Acoustic Cavitation Bubble Dynamics And Cavitation Imaging Based On Improved Keller-Miksis Model

High-intensity Focused Ultrasound(HIFU)is a non-invasive treatment technology.It focuses ultrasound on the lesions in the body using the characteristics of ultrasound’s penetrability and focalization,and kills tumor cells through the high temperature effect and cavitation effect generated by ultrasound,but does not damage the surrounding tissues.Cavitation bubbles play an important role in HIFU treatment.Therefore,in order to ensure the safety and effectiveness of HIFU treatment,it is necessary to study the dynamic monitoring of cavitation bubbles.In order to obtain high-quality ultrasonic cavitation images,this paper studies the single bubble dynamics model,the double bubble dynamics model,the bubble group dynamics model and the ultra-fast active cavitation imaging based on the cavitation bubble wavelet transform(CBWT)technology.(1)In order to describe the motion of the bubble wall in an ultrasonic field that is closer to the actual situation,based on the Keller Miksis model and considering the fact that gas is not infinitely compressible,an improved single bubble dynamic simulation model is established.The effects of cavitation bubble parameters and liquid parameters on the vibration of a single cavitation bubble are analyzed,and the wavelet transform of a single bubble under different parameters is calculated.Ultrasonic cavitation imaging is performed using CBWT technology.The conclusions are as follows:(1)As the initial radius of the cavitation bubble increases,on the one hand,the longer the vibration duration,the greater the vibration radius,the velocity of the bubble wall,and the amplitude of the acceleration first increase and then decrease;On the other hand,the stronger the fundamental component in the scattered echo,the weaker the subharmonic component.When the initial radius of the cavitation bubble is 1.5um,the energy of the subharmonic component is the largest and higher than the energy of the fundamental component.At this time,the cavitation to noise ratio(CNR)value of the ultrasonic cavitation image is the largest;(2)With the increase of liquid surface tension,the vibration amplitude,velocity,and acceleration of cavitation bubbles first increase and then decrease within a certain period of time;At the same time,the fundamental component of the scattered echo is significantly weakened,and the CNR of the cavitation image gradually increases;(3)With the increase of liquid viscosity coefficient,on the one hand,the vibration duration of cavitation bubbles decreases,and the vibration amplitude,as well as the velocity and acceleration of the bubble wall,decreases;On the other hand,the fundamental wave energy in the scattered echo increases,the second harmonic component increases,and the second harmonic component decreases.When the liquid viscosity coefficient is 0.001 Pa ·s,the CNR value is the largest.(4)The effect of liquid saturated vapor pressure on the vibration and echo characteristics of cavitation bubbles is small,but the CNR value decreases with the increase of liquid saturated vapor pressure.(2)Based on the improved dynamic model of double bubbles,this paper studied the vibration characteristics of double bubbles and the factors affecting the sub Bjerknes force,calculated the double bubble waves under different parameters,and combined with CBWT technology to perform ultrasonic cavitation imaging.At the same time,compared with the double bubbles imaging results obtained based on the Keller Miksis model,the effectiveness of the improved model was verified.The results show:(1)When the distance between the two bubbles is fixed,with the increase of the initial radius of the large cavitation bubble,on the one hand,the vibration duration of the large cavitation bubble is longer,and its collapse time is later than that of the small cavitation bubble;On the other hand,multiple collapses of double bubbles have a significant effect on each other,but the secondary Bjerknes force of small cavitation bubbles on large cavitation bubbles is stronger than that of large cavitation bubbles on small cavitation bubbles.At the same time,the CNR value of the ultrasound cavitation image decreases.(2)With the increase of the distance between the two bubbles,on the one hand,the maximum amplitude of the vibration radius of the cavitation bubble increases,but the sub Bjerknes force gradually decreases;On the other hand,it has a certain impact on the collapse time of large cavitation bubbles,with the collapse number changing within 10 us,and small cavitation bubbles have a greater impact on large cavitation bubbles.The CNR value is maximum when the double bubble spacing is 100 um.(3)As the saturated vapor pressure of the liquid increases,on the one hand,the amplitude of the scattered echo first increases and then decreases,and the subharmonic component gradually decreases;On the other hand,the variation range of the maximum attraction of small cavitation bubbles gradually increases,while the variation range of the maximum attraction of large cavitation bubbles first increases and then decreases.At the same time,the CNR value of the ultrasound cavitation image decreases.(3)In this paper,based on an improved bubble dynamics model,a super fast active cavitation imaging method combining multiple bubble wavelet transform(MBWT)is proposed for the first time.Firstly,the effects of initial radius and pulse length of cavitation bubbles on the vibration characteristics of bubble clusters are studied;Secondly,bubble group wavelets with different parameters are calculated,and MBWT cavitation imaging is performed using CBWT technology.MBWT uses a modified Keller Miksis model to construct bubble wavelets for bubble clusters,taking into account the different initial radius distributions of cavitation bubbles under different pulse lengths.The results show that the MBWT cavitation imaging quality considering the initial radius distribution of cavitation bubbles under different pulse lengths is higher.When the pulse lengths are 20 us,1ms,2ms,and 5ms,the CNR values of MBWT cavitation imaging are increased by 3.43 d B,2.58 d B,4.10 d B,and 5.73 d B compared to the traditional single bubble wavelet transform(SBWT).On the one hand,this study can provide theoretical reference for the study of ultrasonic cavitation dynamics and selective enhancement or suppression of cavitation effects.On the other hand,it can also improve the image quality of ultrasonic cavitation imaging,provide new ideas for the development of accurate cavitation monitoring imaging during HIFU treatment,and contribute to improving the safety and accuracy of HIFU treatment.