Papers by Leonid R Gavrilov
The paper presents an analytical method for calculating and analyzing the quality of 3 D acoustic... more The paper presents an analytical method for calculating and analyzing the quality of 3 D acoustic fields of multielement phased arrays used in noninvasive ultrasound surgical devices. An analytical solution for the far field of each of its elements is used when calculating the array field. This method significantly accel erates calculations while preserving the high accuracy of results as compared to conventional direct numerical integration. Radiation from typical phased arrays is calculated using this approach, and the quality of their dynamic focusing is analyzed. Undesired diffraction effects caused by electronic focus steering are consid ered: an amplitude decrease in the main maximum and the appearance of grating lobes. The quality of dynamic focusing of the acoustic fields of two practically interesting arrays with a quasi random element dis tribution (256 and 1024 elements, respectively), as well as of the regular array consisting of 256 elements is compared. In addition as well, a study is made of how the dimensions of the array elements and their spatial distributions affect the dimensions of the areas in which dynamic focusing is possible without occurrence of strong grating lobes and significant decrease in pressure amplitude at the main focus.
The emergence of new ways of applying high power ultrasound in medicine that are based on using n... more The emergence of new ways of applying high power ultrasound in medicine that are based on using nonlinear fields and shock wave operation modes requires a substantial increase in the power of phased arrays used for the generation of these fields. The need to develop a new generation of similar arrays based on employing densely packed elements arranged spirally on their surfaces is shown.
Effect of beam limiting aperture and collector potential on multi-element focused ion beamsa) Rev... more Effect of beam limiting aperture and collector potential on multi-element focused ion beamsa) Rev. Sci. Instrum. 83, 02B714 ; 10.1063/1.3672117 Compact electrostatic beam optics for multi-element focused ion beams: Simulation and experiments Rev. Sci. Instrum. 82, 013501 (2011); 10.1063/1.3514989
The subject of this review is the description and analysis of researches on application of focuse... more The subject of this review is the description and analysis of researches on application of focused ultrasound for stimulation of somatosensory, hearing and other neural structures of the peripheral nervous system. The main parameters of focused ultrasound, factors determining its biological effects, and methods of stimulation of peripheral nervous structures are discussed. Different stimulation effects and sensations are considered. A variety of practical applications of ultrasound stimulation of peripheral nervous structures is presented, including diagnostics of neurological and dermatological diseases, evaluation of the efficiency of anesthetic and analgesic drugs, principles of the development of an ultrasound tactile display, diagnostics of hearing disorders, possibilities of ultrasound hearing prosthetics, etc. The part of the review related with the methods and results (Sections 3-7) is based, first of all, on the data of the studies carried out in a number Russian Institutes from the beginning of 1970s and until last years. These results were published presumably in Russian journals and books and not well known to investigators in other countries. Some of the obtained results and offered approaches still have a current interest and practical significance. During the last decade, investigations of ultrasound stimulation of peripheral nervous structures began to develop actively in a number of countries.
Physics in Medicine and Biology, 2013
The goal of this study was to investigate theoretically the effects of nonlinear propagation in a... more The goal of this study was to investigate theoretically the effects of nonlinear propagation in a high-intensity focused ultrasound (HIFU) field produced by a therapeutic phased array and the resultant heating of tissue behind a rib cage. Three configurations of focusing were simulated: in water, in water with ribs in the beam path and in water with ribs backed by a layer of soft tissue. The Westervelt equation was used to model the nonlinear HIFU field, and a 1 MHz phased array consisting of 254 circular elements was used as a boundary condition to the model. The temperature rise in tissue was modelled using the bioheat equation, and thermally necrosed volumes were calculated using the thermal dose formulation. The shapes of lesions predicted by the modelling were compared with those previously obtained in in vitro experiments at low-power sonications. Intensity levels at the face of the array elements that corresponded to the formation of high-amplitude shock fronts in the focal region were determined as 10 W cm −2 in the free field in water and 40 W cm −2 in the presence of ribs. It was shown that exposures with shocks provided a substantial increase in tissue heating, and its better spatial localization in the main focal region only. The relative effects of overheating ribs and splitting of the focus due to the periodic structure of the ribs were therefore reduced. These results suggest that utilizing nonlinear propagation and shock formation effects can be beneficial for inducing confined HIFU lesions when irradiating through obstructions such as ribs. Design of compact therapeutic arrays to provide maximum power outputs with lower intensity levels at the elements 5
The paper presents an analytical method for calculating and analyzing the quality of 3 D acoustic... more The paper presents an analytical method for calculating and analyzing the quality of 3 D acoustic fields of multielement phased arrays used in noninvasive ultrasound surgical devices. An analytical solution for the far field of each of its elements is used when calculating the array field. This method significantly accel erates calculations while preserving the high accuracy of results as compared to conventional direct numerical integration. Radiation from typical phased arrays is calculated using this approach, and the quality of their dynamic focusing is analyzed. Undesired diffraction effects caused by electronic focus steering are consid ered: an amplitude decrease in the main maximum and the appearance of grating lobes. The quality of dynamic focusing of the acoustic fields of two practically interesting arrays with a quasi random element dis tribution (256 and 1024 elements, respectively), as well as of the regular array consisting of 256 elements is compared. In addition as well, a study is made of how the dimensions of the array elements and their spatial distributions affect the dimensions of the areas in which dynamic focusing is possible without occurrence of strong grating lobes and significant decrease in pressure amplitude at the main focus.
