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Vera Khokhlova

Senior Principal Engineer

Email

vera@apl.washington.edu

Phone

206-221-6585

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.

Publications

2000-present and while at APL-UW

A ptotype therapy system for transcutaneous application of boiling histotripsy

Maxwell, A.D., P.V. Yuldashev, W. Kreider, T.D. Khokhlova, G.R. Schade, T.L. Hall, O.A. Sapozhnikov, M.R. Bailey, and V.A. Khokhlova, "A ptotype therapy system for transcutaneous application of boiling histotripsy," IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 64, 1542-1557, doi:10.1109/TUFFC.2017.2739649, 2017.

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1 Oct 2017

Boiling histotripsy (BH) is a method of focused ultrasound surgery that noninvasively applies millisecond-length pulses with high-amplitude shock fronts to generate liquefied lesions in tissue. Such a technique requires unique outputs compared to a focused ultrasound thermal therapy apparatus, particularly to achieve high in situ pressure levels through intervening tissue. This paper describes the design and characterization of a system capable of producing the necessary pressure to transcutaneously administer BH therapy through clinically relevant overlying tissue paths using pulses with duration up to 10 ms. A high-voltage electronic pulser was constructed to drive a 1-MHz focused ultrasound transducer to produce shock waves with amplitude capable of generating boiling within the pulse duration in tissue. The system output was characterized by numerical modeling with the 3-D Westervelt equation using boundary conditions established by acoustic holography measurements of the source field. Such simulations were found to be in agreement with directly measured focal waveforms. An existing derating method for nonlinear therapeutic fields was used to estimate in situ pressure levels at different tissue depths. The system was tested in ex vivo bovine liver samples to create BH lesions at depths up to 7 cm. Lesions were also created through excised porcine body wall (skin, adipose, and muscle) with 3–5 cm thickness. These results indicate that the system is capable of producing the necessary output for transcutaneous ablation with BH.

Dependence of boiling histotripsy treatment efficiency on HIFU frequency and focal pressure levels

Khokhlova, T.D., Y.A. Haider, A.D. Maxwell, W. Kreider, M.R. Bailey, and V.A. Khokhlova, "Dependence of boiling histotripsy treatment efficiency on HIFU frequency and focal pressure levels," Ultrasound Med. Biol., 9, 1975-1985, doi:10.1016/j.ultrasmedbio.2017.04.030, 2017.

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1 Sep 2017

Boiling histotripsy (BH) is a high-intensity focused ultrasound (HIFU)–based method of mechanical tissue fractionation that utilizes millisecond-long bursts of HIFU shock waves to cause boiling at the focus in milliseconds. The subsequent interaction of the incoming shocks with the vapor bubble mechanically lyses surrounding tissue and cells. The acoustic parameter space for BH has been investigated previously and an inverse dependence between the HIFU frequency and the dimensions of a BH lesion has been observed. The primary goal of the present study was to investigate in more detail the ablation rate and reliability of BH in the frequency range relevant to treatment of deep abdominal tissue targets (1–2 MHz). The second goal was to investigate the effect of focal peak pressure levels and shock amplitude on BH lesion formation, given a constant duty factor, a constant ratio of the pulse duration to the time to reach boiling and a constant number of BH pulses. A custom-built 12-element sector array HIFU transducer with F-number = 1.05 was used in all experiments. BH pulses at 5 different frequencies (1, 1.2, 1.5, 1.7 and 1.9 MHz) were delivered to optically transparent polyacrylamide gel phantoms and ex vivo bovine liver and myocardium tissue to observe cavitation and boiling bubble activity with high-speed photography and B-mode ultrasound imaging, correspondingly. In gel phantoms, a cavitation bubble cloud was shown to form prefocally and to shield the focus in all exposures at 1 and 1.2 MHz and in the highest amplitude exposures at 1.5–1.7 MHz; shielding was not observed at 1.9 MHz. In ex vivo tissue, this shielding effect was observed in 25% of exposures when peak negative in situ pressure exceeded 10.2 MPa at 1 MHz and 14.5 MPa at 1.5 MHz. When shielding occurred, the exposures resulted in mild tissue disruption in the prefocal region, but not liquefaction. The dimensions of liquefied lesions followed the inverse proportionality trend with frequency; consequently, the frequency range of 1.2–1.5 MHz appeared to be preferable for BH exposures in terms of the compromise between the ablation rate and reliability. The lesion size was independent of the duration of the BH pulses (or the total "HIFU on" time), provided that the number of pulses was constant and boiling was induced within each pulse. Thus, the use of shorter (1 ms vs. 10 ms), higher amplitude BH pulses allowed up to 10-fold reduction in treatment time for a given duty factor.

Shock formation and nonlinear saturation effects in the ultrasound field of a diagnostic curvilinear probe

Karzova, M.M., P.V. Yuldashev, O.A. Sapozhnikov, V.A. Khokhlova, B.W. Cunitz, W. Kreider, and M.R. Bailey, "Shock formation and nonlinear saturation effects in the ultrasound field of a diagnostic curvilinear probe," J. Acoust. Soc. Am., 141, 2327-2337, doi:10.1121/1.4979261, 2017.

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1 Apr 2017

Newer imaging and therapeutic ultrasound technologies may benefit from in situ pressure levels higher than conventional diagnostic ultrasound. One example is the recently developed use of ultrasonic radiation force to move kidney stones and residual fragments out of the urinary collecting system. A commercial diagnostic 2.3 MHz C5-2 array probe has been used to deliver the acoustic pushing pulses. The probe is a curvilinear array comprising 128 elements equally spaced along a convex cylindrical surface. The effectiveness of the treatment can be increased by using higher transducer output to provide a stronger pushing force; however nonlinear acoustic saturation can be a limiting factor. In this work nonlinear propagation effects were analyzed for the C5-2 transducer using a combined measurement and modeling approach. Simulations were based on the three-dimensional Westervelt equation with the boundary condition set to match low power measurements of the acoustic pressure field. Nonlinear focal waveforms simulated for different numbers of operating elements of the array at several output power levels were compared to fiber-optic hydrophone measurements and were found to be in good agreement. It was shown that saturation effects do limit the acoustic pressure in the focal region of a diagnostic imaging probe.

More Publications

Inventions

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.

Portable Acoustic Holography Systems for Therapeutic Ultrasound Sources and Associated Devices and Methods

Patent Number: 9,588,491

Oleg Sapozhnikov, Mike Bailey, Vera Khokhlova, Wayne Kreider

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Patent

7 Mar 2017

The present technology relates generally to portable acoustic holography systems for therapeutic ultrasound sources, and associated devices and methods. In some embodiments, a method of characterizing an ultrasound source by acoustic holography includes the use of a transducer geometry characteristic, a transducer operation characteristic, and a holography system measurement characteristic. A control computer can be instructed to determine holography measurement parameters. Based on the holography measurement parameters, the method can include scanning a target surface to obtain a hologram. Waveform measurements at a plurality of points on the target surface can be captured. Finally, the method can include processing the measurements to reconstruct at least one characteristic of the ultrasound source.

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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