Visualization of a focused ultrasound beam to guide radiation force‐induced clearance of kidney stones.

Abstract

The incidence of kidney stones within the US population is now 10%, and rising. Many patients present with small stones, primary or recurrent, do not indicate interventional stone removal. We previously described a new stone removal method employing selective application of acoustic radiation force, at diagnostic output levels, to reposition stones for passive clearance. In this method, an imaging array transducer transmits pulses for image guidance and focused pulses to reposition the stone. Here we propose a new flash imaging modality to visualize the focused pulse to confirm targeting on the stone. To visualize the focused beam, short pulses were phase‐delayed across the transducer aperture to transmit a focused wave, from which echo data were collected, beamformed, and overlaid on a B‐mode image. The beam profile is visible because echo amplitude is higher within the convergent, focal, and divergent regions. During experiment, a stone was placed within a tissue phantom simulating the kidney lower pole and ureter. Once identified with B‐mode imaging, focal delays were calculated, targeting was confirmed by the beam visualization modality, and the stone was repositioned. Flash imaging visualization of the focused beam could be similarly applied to high‐intensity focused ultrasound therapy. [Work supported by NIH DK43881 NSBRI‐SMST01601.]