Olga V. Georg (Bessonova)

• PhD
• Researcher at German National Metrology Institute

Healing therapies that make use of ultrasound are based on raising the temperature in biological tissue. However, it is not possible to heal impaired tissue by applying a high dose of ultrasound. The temperature of the tissue is ultimately the physical quantity that has to be assessed to minimize the risk of undesired injury. Invasive temperature m...

Ultrasound therapy is a promising, non-invasive application with potential to significantly improve cancer therapies like surgery, viro- or immunotherapy. This therapy needs faster, cheaper and more easy-to-handle quality assurance tools for therapy devices as well as possibilities to verify treatment plans and for dosimetry. This limits comparabil...

Background Ultrasound therapies are promising, non-invasive applications with potential to significantly improve, e.g. cancer therapies like viro- or immunotherapy or surgical applications. However, a crucial step towards their breakthrough is still missing: affordable and easy-to-handle quality assurance tools for therapy devices and ways to verif...

Conference Publication ISTU 2014, International Symposium on Therapeutic Ultrasound

The output characterization of medical high intensity therapeutic ultrasonic devices poses several challenges for the hydrophones to be used for pressure measurements. For measurements at clinical levels in the focal region, extreme robustness, broad bandwidth, large dynamic range, and small receiving element size are all needed. Conventional spot-...

The aim of this work is to evaluate measurement methods for dosimetry and exposimetry quantities that were developed in the EMRP project “Dosimetry for Ultrasound Therapy -DUTy” by comparing the measurement results for three common quantities from three national laboratories. It further aims to investigate the general feasibility of possible future...

Methods of derating a nonlinear ultrasound field and associated systems are disclosed herein. A method of derating a nonlinear ultrasound field in accordance with an embodiment of the present technology can include, for example, calibrating an ultrasound source to a first source voltage (Vw) and generating a nonlinear acoustic wave from the ultraso...

The reliable characterization of high intensity therapeutic ultrasound (HITU, HIFU) fields is important regarding the safe and effective clinical application of the modality. However, the required acoustic output measurements pose several metrological challenges. Extreme pressure amplitudes easily cause damage to the typical sensors, pressure wavef...

Numerical modeling has been shown to be an effective tool to characterize nonlinear pressure fields for single?element HIFU transducers, but it has not yet been applied for the much more complex three?dimensional (3?D) fields generated by therapeuticphased arrays. In this work, two approaches are presented to simulate nonlinear effects in the field...

Current methods of determining high intensity focused ultrasound (HIFU) fields in tissue rely on extrapolation of measurements in water assuming linear wave propagation both in water and in tissue. Neglecting nonlinear propagation effects in the derating process can result in significant errors. In this work, a new method based on scaling the sourc...

Nonlinear propagation effects result in the formation of weak shocks in high intensity focused ultrasound (HIFU) fields. When shocks are present, the wave spectrum consists of hundreds of harmonics. In practice, shock waves are modeled using a finite number of harmonics and measured with hydrophones that have limited bandwidths. The goal of this wo...

Numerical simulations based on the Khokhlov-Zabolotskaya-type equation are currently used to characterize therapeutic high-intensity focused ultrasound fields in water and to predict bioeffects in tissue. Here results from three different algorithms that differ in calculating the nonlinear term in the equation are presented. Shock capturing schemes...

Nonlinear propagation causes high-intensity ultrasound waves to distort and generate higher harmonics, which are more readily absorbed and converted to heat than the fundamental frequency. Although such nonlinear effects have been investigated previously and found to not significantly alter high-intensity focused ultrasound (HIFU) treatments, two r...

In this work, a new derating method to extrapolate nonlinear ultrasound fields in water to biological tissue is proposed and tested for therapeutic medical systems. Focal values of acoustic field parameters in absorptive tissue are obtained from a numerical solution to a KZK-type equation and are compared to those derated, using the proposed method...

In this work, the influence of nonlinear and diffraction effects on amplification factors of focused ultrasound systems is investigated. The limiting values of acoustic field parameters obtained by focusing of high power ultrasound are studied. The Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation was used for the numerical modeling. Solutions for the...

Shock waves of up to 100 MPa may form at the focus of high-intensity focused ultrasound (HIFU) transducers at clinically reported in situ intensities of up to 30,000 Wcm(2). The heating due to shocks is sufficient to boil tissue in milliseconds, which dramatically alters the treatment. Quantification of enhanced heating from shocks is therefore cri...

The influence of nonlinear and diffraction effects on distortion of the spatial structure of peak positive and negative pressures in focused acoustic beams was studied for a weakly dissipative propagation medium. The problem was solved numerically based on the Khokhlov-Zabolotskaya-Kuznetsov equation for beams with uniform and Gaussian distribution...

High intensity focused ultrasound (HIFU) therapy is an emerging medical technology in which acoustic pressure amplitudes of up to 100 MPa are used to induce tissue ablation, often in combination with real‐time imaging. The ultrasound energy is typically focused into a millimeter‐size volume and used to thermally coagulate the tissue of interest whi...

The most commonly used method for derating high intensity focused ultrasound (HIFU) fields from water to tissue is based on multiplying the acoustic intensity measured in water by an exponential factor to compensate for attenuation in the tissue path assuming linear wave propagation. Yet, in nonlinear HIFU fields, the intensity provides little info...

In this work, numerical simulations are performed and spatial distributions of specific parameters of nonlinear focused ultrasound beams of various geometry are compared. The numerical algorithm is based on the solution of the Khokhlov‐Zabolotskaya (KZ) equation. Focused acoustic beams of periodic waves with an initially uniform amplitude distribut...

Acoustic characterization of nonlinear HIFU fields is important for both the accurate prediction of ultrasound induced bioeffects and the development of regulatory standards for clinical HIFU devices. In this work a new characterization method is proposed and tested in water, tissue phantoms, and ex-vivo tissues. The method is based on the combined...

Nonlinear acoustic waves have been widely employed in various areas of modern science and technology. Medical ultrasound, that includes both therapeutic and diagnostic techniques, is one of the most exciting examples. In therapy, high intensity focused ultrasound (HIFU) waves provides the ability to localize the deposition of acoustic energy noninv...