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Adam Maxwell

Senior Fellow - Trainee

Email

maxwell@apl.washington.edu

Phone

206-221-6530

Videos

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.

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

Dependence of inertial cavitation induced by high intensity focused ultrasound on transducer F-number and nonlinear waveform distortion

Khokhlova, T., P. Rosnitskiy, C. Hunter, A. Maxwell, W. Kreider, G. Ter Haar, M. Costa, O. Sapozhnikov, and V. Khokhlova, "Dependence of inertial cavitation induced by high intensity focused ultrasound on transducer F-number and nonlinear waveform distortion," J. Acoust. Soc. Am., 144, 1160, doi:10.1121/1.5052260, 2018.

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1 Sep 2018

Pulsed high intensity focused ultrasound was shown to enhance chemotherapeutic drug uptake in tumor tissue through inertial cavitation, which is commonly assumed to require peak rarefactional pressures to exceed a certain threshold. However, recent studies have indicated that inertial cavitation activity also correlates with the presence of shocks at the focus. The shock front amplitude and corresponding peak negative pressure (p–) in the focal waveform are primarily determined by the transducer F-number: less focused transducers produce shocks at lower p–. Here, the dependence of inertial cavitation activity on the transducer F-number was investigated in agarose gel by monitoring broadband noise emissions with a coaxial passive cavitation detector (PCD) during pulsed exposures (pulse duration 1 ms, pulse repetition frequency 1 Hz) with p– varying within 1–15 MPa. Three 1.5 MHz transducers with the same aperture, but different focal distances (F-numbers 0.77, 1.02, 1.52) were used. PCD signals were processed to extract cavitation probability, persistence, and mean noise level. At the same p–, all metrics indicated enhanced cavitation activity at higher F-numbers; specifically, cavitation probability reached 100% when shocks formed at the focus. These results provide further evidence supporting the excitation of inertial cavitation at reduced p– by waveforms with nonlinear distortion and shocks.

Field characterization and compensation of vibrational nonuniformity for a 256-element focused ultrasound phased array

Ghanem, M.A., A.D. Maxwell, W. Kreider, B.W. Cunitz, V.A. Khokhlova, O.A. Sapozhnikov, and M.R. Bailey, "Field characterization and compensation of vibrational nonuniformity for a 256-element focused ultrasound phased array," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 65, 1618-1630, doi:10.1109/TUFFC.2018.2851188, 2018.

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1 Sep 2018

Multielement focused ultrasound phased arrays have been used in therapeutic applications to treat large tissue volumes by electronic steering of the focus, to target multiple simultaneous foci, and to correct aberration caused by inhomogeneous tissue pathways. There is an increasing interest in using arrays to generate more complex beam shapes and corresponding acoustic radiation force patterns for manipulation of particles such as kidney stones. Toward this end, experimental and computational tools are needed to enable accurate delivery of desired transducer vibrations and corresponding ultrasound fields. The purpose of this paper was to characterize the vibrations of a 256-element array at 1.5 MHz, implement strategies to compensate for variability, and test the ability to generate specified vortex beams that are relevant to particle manipulation. The characterization of the array output was performed in water using both element-by-element measurements at the focus of the array and holography measurements for which all the elements were excited simultaneously. Both methods were used to quantify each element’s output so that the power of each element could be equalized. Vortex beams generated using both compensation strategies were measured and compared to the Rayleigh integral simulations of fields generated by an idealized array based on the manufacturer’s specifications. Although both approaches improved beam axisymmetry, compensation based on holography measurements had half the error relative to the simulation results in comparison to the element-by-element method.

Combined burst wave lithotripsy and ultrasonic propulsion fo improved urinary stone fragmentation

Zwaschka, T.A., J.S. Ahn, B.W. Cunitz, M.R. Bailey, B. Dunmire, M.D. Sorensen, J.D. Harper, and A.D. Maxwell, "Combined burst wave lithotripsy and ultrasonic propulsion fo improved urinary stone fragmentation," J. Endourol., 32, 344-349, doi:10.1089/end.2017.0675, 2018.

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1 Apr 2018

Purpose

Burst wave lithotripsy (BWL) is a new technology in development to fragment urinary stones. Ultrasonic propulsion (UP) is a separate technology under investigation for displacing stones. We measure the effect of propulsion pulses on stone fragmentation from BWL.

Materials and Methods

Two artificial stone models (crystalline calcite, BegoStone plaster) and human calcium oxalate monohydrate (COM) stones measuring 5 to 8 mm were subjected to ultrasound exposures in a polyvinyl chloride tissue phantom within a water bath. Stones were exposed to BWL with and without propulsion pulses interleaved for set time intervals depending on stone type. Fragmentation was measured as a fraction of the initial stone mass fragmented to pieces smaller than 2 mm.

Results

BegoStone model comminution improved from 6% to 35% (p < 0.001) between BWL and BWL with interleaved propulsion in a 10-minute exposure. Propulsion alone did not fragment stones, whereas addition of propulsion after BWL slightly improved BegoStone model comminution from 6% to 11% (p < 0.001). BegoStone model fragmentation increased with rate of propulsion pulses. Calcite stone fragmentation improved from 24% to 39% in 5 minutes (p = 0.047) and COM stones improved from 17% to 36% (p = 0.01) with interleaved propulsion.

Conclusions

BWL with UP improved stone fragmentation compared with BWL alone in vitro. The improvement was greatest when propulsion pulses are interleaved with BWL treatment and when propulsion pulses are applied at a higher rate. Thus, UP may be a useful adjunct to enhance fragmentation in lithotripsy in vivo.

More Publications

Inventions

Time-reversal based ultrasound system for processing biological samples

Record of Invention Number: 48375

Brian MacConaghy, Adam Maxwell

Disclosure

10 Jul 2018

Targeting Methods and Devices for Non-invasive Therapy Delivery

Record of Invention Number: 48305

Bryan Cunitz, Mike Bailey, Barbrina Dunmire, Michael Kennedy Hall, Adam Maxwell, Matthew Sorenson

Disclosure

11 Apr 2018

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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Patent

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.

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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