用于肿瘤治疗的高强度聚焦超声换能器及其温度场测量

高强度聚焦超声（HIFU）作为一种具有巨大潜力的、无损的、有效的肿瘤治疗手段,已得到普遍认同。本文介绍了所研制的HIFU治疗系统,对其关键部分高强度聚焦超声换能器的温度场特性,从理论上和实验上进行了深入的研究,并提出了超声声场的理论算法.     

高强度聚焦超声肿瘤治疗系统专项技术研究

本文通过对高强度聚焦超声治疗基本原理介绍,对HY2900聚焦超声肿瘤治疗系统实际工作几项特色专项技术HIFU声场分布参数测量、HIFU温度场测量、三维重建技术中任意方位切面图像浏览及边界轮廓的实现方法等进行讨论,介绍相关技术及方法.     

仿生物组织模型对高强度聚焦超声焦域影响的研究

运用有限元仿真分析了生物组织声学特性对高强度聚焦超声(HIFU)焦域的影响,为HIFU治疗安全性和可靠性提供理论依据。应用超声传播方程以及频域有限元算法(FEM)仿真HIFU治疗过程中因组织特性和厚度引起的焦域变化,并制作仿生物组织模型,进行实验验证焦域变化,分析讨论组织特性和厚度对聚焦区域、位置的影响。结果表明:随着声速增大,焦域尺寸不变,焦域向换能器一侧靠近;随着厚度增大,焦域尺寸基本不变,如果组织声速大于水的声速,则焦域向换能器一侧靠近;如果组织声速小于水的声速,则焦域向远离换能器一侧移动。     

基于超声散射回波的组织损伤程度监测方法

高强度聚焦超声(HIFU)治疗肿瘤过程中,根据组织损伤程度调整HIFU治疗剂量非常重要.本文从信号处理的角度出发,提出基于超声散射回波能量和声衰减系数并结合BP神经网络监测生物组织损伤程度的方法.将高强度聚焦超声打击新鲜猪肉组织前后获得的散射回波通过A/D转换输入到计算机,对接收到的组织散射回波信号进行预处理,再从中提取出超声散射回波能量和声衰减系数参量信息,比较不同参量对损伤程度的辨识效果.实验结果表明:综合超声散射回波能量和声衰减系数特征并输入BP神经网络,相对于仅使用某种特征参数而言能更好地监测HIFU治疗中生物组织的损伤程度,尤其在组织损伤严重时优势更加明显.     

基于近场声全息的聚焦换能器声场测量方法研究

高强度聚焦超声(HIFU)被广泛应用于医疗领域,但聚焦换能器焦点处的声强比较大,直接测量容易造成水听器损坏。为了间接获得焦点处声压,将全息测量面近似等效为声源面,结合空间傅里叶变换算法,提出了一种高测量效率的聚焦换能器声场测量方法。以球面自聚焦换能器为对象,进行声场测量方法的仿真研究和实验验证。结果表明,该方法比积分法推算效率提高了1倍,测量误差保持在有效范围内,该方法可以有效用于聚焦换能器声场测量。     

高强度聚焦超声换能器的新型设计

采用高强度聚焦超声（HIFU）治疗局部肿瘤，如何增强对病变区域的辐照效果，而尽量减少对健康区域的辐照损伤是一个很重要的问题。文章基于目前常用的凹球面自聚焦换能器，提出了解决上述问题的方案，设计了新型的换能器，对其工作方式及声场特性进行了研究。结果表明：采用多换能器轮流发射的方式进行治疗是一种行之有效的解决方案。     

强聚焦换能器冲击波数值模型

0引言高强度聚焦超声(HIFU)技术作为新兴的非侵入式治疗肿瘤方法得到人们极大的关注[1-2]。非线性声场分布是HIFU治疗中的关键物理参数之一,其对准确的预测和评价治疗效果有着重要的作用。Kamakura等人推导了球壳式大张角换能器在椭球坐标系下的非线性方程(spheroidal beam equation,SBE)[3]。通常,将时域波形进行傅里叶级数展开,然后在频域计算SBE模型,得到声场分布。当声功     

高频聚焦球冠阵焦平面声场分布

1引言高强度聚焦超声技术(HIFU)已被当作一种无损的、有效的局部高温肿瘤治疗新技术来研究。其中对声场分布特性的研究是关键的内容。本文给出了球冠阵声压计算的方程,设计制作了36元自聚焦球冠阵,并比较了焦平面声场的理论计算和实测结果,两者在主瓣上吻合较好。     

仿体中超声空化效应的B超图像处理

0引言使用高强度聚焦超声(HIFU)照射组织,将产生声空化现象。在声空化过程中,声场能量于空化气泡内高度集中,当能量积累到一定阈值后,空化气泡瞬间崩溃。在气泡崩溃的瞬间能量会释放出来,形成局部的高温、高压、强冲击波等极端物理现象[1]。这将使周围的组织细胞遭到损伤。因此,对HIFU空化的监控显得尤其重要[2]。本文主要研究不同脉冲宽度的高强度聚焦超声(HIFU)在体外仿体中引起的空化气泡群面积随时间的变化。从而实现对HIFU空化的实时监控。     

