A combined ARFI sequence for 2D displacement imaging and shear wave velocity mapping

As pathological changes are normally accompanied with changes of mechanical properties, tissue elasticity is a potential diagnostic metric for a number of diseases. While elasticity imaging techniques have been successfully applied to delineate different tissues and malignancies based on their relative structural stiffness compared with surrounding tissues, a matched absolute tissue modulus map will provide complimentary and validating information in these relative stiffness images. Acoustic radiation force impulse (ARFI) imaging is a method of imaging the relative stiffness variations inside tissue. By using an impulse acoustic radiation force excitation, ARFI excitation pulses not only generate an on-axis displacement response, but also initiate shear wave propagation away from the region of excitation (ROE), which can be used to estimate the shear wave speed, and thus quantify the shear modulus of tissue. The goal of this study is to design and implement a combined sequence capable of acquiring 2D ARFI images (relative stiffness) and shear wave elasticity images (SWEI) (quantitative method). By utilizing parallel receive tracking techniques and temporal interleaving, the sequences developed herein monitor the on-axis displacements and subsequent lateral shear wave propagation serially without increasing the total number of excitation pulses compared to conventional ARFI imaging sequences.