Research On Efficacy Monitoring And Dose Control Of High-intensity Focused Ultrasound Based On Electrical Impedance Distribution

As an effective therapeutic modality,high intensity focused ultrasound(HIFU)can destroy tumor tissues by thermocoagulation with less metastasis,but it is still limited by inaccurate non-invasive temperature monitoring and efficacy evaluation.The distribution of acoustic pressure and temperature at the tissue phantom during HIFU therapy was analyzed,and based on the temperature-impedance relationship,the model of HIFU treatment and electrical impedance measurement was established.With the simulations of acoustic pressure,temperature and electrical conductivity,the impedance of the phantom was calculated at different acoustic powers and treatment times through the distribution variation of electric potential and current density.It is proved that the relative impedance variation increases linearly with the increasing treatment time at a fixed acoustic power,and the relative impedance variation rate shows a linear relationship with acoustic power.To reach HIFU treatment efficacy(the temperature of focal region in radial ± 0.4 mm and in axial ± 2 mm reached 70 ?),the required relative impedance variation is inversely proportional to acoustic power,and the required treatment time shows inverse proportion to the square of acoustic power.The experimental results agreed with the theoretical simulations,after the establishment of the experimental system.Finally,for the universality of the conclusion,the impact of the transducers' structural parameters was discussed.It is proved for different transducers,in addition to the changes of the correlation coefficient,the proposed relative impedance variation rules were still valid.Because the proposed HIFU temperature monitoring method which was based on the relative electrical impedance variation,was combined effect during the measurement and treatment,existing the problem of inaccurate positioning.Therefore,based on EIT,an electrical impedance reconstruction method at HIFU focal region was proposed,which was on the base of the potential distribution on the surface of the tissue phantom.The two-dimensional electrical impedance reconstruction model at HIFU focal region was established,the simulated reconstruction at different treatment time with the same acoustic power was compared,and the effect of decentration on the results was considered.It is proved that based on EIT,the electrical impedance reconstruction at HIFU focal region could not only achieve the accurate positioning of the focal region,but also reflect the electrical impedance distribution and the temperature variation,which changed with the varying treatment time.The reconstruction method completed the noninvasive temperature measurement theory at the focal region,which was based on the electrical impedance variation.In this paper,the relative electrical impedance variation of the tissue phantom and the electrical impedance reconstruction were combined,to offer a new noninvasive temperature measurement method at HIFU focal region,which was fast,accurate and real-time.The new method could achieve efficacy monitoring and precise dose control,has a positive meaning to realize accurate control of HIFU treatment and offers new thoughts and research direction for subsequent theorical studies and clinical application.