Based On The Dynamic Behavior Of Microbubbles In Focused Ultrasound To Estimate And Compensate For The Study Of The In-situ Sound Field

The localized bioeffects of the targeted tissue are highly dependent on acoustic parameters during FUS treatment,but,when the therapeutic ultrasound through the tissue layer to the target,resulting in the key ultrasonic parameters unknown,due to the acoustic attenuation of 20-200 mm tissue medium on the ultrasound path.For this problem,Microbubbles has been investigated as a biocompatible,internal “probe” to convert a local parameter to a echo characteristic that can be measured externally.We accessed the main challenge is that the multiple acoustic parameters are not easily isolated from the multiple measureable characteristics of the echo signals.In order to isolate the multiple factors(such as attenuation and perfusion rate)contributing to measurable echo characteristics,we sought to exploit the highly specific behaviors of microbubble destruction when exposed to intense ultrasound.This paper reports a feasibility study of a pre-treatment scheme to noninvasively determine effective attenuation and other relevant parameters and subsequently compensate for them during the actual therapeutic procedure.Focused on the key tissue features-tissue attenuation and organizational environment,we designed a controlled PVA phantom which can effectively simulate the tissue features.A programmable high frame rate scanner system(Verasonic Vantage-128,USA)was used to capture echo data at very high spatial and temporal resolutions.A custom imaging sequence produced good quality B-scan frames at a rate of 1 k Hz,which are interleaved between FUS exposure at various burst lengths and amplitudes.The destruction of microbubbles by the treatment beam increases with treatment amplitude and burst length,as expected.The data sets of destruction curves obtained with attenuating layers were matched to the un-attenuated reference data set using image matching and mathematical statistics algorithm.The resulting fitted attenuation was found to match closely the actual values,verified by independent measurement of attenuation using pulse insertion method.The errors of in situ beam intensity measured with the proposed method were found to be less than 1.5 d B.However,any single measurement cannot reliably reveal the in situ beam intensity without controlling the microbubble concentration.Analyzing the complete destruction characteristics produced a feature-rich data set that can be fitted to more than one unknown parameters simultaneously.