Modeling of Nonlinear Propagation Effects in Ultrasound Exposimetry

Accurate measurements of ultrasound safety parameters is a constant priority, given the imaging modality’s unprecedented usage and cost-effectiveness. Both research and business institutions are interested in the biological limiting factors of ultrasound resolution and penetration, making ultrasound exposimetry a necessary field of ongoing study. Traditionally, ultrasound parameters have been 36 MICHIGAN ACADEMICIAN measured in water with a derating factor applied to realize the differences in tissue. In recent decades, tissue-mimicking (TM) samples have been used in place of water to gain more accurate data. These samples would, ideally, exhibit the same attenuation, diffraction, and non-linear properties as normal tissue, while at the same time being easy to reproduce and preserve. A new TM material has been constructed which manifests many of these desired qualities— it is the goal of this paper to research how well this TM material corresponds to tissue in the resultant beam profile. Measurements of absolute pressure in the far field are used to extrapolate the important parameters inherent in the TM material. These measurements are carried out using a calibrated, mechanically positioned hydrophone and a focused single-element transducer. The calculated parameters are then compared to computationally expected values for real tissue.