Measurement And Study Of Acoustic Attenuation And Acoustic Impedance During HIFU Therapy

High-intensity focused ultrasound(HIFU)is a new type technology to treat cancer that has emerged in recent years.It has the advantages of non-destructive,local green and great potential for clinical application.When the HIFU signal passes through human tissue,due to the complexity of organ structure,many of the Ultrasonic signal components are reflected,transmitted,refracted and absorbed within the tissue,so the amplitude,energy,frequency,phase,speed,etc.of the signal are changed with temperature changing,and certain acoustic characteristic parameters of the tissue exhibit regular changes to reflect the micro-structural characteristics of the biological tissue to feedback the therapeutic effect.Based on the theories of ultrasonic transmission and related methods of signal processing,this paper discusses the measurement methods and related properties of tissue acoustic characteristic parameters(acoustic attenuation and acoustic impedance).The main contents are as follows:1.Introducing The theory of ultrasonic transmission and the construction of the experimental system.First,The theory of acoustic wave propagation in biological tissues was introduced.Then,The HIFU experimental system and the constant temperature water bath experimental system were set up.The isolated pork tissue was selected asthe experimental object.The experimental data was obtained by the above experimental system,and then the signal was intercepted and filtered to analyze the effect.2.Measurement and study of attenuation coefficient.A method of weighted inversion of attenuation coefficient by quality factor is proposed.The quality factor is extracted by the signal center frequency,and the influence of the center frequency on the measurement accuracy of the attenuation coefficient is determined by using the frequency division algorithm and the ITD and EMD frequency division algorithms respectively.The simulation results show that the sound attenuation coefficient error obtained by using the frequency division algorithm to obtain the quality factor extracted from the center frequency of each layer is obviously lower than that without the frequency division algorithm,and the result obtained by the EMD method is better than the ITD method.By studying the acoustic attenuation coefficient of the tissue in the HIFU experiment,it is found that the acoustic attenuation coefficient has a linear relationship with the frequency in the overall trend,and the temperature increases and the attenuation coefficient increases in a square.3.Measurement and study of acoustic impedance.According to the principle of ultrasonic transmission,the model of isolated pork tissue was established.The mathematical relationship between acoustic impedanceand echo energy was derived and applied to the measurement of acoustic impedance in HIFU treatment area.The water bath system design comparison experiment was used for verification analysis.The results show that the relative error of acoustic impedance measured by the two methods is controlled within 0.5%,and both of them show good consistency with temperature.It also proves that the echo energy method proposed in this paper can effectively measure the acoustic impedance of tissue in HIFU treatment area.