Method for Correcting the Muscle Fiber Orientation Determined by a T-Shaped Transducer in Ultrasound Shear Wave Elastography

Shear wave elastography (SWE) is a quantitative imaging method that could be used for clinical assessment of musculoskeletal stiffness, particularly in disease diagnosis and rehabilitation evaluation. However, the elastic anisotropy of skeletal muscle leads to uncertainties in shear wave velocity (SWV) measurements in SWE because the SWV varies with muscle fiber orientation. Therefore, many studies have conducted 360° rotational measurements of SWV to determine the elastic anisotropy of muscle; however, the extended data acquisition time of this approach limits its clinical utility. In this study, a T-shaped transducer was used for rapidly measuring the longitudinal and transverse SWVs ( $\textit {SWV}_{L}$ and $\textit {SWV}_{T}$ ) of muscle through an ellipse fitting method to estimate the fiber orientation angle when the excitation is normal to the material axis. The performance of this approach was examined by conducting a homogeneous elastic phantom experiment, which indicated that the proposed T-shaped transducer generated shear waves in three directions by applying a supersonic push at the junction of the transducer. The error between the measured SWVs and ground truth was approximately 6.5%. The proposed T-shaped transducer was also used to measure the SWV in the biceps brachii of four healthy individuals. The $\textit {SWV}_{L}$ and $\textit {SWV}_{T}$ values measured with this transducer were 2.47 and 1.09 m/s, respectively, which were consistent with the SWVs obtained under 360° rotation and in the literature (an error of ~4%). All experimental results were consistent with the results obtained under 360° rotation, which indicates that the proposed method enables the rapid and stable estimation of muscle fiber orientation in SWE.