from T2-weighted MRI images and tracking node trajectories using CPC data as the ankle is passively rotated between 0 and 26 degrees of plantarflexion. The volumetric strain of each element within the mesh is then quantified. The accuracy and precision of this biomechanical measurement technique were rigorously assessed through three validation tests. These tests included quantifying leg position drift (mean RMS error of 1.5±0.7 mm), assessing surface node trajectory accuracy by comparing the deformed mesh to segmented TA at plantarflexion (mean RMS error of 0.6±0.2 mm), and determining between-day variability of volumetric strain (median of 0.06 mm³/mm³). The results demonstrated excellent accuracy and precision, suggesting the validity of the final deformed mesh and the potential for this method to identify regional differences in volumetric strain within individual muscles. This foundational work establishes a critical link between muscle strain and IMP, bridging a gap in current clinical assessment methods and advancing the understanding and modeling of muscle mechanics in vivo.
