脉冲高强度聚焦超声脉冲参数与焦点声压的关系研究

发布时间：2018-08-27 12:21

【摘要】：高强度聚焦超声（HighIntensity Focused Ultrasound，HIFU）技术是一种新兴的发展迅速的非侵入治疗技术，目前已经被用于多种肿瘤、非肿瘤疾病的临床治疗中，并取得了很好的疗效。HIFU的作用机制主要是热效应、空化效应和机械效应，临床上主要依靠HIFU的热效应及空化效应达到肿瘤消融的目的。HIFU治疗过程中，空化现象产生的空化气泡能促使靶区温度的进一步升高，一定程度上有助于目标的消融，但持续的HIFU辐照过程中，大量的空化气泡使声波在焦前区发生散射产生屏蔽作用，热量随之在焦前区累积，使辐照的损伤横向面积变得更大，同时损伤位置向换能器方向移动，损伤形状也由分布均匀的“雪茄型”变化为“蝌蚪形”，影响治疗的精度。随着HIFU研究的不断深入和临床应用，人们发现低占空比、短持续时间的脉冲高强度聚焦超声（Pulsed High Intensity FocusedUltrasound,PHIFU）辐照生物组织时，能够依靠超声的机械效应精准地摧毁靶区组织而不引起焦区温度的显著上升，PHIFU辐照过程中由于脉冲持续时间短，空化现象未及发生或者会有少量空化出现，但少量的空化气泡不会对声能产生显著的屏蔽作用，同时焦点声压值能够瞬时达到很高数值，依靠PHIFU焦区的高声压作用达到对摧毁靶区组织的目的，这对于提高治疗精确性和操作可控性具有潜在优势。PHIFU辐照过程中不同脉冲宽度及占空比参数对焦点声压会有怎样的影响、空化现象出现后焦区声压的具体变化，成为目前亟待研究的问题。基于此，本文分析了现有声场测量的方法，并对声光折射法进行了近似，用于测量脉冲聚焦声场的焦点声压；针对现有超声换能器不能方便地进行脉冲参数调整，，本文提出了一种基于AD9850的可调脉冲信号发射器，可方便进行脉冲宽度的调整，最小脉冲宽度可至0.1ms，在此基础上测量了不同脉冲宽度参数，及脉冲间隔参数下，焦点声压随输入电压的变化数据，并与连续波辐照下进行对比，得出不同的脉冲参数下，焦点声压的变化规律及焦点的声压极值，为后续临床实验及仪器开发提供基础，结果显示在脉冲宽度大于1ms时，不同的脉冲宽度参数及脉冲间隔参数输入下，焦点声压随电压变化规律一致，空化现象出现后焦点声压仍会继续升高并达到极值，空化气泡大量出现后焦区声压下降，焦区声压极值达10MPa。
[Abstract]:High intensity focused ultrasound (HighIntensity Focused Ultrasound,HIFU) is a new and rapidly developing non-invasive treatment technique, which has been used in clinical treatment of many kinds of tumor and non-tumor diseases. The effect of cavitation and mechanical effect, mainly depends on the thermal effect and cavitation effect of HIFU to achieve the purpose of tumor ablation. During the treatment of HIFU, cavitation bubbles produced by cavitation can further increase the temperature of target area. To some extent, it is helpful to the ablation of the target, but during the continuous HIFU irradiation, a large number of cavitation bubbles cause the scattering of sound waves in the prefocal region to produce shielding effect, and the heat accumulates in the prefocal region, which makes the transverse area of radiation damage become larger. At the same time, the damage position moved to the direction of transducer, and the damage shape changed from "cigar shape" to "tadpole shape", which affected the treatment accuracy. With the development of HIFU research and clinical application, it has been found that when low duty cycle, short duration of pulsed high-intensity focused ultrasound (Pulsed High Intensity FocusedUltrasound,PHIFU) irradiation of biological tissue, It is possible to destroy the target tissue accurately by the mechanical effect of ultrasound without causing a significant rise in the temperature of the focal area. Due to the short duration of the pulse, cavitation does not occur or a small amount of cavitation occurs during PHIFU irradiation. However, a small amount of cavitation bubbles will not have a significant shielding effect on the sound energy, and the focal sound pressure can reach a very high value at the same time, which depends on the hypersonic pressure in the PHIFU focal region to destroy the target tissue. This has potential advantages for improving treatment accuracy and operational controllability. How do different pulse width and duty cycle parameters affect focal sound pressure during PHIFU irradiation, and the specific changes of sound pressure in focal area after cavitation occur. It has become an urgent problem to be studied at present. Based on this, the existing methods of sound field measurement are analyzed, and the acousto-optic refraction method is approximated to measure the focus sound pressure of the pulse focusing sound field, and the current ultrasonic transducer can not easily adjust the pulse parameters. In this paper, an adjustable pulse signal transmitter based on AD9850 is proposed, which can easily adjust the pulse width. The minimum pulse width can be up to 0.1 ms. on this basis, different pulse width parameters and pulse interval parameters are measured. The variation of focus sound pressure with input voltage is compared with that of continuous wave irradiation. The variation law of focus sound pressure and the sound pressure extremum of focus under different pulse parameters are obtained, which provides the basis for subsequent clinical experiment and instrument development. The results show that when the pulse width is larger than 1ms, under the input of different pulse width parameters and pulse interval parameters, the variation rule of focus sound pressure with voltage is the same, and the focus sound pressure will continue to rise and reach the extreme value after cavitation. The sound pressure of the focal region decreases after the cavitation bubble appears in large numbers, and the maximum of the sound pressure in the focal region reaches 10 MPA.
【学位授予单位】：重庆医科大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R318.0

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