经颅HIFU激励信号的调控及其形成温度场的数值仿真研究

发布时间：2018-05-28 20:38

本文选题：HIFU + 经颅聚焦　；参考：《天津医科大学》2015年硕士论文

【摘要】：高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)技术已被应用于临床治疗实体性肝肿瘤、子宫肌瘤等,因其具有的非侵入性和可重复治疗性被引入经颅脑肿瘤治疗和经颅药物传递等。由于颅内靶区被颅骨包围,颅骨与脑组织的声学参数存在巨大差异,使经颅传播的声波发生相位和幅值畸变,导致经颅骨声波偏离设定焦点聚焦、对颅骨及周边组织可能造成热损伤等问题的发生。研究精确有效的经颅聚焦方法和降低对颅骨及周边组织热损伤的方法非常必要。研究目的由于HIFU经非均质颅骨传播时发生相位失真、幅值畸变导致经颅HIFU声波在颅内设定焦点处不能聚焦,对颅骨及其周边组织造成热损伤。本文通过对相控换能器阵元激励信号相位、幅值及消除颅骨内高声压的信号相位和幅值的调控,调控经颅聚焦形成的声场及温度场,实现颅骨及周边组织无伤的HIFU经颅内高效精确聚焦,为经颅HIFU应用于临床治疗提供理论参考。研究方法本研究以人体头颅CT扫描数据的重建图像为基础,结合小开口64阵元球冠状相控换能器,建立三维HIFU经颅数值仿真模型,以时域有限差分法(Finite Difference Time Domain,FDTD)数值解析Westervelt非线性声波传播方程和Pennes生物热传导方程,分析HIFU经颅后形成的声场及温度场分布。应用基于时间反转的相位和幅值调制法获得相控换能器阵元的激励信号,根据这些激励信号形成的声场及温度场,分析与讨论不同阵元激励信号对其形成声场及温度场的影响及调控作用;利用温度阈值和热剂量法分析对正常组织可能存在的伤害和靶区内形成的治疗焦域体积;在对正常组织无伤害的前提下分析相控换能器可实现的调控区域,并对形成的可治疗焦域体积进行调控。研究结果1.调控换能器阵元激励信号对经颅声波进行相位校正聚焦时,形成焦点在设定位置处,但颅骨内可能存在高声压,颅骨处高声压与焦点声压比值(骨焦比)较大;再结合幅值校正后,焦点处声压较仅作相位校正时的声压有所升高,颅骨内声压略有降低,骨焦比略降低;采用相位校正结合降低颅骨内高声压后,骨焦比降低,颅骨内高声压降低,但焦点处声压也降低;采用相位及幅值校正结合降低颅骨内高声压调控法后,骨焦比和颅骨内高声压继续降低,焦点处声压相对于相位校正后的无变化。2.声轴上聚焦时,采用幅值校正后,焦点声压和可治疗焦域体积比不做幅值校正时均有增大。3.基于时间反转的数值拟合法与互相关法获得的调控阵元激励信号的相位信息,都可用于经颅声场的相位校正。4.对相控换能器不同环上阵元激励信号进行相位和幅值调制,以调制换能器外环阵元信号的幅值作用较佳,这种调节模式既可使焦点达到可治疗的温度,也可使颅骨与水的临界面温度降低。5.经颅声波的非线性导致焦点处的声压、温度和热量沉积均大于线性。6.经枕骨窗聚焦时,在聚焦深度为25 mm的条件下,沿垂直于换能器声轴的Y轴方向偏离距离小于等于5 mm的范围内可实现仅针对靶区组织且对非靶区组织不会造成伤害的聚焦,而不能在沿Z方向偏离声轴实现安全聚焦。7.经颅声波调控后聚焦形成的焦域体积随垂直偏离换能器声轴距离增大而减小;当偏离声轴距离一定时,焦域体积随输入声强增大而呈近似线性关系增大;调控换能器阵元的输入声强,可调控偏离换能器声轴聚焦时焦域体积的大小,使不同偏离距离下聚焦形成的焦域体积与在轴聚焦时体积相同。研究结论1.相控换能器阵元激励信号直接影响相控换能器经颅聚焦形成声压场和温度场,通过调制相控换能器阵元激励信号相位和幅值,可使经颅声波精确聚焦,提高焦点处最大声压和最高温度,增大在焦点处的经颅声能量聚积。2.通过叠加降低颅骨内高声压的激励信号,可使声波在颅骨内的能量沉积减小,避免声波对颅骨造成热损伤;也可针对换能器不同环阵元激励信号的幅值进行调控,尤其只对换能器外环阵元信号调控时,可使颅骨与水的临界面的温度降低。3.经颅声波的非线性影响聚焦形成的声压场和温度场,经颅HIFU治疗时需要考虑其非线性。4.当声窗一定时,存在声波经颅偏离换能器声轴安全聚焦的距离,且随垂直偏离声轴距离的增大,聚焦形成的体积减小,但可根据垂直偏离声轴的距离及声强的线性关系,调节换能器阵元的输入声强,使偏离声轴聚焦时形成的焦域体积与在轴聚焦时一致。本研究通过数值仿真方法,研究调控经颅声波聚焦形成温度场的方法,解决了经颅声波不能在设定焦点聚焦且对颅骨造成热损伤的问题,在完成颅内精确聚焦且不热损伤颅骨的同时,通过调控声波幅值的方法提升了焦点处的能量沉积,使声波能量更加集中于需治疗的焦域处。并通过调控声强的方法,提供补偿声强及偏离声轴聚焦的关系,对临床聚焦治疗剂量提供理论参考。
[Abstract]:High intensity focused ultrasound (High Intensity Focused Ultrasound, HIFU) technology has been applied to the clinical treatment of solid liver tumors, uterine leiomyoma, etc. because of its noninvasive and repeatable therapeutic effects that are introduced through Craniocerebral Tumor Therapy and transcranial drug delivery. The acoustic parameters of the skull and brain tissue are surrounded by skull targets. There is a huge difference in the distortion of the phase and amplitude of the acoustic wave transmitted by the cranium, which causes the deviation of the skull sound wave from the focus focus and may cause heat damage to the skull and the surrounding tissue. It is necessary to study the accurate and effective methods of transcranial focusing and to reduce the heat damage to the skull and the surrounding tissues. The phase distortion is caused by the transmission of HIFU through heterogeneous skull. The amplitude distortion leads to the inability of the cranial HIFU acoustic wave to focus at the set focal point and causes heat damage to the skull and its surrounding tissue. This paper regulates the phase and amplitude of the signal phase, amplitude and the high sound pressure in the skull to regulate the phase and amplitude of the phase controlled transducer array element. The sound field and temperature field formed by craniofacial focus can be used to provide a theoretical