Elena Filonenko
 

Work: Modeling of heating of biological tissue by high intensity focused ultrasound using transducers of different geometry. Dept. of Acoust., Phys. Faculty, Moscow State Univ.

Main results: Absorption of acoustic energy in focused ultrasound beam propagating through tissue can create local heating deep in tissue volume. Fast heating up to 60 C and higher by intense ultrasound leads to destruction of tissue. This effect can be used in medicine for noninvasive treatment of cancer tumors and hemostasis. Various physical effects, such as acoustic nonlinearity, absorption, reflections are of importance and thus it is necessary to investigate their benefits and disadvantages. The heating process also depends on the structure of acoustic field that varies with the geometry of transducer. Theoretical models and corresponding numerical algorithms are developed in this work in order to obtain spatial distributions of acoustic field parameters and temperature. Temperature distributions were obtained by solution of the bioheat equation. Heat sources were calculated from the acoustic field modeled with account of acoustic nonlinearity, absorption, dispersion, focusing, reflection, and diffraction phenomena. Several transducers with different geometry such as a piston, an ultrasound phased array were investigated. The results, which were obtained by using our codes, were in good agreement with experiment data. For example, nonlinear absorption of the ultrasound beam leads to increase of temperature in the focal area and better locality of heating. A shift of the focal area toward the transducer is a result of the presence of interfaces between tissues with different acoustical and temperature parameters. It was shown that random distribution of elements of the array eliminates the appearance of grating lobes and overheating of undesirable regions as compared with regularly distributed elements.