Holographic reconstruction of therapeutic ultrasound sources.

Abstract

Clinical therapeutic ultrasound systems rely on the delivery of known acoustic pressures to treatment sites. Assessing the safety and efficacy of these systems relies upon characterization of ultrasound sources in order to determine the acoustic fields they produce and to understand performance changes over time. While direct hydrophone measurements of intense acoustic fields are possible, data acquisition throughout a treatment volume can be time‐consuming and is only applicable to the specific source conditions tested. Moreover, measuring intense acoustic fields poses challenges for the hydrophone. An alternate approach combines low‐amplitude pressure measurements with modeling of the nonlinear pressure field at various transducer power levels. In this work, low‐intensity measurements were acquired for several therapeutic transducers. Pressure amplitude and phase were measured on a plane near the test transducer; the Rayleigh integral was used to back‐propagate the acoustic field and mathematically reconstruct relative vibrations of the transducer surface. Such holographic reconstructions identified the vibratory characteristics of different types of transducers, including a 256‐element clinical array. These reconstructions can be used to define boundary conditions for modeling and to record characteristics of transducer performance. [Work supported by NIH EB007643, NSBRI through NASA NCC 9‐58, and RFBR].