We present a method for estimating the shear modulus of tissue using impulsively applied acoustic radiation force with a specific spatial variation in intensity. Using one of several proposed techniques, we phase elements of a linear array to generate a lateral intensity variation of a desired spatial frequency. The temporal frequency of the shear wave generated by this spatially modulated force is directly related to the shear modulus at the pushing location. A Siemens Antares scanner was used to generate the spatially varying pushing beams and track motion in graphite/gelatin phantoms. The phantoms had shear moduli of 1.5 and 5.6kPa as measured with standard mechanical testing methods. Using spatially modulated radiation force with a wavelength of 1mm, we estimated the gelatin phantom shear moduli to be 1.4 and 5.8kPa, within 7% and 4% of the mechanically measured values. Simulated and experimentally measured images of induced vibration frequency and modulus in lesion phantoms are presented.
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