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Adam Maxwell

Senior Fellow - Trainee






Mechanical Tissue Ablation with Focused Ultrasound

An experimental noninvasive surgery method uses nonlinear ultrasound pulses to liquefy tissue at remote target sites within a small focal region without damaging intervening tissues.

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23 Mar 2017

Boiling histotripsy utilizes sequences of millisecond-duration HIFU pulses with high-amplitude shocks that form at the focus by nonlinear propagation effects. Due to strong attenuation of the ultrasound energy at the shocks, these nonlinear waves rapidly heat tissue and generate millimeter-sized boiling bubbles at the focus within each pulse. Then the further interaction of subsequent shocks with the vapor cavity causes tissue disintegration into subcellular debris through the acoustic atomization mechanism.

The method was proposed at APL-UW in collaboration with Moscow State University (Russia) and now is being evaluated for various clinical applications. It has particular promise because of its important clinical advantages: the treatment of tissue volumes can be accelerated while sparing adjacent structures and not injuring intervening tissues; it generates precisely controlled mechanical lesions with sharp margins; the method can be implemented in existing clinical systems; and it can be used with real-time ultrasound imaging for targeting, guidance, and evaluation of outcomes. In addition, compared to thermal ablation, BH may lead to faster resorption of the liquefied lesion contents.

Burst Wave Lithotripsy: An Experimental Method to Fragment Kidney Stones

CIMU researchers are investigating a noninvasive method to fragment kidney stones using ultrasound pulses rather than shock waves. Consecutive acoustic cycles accumulate and concentrate energy within the stone. The technique can be 'tuned' to create small fragments, potentially improving the success rate of lithotripsy procedures.

20 Nov 2014


2000-present and while at APL-UW

Design and characterization of a 2-dimensional focused 1.5-MHz ultrasound array with a compact spiral arrangement of 256 circular elements

Sapozhnikov, O., M. Ghanem, A. Maxwell, P. Rosnitskiy, P. Yuldashev, W. Kreider, B. Cunitz, M. Bailey, and V. Khokhlova, "Design and characterization of a 2-dimensional focused 1.5-MHz ultrasound array with a compact spiral arrangement of 256 circular elements," Proc., IEEE International Ultrasonics Symposium, 6-9 September, Washington, D.C., doi:10.1109/ULTSYM.2017.8092165 (IEEE, 2017).

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2 Nov 2017

Multi-element ultrasound arrays are increasingly used in clinical practice for both imaging and therapy. In therapy, they allow electronic steering, aberration correction, and focusing. To avoid grating lobes, an important requirement for such an array is the absence of periodicity in the arrangement of the elements. A convenient solution is the arrangement of the elements along spirals. The objective of this work was to design, fabricate, and characterize an array for boiling histotripsy applications that is capable of generating shock waves in the focus of up to 100 MPa peak pressure while having a reasonable electronic steering range.

Design and characterization of a research phantom for shock-wave enhanced irradiations in high intensity focused ultrasound therapy

Kreider, W., B. Dunmire, J. Kucewicz, C. Hunter, T. Khokhlova, G. Schade, A. Maxwell, O. Sapozhnikov, L. Crum, and V. Khokhlova, "Design and characterization of a research phantom for shock-wave enhanced irradiations in high intensity focused ultrasound therapy," Proc., IEEE International Ultrasonics Symposium, 6-9 September, Washington, D.C., doi:10.1109/ULTSYM.2017.8092866 (IEEE, 2017).

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2 Nov 2017

The use of shock waves for enhancing thermal effects and mechanically ablating tissue is gaining increased attention in high intensity focused ultrasound (HIFU) applications such as tumor treatment, drug delivery, noninvasive biopsy, and immunotherapy. For abdominal targets, the presence of ribs and inhomogeneous adipose tissue can affect shock formation through aberration, absorption, and diffraction. The goal of this study was to design and validate a phantom for investigating the impact of different tissue structures on shock formation in situ. A transducer with driving electronics was developed to operate at 1.2 MHz with the ability to deliver either short pulses at high powers (up to 5 kW electric power) or continuous output at moderate powers (up to 700 W). Fat and muscle layers were represented by phantoms made from polyvinyl alcohol. Ribs were 3D-printed from a photopolymer material based on 3D CT scan images. Representative targeted tissue was comprised of optically transparent alginate or polyacrylamide gels. The system was characterized by hydrophone measurements free-field in water and in the presence of a body wall or rib phantoms. Shocked waveforms with peak positive/negative pressures of +100 / –20 MPa were measured at the focus in a free field at 1 kW electric source power. When ribs were present, shocks formed at about 50% amplitude at the same power, and higher pressures were measured with ribs positioned closer to the transducer. A uniform body wall structure attenuated shock amplitudes by a smaller amount than non-uniform, and the measurements were insensitive to the axial position of the phantom. Signal magnitude loss at the focus for both the rib phantoms and abdominal wall tissue were consistent with results from real tissues. In addition, boiling histotripsy lesions were generated and visualized in the target gels. The results demonstrate that the presence of ribs and absorptive tissue-mimicking layers do not prevent shock formation at the focus. With real-time lesion visualization, the phantom is suitable for adaptation as a training tool.

Stress waves in model kidney stones exposed to burst wave lithotripsy

Maxwell, A., B. MacConaghy, M. Bailey, and O. Sapozhnikov, "Stress waves in model kidney stones exposed to burst wave lithotripsy," Proc., IEEE International Ultrasonics Symposium, 6-9 September, Washington, D.C., doi:10.1109/ULTSYM.2017.8092870 (IEEE, 2017).

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2 Nov 2017

Burst wave lithotripsy (BWL) is an experimental method to noninvasively fragment urinary calculi using low-frequency focused bursts of ultrasound. To optimize many of the acoustic parameters for this technology, it is necessary to understand the physical interactions between ultrasound bursts and stones. In this study, the interaction of elastic waves with model stones was simulated and experimentally visualized by photoelastography, a technique using polarized light to spatially and temporally visualize stress patterns.

More Publications


Pulse Amplifier for Driving Ultrasound Transducers

Patent Number: 9,867,999

Adam Maxwell, Bryan Cunitz, Mike Bailey, Vera Khokhlova, Timothy Hall

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16 Jan 2018

Embodiments of the invention include improved radiofrequency (RF) pulse amplifier systems that incorporate an energy array comprising multiple capacitors connected in parallel. The energy array extends the maximum length of pulses and the maximum achievable peak power output of the amplifier when compared to similar systems. Embodiments also include systems comprising the amplifier configured to drive a load, wherein the load may include one or more ultrasound (e.g., piezoelectric) transducers Related methods of using the amplifier are also provided.

Holographic Beam Shaping for Ultrasound Therapy Transducers

Record of Invention Number: 48221

Adam Maxwell, Mike Bailey, Mohamed Ghanem


1 Dec 2017

MRI-Guided Lithotripsy of Urinary Tract Stones

Record of Invention Number: 47984

Mike Bailey, Wayne Kreider, Adam Maxwell, Yak-Nam Wang


23 Feb 2017

More Inventions

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center