Acoustic Characteristics Of Microbubbles In Vessels And Its Applications In The Evaluation Of HIFU Treatment

HIFU can be used for ablation of breast tumor tissue, and it can destroy the microcirculation of tumor. Through contrast-enhanced ultrasound imaging and other methods to analyze the condition of blood perfusion and blood supply of breast tumor before and after HIFU treatment, the effect of HIFU treatment can be evaluated. Strong scattering effect and non-linear characteristics of ultrasound microbubbles are used in Contrast-enhanced ultrasound imaging, while targeted ultrasound microbubbles are used in targeted imaging to achieve specific contrast enhancement. The theoretical study of acoustic properties of ultrasound microbubbles in blood vessels are theoretical bases of applications of contrast-enhanced ultrasound imaging used in the evaluation of HIFU treatment efficacy. And in order to make better applications of contrast-enhanced ultrasound imaging technology in HIFU treatment evaluation, we should optimize the parameters of tumor microvascular imaging with contrast-enhanced ultrasound. Based on the optimized parameters, we can achieve contrast enhancement of breast tumor vessels before and after HIFU treatment and assess efficacy of HIFU treatment.The dynamic model of adherent microbubbles has been established. The acoustic effects of free microbubbles and adherent microbubbles in vessels have been simulated. The effect of different parameters of instrument and microbubbles on the acoustic characteristics of microbubbles in vessels is studied. The results show that the two kinds of multiple microbubbles both have better scattering efficiency and second harmonic effect at low frequencies while they have higher scattering signal and second harmonic effect at driving pressure of 160KPa and 130KPa respectively. In low concentrations, scattering efficiency increases as the concentration of microbubbles increases. When the radius of microbubble is between 0.5 and 3μm, the scattering cross section of microbubble increases as the radius of microbubble increases. These provide theoretical guidance for the application of contrast-enhanced ultrasound imaging used in HIFU treatment evaluation.Animal experiments of microvessel perfusion imaging of tumor have been made. The effects of different parameters such as direct pressure, frequency and concentration of microbubble on contrast-enhanced ultrasound imaging of tumor microvessels have been studied. Combined with theoretical analysis, it is concluded that when DP reaches at 70KPa around with the other parameters fixed, the tumor has the best contrast-enhanced effect. The result shows that the overall contrast-enhanced effect is better when the driving frequency is low with the other parameters fixed. The result also shows that the overall contrast-enhanced effect is the best when the dose of microbubbles reaches 0.1ml/kg with the other parameters fixed. After the optimization of parameters, contrast-enhanced ultrasound imaging can be better be used in HIFU treatment evaluation.The method of animal experiments have been used in the validation of the application value of ultrasound imaging in the evaluation of diagnosis and evaluation before HIFU ablation for the treatment of breast cancer . Contrast-enhanced ultrasound imaging of breast tumor before and after the treatment using a small HIFU instrument has been experimented, and the analysis of efficacy of HIFU treatment under different exposure time has been achieved using perfusion parameters. The results show that the degree of microvascular damage increases with the exposure time increases. When the exposure time of this HIFU instrument reaches 10s, 30s and 60s with the other parameters remaining constant, the efficacy was at level-2, level-3 and level-4 respectively. When the exposure time of this HIFU instrument reaches 60s, the requirements of HIFU tumor ablation can be achieved.