Modeling, Evaluation, and In Vivo Estimation of Muscle Cell Diameter With the Random Permeable Barrier Model:...

Area of Science:

• Biophysics
• Muscle Physiology
• Medical Imaging

Background:

• The random permeable barrier model (RPBM) analyzes water diffusion in muscle tissue to assess microstructure.
• Limited research exists on RPBM fitting stability, limitations, and its relationship with conventional diffusion tensor imaging (DTI) metrics and functional outcomes.

Purpose of the Study:

• To comprehensively evaluate the RPBM's forward and inverse behavior through simulations and model fitting.
• To quantify muscle cell diameters in healthy adults and investigate relationships between RPBM-derived parameters, DTI metrics, subject characteristics, and muscle function.

Main Methods:

• Simulations were used to analyze RPBM forward behavior.
• Model fitting was employed to assess inverse behavior and parameter stability.
• Muscle cell diameters were quantified across six muscle groups in 100 healthy adults.

Main Results:

• Simulations revealed that stable RPBM estimates for cell diameter and membrane permeability require constrained parameters, particularly $\tau$ and a fixed $D_0$ (0.9 axial diffusivity).
• In vivo, significant differences in muscle cell diameter were observed across muscle groups, with men consistently having larger diameters than women.
• No significant correlation was found between peak torque and muscle cell diameter or membrane permeability.

Conclusions:

• The RPBM is a valuable tool for assessing muscle microstructure, complementing DTI metrics.
• Careful consideration of modeling limitations is crucial for accurate RPBM application in muscle health studies.
• Sex is a significant determinant of muscle cell diameter, independent of anthropometric factors.