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Oleg Sapozhnikov

Senior Principal Engineer

Email

olegs@apl.washington.edu

Phone

206-543-1385

Education

M.S. Physics, Moscow State University, 1985

Ph.D. Acoustics, Moscow State University, 1988

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.

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

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Publications

2000-present and while at APL-UW

In vivo aberration correction for transcutaneous HIFU therapy using a multielement array

Thomas, G.P.L., T.D. Khokhlova, O.A. Sapozhnikov, Y.-N. Wang, S.I. Totten, and V.A. Khokhlova, "In vivo aberration correction for transcutaneous HIFU therapy using a multielement array," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 69, 2955-2965, doi:10.1109/TUFFC.2022.3200309, 2022.

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1 Oct 2022

One of the challenges of transcutaneous high-intensity focused ultrasound (HIFU) therapies, especially ones relying heavily on shock formation, such as boiling histotripsy (BH), is the loss of focusing from aberration induced by the heterogeneities of the body wall. Here, a methodology to execute aberration correction in vivo is proposed. A custom BH system consisting of a 1.5-MHz phased array of 256 elements connected to a Verasonics V1 system is used in pulse/echo mode on a porcine model under general anesthesia. Estimation of the time shifts needed to correct for aberration in the liver and kidney is done by maximizing the value of the coherence factor on the acquired backscattered signals. As this process requires multiple pulse/echo sequences on a moving target to converge to a solution, tracking is also implemented to ensure that the same target is used between each iteration. The method was validated by comparing the acoustic power needed to generate a boiling bubble at one target with aberration correction and at another target within a 5-mm radius without aberration correction. Results show that the aberration correction effectively lowers the acoustic power required to reach boiling by up to 45%, confirming that it indeed restored formation of the nonlinear shock front at the focus.

Improving burst wave lithotripsy effectiveness for small stones and fragments by increasing frequency: Theoretical modeling and ex vivo study

Bailey, M.R., A.D. Maxwell, S. Cao, S. Ramesh, Z. Liu, J.C. Williams, J. Thiel, B. Dunmire, T. Colonius, E. Kuznetsova, W. Kreider, M.D. Sorensen, J.E. Lindeman, and O.A. Sapozhnikov, "Improving burst wave lithotripsy effectiveness for small stones and fragments by increasing frequency: Theoretical modeling and ex vivo study," J. Endourol., 36, doi:10.1089/end.2021.0714, 2022.

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5 Jul 2022

Introduction and Objective: In clinical trial NCT03873259, a 2.6-mm lower pole stone was treated transcutaneously and ex vivo with 390-kHz burst wave lithotripsy (BWL) for 40 minutes and failed to break. The stone was subsequently fragmented with 650-kHz BWL after a 4-minute exposure. This study investigated how to fragment small stones and why varying the BWL frequency may more effectively fragment stones to dust.

Methods: A linear elastic theoretical model was used to calculate the stress created inside stones from shock wave lithotripsy (SWL) and different BWL frequencies mimicking the stone's size, shape, lamellar structure, and composition. To test model predictions about the impact of BWL frequency, matched pairs of stones (1–5 mm) were treated at (1) 390 kHz, (2) 830 kHz, and (3) 390 kHz followed by 830 kHz. The mass of fragments > 1 and 2 mm was measured over 10 minutes of exposure.

Results: The linear elastic model predicts that the maximum principal stress inside a stone increases to more than 5.5 times the pressure applied by the ultrasound wave as frequency is increased, regardless of the composition tested. The threshold frequency for stress amplification is proportionate to the wave speed divided by the stone diameter. Thus, smaller stones may be likely to fragment at a higher frequency, but not at a lower frequency below a limit. Unlike with SWL, this amplification in BWL occurs consistently with spherical and irregularly shaped stones. In water tank experiments, stones smaller than the threshold size broke fastest at high frequency (p = 0.0003), whereas larger stones broke equally well to submillimeter dust at high, low, or mixed frequencies.

Conclusions: For small stones and fragments, increasing frequency of BWL may produce amplified stress in the stone causing the stone to break. Using the strategies outlined here, stones of all sizes may be turned to dust efficiently with BWL.

