Wearable Ultrasound Imaging Device for Dynamic Dual-Direction Shear Wave Elastography of Shoulder Muscle.

The shoulder is the most mobile joint in the human body, thus requiring intricate coordination of adjacent muscles. Patients suffered from rotator cuff muscle Injuries have several typical symptoms include shoulder pain and difficulty raising the arm, thus reducing work efficiency, and compromising the quality of life. Ultrasound has been used widely for shoulder soft tissue imaging as well as ultrasound elastography was introduced in shoulder examination for the dilemma of treating degenerative rotator cuff tears. However, most of ultrasound examination was performed under a static condition. Providing dynamic information from shoulder muscle are important in clinical applications because the pains sometime come from various positions of shoulder during moving. In this study, a customized wearable T-shaped ultrasound transducer (128+128 elements) was proposed for shoulder dual-direction shear wave elastography (DDSWE) which provides the SWE for both longitudinal (SW along the muscle fiber) and transverse (SW cross the muscle fiber) directions dynamically. An optical tracking system was synchronized with ultrasound imaging system to capture shoulder movements in 3-D space with their corresponding ultrasound images. The performance of DDSWE and the accuracy of optical tracking were verified by phantom experiments. Human studies were carried out from volunteers as they are moving their arms. Experimental results shows that the bias and precision for the proposed DDSWE in elastic phantom were about 6% and 1.2 % for both directions, respectively. A high accuracy of optical tracking was observed using 3-D motor stage experimental setup. Human experiments shows that the shear wave velocities (SWVs) were increased with the angles of shoulder abduction, the average transverse and longitudinal SWVs were increase from 2.24 m/s to 3.35 m/s and 2.95 m/s to 5.95 m/s with abduction angle from 0° to 60°, respectively, which they are anisotropic-dependent. All the experimental results indicates that the proposed wearable ultrasound DDSWE can quantify the mechanical properties of shoulder muscles dynamically, thereby may help surgeons and physical therapists determine whether the intensity of rehabilitation shoulder be tuned down or escalated in the future.