Publications by authors named "P V Yuldashev"

23 Publications

"HIFU beam": a Simulator for Predicting Axially Symmetric Nonlinear Acoustic Fields Generated by Focused Transducers in a Layered Medium.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 Apr 20;PP. Epub 2021 Apr 20.

"HIFU beam" is a freely available software tool that comprises a MATLAB toolbox combined with a user-friendly interface and binary executable compiled from FORTRAN source code HIFU beam. (2021). Available: http://limu.msu.ru/node/3555?language=en. It is designed for simulating high-intensity focused ultrasound (HIFU) fields generated by single-element transducers and annular arrays with propagation in flat-layered media that mimic biological tissues. Numerical models incorporated in the simulator include evolution-type equations, either the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation or one-way Westervelt equation, for radially symmetric ultrasound beams in homogeneous and layered media with thermoviscous or power law acoustic absorption. The software uses shock-capturing methods that allow for simulating strongly nonlinear acoustic fields with high-amplitude shocks. In this paper, a general description of the software is given along with three representative simulation cases of ultrasound transducers and focusing conditions typical for therapeutic applications. The examples illustrate major nonlinear wave effects in HIFU fields including shock formation. Two examples simulate propagation in water, involving a single-element source (1 MHz frequency, 100 mm diameter, 90 mm radius of curvature) and a 16-element annular array (3 MHz frequency, 48 mm diameter, and 35 mm radius of curvature). The third example mimics the scenario of a HIFU treatment in a 'water-muscle-kidney' layered medium using a source typical for abdominal HIFU applications (1.2 MHz frequency, 120 mm diameter and radius of curvature). Linear, quasi-linear, and shock-wave exposure protocols are considered. It is intended that "HIFU beam" can be useful in teaching nonlinear acoustics; designing and characterizing high-power transducers; and developing exposure protocols for a wide range of therapeutic applications such as shock-based HIFU, boiling histotripsy, drug delivery, immunotherapy, and others.
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http://dx.doi.org/10.1109/TUFFC.2021.3074611DOI Listing
April 2021

Dual-Use Transducer for Ultrasound Imaging and Pulsed Focused Ultrasound (pFUS) Therapy.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 Apr 1;PP. Epub 2021 Apr 1.

Pulsed focused ultrasound (pFUS) uses short acoustic pulses delivered at low duty cycle and moderate intensity to non-invasively apply mechanical stress or introduce disruption to tissue. Ultrasound-guided pFUS has primarily been used for inducing cavitation at the focus, with or without contrast agents, to promote drug delivery to tumors. When applied in tandem with contrast agents, pFUS is often administered using an ultrasound imaging probe, which has a small footprint and does not require a large acoustic window. The use of nonlinear pFUS without contrast agents was recently shown to be beneficial for localized tissue disruption, but required higher ultrasound pressure levels than a conventional ultrasound imaging probe could produce. In this work, we present the design of a compact dual-use 1 MHz transducer for ultrasound-guided pFUS without contrast agents. Nonlinear pressure fields that could be generated by the probe, under realistic power input, were simulated using the Westervelt equation. In water, fully developed shocks of 42 MPa amplitude and peak negative pressure of 8 MPa were predicted to form at the focus at 458 W acoustic power or 35% of the maximum reachable power of the transducer. In absorptive soft tissue, fully developed shocks formed at higher power (760 W or 58% of the maximum reachable power) with the shock amplitude of 33 MPa and peak negative pressure of 7.5 MPa. The electronic focus steering capabilities of the array were evaluated and found to be sufficient to cover a target with dimensions of 19 mm in axial direction and 44 mm in transversal direction.
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http://dx.doi.org/10.1109/TUFFC.2021.3070528DOI Listing
April 2021

Bilayer aberration-inducing gel phantom for high intensity focused ultrasound applications.

J Acoust Soc Am 2020 12;148(6):3569

Department of Acoustics, Physics Faculty, Moscow State University, Leninskie Gory, Moscow 119991, Russia.

