Abstract
Harmonic Motion Imaging (HMI) uses an amplitude-modulated (AM) beam to induce an oscillatory radiation force before, during and after ablation. In this paper, the findings from a numerical analysis of the effects related with the nonlinear propagation of AM focused ultrasonic beams in water on the radiation force and the location of its maxima will be presented. The numerical modeling is performed using the KZK nonlinear parabolic equation. The radiation force is generated by a focused transducer with a gain of 18, a carrier frequency of 1 MHz and a modulation frequency of 25 kHz. The modulated excitation generates a spatially-invariant force proportional to the intensity. Regarding the nonlinear wave propagation, the force is no longer proportional to the intensity, reaching a factor of eight between the nonlinear and linear estimations. Also, a 9 mm shift in the on-axis force peak occurs when the initial pressure increased from 1 to 300 kPa. This spatial shift, due to the nonlinear effects, becomes dynamic in AM focused beams, as the different signal periods have different amplitudes. This study shows that both the value and the spatial position of the force peak are affected by the nonlinear propagation of the ultrasonic waves.
BibTeX citation
@inproceedings{Gonzalez-Salido2011a,
author = {Nuria González-Salido and Noé Jiménez and Javier Redondo and Bernardino Roig and Rubén Picó and Víctor Sánchez-Morcillo and Elisa E. Konofagou and Francisco Camarena},
booktitle = {ISTU 2011: 11th International Society for Therapeutic Ultrasound Symposium. New York, USA. 11-13 April},
doi = {https://doi.org/10.1063/1.4757320},
editor = {AIP Conference Proceedings},
month = {4},
number = {1},
organization = {International Society for Therapeutic Ultrasound},
pages = {112-118},
publisher = {AIP Publishing},
series = {Poster},
title = {Nonlinear effects in the radiation force generated by amplitude-modulated focused beams},
url = {https://aip.scitation.org/doi/10.1063/1.4757320},
volume = {1481},
year = {2011}
}