A Row-Column Arraya for Ultrasound-Based Tissue Anisotropy Measurement

Degree of anisotropy (DoA) in mechanical properties is a rapidly emerging biomarker for tissue pathology that has shown to be correlated to fatty infiltration in dystrophic skeletal muscle. DoA can be assessed either using ratio of shear wave velocities (SWV) or using acoustic radio forced impulse (ARFI)-induced peak displacements (PD) measured along versus across the muscle fibers. Whether using SWV or PD as a basis, DoA expressed as the ratio of values requires 90°transducer rotation when a linear array is employed. This large rotation angle is prone to misalignment error. Though fully sampled matrix arrays could enable electronic aperture rotation and reduce misalignment errors, their high fabrication cost and complicated fabrication procedures are challenges. To solve these problems, a custom row-column array is proposed in this paper. The row-column array contains $3\times 64$ elements. The orthogonal pushing beam can be realized by x group pushing beam in which 5 rows on lateral-direction are fired together and the y-pushing beam in which center column in elevational-direction are fired. A custom designed flex circuit was applied to fabricate the array with simpler electrode connection than fully sampled matrix array. The performance of the array is evaluated in Field II simulation and experiment. The output pressure was 0.56 MPa output under a 40 Vpp excitation with similar beam-profile in orthogonal directions. With the capability of rotating the pushing beam electronically, the array has the potential for DoA assessment with reduce misalignment errors.