Time-shift Study Of Ultrasound Temperature-dependent Echo In Biological Tissues Based On RANSAC Algorithm For Removing Outliers

Tumor hyperthermia refers to a treatment method that raises the temperature of human tissue to a certain temperature by heating to cause cancer cells to die but does not affect normal cells.It is one of the important means for treating malignant tumors.In the course of treatment,real-time monitoring of tissue temperature is one of the keys to ensure the therapeutic effect of hyperthermia.Traditionally,invasive temperature measurement is adopted,that is,temperature sensors such as thermocouples and thermistors are inserted into tissues for temperature measurement.This way can cause damage to human tissues and can only be measured at a fixed point.Because of the obvious shortcomings of invasive temperature measurement technology,a non-invasive temperature measurement technology is urgently needed to replace it in cancer treatment.By studying the correlation between the time shift of the ultrasonic echo and the temperature change,the relationship between time shift and temperature is established,so that the non-invasive temperature measurement of the tissue can be realized.Due to the complexity of ultrasound propagation in tissues,the parameters related to echo time-shift and temperature obtained in existing studies are difficult to unify,and further research is needed to improve its accuracy.The work of this paper is to analyze the echo time shift from the perspective of signal processing,and get more accurate echo strain.Ultrasonic temperature measurement experiments were carried out with gelatin phantom and pig liver as experimental objects to verify the feasibility of signal analysis algorithm,and to analyze the relationship between temperature and echo time-shift strain,and further explore the feasibility of non-invasive temperature measurement technology.The main contents of the thesis include:1.Analysing the obtained ultrasound signals.Firstly,the signal is subjected to crosscorrelation analysis.By performing cross-correlation analysis on the entire segment of the ultrasonic signal,the ultrasonic echo displacement of each segment in the tissue is obtained.The general cross-correlation calculation of echo time shift is to directly calculate the difference of the time when the ultrasound passes through the upper and lower surfaces of the tissue at different temperatures,and the average echo time shift of the whole tissue is obtained.The method used in this paper is more representative of the temperature state at different locations in the organization.Then,the obtained echo displacement is subjected to the outlier detection to further improve the accuracy of the echo displacement.Firstly,median filter is used to smooth the echo.When there are many outliers in the echo displacement,the result of median filter is not good.Random sampling consistency(RANSAC)algorithm is proposed to remove outliers by establishing models and comparing thresholds.The results show that the method is effective in removing outliers and has no effect on the normal data..Finally,combined with the law of ultrasonic signal propagation in the tissue,the echo strain is analyzed,and the slope of the straight line obtained by fitting the echo displacement data after the outlier is the echo strain.2.Designing the experimental scheme of non-invasive temperature measurement by ultrasound.First,the gelatin model was used as the experimental object for analysis,and then the fresh porcine liver was used as the experimental object for analysis.In the experiment,the ultrasonic testing equipment adopts OPBOX 2.1,which can transmit and receive the ultrasonic signal,and directly connect with the computer through the USB interface,and set the signal acquisition parameters on the computer software interface,it is more convenient and fast to start to acquire the accurate echo signal.Through these two experiments,the feasibility of the above algorithm is further verified,and the operation process and experimental results are analyzed and calculated,and the correlation between echo strain and temperature is obtained.The results show that echo strain increases with the increase of temperature.In summary,through the research and analysis of this paper,the influence of outliers on the estimation of echo strain is eliminated,and the correlation between echo strain and temperature is verified,which provides a certain basis for non-invasive temperature measurement.