一种消除浅表组织病灶的微型线聚焦换能器声场的数值计算与仿真方法

目的:本文涉及一种消除浅表组织病灶的微型线聚焦超声声场的数值计算与仿真,通过计算得出声场的三维分布,同时研究柱面自聚焦换能器各个参数对声场的影响,以指导微型自聚焦换能器的设计。方法:本文通过建立三维直角坐标系,应用Rayleigh积分得出微型线聚焦超声换能器聚焦区域内每一点的声强表达式,运用C语言和matlab采用直接数值积分的方法对柱面聚焦超声换能器的声场进行了数值计算和仿真,得出声场的三维分布。结果:从声场的三维分布可以看出:按照本文给定的条件设计,微型线聚焦超声换能器展现出良好的聚焦性能,形成明显的焦域。和普通的柱面超声换能器相比,小型的柱面超声换能器形成的声场在z轴上的声场分布更均匀,x,y方向上衰减更快。结论:通过不同的参数对声场三维分布影响可以看出:微型线聚焦超声换能器的厚度,半径,张角和长度对聚焦的效果有明显影响。与给定的条件相比,选择较厚、半径和张角较大的换能器,能提高聚焦性能,而换能器的长度对聚焦效果影响不大。     

用于磁声耦合刺激的64阵元相控阵超声换能器的设计

本研究基于磁声耦合刺激技术(transcranial magneto-acoustic stimulation,TMAS)的需求,设计了用于线性64阵元相控阵的超声换能器,探究相控阵超声换能器压电晶体宽度及间距,优化超声换能器聚焦声场分布.采用MATLAB软件建立相控阵换能器模型,仿真聚焦声场分布.搭建三维声场分布测试...     

高强度聚焦超声换能器声场的数值仿真与实验测量

目的 高强度聚焦超声(HIFU)肿瘤治疗过程中,HIFU换能器形成的声场分布是决定其治疗效果的关键因素之一,为了提高HIFU肿瘤治疗的安全性和可靠性,需要对HIFU换能器形成的声场进行预测.方法 采用时域有限差分(FDTD)法数值仿真水体内形成的声压分布与实验测量结果对比的研究方法,分析讨论了HIFU换能器在不同激励功...     

HIFU治疗中媒质特性对声聚焦影响的研究

目的:研究声衰减系数、声速、温度等媒质参数对声聚焦的影响。方法:用瑞利积分对凹球面自聚焦超声换能器进行声场模拟。结果及结论:媒质的特性参数不同,聚焦表现不同的特点。声衰减系数增大,焦斑向声源靠近,且焦斑缩短;声速越大,焦距越小,但焦区最大声压升高,焦斑的面积增大;温度变化不大时对声聚焦的影响不明显。     

任意三角形和六边形超声阵元及其高填充率阵列的声场仿真研究

为提高超声设备中二维相控阵列聚焦换能器的面积填充率,提升聚焦区域的超声能量和治疗效率,本研究利用空间脉冲响应理论对任意三角形阵元进行声场计算,通过对三角形阵元进行二维平面旋转完成了六边形阵元声场仿真,并通过对六边形阵元进行三维空间旋转实现了球面阵列聚焦换能器声场仿真。仿真结果显示,六边形7阵元球面填充率提高了6.1%,其-6 dB焦域横向宽度为2.0 mm、纵向长度为30.1 mm; 19阵元球面填充率提高了5.5%,其-6 dB焦域横向宽度为1.2 mm、纵向长度为9.8 mm,可实现高精度超声治疗。本研究可为任意三角形和六边形及不规则形状阵元声场仿真提供新方法,且为高填充率的球面聚焦超声换能器设计提供新思路。     

用于治疗宫颈疾病的微型自聚焦超声换能器聚焦特性与图像特征

目的:设计用于治疗妇科宫颈疾病的环状凹球面自聚焦超声换能器,并对其聚焦性能进行检验.方法:采用正负声源的方法,对该环状凹球面自聚焦超声换能器的轴向声场强度分布进行模拟仿真,并利用自定义的声场分布系数(SIDC)的物理意义对该换能器进行优化设计.最后采用离体器官组织牛肝实验所得损伤区域的图像特征分析来检验该换能器的聚焦特性.结果:在保证一定的机械强度和设计约束条件的基础上(固有频率为6 MHz～12 MHz),所设计的内环直径为6 mm,外环直径为12mm的Ⅰ型和内环直径为3 mm,外环直径为7.5 mm的Ⅱ型换能器的SIDC都达到了各自约束条件下的最大值.离体器官组织牛肝实验的结果也显示了焦点附近的损毁区域的轴向长度与仿真结果一致:且Ⅱ型换能器的SIDC值大于Ⅰ型换能器,其损伤区域的轴向长度更长且分布也更加均匀.结论:相同能量条件下,SIDC值较大的自聚焦超声换能器的损伤区域轴向长度更大且分布更加均匀.     