B/A measurement of clear cell renal cell carcinoma versus healthy kidney tissue

Panfilova, A., X. Chen, C. Widdershoven, J.E. Freund, D.S. Heijink, P. Zondervan, R.G. Van Sloun, O. Sapozhnikov, H. Wukstra, and M. Mischi, "B/A measurement of clear cell renal cell carcinoma versus healthy kidney tissue," Ultrasound Med. Biol., 48, 1348-1355, doi:10.1016/j.ultrasmedbio.2022.02.024, 2022.

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1 Jul 2022

The acoustic parameter of non-linearity B/A has been found capable of discriminating some types of pathological tissue from healthy tissue. The literature on the utility of B/A for cancer diagnostics is very limited, with measurements on the human breast and liver. This work expands the current research on cancer diagnostics by B/A assessment of eight slices of human clear cell renal cell carcinoma (ccRCC) from two patients and four slices of healthy kidney tissue from two healthy kidney samples. The Wilcoxon test identified the B/A distribution of malignant tissue as not significantly different from that of healthy tissue. An alternative way of defining outliers resulted in median B/A values of 8.1 for ccRCC and 6.8 for healthy tissue (p < 0.05). Acoustic attenuation at 2.1 MHz was significantly greater (p < 0.05) for ccRCC (1.7 dB/cm) than for healthy tissue (1.0 dB/cm). The observed differences in the measured values suggest that B/A and acoustic attenuation may represent potential diagnostic markers of ccRCC. More data and an improved experimental design are required to provide a definitive conclusion on the utility of B/A for cancer diagnostics.

More Publications

Inventions

Methods for Separating, Concentrating, and/or Differentiating Between Cells from a Cell Sample

Patent Number: 10,794,827

Tom Matula, Oleg Sapozhnikov, Brian MacConaghy

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Patent

6 Oct 2020

Embodiments are generally related to differentiating and/or separating portions of a sample that are of interest from the remainder of the sample. Embodiments may be directed towards separating cells of interest from a cell sample. In some embodiments, acoustic impedances of the cells of interest may be modified. For example, the acoustic properties of the cells of interest may be modified by attaching bubbles to the cells of interest. The cell sample may then be subjected to an acoustic wave. The cells of interest may be differentiated and/or separated from the remainder of the sample based on relative displacements and/or volumetric changes experienced by the cells of interest in response thereto. The cells of interest may be separated using a standing wave and sorted into separate channels of a flow cell. Optionally, the cells may be interrogated by a light source and differentiated by signals generated in response thereto.

Systems and Methods for Measuring Pressure Distributions of Acoustic Beams from Ultrasound Sources

The present technology relates generally to receiving arrays to measure a characteristic of an acoustic beam and associated systems and methods.

Patent Number: 10,598,773

Oleg Sapozhnikov, Wayne Kreider, Adam Maxwell, Vera Khokhlova

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Patent

24 Mar 2020

The present technology relates generally to receiving arrays to measure a characteristic of an acoustic beam and associated systems and methods. The receiving arrays can include elongated elements having at least one dimension, such as a length, that is larger than a width of an emitted acoustic beam and another dimension, such as a width, that is smaller than half of a characteristic wavelength of an ultrasound wave. The elongated elements can be configured to capture waveform measurements of the beam based on a characteristic of the emitted acoustic beam as the acoustic beam crosses a plane of the array, such as a transverse plane. The methods include measuring at least one characteristic of an ultrasound source using an array-based acoustic holography system and defining a measured hologram at the array surface based, at least in part, on the waveform measurements. The measured hologram can be processed to reconstruct a characteristic of the ultrasound source. The ultrasound source can be calibrated and/or re-calibrated based on the characteristic.

Confinement or Movement of an Object Using Focused Ultrasound Waves to Generate an Ultrasound Intensity Well

Patent Number: 10,535,332

Adam Maxwell, Oleg Sapozhnikov, Wayne Kreider, Mike Bailey

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Patent

14 Jan 2020

A method includes transmitting a focused ultrasound wave into a medium to form (i) an ultrasound intensity well within the medium that exhibits a first range of acoustic pressure and (ii) a surrounding region of the medium that surrounds the ultrasound intensity well and exhibits a second range of acoustic pressure that exceeds the first range of acoustic pressure. The method further includes confining an object within the ultrasound intensity well. Additionally, an acoustic lens is configured to be acoustically coupled to an acoustic transducer. The acoustic lens has a varying longitudinal thickness that increases proportionally with respect to increasing azimuth angle of the acoustic lens. Another acoustic lens is configured to be acoustically coupled to an acoustic that increases proportionally with respect to increasing azimuth angle of the segment.

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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