Aberrations induced by soft tissue inhomogeneities often complicate high-intensity focused ultrasound (HIFU) therapies. In this work, a bilayer phantom made from polyvinyl alcohol hydrogel and ballistic gel was built to mimic alternating layers of water-based and lipid tissues characteristic of an abdominal body wall and to reproducibly distort HIFU fields. The density, sound speed, and attenuation coefficient of each material were measured using a homogeneous gel layer. A surface with random topographical features was designed as an interface between gel layers using a 2D Fourier spectrum approach and replicating different spatial scales of tissue inhomogeneities. Distortion of the field of a 256-element 1.5 MHz HIFU array by the phantom was characterized through hydrophone measurements for linear and nonlinear beam focusing and compared to the corresponding distortion induced by an ex vivo porcine body wall of the same thickness. Both spatial shift and widening of the focal lobe were observed, as well as dramatic reduction in focal pressures caused by aberrations. The results suggest that the phantom produced levels of aberration that are similar to a real body wall and can serve as a research tool for studying HIFU effects as well as for developing algorithms for aberration correction.
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http://dx.doi.org/10.1121/10.0002877DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8097711PMC
December 2020

A Prototype Therapy System for Boiling Histotripsy in Abdominal Targets Based on a 256-Element Spiral Array.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 May 26;68(5):1496-1510. Epub 2021 Apr 26.

Boiling histotripsy (BH) uses millisecond-long ultrasound (US) pulses with high-amplitude shocks to mechanically fractionate tissue with potential for real-time lesion monitoring by US imaging. For BH treatments of abdominal organs, a high-power multielement phased array system capable of electronic focus steering and aberration correction for body wall inhomogeneities is needed. In this work, a preclinical BH system was built comprising a custom 256-element 1.5-MHz phased array (Imasonic, Besançon, France) with a central opening for mounting an imaging probe. The array was electronically matched to a Verasonics research US system with a 1.2-kW external power source. Driving electronics and software of the system were modified to provide a pulse average acoustic power of 2.2 kW sustained for 10 ms with a 1-2-Hz repetition rate for delivering BH exposures. System performance was characterized by hydrophone measurements in water combined with nonlinear wave simulations based on the Westervelt equation. Fully developed shocks of 100-MPa amplitude are formed at the focus at 275-W acoustic power. Electronic steering capabilities of the array were evaluated for shock-producing conditions to determine power compensation strategies that equalize BH exposures at multiple focal locations across the planned treatment volume. The system was used to produce continuous volumetric BH lesions in ex vivo bovine liver with 1-mm focus spacing, 10-ms pulselength, five pulses/focus, and 1% duty cycle.
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http://dx.doi.org/10.1109/TUFFC.2020.3036580DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8191454PMC
May 2021

Effect of surface roughness on nonlinear reflection of weak shock waves.

J Acoust Soc Am 2019 Nov;146(5):EL438

Université de Lyon, Ecole Centrale de Lyon, Institut National des Sciences Appliquées de Lyon, Université Claude Bernard Lyon I, Centre National de la Recherche Scientifique, Laboratoire de Mécanique des Fluides et d'Acoustique, Unité Mixte de Recherche 5509, 36 Avenue Guy de Collongue, F-69134, Ecully, France.

The authors have recently shown that irregular reflections of spark-generated pressure weak shocks from a smooth rigid surface can be studied using an optical interferometer [Karzova, Lechat, Ollivier, Dragna, Yuldashev, Khokhlova, and Blanc-Benon, J. Acoust. Soc. Am. 145(1), 26-35 (2019)]. The current study extends these results to the reflection from rough surfaces. A Mach-Zehnder interferometer is used to measure pressure waveforms. Simulations are based on the solution of axisymmetric Euler equations. It is shown that roughness causes a decrease of the Mach stem height and the appearance of oscillations in the pressure waveforms. Close to rough surfaces, the pressure was higher compared to the smooth surface.
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http://dx.doi.org/10.1121/1.5133737DOI Listing
November 2019