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Adam Maxwell

Research Assistant Professor, Urology

Email

maxwell@apl.washington.edu

Phone

206-221-6530

Videos

Ultrasonic tweezers: Technology to lift and steer solid objects in a living body

In a recent paper, a CIMU team describes successful experiments to manipulate a solid object within a living body with ultrasound beams transmitted through the skin.

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15 Jul 2020

A collaborative, international research teams developed and tuned an ultrasound transducer to create vortex shaped beams that can trap, grab, levitate, and move in three dimensions mm-scale objects. The team is working to apply this technology to their all-in-one kidney stone treatment system that, in clinical trials, uses ultrasound to non-invasively break, erode, and move stones and stone fragments out of the kidney so that they may pass naturally from the body.

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. A multi-institution, international team led by CIMU researchers is applying the method to the focal treatment of prostate tumors.

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19 Mar 2020

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.

PIXUL: PIXelated ULtrasound Speeds Disease Biomarker Search

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26 Apr 2018

Accurate assessment of chromatin modifications can be used to improve detection and treatment of various diseases. Further, accurate assessment of chromatin modifications can have an important role in designing new drug therapies. This novel technology applies miniature ultrasound transducers to shear chromatin in standard 96-well microplates. PIXUL saves researchers hours of sample preparation time and reduces sample degradation.

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Publications

2000-present and while at APL-UW

Inertial cavitation behaviors induced by nonlinear focused ultrasound pulses

Bawiec, C.R., P.B. Rosnitskiy, A.T. Peek, A.D. Maxwell, W. Kreider, G.R. Ter Haar, O.A. Sapozhnikov, V.A. Khokhlova, and T.D. Khokhlova, "Inertial cavitation behaviors induced by nonlinear focused ultrasound pulses," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 68, 2884-2895, doi:10.1109/TUFFC.2021.3073347, 2021.

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1 Sep 2021

Inertial cavitation induced by pulsed high-intensity focused ultrasound (pHIFU) has previously been shown to successfully permeabilize tumor tissue and enhance chemotherapeutic drug uptake. In addition to HIFU frequency, peak rarefactional pressure, and pulse duration, the threshold for cavitation-induced bioeffects has recently been correlated with asymmetric distortion caused by nonlinear propagation, diffraction and formation of shocks in the focal waveform, and therefore with the transducer F-number. To connect previously observed bioeffects with bubble dynamics and their attendant physical mechanisms, the dependence of inertial cavitation behavior on shock formation was investigated in transparent agarose gel phantoms using high-speed photography and passive cavitation detection (PCD). Agarose phantoms with concentrations ranging from 1.5% to 5% were exposed to 1-ms pulses using three transducers of the same aperture but different focal distances (F-numbers of 0.77, 1.02, and 1.52). Pulses had central frequencies of 1, 1.5, or 1.9 MHz and a range of peak rarefactional pressure at the focus varying within 1–18 MPa. Three distinct categories of bubble behavior were observed as the acoustic power increased: stationary near-spherical oscillation of individual bubbles, proliferation of multiple bubbles along the pHIFU beam axis, and fanned-out proliferation toward the transducer. Proliferating bubbles were only observed under strongly nonlinear or shock-forming conditions regardless of frequency, and only where the bubbles reached a certain threshold size range. In stiffer gels with higher agarose concentrations, the same pattern of cavitation behavior was observed, but the dimensions of proliferating clouds were smaller. These observations suggest mechanisms that may be involved in bubble proliferation: enhanced growth of bubbles under shock-forming conditions, subsequent shock scattering from the gel–bubble interface, causing an increase in the repetitive tension created by the acoustic wave, and the appearance of a new growing bubble in the proximal direction. Different behaviors corresponded to specific spectral characteristics in the PCD signals: broadband noise in all cases, narrow peaks of backscattered harmonics in the case of stationary bubbles, and broadened, shifted harmonic peaks in the case of proliferating bubbles. The shift in harmonic peaks can be interpreted as a Doppler shift from targets moving at speeds of up to 2 m/s, which correspond to the observed bubble proliferation speeds.

