Holographic measurement and simulation of 3-D ultrasound fields distorted by soft-tissue phantoms

Abstract

Applications of high intensity therapeutic ultrasound (HITU) rely on the accurate delivery of ultrasound to targeted tissues. However, because in situ measurement of 3-D ultrasound fields in tissue is not possible, knowledge of such fields depends upon some form of calculation. Standard approaches utilize measurements in water to characterize the ultrasound source, with fields in tissue estimated by derating or numerical simulation. To evaluate the accuracy of numerical models, simulations and measurements have been performed based on tissue phantoms with known geometries and physical properties. In this work, holography measurements were used to characterize a 256-element HITU transducer in water and to measure directly the 3-D fields behind soft-tissue phantoms designed to introduce refraction, attenuation, and/or aberration. Using synchronization between a waveform digitizer and a computer-controlled positioner, accelerated recording of each hologram (representing over 40 000 points) was performed in about an hour by continuously scanning a capsule hydrophone line-by-line in the measurement plane. Linear measurements are compared with simulations performed using the k-Wave toolbox, and various uncertainties are quantified. It is shown that holography-based modeling accurately represents fields distorted by inhomogeneous layers mimicking body wall. [Funding support by NIH R01-EB025187, R01-EB007643, R01-R01GM122859, and RSF Grant No. 19-12-00148.]