A multi-directional transducer array for muscle shear wave anisotropy estimation

Ultrasound elastography based on shear wave imaging has been widely used in clinical applications. However, the elasticity of anisotropic tissues, such as muscle and tendon, cannot be measured accurately using shear wave imaging because the shear wave velocity (SWV) varies with tissue fiber orientations. Recently, some researchers reported that anisotropic properties of muscles can be estimated by rotating the transducer for shear wave imaging. However, this approach may be difficult for clinical practices because of the relatively long data acquisition time and the misalignment errors associated with mechanical rotation of the array. Although fully sampled 2-D array can accomplish rotation electrically, the high cost and complexity of imaging hardware system can be a concern. Thus, in this work, we designed and fabricated a multi-directional transducer array in order to measure SWV for exploring the anisotropic properties of muscles. This novel star-shape transducer includes a middle element to generate acoustic radiation force for creating shear wave in tissue, and another 32 elements was alignment to form 4-element arrays for detecting the shear waves in 8 different directions (360°) without physically rotating the transducer. With a wide -6 dB bandwidth (50.9%) and high sensitivity from the receiving elements, the array showed a great potential in assessment of tissue anisotropy.