Shear Wave Anisotropic Imaging for Pennate Muscle Assessment Using a Tilted Supersonic Push with Elliptical Analytical Inversion

Accurate muscle anisotropy assessment is crucial for understanding muscle mechanics and diagnosing pathologies. Shear wave (SW) elastography struggles with the varying fiber orientations in pennate muscles. Rotating the ultrasound probe offers a solution but is cumbersome in clinical practice. This study presents a tilted supersonic push (TSP) method with elliptical analytical inversion to overcome this limitation. TSP method can generate multi-angle (0°–15°) SWs within a single scan plane, creating an elliptical shear wave velocity (SWV) distribution that enables calculation of fiber-aligned and perpendicular SWVs without probe rotation. The TSP method's accuracy was validated through ex vivo experiments on porcine muscles, and in vivo studies on human gastrocnemius muscles. Results consistently demonstrated accurate SWV measurements, even in the presence of significant pennate angles. For instance, in ex vivo porcine muscles with a 25° pennate angle, TSP corrected longitudinal and transverse SWVs of 3.33 m/s and 2.15 m/s, respectively, consistent with reference values without pennate angle obtained via the traditional rotation method. Similarly, in vivo measurements on human gastrocnemius muscle showed longitudinal and transverse SWVs of 2.55 m/s and 1.21 m/s in a relaxed state, increasing to 4.07 m/s and 1.70 m/s during stretching. These findings highlight the method's ability to capture dynamic changes in muscle stiffness. The TSP method provides a clinically viable and robust approach for comprehensive muscle anisotropy assessment, especially in complex pennate muscles. This technique simplifies the measurement process and offers potential for improved diagnosis and management of musculoskeletal disorders.