A comparison between 1D and 1.5D arrays for the formation of Spatially Modulated Ultrasound Radiation Force beams

Spatially Modulated Ultrasound Radiation Force (SMURF) imaging is an Elastography technique based on estimating the shear modulus of an elastic material . SMURF determines shear modulus through measurement of the frequency of shear waves of known wavelength propagating in a medium of unknown modulus. Shear modulus is then computed using the relationship G = (¿f)²Â¿. The spatial frequency k of the force variation is equal to the desired spatial frequency of the shear wave, that is, k = 2¿/¿. Because acoustic radiation force used to create the shear waves is proportional to intensity, generation of this spatially varying force is a matter of determining how to generate an equivalently varying ultrasound intensity field. Presented in this study is the Focal Fraunhofer method, which is one of the techniques that can be used to create the desired beam intensity pattern within a region of interest. To create a push that results in discernible displacements while minimizing tissue heating in the near field, we investigate the use of both a linear and a multi-row 1.5D array. A 1.5D array allows for more aggressive focusing in the elevation direction and thus a greater intensity in the region of interest. The efficacy of both configurations is analyzed based on the ability to generate beams of the desired well-defined spatial wavelength at various focal depths, the ability to localize the pushing beam to the region of interest and the ability to maximize the depth-of-field.