HIFU治疗中生物组织对声学焦域及声的非线性影响的研究

生物分层组织是高强度聚焦超声治疗中最常见的声通道组织。通过研究生物组织对声学焦域的影响,可以为高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)治疗安全性和可靠性提供理论依据。基于Westervelt方程,利用频域和时域有限元算法仿真HIFU治疗过程中超声透过分层组织后的焦域变化,并用新鲜离体猪肉组织进行实验验证。结果表明:生物组织声学特性的差异性和结构的不均一性使HIFU的声学焦域位置发生改变,尤其在声焦平面内,相对2.5mm的焦域宽度,1mm的偏移量将会对HIFU治疗精准性产生影响;声通道中存在生物组织,超声声束不会发生扩散,没有散焦现象,焦域宽度维持在2.38~2.79mm范围内;HIFU透射生物组织,声学焦域的非线性有明显的减弱,谐波次数越高,衰减程度越大,实验中基波声衰减值为9.97dB,二次谐波声衰减值为22.33dB,三次谐波声衰减值为28.05dB,四次谐波声衰减值为31.06dB,五次谐波已衰减消失。     

A High-Precision US-Guided Robot-Assisted HIFU Treatment System for Breast Cancer

Breast cancer is the most commonly diagnosed cancer in women. A strong treatment candidate is high-intensity focused ultrasound (HIFU), a non-invasive therapeutic method that has already demonstrated its promise. To improve the precision and lower the cost of HIFU treatment, our group has developed an ultrasound (US)-guided, five-degree-of-freedom (DOF), robot-assisted HIFU system. We constructed a fully functional prototype enabling easy three-dimensional (3D) US image reconstruction, target segmentation, treatment path generation, and automatic HIFU irradiation. The position was calibrated using a wire phantom and the coagulated area was assessed on heterogeneous tissue phantoms. Under the US guidance, the centroids of the HIFU-ablated area deviated by less than 2 mm from the planned treatment region. The overshoot around the planned region was well below the tolerance of clinical usage. Our system is considered to be sufficiently accurate for breast cancer treatment.     

Thresholds for nonlinear effects in high- intensity focused ultrasound propagation and tissue heating

For a variety of reasons, including their simplicity and ability to capitalize upon superposition, linear acoustic propagation models are preferable to nonlinear ones in modeling the propagation of high-intensity focused ultrasound (HIFU) beams. However, under certain conditions, nonlinear models are necessary to accurately model the beam propagation and heating. In analyzing the performance of a HIFU system, it is advantageous to know before the analysis whether a linear model suffices. This paper examines the problem of determining the thresholds at which nonlinear effects become important. It is demonstrated that nonlinear interaction has different effects on different physical and derived quantities, such as compressional pressure, rarefactional pressure, intensity, heat rate, temperature rise, and thermal lesion volume. Thresholds are determined as a function of the dimensionless gain, nonlinearity, and absorption parameters. The relative difference between linear and nonlinear predictions is plotted as a series of contours, enabling practitioners to locate their system in parameter space and determine whether nonlinearity significantly affects the quantities of interest.     

A real-time controller for sustaining thermally relevant acoustic cavitation during ultrasound therapy

A novel method for sustaining inertial cavitation during high-intensity focused ultrasound (HIFU) exposure in an agar-based tissue-mimicking material is presented. Inertial cavitation occurs during HIFU therapy when the local rarefaction pressure exceeds the inertial cavitation threshold of the insonated medium, and is characterized by broadband acoustic emissions which can be easily detected non-invasively using a passive cavitation detector (PCD). Under the right conditions, inertial cavitation has been previously shown to greatly enhance the rate of heat deposition by redistributing part of the energy carried at the fundamental HIFU frequency to higher frequencies, which are more readily absorbed by visco-elastic media such as soft tissue. However, in the absence of any cavitation control, inertial cavitation activity at the focus decays rapidly over a few seconds of exposure because of the combined effects of cavitation nuclei depletion, bubble dissolution, bubble-bubble interactions, increased vapor pressure caused by heating, and focal shielding caused by pre-focal bubble activity. The present work describes the design, validation, and testing of a real-time adaptive controller, with integrated passive localization capabilities, for sustaining inertial cavitation within the focal region of a HIFU transducer by modulation of the HIFU amplitude. Use of the controller in agar gel, originally at room temperature, has enabled therapeutically relevant temperatures in excess of 55°C to be maintained continuously in the focal region for more than 20 s using significantly less acoustic energy than is required to achieve the same temperature rise in the absence of cavitation control.     

界面层对高强度聚焦超声所致焦斑的影响

用纳米铁磁性颗粒胶合体制作界面层,用同一剂量高强度聚焦超声(HIFU)在该界面层下方不同深度定点辐照.结果显示:焦点上缘与声学界面重合时,HIFU所致焦斑/损伤点(lesion)的体积增大,说明声学界面能够提高治疗效率；当焦点距离界面层10mm时,焦点处HIFU所致焦斑/损伤点的大小和形态与对照组相似,而界面处出现另一...     

