Shear wave elasticity imaging (SWEI) usually assumes an isotropic material; however skeletal muscle is typically modeled as a transversely isotropic material with independent shear wave speeds in the directions along and across the muscle fibers. To capture these direction-dependent properties we implemented a rotational 3D-SWEI system which measures the shear wave speed both along and across the fibers in a single 3D-acquisition with automatic detection of the muscle fiber orientation. Herein we tested and examined the repeatability of this system's measurements in the vastus lateralis of 10 healthy volunteers. The average coefficient of variation of the measurements from this 3D-SWEI system was 5.3% along the fibers and 8.1% across the fibers. When compared to estimated respective 2D-SWEI values of 16.0% and 83.4% these results suggest using 3D-SWEI has potential to improve the precision of SWEI measurements in muscle. Additionally we observed no significant difference in shear wave speed between the dominant and non-dominant legs along (p=0.26) or across (p=0.65) the muscle fibers.
