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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

The role of trapped bubbles in kidney stone detection with the color Doppler ultrasound twinkling artifact

Simon, J.C., O.A. Sapozhnikov, W. Kreider, M. Breshock, J.C. Williams Jr., and M.R. Bailey, "The role of trapped bubbles in kidney stone detection with the color Doppler ultrasound twinkling artifact," Phys. Med. Biol., 63, 025011, doi:10.1088/1361-6560/aa9a2f, 2018.

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9 Jan 2018

The color Doppler ultrasound twinkling artifact, which highlights kidney stones with rapidly changing color, has the potential to improve stone detection; however, its inconsistent appearance has limited its clinical utility. Recently, it was proposed stable crevice bubbles on the kidney stone surface cause twinkling; however, the hypothesis is not fully accepted because the bubbles have not been directly observed. In this paper, the micron or submicron-sized bubbles predicted by the crevice bubble hypothesis are enlarged in kidney stones of five primary compositions by exposure to acoustic rarefaction pulses or hypobaric static pressures in order to simultaneously capture their appearance by high-speed photography and ultrasound imaging. On filming stones that twinkle, consecutive rarefaction pulses from a lithotripter caused some bubbles to reproducibly grow from specific locations on the stone surface, suggesting the presence of pre-existing crevice bubbles. Hyperbaric and hypobaric static pressures were found to modify the twinkling artifact; however, the simple expectation that hyperbaric exposures reduce and hypobaric pressures increase twinkling by shrinking and enlarging bubbles, respectively, largely held for rough-surfaced stones but was inadequate for smoother stones. Twinkling was found to increase or decrease in response to elevated static pressure on smooth stones, perhaps because of the compression of internal voids. These results support the crevice bubble hypothesis of twinkling and suggest the kidney stone crevices that give rise to the twinkling phenomenon may be internal as well as external.

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.

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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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