医用高斯型聚焦超声换能器

本文说明了具有高斯型表面速度分布的医用聚焦超声换能器的理论分析、结构设计和声场测试方法。该换能器由N_8S_2压电陶瓷制成,等效半径3mm,谐振频率2.5MHz。焦长5.9cm的声透镜由环氧树脂制作。利用声场测试仪测量了该换能器的发射声压分布状况,其发射声束出声光衍射装置成象。所研制的换能器的近场特性比常用的具有均匀振速分布的平片换能器及具有4.8mm等效半径的高斯聚焦超声换能器好得多。在发射束中几乎见不到声压的极大和极小值起伏,而且副瓣减少。     

柱面换能器声场在组织中的温度分布估计

本文分析了柱面聚焦换能器的声场特点,剖析了方向比（ratio）与声场的关系。结果表明：声场随方向比的降低而焦点强度减弱,声强最大值前移。在求解声场的基础上,对该类换能器的声场在组织中的温度分布进行估计,给出了组织内温度随时间变化的曲线,分析了方向比（ ratio）对焦区温度分布的影响,为该类换能器的参数选择和组织中的温度分布估计提供了参考。     

新型相控聚焦超声声场测量实验研究

目的:相控聚焦超声是热物理治疗领域的研究热点之一,而对其声场的研究是其中最重要的技术环节.本文分析了新型相控聚焦超声声场仿真和实验测量的声场结果.方法:运用LabVIEW虚拟仪器平台开发了超声声场测量系统.该系统用水听器声场扫描法测量了单焦点模式下新型相控聚焦超声声场分布,并用MATLAB等工具包对单焦点模式下的声场分布进行仿真.结果:仿真数据和实验结果基本一致.结论:本文验证了理论模型的正确性及本系统测量相控型聚焦超声声场可行性和有效性.     

基于磁性纳米粒子磁声B型扫描成像的仿真研究

磁性纳米粒子作为药物载体能够与肿瘤特异性结合,具有靶向治疗的潜力。探索用于检测磁性纳米粒子分布的无创成像方法具有重要意义。本文基于磁性纳米粒子在脉冲磁场激励下产生超声波的机制,推导含有磁性纳米粒子浓度信息的声压波动方程。利用有限元法和解析解得到一致的瞬态脉冲磁场。建立三维模型用于电磁场和声场耦合计算,仿真结果验证了检测点处的声压波形能够反映磁性纳米粒子区域在生物组织中的位置信息。利用超声换能器采集的声压数据,实现磁性纳米粒子的B型扫描成像。目标区域位置的最大误差为1.56%,通过比较图像中边界信号的幅值可以区分不同浓度的纳米粒子区域。本文研究表明B型扫描成像能够快速、准确地获取目标区域的尺寸和位置信息,有望用于靶向治疗中磁性纳米粒子的检测。     

凹球面聚焦超声换能器用于热疗时在人体内引起的瞬态温度场

本文引入了虚拟热源的概念,分析了边界条件对升温的影响及加热时间及温度场点位置的关系,详细研究了声源参数及生物组织特性参数对治疗区升温快慢的影响,比较了聚焦参数相同的册球面换在和高斯换能器声焦点的瞬态温度,所得结果对超声热疗的实施具有指导作用。     

Theoretical evaluation of moderately focused spherical transducers and multi-focus acoustic lens/transducer systems for ultrasound thermal therapy

Impractically long treatment times are required for highly focused spherical transducers to destroy large tumours because thermal lesions generated by these transducers are small and a large number of such lesions are required. Moderately focused spherical transducers and multi-focus acoustic lens/transducer systems can generate larger thermal lesions compared to those produced by highly focused spherical transducers, and therefore shorter treatment times can be expected. The decrease in total treatment time by the use of moderately focused spherical transducers and acoustic lens/transducer systems was quantified in this study. A 3D ultrasound thermal model was developed to predict thermal lesion volumes generated by ultrasound transducers. A target model was constructed in order to compare various transducer designs under identical treatment conditions and with identical treatment goals. A design method was developed to determine the thickness of lens elements for production of specified multi-focus fields. Then, a highly focused and a moderately focused spherical transducer, and an acoustic lens/transducer system were compared in terms of total time required to treat a tumour. These transducers had identical apertures and operating frequencies. The radius of curvature of the moderately focused spherical transducer was chosen such that the length of thermal lesions it generated over 10 s single exposures was slightly greater than that of the target. The lens/transducer system was designed to produce a 9 focus field. The simulation results show that for the treatment of a 2 x 2 x 2 cm3 tumour at a depth of 5 cm in the body, the highly focused spherical transducer, the moderately focused spherical transducer and the lens/transducer system required 150, 42 and 30 min, respectively.     

组织声学特性对高强度聚焦超声温度场的影响

目的 数值仿真组织声学特性对高强度聚焦超声（HIFU）焦域处温度场的影响,为HIFU治疗安全性和可靠性提供理论依据.方法 以实测新鲜离体猪肝组织不同温度下的声速和衰减系数为依据,利用时域有限差分（FDTD）法数值仿真研究HIFU治疗过程中组织内声速、衰减系数的变化和温度场的分布,分析讨论声速和衰减系数变化对60 ℃以上可治疗区域大小、位置的影响.结果 随着照射时间的延长,焦域处肝组织温升增大,声速下降,声衰减系数增大.随着声速的变化,形成的可治疗区域变大,焦点位置向远离换能器方向移动;随着声衰减系数的变化,焦域大小和焦点位置几乎不变.结论 猪肝组织内声速的变化对可治疗焦域的位置和大小影响较大;声衰减系数的变化对焦域的影响较小.     

