Application of sound speed estimation and mapping to multi-layer media and in vivo data

The application of a pulse-echo sound speed estimation technique to multi-layered and biological media is discussed and demonstrated in simulation, phantom, and clinical experiments. The authors have recently described and demonstrated a technique which estimates the mean sound speed in a homogeneous medium. Given a homogeneous medium, the arrival times across a transducer array of ultrasound echoes from a target or region of interest, calculated to include the one-way transit time, are a unique function of sound speed. The sound speed estimator the authors describe analyzes the arrival time information in the RF data recorded on individual elements of an array following a single conventional transmittal. This method uses a single transducer array and has been shown to have accuracy on the order of 0.4% for wire targets in a variety of fluids and 0.5% in an attenuating, speckle-generating phantom medium. This method has potential applications in the correction of beam-forming errors caused by sound speed errors and in the mapping of tissue velocity over range and/or throughout a region of interest. The authors present simulation and phantom experiments demonstrating the ability of this technique to map mean tissue sound speed for simple geometries of multi-layered media. The authors also present in vivo sound speed estimates in the breast and compare these to published values for breast tissues