Methods Of Noninvasive Temperature Estimation In RFA Therapy Based On B-ultrasound Image Processing

Radiofrequency ablation(RFA)is a new method for tumor treatment using radiofrequency electric field heating to kill cancer cells.It is a commonly used technique for minimally invasive treatment of tumors.As the incidence of small renal cancer increases and the average volume of T1 renal cancer is reduced year by year,doctors are increasingly inclined to use radiofrequency ablation techniques that preserve nephron to treat small renal cancer.The control of ablation tissue temperature is the key to determine the therapeutic effect.In clinical practice,the doctor mainly controls the degree of ablation according to experience.Therefore,a noninvasive temperature measurement method is urgently needed to ensure the inactivation of cancer cells while protecting normal tissue.As a real-time monitoring device in radio frequency ablation,B-ultrasound has a unique advantage in many non-destructive temperature measurement methods.Kidney was used as a material to study the noninvasive temperature measurement method in radiofrequency ablation based on B-ultrasound image,to explore the relationship between the characteristic parameters of ultrasound images and temperature.The radiofrequency ablation experiment of the kidney was designed and carried out.The experimental system consisted of three modules: radio frequency ablation system,temperature measurement system and ultrasonic measurement system.The experiment used in vitro healthy pig kidney and in vivo healthy pig kidney as biomaterials,and collected B-ultrasound image data and real-time temperature data during radiofrequency ablation.After the data acquisition is completed,the image data of the ultrasound image data is processed,and the image filtering is first performed to eliminate the high frequency noise.In order to determine the center of the region of interest of the ultrasound image,the temperature probe center is marked by manual marking method and automatic marking method respectively,and the marking result is used as the center of the region of interest.In order to eliminate the high echo interference of the temperature probe in the image,a fixed threshold method is selected after comparing various threshold segmentation methods.The segmentation of the needle ultimately results in an area of interest in the ultrasound image from which the temperature probe is removed.Ultrasound characteristic parameters in the region were calculated,including gray mean,gray standard deviation,and gray gradient values.MATLAB was used to analyze the relationship between two characteristic parameters and temperature data,and the average gray level-temperature and gray standard deviation-temperature regression model were obtained.The average gray leveltemperature model is used to predict the temperature in the region of the ultrasound video to obtain the 2D pseudo color temperature distribution result.The results show that there is a significant positive correlation between the gray mean value,the gray standard deviation of the ultrasound image of the heated tissue and the temperature value during the radiofrequency ablation of the kidney.This relationship can be described by a piecewise function model,the model segmentation point is 65 °C.The model is a linear function when it is less than the segmentation point,and is a quadratic polynomial when it is greater than the segmentation point.The fitting goodness--R2 of the fitting results obtained by this model is greater than 0.9.The results of this study preliminarily showed that in the radiofrequency ablation treatment of renal tumors,the mean of gray scale and gray standard deviation of the B-ultrasound images can be used to nondestructively measure the temperature of the tissue.It provides a basis for clinical use of non-destructive temperature measurement based on B-ultrasound image in tumor ablation.