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Oleg Sapozhnikov

Senior Principal Engineer

Email

olegs@apl.washington.edu

Phone

206-543-1385

Videos

Characterizing Medical Ultrasound Sources and Fields

For every medical ultrasound transducer it's important to characterize the field it creates, whether for safety of imaging or efficacy of therapy. CIMU researchers measure a 2D acoustic pressure distribution in the beam emanating from the source transducer and then reconstruct mathematically the exact field on the surface of the transducer and in the entire 3D space.

11 Sep 2017

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

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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.

Ultrasound-based cell sorting with microbubbles: A feasibility study

Matula, T.J. O.A. Sapozhnikov, L.A. Ostrovsky, A.A. Brayan, J. Kucewicz, B.E. MacConaghy, and D. De Raad, "Ultrasound-based cell sorting with microbubbles: A feasibility study," J. Acoust. Soc. Am., 144, doi:10.1121/1.5044405, 2018.

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1 Jul 2018

The isolation and sorting of cells is an important process in research and hospital labs. Most large research and commercial labs incorporate fluorescently or magnetically labeled antibodies adherent to cell surface antigens for cell identification and separation. In this paper, a process is described that merges biochemical labeling with ultrasound-based separation. Instead of lasers and fluorophore tags, or magnets and magnetic particle tags, the technique uses ultrasound and microbubble tags. Streptavidin-labeled microbubbles were mixed with a human acute lymphoblastic leukemia cell line, CCL 119, conjugated with biotinylated anti-CD7 antibodies. Tagged cells were forced under ultrasound, and their displacement and velocity quantified. Differential displacement in a flow stream was quantified against erythrocytes, which showed almost no displacement under ultrasound. A model for the acoustic radiation force on the conjugated pairs compares favorably with observations. This technology may improve on current time-consuming and costly purification procedures.

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Inventions

Design of a Transrectal Ultrasound Probe for Boiling Histotripsy Ablation of Prostate

Record of Invention Number: 48264

Tanya Khokhlova, Oleg Sapozhnikov, George Schade

Disclosure

6 Feb 2018

Imaging Bubbles in a Medium

Patent Number: 9,743,909

Oleg Sapozhnikov, Mike Bailey, Joo Ha Hwang, Tatiana Khokhlova, Vera Khokhlova, Tong Li, Matthew O'Donnell

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Patent

29 Aug 2017

A method for imaging a cavitation bubble includes producing a vibratory wave that induces a cavitation bubble in a medium, producing one or more detection waves directed toward the induced cavitation bubble, receiving one or more reflection waves, identifying a change in one or more characteristics of the induced cavitation bubble, and generating an image of the induced cavitation bubble using a computing device on the basis of the identified change in the one or more characteristics. The one or more received reflection waves correspond to at least one of the one or more produced detection waves reflection from the induced cavitation bubble. The identified change in one or more characteristics corresponds to the one or more received reflection waves.

Methods and Systems for Non-invasive Treatment of Tissue Using High Intensity Focused Ultrasound Therapy

Patent Number: 9,700,742

Michael Canney, Mike Bailey, Larry Crum, Joo Ha Hwang, Tatiana Khokhlova, Vera Khokhlova, Wayne Kreider, Oleg Sapozhnikov

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Patent

11 Jul 2017

Methods and systems for non-invasive treatment of tissue using high intensity focused ultrasound ("HIFU") therapy. A method of non-invasively treating tissue in accordance with an embodiment of the present technology, for example, can include positioning a focal plane of an ultrasound source at a target site in tissue. The ultrasound source can be configured to emit HIFU waves. The method can further include pulsing ultrasound energy from the ultrasound source toward the target site, and generating shock waves in the tissue to induce boiling of the tissue at the target site within milliseconds. The boiling of the tissue at least substantially emulsifies the tissue.

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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