Factors affecting tissue cavitation during burst wave lithotripsy

Maxwell, A.D., C. Hunter, B.W. Cunitz, W. Kreider, S. Totten, and Y.-N. Wang, "Factors affecting tissue cavitation during burst wave lithotripsy," Ultrasound Med. Biol., 47, 2286-2295, doi:10.1016/j.ultrasmedbio.2021.04.021, 2021.

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1 Aug 2021

Burst wave lithotripsy (BWL) is a technology under clinical investigation for non-invasive fragmentation of urinary stones. Under certain ranges of ultrasound exposure parameters, this technology can cause cavitation in tissue leading to renal injury. This study sought to measure the focal pressure amplitude needed to cause cavitation in vivo and determine its consistency in native tissue, in an implanted stone model and under different exposure parameters. The kidneys of eight pigs were exposed to transcutaneous BWL ultrasound pulses. In each kidney, two locations were targeted: the renal sinus and the kidney parenchyma. Each was exposed for 5 min at a set pressure level and parameters, and cavitation was detected using an active cavitation imaging method based on power Doppler ultrasound. The threshold was determined by incrementing the pressure amplitude up or down after each 5-min interval until cavitation occurred/subsided. The pressure thresholds were remeasured postsurgery, targeting an implanted stone or collecting space (in sham). The presence of a stone or sham surgery did not significantly impact the threshold for tissue cavitation. Targeting parenchyma instead of kidney collecting space and lowering the ultrasound pulse repetition frequency both resulted in an increased pressure threshold for cavitation.

Mechanical characterization of fibrotic and mineralized tissue in Peyronie's disease

Brady, L., C.J. Stender, Y.-N. Wang, G.R. Schade, A.D. Maxwell, H. Wessells, and W.R. Ledoux, "Mechanical characterization of fibrotic and mineralized tissue in Peyronie's disease," Int. J. Impotence Res., EOR, 10.1038/s41443-021-00439-2, 2021.

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25 May 2021

Peyronie's disease affects penile mechanics, but published research lacks biomechanical characterization of affected tunica albuginea. This work aims to establish mechanical testing methodology and characterize pathological tissue mechanics of Peyronie's disease. Tunica albuginea was obtained from patients (n = 5) undergoing reconstructive surgery for Peyronie's disease, sectioned into test specimens (n = 12), stored frozen at –20°C, and imaged with micro-computed tomography (μCT). A tensile testing protocol was developed based on similar soft tissues. Correlation of mechanical summary variables (force, displacement, stiffness, work, Young’s modulus, ultimate tensile stress, strain at ultimate tensile stress, and toughness) and μCT features were assessed with linear regression. Specimens empirically grouped into hard or soft stress–strain behavior were compared using a Student's t-test. Surface strain and failure patterns were described qualitatively. Specimens displayed high inter- and intra-subject variability. Mineralization volume was not correlated with mechanical parameters. Empirically hard tissue had higher ultimate tensile stress. Failure mechanisms and strain patterns differed between mineralized and non-mineralized specimens. Size, shape, and quantity of mineralization may be more important in determining Peyronie's disease plaque behavior than presence of mineralization alone, and single summary variables like modulus may not fully describe mechanical behavior.

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Inventions

Bonding of structures using high intensity focused ultrasound (HIFU)

Record of Invention Number: 49327

Tom Matula, Ekaterina Kuznetsova, Adam Maxwell

Disclosure

17 Aug 2021

Non-planar holographic beam shaping lenses for acoustics

Record of Invention Number: 49310

Mike Bailey, Mohamed Ghanem, Adam Maxwell

Disclosure

20 Jul 2021

Lithotripsy That Tunes the Frequency to the Stone Size

Record of Invention Number: 49262

Mike Bailey, Adam Maxwell, Oleg Sapozhnikov

Disclosure

12 May 2021

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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