Shear modulus imaging by Spatially Modulated Ultrasound Radiation Force

Spatially Modulated Ultrasound Radiation Force (SMURF) uses impulsive acoustic radiation force to generate a shear wave of known spatial frequency in a medium of unknown shear modulus. The velocity of the induced shear wave, and hence the shear modulus of the medium, is determined from the period of the induced shear wave. Here we present the first experimentally obtained images of shear modulus using the SMURF method. Images of spherical (shown below), conical, and step edge phantoms are presented. Agreement within 8% is found between SMURF and unconfined compression measurements of uniform phantoms. Image resolution on the order of the push beam spacing is observed. A key advantage of this method is that tracking is performed along a single a-line, avoiding correlated noise bias errors encountered in multiple-track location methods. We describe the source of this noise. Modulus estimates are obtained without extensive spatial averaging, allowing high resolution to be obtained.