高强度聚焦超声在医学领域中应用的新进展

本文综述了国内外在高强度聚焦超声（high intensity focused ultrasound，HIFU）技术方面研究与应用的新进展。介绍了HIFU的治疗功能原理，特别给出了焦斑半径的具体计算公式和对相关组织的热效应、空化效应、机械效应，辐照效应等损伤机理，重点研究了热效应随声波频率及声强变化的规律。给出了HIFU的一般试验模型即分层组织模型以及HIFU应用与临床的情况。重点研究了HIFU源，主要讨论了换能器的聚焦方式（1）球面自聚焦换能器，（2）声透镜聚焦换能器，（3）大功率多元超声换能器，（4）电子扫描或相控阵列聚焦换能器，以及频率选择与目标深度和辐照强度的关系，并指出与其匹配的几类聚焦换能器的优缺点，列举了HIFU技术在泌尿科、肿瘤学、神经外科、眼科、妇科、止血以及其他医学领域中的最新应用。最后评价了目前HIFU在治疗方面的优势与某些不足以及可能改进的有效措施．展望了HIFU技术广阔的应用前景．     

声衰减与非线性对双频聚焦声焦域的影响

目的：探讨声衰减与非线性对双频聚焦超声声焦域的影响。方法：利用瑞利积分的线性叠加算法数值模拟计算。并在辐照离体生物组织中进行实验验证。结果：随着声衰减系数的增大与非线性的增强．双频声焦域从“椭球形”变成“蝌蚪形”,并且焦域向着换能器方向移动,但声衰减的影响较非线性大。结论：声衰减与非线性对焦域影响较大,在实际应用中应予考虑。本文在利用瑞利积分的线性叠加算法,研究了媒介声衰减与高声强引起的非线性对差频相干模式下的双频聚焦声场焦域的影响。结果表明,随着声衰减系数的增大与非线性的增加。双频声焦域从“椭球形”变为“蝌蚪形”．并且焦域向着换能器方向移动．但声衰减的影响较非线性大。并在离体牛肝的损伤实验中得到初步验证。     

Optimizing the shape of ultrasound transducers for interstitial thermal ablation

Heat deposition by interstitial routes, especially with ultrasound-based instruments, is becoming a valuable therapeutic option for the treatments of sites, which are difficult to access from outside of the body. The active part of most interstitial ultrasound applicators described in the literature is logically tubular to induce cylindrical volumes of coagulation necrosis. Because the pressure generated by such tubular transducers falls off rapidly with radial distance, we previously proposed using a rotating plane transducer. For a plane wave, the pressure fall-off is only due to attenuation, which makes deeper lesions and shorter treatment times possible. This work represents an advance in the development of ultrasound applicators designed for interstitial applications. This new applicator used a rotating slightly focused transducer. A brief theoretical analysis resulted in the choice of a long focal distance of 22 mm to obtain a nearly constant pressure all along the therapeutic depth. To experimentally validate this focal distance, pressure measurements were made in a tissue mimicking liquid phantom and the results were compared with those obtained with a plane transducer. In vitro experiments showed that necrosis could be induced at a depth of 15 mm. In the same conditions, the greatest depth attained with a plane transducer was only 10 mm. Because each individual lesion is narrower, more lesions and more time are required to necrose a cylindrical volume. The main advantage of this new type of applicator is that it can be used to induce necrosis at a greater depth without varying either the frequency, the intensity or the transducer cooling efficiency.     

Investigation of a scanned cylindrical ultrasound system for breast hyperthermia

This paper investigates the feasibility of a scanned cylindrical ultrasound system for producing uniform heating from the central to the superficial portions of the breast or localized heating within the breast at a specific location. The proposed system consists of plane ultrasound transducer(s) mounted on a scanned cylindrical support. The breast was immersed in water and surrounded by this system during the treatment. The control parameters considered are the size of the transducer, the ultrasound frequency, the scan angle and the shifting distance between the axes of the breast and the system. Three-dimensional acoustical and thermal models were used to calculate the temperature distribution. Non-perfused phantom experiments were performed to verify the simulation results. Simulation results indicate that high frequency ultrasound could be used for the superficial heating, and the scan angle of the transducer could be varied to obtain an appropriate high temperature region to cover the desired treatment region. Low frequency ultrasound could be used for deep heating and the high temperature region could be moved by shifting the system. In addition, a combination of low and high frequency ultrasound could result in a portion treatment from the central to the superficial breast or an entire breast treatment. Good agreement was obtained between non-perfused experiments and simulation results. The findings of this study can be used to determine the effects of the control parameters of this system, as well as to select the optimal parameters for a specific treatment.