reference for the application of cranial and peripheral HIFU to the clinical treatment of HIFU. The research method based on the reconstruction image of the CT scan data of human head, combined with the small opening 64 array element ball coronal phase controlled transducer, to establish a three-dimensional HIFU Through the numerical simulation model of Finite Difference Time Domain (FDTD), the Westervelt nonlinear acoustic wave propagation equation and the Pennes biologic heat conduction equation are numerically analyzed, and the distribution of sound field and temperature field formed after HIFU's transcranial is analyzed. The phase and amplitude modulation method based on time reversal is applied to obtain the phased transducer array element. The excitation signal, based on the sound field and temperature field formed by these excitation signals, analyzes and discusses the influence and regulation effect of different array element excitation signals on its sound field and temperature field, and uses the temperature threshold and thermal dose to analyze the possible damage to normal tissues and the volume of the focal area formed in the target area; in the normal tissue, there is no injury to normal tissues. On the premise of damage, we analyze the control area that the phase controlled transducer can realize, and regulate the volume of the treatable focal region. Results 1., when the transducer array element excitation signal focuses on the phase correction of the transcranial acoustic wave, the focus is at the set position, but there may be high sound pressure in the skull, the high acoustic pressure and the focus pressure in the skull. The ratio (bone coke ratio) is larger, and the sound pressure in the focus is higher than that of phase correction, the sound pressure in the skull is slightly lower and the bone coke ratio decreases slightly. The bone coke ratio is reduced, the high sound pressure in the skull is reduced, but the sound pressure in the skull is reduced, and the phase and amplitude are also used. After correction and reduction of the high acoustic pressure control method in the skull, the bone coke ratio and the high acoustic pressure in the skull continue to decrease. When the sound pressure at the focal point is focused on the non changing.2. sound axis after the phase correction, the numerical fitting of the focal sound pressure and the therapeutic focal area volume ratio increases.3. based on the time reversal when the amplitude correction is adopted. The phase information of the modulated array element excitation signal obtained by the cross correlation method can be used in the phase and amplitude modulation of the array element excitation signal on the different loop of the phase controlled transducer by the phase correction.4. of the transcranial sound field. The amplitude of the outer ring element signal of the modulating transducer is better. The surface temperature of the skull and water can also be reduced by the nonlinearity of.5. through the acoustic wave of the cranium resulting in the sound pressure at the focal point. Both the temperature and the heat deposition are greater than the linear.6. focusing on the occipital window. Under the condition of the focusing depth of 25 mm, the deviation distance from the Y axis perpendicular to the transducer sound axis is less than equal to 5 mm, and the target area can be achieved only for the target area. The focus