The emergence of new ways of applying highpower ultrasound in medicine that are based on
using n... more The emergence of new ways of applying highpower ultrasound in medicine that are based on
using nonlinear fields and shockwave operation modes requires a substantial increase in the power of phased
arrays used for the generation of these fields. The need to develop a new generation of similar arrays based on
employing densely packed elements arranged spirally on their surfaces is shown.
These reviews of books and other forms of information express the opinions of the individual revi... more These reviews of books and other forms of information express the opinions of the individual reviewers and are not necessarily endorsed by the Editorial Board of this Journal.
Journal of The Acoustical Society of America, 1987
Short pulses of focused ultrasound can stimulate the superficial and deep-seated receptor structu... more Short pulses of focused ultrasound can stimulate the superficial and deep-seated receptor structures of human tissues and induce different somatosensory sensations including, in particular, pain sensations. Focused ultrasound as a new artificial stimulus for inducing pain has a number of advantages related with its non-invasiveness, the possibility of the precise control of stimulus parameters and the location of its action. The experimental procedures and the results of the application of focused ultrasound as a painful stimulus in physiological research and in clinical practice are discussed. Data concerning various kinds of pain sensations, values of ultrasound thresholds of pain in different parts of the hand, as well as the discussion of the main effective factors of focused ultrasound responsible for the induction of pain, are presented in this review.
Considerable progress has been achieved in the use of infrared (IR) techniques for qualitative ma... more Considerable progress has been achieved in the use of infrared (IR) techniques for qualitative mapping of acoustic fields of high intensity focused ultrasound (HIFU) transducers. The authors have previously developed and demonstrated a method based on IR camera measurement of the temperature rise induced in an absorber less than 2 mm thick by ultrasonic bursts of less than 1 s duration. The goal of this paper was to make the method more quantitative and estimate the absolute intensity distributions by determining an overall calibration factor for the absorber and camera system. The implemented approach involved correlating the temperature rise measured in an absorber using an IR camera with the pressure distribution measured in water using a hydrophone. The measurements were conducted for two HIFU transducers and a flat physiotherapy transducer of 1 MHz frequency. Corresponding correction factors between the free field intensity and temperature were obtained and allowed the conversion of temperature images to intensity distributions. The system described here was able to map in good detail focused and unfocused ultrasound fields with sub-millimeter structure and with local time average intensity from below 0.1 W/cm 2 to at least 50 W/cm 2 . Significantly higher intensities could be measured simply by reducing the duty cycle.
Journal of The Acoustical Society of America, 2003
The goal of this study was to investigate theoretically the effects of nonlinear propagation in a... more The goal of this study was to investigate theoretically the effects of nonlinear propagation in a high-intensity focused ultrasound (HIFU) field produced by a therapeutic phased array and the resultant heating of tissue behind a rib cage. Three configurations of focusing were simulated: in water, in water with ribs in the beam path and in water with ribs backed by a layer of soft tissue. The Westervelt equation was used to model the nonlinear HIFU field, and a 1 MHz phased array consisting of 254 circular elements was used as a boundary condition to the model. The temperature rise in tissue was modelled using the bioheat equation, and thermally necrosed volumes were calculated using the thermal dose formulation. The shapes of lesions predicted by the modelling were compared with those previously obtained in in vitro experiments at low-power sonications. Intensity levels at the face of the array elements that corresponded to the formation of high-amplitude shock fronts in the focal region were determined as 10 W cm −2 in the free field in water and 40 W cm −2 in the presence of ribs. It was shown that exposures with shocks provided a substantial increase in tissue heating, and its better spatial localization in the main focal region only. The relative effects of overheating ribs and splitting of the focus due to the periodic structure of the ribs were therefore reduced. These results suggest that utilizing nonlinear propagation and shock formation effects can be beneficial for inducing confined HIFU lesions when irradiating through obstructions such as ribs. Design of compact therapeutic arrays to provide maximum power outputs with lower intensity levels at the elements 5
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Papers by Leonid R Gavrilov
using nonlinear fields and shockwave operation modes requires a substantial increase in the power of phased
arrays used for the generation of these fields. The need to develop a new generation of similar arrays based on
employing densely packed elements arranged spirally on their surfaces is shown.
using nonlinear fields and shockwave operation modes requires a substantial increase in the power of phased
arrays used for the generation of these fields. The need to develop a new generation of similar arrays based on
employing densely packed elements arranged spirally on their surfaces is shown.