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Adam Maxwell

Senior Fellow - Trainee

Email

maxwell@apl.washington.edu

Phone

206-221-6530

Videos

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

Publications

2000-present and while at APL-UW

Ultrasound-induced bubble clusters in tissue-mimicking agar phantoms

Movahed, P., W. Kreider, A.D. Maxwell, B. Dunmire, and J.B. Freund, "Ultrasound-induced bubble clusters in tissue-mimicking agar phantoms," Ultrasound Med. Biol., 43, 2318-2328, doi:10.1016/j.ultrasmedbio.2017.06.013, 2017.

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1 Oct 2017

Therapeutic ultrasound can drive bubble activity that damages soft tissues. To study the potential mechanisms of such injury, transparent agar tissue-mimicking phantoms were subjected to multiple pressure wave bursts of the kind being considered specifically for burst wave lithotripsy. A high-speed camera recorded bubble activity during each pulse. Various agar concentrations were used to alter the phantom's mechanical properties, especially its stiffness, which was varied by a factor of 3.5. However, the maximum observed bubble radius was insensitive to stiffness. During 1000 wave bursts of a candidate burst wave lithotripsy treatment, bubbles appeared continuously in a region that expanded slowly, primarily toward the transducer. Denser bubble clouds are formed at higher pulse repetition frequency. The specific observations are used to inform the incorporation of damage mechanisms into cavitation models for soft materials.

Design of HIFU transducers for generating specified nonlinear ultrasound fields

Rosnitskiy, P.B., P.V. Yuldashev, O.A. Sapozhnikov, A.D. Maxwell, W. Greider, M.R. Bailey, and V.A. Khokhlova, "Design of HIFU transducers for generating specified nonlinear ultrasound fields," IEEE Trans. Ultrason., Ferroelect., Freq. Control, 64, 374-390, doi:10.1109/TUFFC.2016.2619913, 2017.

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1 Feb 2017

Various clinical applications of high-intensity focused ultrasound have different requirements for the pressure levels and degree of nonlinear waveform distortion at the focus. The goal of this paper is to determine transducer design parameters that produce either a specified shock amplitude in the focal waveform or specified peak pressures while still maintaining quasi-linear conditions at the focus. Multiparametric nonlinear modeling based on the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation with an equivalent source boundary condition was employed. Peak pressures, shock amplitudes at the focus, and corresponding source outputs were determined for different transducer geometries and levels of nonlinear distortion. The results are presented in terms of the parameters of an equivalent single-element spherically shaped transducer. The accuracy of the method and its applicability to cases of strongly focused transducers were validated by comparing the KZK modeling data with measurements and nonlinear full diffraction simulations for a single-element source and arrays with 7 and 256 elements. The results provide look-up data for evaluating nonlinear distortions at the focus of existing therapeutic systems as well as for guiding the design of new transducers that generate specified nonlinear fields.

Cavitation-induced damage of soft materials by focused ultrasound bursts: A fracture-based bubble dynamics model

Movahed, P., W. Kreider, A.D. Maxwell, S.B. Hutchens, and J.B. Freund, "Cavitation-induced damage of soft materials by focused ultrasound bursts: A fracture-based bubble dynamics model," J. Acoust. Soc. Am., 140, 1374-1386, doi:10.1121/1.4961364, 2016.

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1 Aug 2016

A generalized Rayleigh–Plesset-type bubble dynamics model with a damage mechanism is developed for cavitation and damage of soft materials by focused ultrasound bursts. This study is linked to recent experimental observations in tissue-mimicking polyacrylamide and agar gel phantoms subjected to bursts of a kind being considered specifically for lithotripsy. These show bubble activation at multiple sites during the initial pulses. More cavities appear continuously through the course of the observations, similar to what is deduced in pig kidney tissues in shock-wave lithotripsy. Two different material models are used to represent the distinct properties of the two gel materials. The polyacrylamide gel is represented with a neo-Hookean elastic model and damaged based upon a maximum-strain criterion; the agar gel is represented with a strain-hardening Fung model and damaged according to the strain-energy-based Griffith's fracture criterion. Estimates based upon independently determined elasticity and viscosity of the two gel materials suggest that bubble confinement should be sufficient to prevent damage in the gels, and presumably injury in some tissues. Damage accumulation is therefore proposed to occur via a material fatigue, which is shown to be consistent with observed delays in widespread cavitation activity.

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Inventions

MRI-Guided Lithotripsy of Urinary Tract Stones

Record of Invention Number: 47984

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

Disclosure

23 Feb 2017

Combination Burst Wave Lithotripsy and Ultrasonic Propulsion for Improved Stone Fragmentation

Record of Invention Number: 47817

Adam Maxwell, Mike Bailey, Bryan Cunitz, Annie Zwaschka

Disclosure

9 Sep 2016

Methods and Devices for Improved Cavitation-Induced Drug Delivery Using Pulsed Focused Ultrasound with Shocks

Record of Invention Number: 47734

Vera Khokhlova, Joo Ha Hwang, Tatiana Khokhlova, Wayne Kreider, Adam Maxwell, Oleg Sapozhnikov

Disclosure

1 Jun 2016

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
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