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。     

HIFU技术的研究

高强度聚焦超声技术起源于４０年代,当时由于缺乏高精的成像和定位技术,影响其发展,该项技术在许多方面优越于传统外科手术,具有极大的潜在临床应用价值。高强度聚焦超声对组织切换除有很高的精确性,换能器探头的选择也为灵活。该技术在对机体的生物效应包括：热效应,空化效应,与药物的相互作用和提高机体免疫机能等。该技术的应用已深入到社会科,泌尿科,等领域。     

C形纵剖面部分球冠换能器结构对声焦域的影响

在球带腔形聚焦超声换能器的基础上,设计一种C形纵剖面部分球冠聚焦超声换能器,研究其结构参数变化对声焦域形态的影响。通过建立的有限元仿真模型,分别讨论了换能器的球带高度和聚焦夹角与焦域形态的变化关系。结果表明,球带高度越高、聚焦夹角越大,其焦域尺寸越小,焦域长轴与短轴的比值越低,焦域趋近于圆形,尤其是当球带高度为1.6F（F为焦距）、聚焦夹角≥210°时,其焦域三轴尺寸均可达到亚波长尺度。为验证仿真结果的正确性,设计制作了一个可改变聚焦夹角的换能器并进行了测试,实验与仿真结果大致相符。设计的换能器相对于传统行波换能器,焦域形态得到了明显改善,能够压缩焦域长短轴之比,有效提高聚焦精度,为改善聚焦超声换能器焦域形态提供了一种设计方法。     

超声治疗中耦合液对声聚焦影响的研究

本文推导了凹球面聚焦换能器产生的声波经耦合液进入软组织后的声场计算公式，并对不同耦合液，耦合层厚度，温度对声聚焦的影响进行了研究，得到一一些对超声热疗具有指导意义的结果。     

高强度聚焦超声作用下体模组织温度上升研究

为研究高强度聚焦超声(HIFU)作用下组织温度上升规律,建立了高强度聚焦声场和组织温度场有限元仿真模型,并通过体外辐照实验对仿真模型进行了验证。通过仿真对水和组织域中的聚焦声场进行建模,计算吸收声能并将其用作热源以计算组织内的温升。进一步制备仿生物组织凝胶体模,利用热电偶进行HIFU作用下体模组织焦点处的测温。结果表明:该模型可有效预测HIFU治疗时的温度上升,与实验所得温度误差不超过 3℃;体模组织受到超声辐照时温度会立即升高,起初温升速率较快,随着辐照时间延长,温升速率逐渐降低,停止辐照后温度立即下降。     

超声造影早期评价HIFU治疗兔移植性骨肿瘤的初步研究

目的:观察兔VX2移植性骨肿瘤经高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)治疗前后超声造影的图像变化,以评价高强度聚焦超声治疗骨肿瘤的疗效。方法:将VX2瘤块植入20只兔的右侧胫骨髓腔内,三周后进行HIFU治疗。治疗前后均推注超声微泡造影剂,对肿瘤治疗前后的超声造影图像进行比较。结果:治疗前超声造影显示,右侧胫骨髓内肿瘤快速、明显强化,与周边组织分界清楚,测得病灶平均大小为,上下径(17.614±0.955)mm,前后径(10.414±1.142)mm。治疗后造影,治疗区域显示为造影剂灌注缺损区,平均范围为上下径(8.010±0.584)mm,前后径(7.540±0.499)mm,未经治疗的肿瘤组织仍有超声造影剂灌注。结论:超声造影成像清楚地显示肿瘤范围以及治疗后灌注缺损区的大小,通过反映治疗后肿瘤的血供改变来评价HIFU治疗肿瘤的疗效。     

HIFU治疗裸鼠皮下移植瘤超声和磁共振变化的初步观察

目的初步探讨高强度聚焦超声对裸鼠卵巢癌皮下移植瘤治疗前后的超声和磁共振变化.方法HIFU治疗裸鼠卵巢癌模型12例,高强度聚焦超声治疗肿瘤外侧1/2,治疗前后进行超声和磁共振检查.结果(1)治疗前肿瘤组织超声表现为低回声,彩色和能量多普勒检测肿瘤内部及周边均有少许血流信号;治疗后肿瘤组织回声增强,彩色和能量多普勒检测肿瘤治疗区域内部及周边均无血流信号.(2)磁共振检查治疗区域肿瘤组织增强后未见明显强化.结论HIFU能准确破坏卵巢肿瘤,治疗过程中超声定位准确、方便,治疗后磁共振有助于评价其疗效,为临床应用提供实验依据.     

基于回波能量的HIFU治疗区声阻抗测量方法

在高强度聚焦超声(HIFU)治疗过程中,组织声阻抗对于超声成像、表征组织特性具有重要意义.治疗区域一般位于组织内部,难以直接测出其声阻抗.本文通过建立离体猪肉组织模型,模拟超声信号在组织中的传播路径,推导出声阻抗与回波信号能量差的数学关系并应用于HIFU治疗区声阻抗的测量.为验证该方法的有效性,将上述测量的声阻抗与利用水浴锅直接测量的组织声阻抗值进行对比.实验结果表明:利用回波能量差测得的治疗区组织声阻抗与直接测量法测得的同一温度下组织声阻抗值相差较小,相对误差控制在0.5%以内,且两者随温度变化趋势表现出良好的一致性,即都随温度升高呈非线性增加趋势.     

