Time-resolved 3D imaging and strain analysis of the skeletal muscle

Purpose: To develop and validate a method for time-resolved 3D imaging and strain analysis that enables quantification of dynamic in vivo muscle deformations from aperiodic continuous motion. Theory and Methods: Controlled deformations were induced in the thigh muscles of eight healthy volunteers using a pneumatic pressure cuff, both under passive conditions and during isometric muscle contractions. An iterative reconstruction approach based on the Spectro-Dynamic MRI framework was formulated for joint reconstruction of time-resolved 3D images and velocity fields from highly undersampled k-space data at 1.4 Hz. The accuracy of the results was evaluated against fully sampled images, acquired under static conditions with similar deformations. Octahedral shear strain (OSS) values were computed from the estimated motion fields. Mean OSS values were calculated for all thigh muscles, and differences in the mean OSS values between passive and isometric contraction conditions were assessed. Results: The reconstructed time-resolved images closely matched the fully sampled validation images and the estimated motion fields accurately captured the deformations. Isometric muscle contraction resulted in reduced displacements and lower mean OSS values compared with the passive condition. The largest reduction in mean OSS value was consistently observed in the hamstring muscles, which become stiffer during isometric knee flexion. Conclusion: Our proposed reconstruction approach enables robust time-resolved 3D strain estimates in muscles using data from a single motion repetition. This method provides new opportunities for investigating the temporal evolution of in vivo displacements and strains in a dynamic setting.

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