The role of numerical simulation for the development of an advanced HIFU system

High-intensity focused ultrasound (HIFU) has been used clinically and is under clinical trials to treat various diseases. An advanced HIFU system employs ultrasound techniques for guidance during HIFU treatment instead of magnetic resonance imaging in current HIFU systems. A HIFU beam imaging for monitoring the HIFU beam and a localized motion imaging for treatment validation of tissue are introduced briefly as the real-time ultrasound monitoring techniques. Numerical simulations have a great impact on the development of real-time ultrasound monitoring as well as the improvement of the safety and efficacy of treatment in advanced HIFU systems. A HIFU simulator was developed to reproduce ultrasound propagation through the body in consideration of the elasticity of tissue, and was validated by comparison with in vitro experiments in which the ultrasound emitted from the phased-array transducer propagates through the acrylic plate acting as a bone phantom. As the result, the defocus and distortion of the ultrasound propagating through the acrylic plate in the simulation quantitatively agree with that in the experimental results. Therefore, the HIFU simulator accurately reproduces the ultrasound propagation through the medium whose shape and physical properties are well known. In addition, it is experimentally confirmed that simulation-assisted focus control of the phased-array transducer enables efficient assignment of the focus to the target. Simulation-assisted focus control can contribute to design of transducers and treatment planning.     

A method to synchronize high-intensity, focused ultrasound with an arbitrary ultrasound imager

Ultrasound imaging is useful for monitoring high-intensity, focused ultrasound (HIFU) therapy; however, interference on the ultrasound image, caused by HIFU excitation, must be avoided. A method to synchronize HIFU excitation with ultrasound imaging is described here. Synchronization was tested with two unmodified, commercial imagers and two tissue phantoms.     

A new high intensity focused ultrasound applicator for surgical applications

Improved high-intensity focused ultrasound (HIFU) surgical applicators are required for use in a surgical environment. We report on the performance and characteristics of a new solid-cone HIFU applicator. Previous HIFU devices used a water-filled stand-off to couple the ultrasonic energy from the transducer to the treatment area. The new applicator uses a spherically-focused element and a solid aluminum cone to guide and couple the ultrasound to the tissue. Compared with the water-filled applicators, this new applicator is simpler to set up and manipulate, cannot leak, prevents the possibility of cavitation within the coupling device, and is much easier to sterilize and maintain during surgery. The design minimizes losses caused by shear wave conversion found in tapered solid acoustic velocity transformers operated at high frequencies. Computer simulations predicted good transfer of longitudinal waves. Impedance measurements, beam plots, Schlieren images, and force balance measurements verified strong focusing and suitable transfer of acoustic energy into water. At the focus, the -3 dB beam dimensions are 1.2 mm (axial)×0.3 mm (transverse). Radiation force balance measurements indicate a power transfer efficiency of 40%. In vitro and in vivo tissue experiments confirmed the applicator's ability to produce hemostasis     

HIFU focusing efficiency and a twin annular array source for prostate treatment

A measure of focusing efficiency is introduced for high-intensity, focused ultrasound (HIFU). The measure consists of the fraction of the total acoustic power emitted that linearly propagates through a circle located at the focus. The medium is absorption-free water, and power is computed using pressure and the normal component of velocity. 3 MHz phased-array designs involving different element layouts and curvatures are placed in square apertures of length 2.2 cm. The acoustic fields of these devices then are propagated to on-axis foci. The resulting focal efficiencies then are calculated using a two wavelength (0.1 cm) radius circle. Among these array designs, an annular array with 27 wavelength-wide rings then is extended to be the basis of a twin phased-array device for prostate hyperthermia treatment. The two annular arrays are attached to door-like hinges to allow for joint two-dimensional focusing. The focusing efficiency of this device then is compared to rectangular element-array devices with the same 5.4 by 2.2 cm source extent. With the addition of absorption and finite-amplitude distortion, the heating rate and temperature rise produced by the twin annular device in prostate tissue is considered. As a final look at the potential of annular array-based designs, three larger 2 MHz devices are briefly considered for abdominal treatment.     

The monopole-source solution for estimating tissue temperatureincreases for focused ultrasound fields

The monopole-source solution to the problem of estimating tissue temperature rise generated by a focused ultrasound beam is presented. The acoustic pressure field generated by a focused, continuous-wave ultrasound source using the acoustic monopole-source method is developed. The point-source solution to the linear bio-heat transfer equation is used to calculate the axial, steady-state temperature increase for both circular and rectangular apertures. The results of the circular aperture are compared with the temperature increase calculated using the heated-disc method and are shown to be in substantial agreement. Finally, the temperature increase generated by the circular aperture is compared to that of the rectangular aperture for the same source power, aperture surface area, operating frequency, and medium properties, and it is shown that the rectangular source generates temperature increases less than those of the circular source under these conditions