Magnetic Resonance Monitoring Based On Acoustic Radiation Imaging For HIFU Treatment

High intensity focused ultrasound(HIFU)is an emerging technology for precise tumor treatment.It uses low-energy ultrasound to focus instantaneously(0.5~5s)to form a high-temperature region(above 65°C),and to cause irreversible coagulative necrosis in the tissue through thermal effects,cavitation effects and mechanical effects.without damaging the surrounding normal tissue.This technology has been applied to the treatment of various benign or malignant tumors such as uterine fibroids due to its non-wound and non-invasive advantages.Accurate and effective monitoring is critical to ensuring the safety and efficacy of treatment.Currently,common monitoring methods are ultrasound and magnetic resonance imaging.Compared to ultrasound monitoring,MRI is the preferred method of monitoring HIFU because of its good imaging contrast of soft tissue and real-time,non-destructive capability of temperature imaging.MRT based on PRFS can realize fast and accurate measurement of tissue temperature,however this method is ineffective for adipose tissue.In order to monitor the process of HIFU treatment safely and efficiently,this study is based on the ARFI sequence based on dual TE,the T2 and proton density of the tissue are obtained by fitted.Based on the fitted T2 and proton density and its weighted image,the linear relationship between the T2 & proton density and the fat temperature was studied,and the magnetic resonance monitoring method based on the ARFI sequence for simultaneous measurement of tissue temperature and displacement was realized.Based on the ARFI sequences with and without gradient,the feasibility of ARFI to measure the apparent diffusion coefficient of the tissue was investigated,and the feasibility of the ARFI sequence to measure tissue T2 was confirmed.Cavitation may occur during the action of HIFU,which will cause the temperature of the tissue to rise rapidly.Improper monitoring may result in unnecessary damage in surrounding tissue.Rational use of cavitation can improve the treatment efficiency of HIFU.In this paper,the temperature rise curve of tissue under different ultrasonic powers was studied by MRT;The displacement variation regular pattern of tissue after different power action was studied by MR-ARFI;And Passive cavitation noise of tissue under different power HIFU effects was detected.No significant cavitation threshold was found in the detection of passive cavitation noise of the organization,which confirmed that the ultrasonic power in this paper did not reach the cavitation threshold.