Research On Ultrasound Monitoring Of Thermal Ablation Induced By High-intensity Focused Ultrasound

Tumor is one of the most serious diseases that endanger people's health nowadays.However,the current treatment methods such as surgery,radiotherapy and chemotherapy,have the problems of high recurrence rate and large side effects.Therefore,minimally invasive and even non-invasive treatment of tumors has attracted much attention in recent years.High-intensity focused ultrasound(HIFU)is used to treat tumors by focusing ultrasound on the ablation area of tissue in vivo to form local thermal energy.This thermal energy can make the tissue temperature in the ablation area reach 65 C instantaneously,which promotes irreversible coagulative necrosis in the ablation area.At present,the clinical real-time monitoring method based on B-mode ultrasound imaging is mainly adopted,but the image resolution is low and it is easily interfered by cavitation.In this paper,the ultrasonic monitoring imaging algorithms for HIFU treatment include elastography,Nakagami parameter estimation imaging and backscatter integral imaging.The main work is to improve the quality of the surveillance image and the accuracy of monitoring the ablation area through research and optimization of these algorithms.The details are as follows:(1)In the study of elastography,this paper first establishes the relationship between tissue hardness and displacement/strain through biomechanical analysis on COMSOL software.Then,the relationship is used for the ultrasonic elastic imaging of injury.The traditional time-domain cross-correlation algorithm and frequency-domain correlation algorithm are researched and optimized through the hard core phantom experiment and the HIFU radiation bovine liver experiment respectively.A method based on a combination of data preprocessing and post-elastography imaging is achieved to estimate the elastic strain of tissue.This optimized algorithm can largely reflect the internal hardness information of the tissue,so as to monitor the damaged area in the tissue.(2)In the study of Nakagami parameter estimation imaging,two kinds of damage models are simulated by Field II,and Nakagami parameter estimation imaging is studied by using the simulation data of this model.The influence of echo signal before and after logarithmic compression on Nakagami parameter estimation imaging is analyzed and compared.In this paper,the traditional Nakagami parameter estimation imaging algorithm is optimized,and pyramid-based Nakagami parameter estimation imaging is realized.The optimized algorithm and the traditional Nakagami parameter estimation imaging algorithm are imaged by model simulation data and HIFU radiation bovine liver experimental data respectively.The results show that the monitoring image obtained by this optimization algorithm improves the contrast between the damage and the tissue area,highlights the contour information of the damage area,and can more intuitively observe the damage situation.(3)In the study of integrated backscatter imaging,the backscattered integrated imaging and digital subtraction imaging are first studied by HIFU irradiation of bovine liver experiments.Then,the three common methods in digital subtraction imaging are compared and sum of squared differences(SSD)algorithm has a strong anti-noise effect.The algorithm combining backscatter integral imaging with SSD subtraction imaging is used to detect the ablation of bovine liver irradiated by HIFU,and the factors affecting the effect of backscatter integral subtraction imaging are studied.Finally,the ablation area is color-coded and superimposed on the B-mode ultrasound image to facilitate the monitoring of the damage.The results show that the acquired back integral subtraction image reduces the noise effect of the tissue background and highlights the location and shape of the damaged area.This paper mainly studies and optimizes the elastic imaging,Nakagami parameter imaging and integrated backscatter imaging from different monitoring imaging principles,which improves the quality of monitoring images and the accuracy of ablation area detection from multiple angles.It can provide reference for accurate HIFU treatment..