驻波聚焦在体模中形成的精细损伤

doi:10.16337/j.1004-9037.2021.04.010

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驻波聚焦在体模中形成的精细损伤
DOI:
                        10.16337/j.1004-9037.2021.04.010
                    
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作者单位:1.重庆医科大学生物医学工程学院超声医学工程国家重点实验室，重庆 400016;2.超声医疗国家工程研究中心，重庆 401121
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基金项目:国家自然科学基金重大科学仪器设备研制专项（81127901）资助项目;国家自然科学基金（12074051，12004059）资助项目;重庆市自然科学基金（cstc2020jcyj-msxmX0456）资助项目。

Precise Lesion Formed by Standing Wave Focused Ultrasound in Tissue-Mimicking Phantom

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Affiliation:

1.State Key Laboratory of Ultrasound in Medicine and Engineering, College of Biomedical Engineering, Chongqing Medical University, Chongqing 400016, China;2.National Engineering Research Center of Ultrasound Medicine, Chongqing 401121, China

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摘要:

为了提高聚焦超声的治疗精度，本文通过将两个完全相同，频率为0.6 MHz的行波聚焦换能器同轴共焦相向放置实现驻波聚焦。在相同焦点峰值正声压（17 MPa）条件下，结合组织中的声场数值仿真、空化和非线性测量，对比研究了驻波聚焦和行波聚焦超声分别辐照仿组织体模过程中的损伤变化及形成机制。研究可见：（1）相同焦点峰值正声压条件下，驻波聚焦和行波聚焦辐照形成的初始损伤尺寸分别为0.18λ×0.25λ、0.91λ×0.3λ，而达到相同焦点峰值正声压驻波聚焦所需的换能器表面声压仅为行波聚焦的0.46倍，表明驻波聚焦可以实现更精细的损伤同时降低声通道上声压幅值保护声通道的安全性。（2）相同焦点峰值正声压条件下，行波聚焦更快出现损伤，相比于空化，非线性效应影响更大。研究说明基于同轴共焦相向放置两换能器形成的驻波聚焦相比行波聚焦可以实现更精细的损伤，且声通道更安全，为驻波聚焦应用于临床提供了理论参考。

Abstract:

To improve the treatment precision of focused ultrasound， two traveling wave focusing （TWF） transducers with the same frequency of 0.6 MHz are placed in opposite direction coaxially and confocally to realize standing wave focusing （SWF）. Combining with the numerical simulation of sound field， cavitation and nonlinear research， lesion changes in tissue-mimicking phantom and the formation mechanism of lesion during SWF and TWF ultrasonic irradiation are compared under the same peak focus acoustic pressure about 17 MPa. The results demonstrate that the size of initial lesion formed by SWF ultrasonic irradiation is 0.18λ×0.25λ， which is significant smaller than that of TWF， 0.91λ×0.3λ， under the same peak focus acoustic pressure. But the surface sound pressure of the SWF transducers is only 0.46 times that of TWF. It shows that SWF can significantly compress the lesion size in the transverse direction and can protect organs and tissues by reducing the amplitude of acoustic pressure. And the lesion caused by TWF ultrasound appeared faster than SWF， which is related to the strong nonlinear effect of TWF. The results in this paper show that SWF can achieve more precise lesion than TWF， and the acoustic path is safer， which provides a theoretical reference for the application of SWF in clinic.

表 1 各次谐波幅值与基波幅值的比值Table 1 Ratio of the amplitude of each harmonic to fundamental frequency

图1 Radar basic reflectance image (color from green to red means the reflectivity gradually increasing)Fig.1

图2 General structure of the Guangzhou Terminal AreaFig.2

图3 Framework of the deep learning modelFig.3

图4 Core process of convolutional layer processingFig.4

图5 Structure of a basic LSTM cellFig.5

图6 Structure and parameters of MICL model with 1-hour forecast periodFig.6

图7 Correlation coefficient heat map of featuresFig.7

图8 Convective weather scenarios at the beginning of each period (the avoided area marked in red)Fig.8

图9 Actual and predicted flow value compared in three scenariosFig.9

图1 聚焦超声换能器Fig.1 Focused ultrasound transducer

图2 实验装置结构示意图Fig.2 Schematic diagram of experimental device

图3 SWF的损伤形成过程Fig.3 Lesion formation process of SWF

图4 TWF的损伤形成过程Fig.4 Lesion formation process of TWF

图5 SWF与TWF的损伤轴向与径向尺寸比随辐照时间的变化曲线Fig.5 Change curve of lesion axial and radial size ratio with irradiation time during SWF and TWF ultrasonic irradiation