of non target tissue does not cause damage, but it can not achieve the focus volume formed by focusing.7. through the cranial sound wave in the direction of the Z direction. The focus volume decreases with the increase of the acoustic axis distance of the transducer perpendicular to the transducer, and the volume of the focal region is approximately linear when the distance from the acoustic axis is fixed. Increasing the input sound intensity of the transducer array element can regulate the size of the focal volume when the focus of the transducer is focused. The volume of focal region formed by focusing at different deviations is the same as that of the axis focusing on the axis. It is concluded that the excitation signal of the 1. phased transducer array element directly affects the acoustic pressure field and temperature of the phase controlled transducer through the transcranial focus. The field, by modulating the phase and amplitude of the excitation signal of the phased transducer array element, the transcranial acoustic wave can be focused accurately, and the maximum sound pressure and maximum temperature at the focal point can be increased, and the transcranial acoustic energy accumulation.2. at the focal point can reduce the energy deposition in the skull by superposition and reduce the high acoustic pressure in the skull, so that the acoustic wave can be reduced and the sound wave is avoided. The heat damage of the skull is caused by the skull, and the amplitude of the excitation signal of the transducer with different ring element can be regulated, especially when the outer ring element signal of the transducer is regulated, the temperature of the surface of the skull and water can be reduced by the nonlinear influence of the cranial acoustic wave on the acoustic pressure field and temperature field of the.3., and the nonlinearity of the transcranial magnetic field should be considered when the cranial HIFU is treated. .4. when the sound window is fixed, there is a distance between the sound axis and the sound axis of the transducer, and the volume of the focusing is reduced with the increase of the vertical deviation from the sound axis, but the input sound intensity of the transducer array element can be adjusted according to the vertical deviation of the sound axis and the linear relationship between the sound intensity. The focal volume formed when the acoustic axis is focused is formed. It is consistent with the axis focusing. In this study, the method of numerical simulation is used to study the method of regulating the temperature field of the transcranial acoustic focusing, which solves the problem that the transcranial acoustic wave can not focus on the focus and causes the heat damage to the skull. It is promoted by the method of regulating the amplitude of sound waves while completing the precise focus of the skull and without the heat damage of the skull. The energy deposition at the focal point makes the acoustic energy more concentrated in the focal region that needs to be treated. Through the method of regulating the sound intensity, the relationship between the compensation sound intensity and the deviation of the focus of the acoustic axis is provided, and the theoretical reference for the clinical focus treatment dose is provided.
【学位授予单位】：天津医科大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：R454.3

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