高强度聚焦超声作用下的组织温度场测量技术的研究进展

高强度聚焦超声是近年来兴起的一种肿瘤无创治疗新技术,而温度监控是该治疗的关键,故温度场检测成为超声医学工程学研究的热点。该测量方法中的有损测温对实验操作要求较高,且易引起肿瘤细胞的转移;无损测温方法包括超声、微波辐射、电阻抗成像和MRI(磁共振)等,文章对这些新技术的优点和局限性作出综述。     

用于高强度聚焦超声热消融的PAA模块:模块的制作及声学参数的测量

目的研制一种透明的用于高强度聚焦超声热消融的PAA模块,并对其声学参数进行测量。方法观察模块浓度的不同所致颜色与透明度的变化,并对PAA模块的声学特性包括密度、声速及声衰减进行测量。结果(1)PAA模块为透明的琥珀色,蛋白浓度越高,颜色越深,透明度越低。(2)PAA模块的密度与水相近,为1.0250g/cm3至1.0617g/cm3。声速与模块浓度之间有明显的相关性。声衰减从0.125dB/cm至0.329dB/cm,随着模块密度与探头频率的增加而增加。结论PAA模块是一种较好的用于高强度聚焦超声热消融的均质仿体,实验结果有较好的重复性。     

高强度聚焦超声治疗的实时被动空化检测系统及其实验研究

高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)所致空化效应在临床应用中扮演着重要角色,对HIFU临床治疗过程中的空化活动进行实时监测,结合数据分析与治疗过程中实时反馈,可进一步提高HIFU治疗的安全性和有效性.在现有HIFU临床治疗系统的基础上,将两个被动空化检测探头与H...     

Effect of material gradation on K-dominance of fracture specimens

This work describes the effect of material gradation (parallel to the crack plane) on stress intensity factors and K-dominance, i.e. the dominance of the singular region, of fracture specimens; SE(T), SE(B) and C(T). The extent of K-dominance is investigated by comparing the actual stress field with the Williams’ asymptotic stress field. Linear-elastic finite element analyses are performed using graded elements which incorporate graded material properties at the element level. Material gradation and crack geometry are systematically varied to perform the parametric study. Results reveal that the effect of material gradation on K_I is most pronounced when a short crack is located on the stiffer side of the fracture specimen. For a given specimen and crack geometry, the extent of K-dominance yields a curve with a peak point at a certain material gradation. Results of the present study provide valuable insight into the K-dominance of FGMs.     

Harmonic enrichment functions: A unified treatment of multiple,intersecting and branched cracks in the extended finite element method

A unifying procedure to numerically compute enrichment functions for elastic fracture problems with the extended finite element method is presented. Within each element that is intersected by a crack, the enrichment function for the crack is obtained via the solution of the Laplace equation with Dirichlet and vanishing Neumann boundary conditions. A single algorithm emanates for the enrichment field for multiple cracks as well as intersecting and branched cracks, without recourse to special cases, which provides flexibility over the existing approaches in which each case is treated separately. Numerical integration is rendered to be simple—there is no need for partitioning of the finite elements into conforming subdivisions for the integration of discontinuous or weakly singular kernels. Stress intensity factor computations for different crack configurations are presented to demonstrate the accuracy and versatility of the proposed technique. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of interphase and thermal environment on the effective properties of Macro-Fiber Composites (MFC)

A simplified analytical model is devised based on equivalent layered approach using the concepts of ‘rule of mixtures’ and ‘series and parallel capacitance theory’ to find the effect of bonding layer thickness and the thermal environment on the effective properties of Macro-Fiber Composites (MFC). A thermo–electro–mechanical analysis is performed based on finite element calculations using unit-cell method accounting for the geometric properties of constituents and non-uniform electric field distribution across the electrodes. Also, experiments are performed on commercially available MFCs under electrical load in various thermal environments to evaluate the coupling constants. The predictions based on the proposed models are validated with experimental results and data from the manufacturer.     

Advances in piezoelectric thin films for acoustic biosensors,acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.     

Advances in metals and alloys for joint replacement

Metals, ceramics, polymers, and composites have been employed in joint arthroplasty with ever increasing success since the 1960s. New materials to repair or replace human skeletal joints (e.g. hip, knee, shoulder, ankle, fingers) are being introduced as materials scientists and engineers develop better understanding of the limitations of current joint replacement technologies. Advances in the processing and properties of all classes of materials are providing superior solutions for human health. However, as the average age of patients for joint replacement surgery decreases and the average lifespans of men and women increases worldwide, the demands upon the joint materials are growing. This article focuses solely on advances in metals, highlighting the current and emerging technologies in metals processing, metal surface treatment, and integration of metals into hybrid materials systems. The needed improvements in key properties such as wear, corrosion, and fatigue resistance are discussed in terms of the enhanced microstructures that can be achieved through advanced surface and bulk metal treatments. Finally, far reaching horizons in metals science that may further increase the effectiveness of total joint replacement solutions are outlined.