骨折长骨中超声导波传播特性的仿真研究

采用超声导波评价长骨骨折已成为近两年来的一个研究热点.本文采用混合边界元方法(HBEM)对超声导波在骨裂长骨中的传播情况以及各导波模式的反射系数和透射系数进行了数值分析.研究结果表明,入射导波模式经由裂纹处模式转换后依然保持为主要接收模式不变.对某一裂纹,各模式透射系数常在相近的频率点上达到局部峰值.对于不同深宽比(d/w)裂纹,某些模式透射系数曲线局部峰值所对应的频率存在着相互错开的现象,这些结果可用于选择最优入射导波模式和频率,以便更好地定量评价骨质以及骨裂状况.     

长骨裂纹宽度和角度对低阶超声导波的影响

超声导波检测长骨骨折和监测骨折愈合已成为一种极具前景的课题,但高频厚积下导波多模式混叠带来的模式识别和分离问题一直是一个难点。为避免上述问题,在低频下仅激励两个低阶兰姆波SO和AO模式,采用二维时域有限差分(2DFDTD)法定量分析裂纹宽度和骨折角度对SO和AO幅度的影响。结果表明,SO与AO模式的幅度均随裂纹宽度的增加而下降;AO的幅度随骨折角度增大而上升,SO幅度随骨折角度增大先下降后上升,转折点约为45°。SO与AO的幅度比值在不同骨折角度下均能较好地表征裂纹宽度的变化,可为横断型和斜切型长骨骨折状况的超声评价及骨折愈合监测提供依据。     

基于时频分布的盲信号分离方法研究长骨中的多模式导波信号

由于超声导波对长骨皮质骨的材料特性及厚度变化非常敏感,因此用导波评价长骨状况的研究已成为近年来的一个研究热点.在接收到的导波中,往往多种模式混叠在一起,使得进一步求取每种导波模式的群速度等与骨质状况密切相关的参数时遇到困难.本文采用基于时频分布的盲信号分离(TFBSS)方法对长骨中混叠的多模式进行分离,然后对分离后的单...     

长骨裂纹宽度和角度对低阶超声导波的影响

超声导波检测长骨骨折和监测骨折愈合已成为一种极具前景的课题,但高频厚积下导波多模式混叠带来的模式识别和分离问题一直是一个难点。为避免上述问题,在低频下仅激励两个低阶兰姆波SO和AO模式,采用二维时域有限差分(2DFDTD)法定量分析裂纹宽度和骨折角度对SO和AO幅度的影响。结果表明,SO与AO模式的幅度均随裂纹宽度的增加而下降;AO的幅度随骨折角度增大而上升,SO幅度随骨折角度增大先下降后上升,转折点约为45°。SO与AO的幅度比值在不同骨折角度下均能较好地表征裂纹宽度的变化,可为横断型和斜切型长骨骨折状况的超声评价及骨折愈合监测提供依据。      

时频方法分析长骨中的超声导波及皮质骨厚度

超声导波在长骨中传播时,接收信号中含有相互叠加的多个导波模式。本文提出将希尔伯特-黄变换(HHT)用于分析叠加的多模式导波信号,将其分解成许多单个独立的模式,然后对分解出的模式求得其对应频率下的群速度,并与短时傅里叶变换所得的结果进行比较。通过与理论计算结果比较,可得到长骨皮质骨的厚度。研究结果表明,实验得到的厚度与实际厚度一致。说明通过测量导波模式的速度可以评价皮质骨的厚度,也说明HHT方法是一种识别叠加多模式导波信号的有效方法。      

长骨中振动声激发超声导波的方法

为了实现一定频段内任意低频下在长骨中激励导波信号,本文提出一种采用聚焦高频(5 MHz)超声换能器在长骨皮质骨中激发低频(150 kHz)超声导波的振动声方法.首先介绍了板状超声导波理论和双声束共聚焦法与单声束调幅法激发振动声的基本原理;进而采用三维有限元仿真方法分析振动声激发低频超声导波的基本现象,然后结合牛胫骨板离体实验,验证振动声激发低频超声导波的可行性.结果均表明,双声束共焦与单声束振动超声均可在骨板中激发低频超声导波.相关研究方法有助于提高空间域长骨中超声导波测量精度,以及在一定频段内实现任意频率激励等,对发展低频超声导波在体测量长骨皮质骨的新技术具有一定的指导意义.     

基于弹性模量检测骨疲劳的超声导波方法研究

研究早期诊断骨疲劳的方法是当前骨质评价方面的研究热点之一. 本文对不同弹性模量下长骨中超声导波的传播特性进行了理论分析和仿真研究.首先, 通过数值计算得到导波在管状长骨中的理论解析解.然后对管状长骨进行了时域有限差分(FDTD) 仿真, 并验证了它与理论解析解的一致性, 同时得到长骨中不同模式导波群速度、 中心频率和衰减与弹性模量的关系.研究结果表明各个导波模式的群速度和中心频率均随弹性模量的增加而增加, 而衰减随弹性模量的增加而减小.说明超声导波的传播特性参量可以反映长骨弹性模量的变化, 从而为长骨的早期疲劳诊断提供理论依据.     

超声轴向传播技术评价长骨的研究

用超声轴向传播技术评价长骨状况已成为近年来的一个研究热点。本文首先介绍了第一到达波(FAS)法、超声Lamb波及柱面导波法在评价长骨皮质骨状况方面的研究进展,最后分析和讨论了当前研究中存在的问题及应该研究的方向。     

超声导波的频散补偿与模式分离算法研究

超声导波已被广泛应用于无损检测与评价,针对超声导波应用中普遍存在的模式混叠与频散问题,本文在采用频谱相位与信号时延函数建模导波频散信号传递系统的基础上,提出了一种单一模式的频散补偿算法。进一步地,通过将选择性频散补偿技术与导波模式分离相结合,本文算法克服了传统补偿算法所不能解决的多模式导波频散问题。板中的Lamb波A0,A1和S0混合模式仿真分析表明,本算法不仅可用于单一导波模式信号合成与频散补偿,而且可在实现多模式混合导波信号选择性频散补偿基础上,解决多模式导波信号中单一模式提取与分离。本文研究有助于超声导波多模式频散信号的分析与处理.      

Barker码激励超声导波在长骨检测中的应用

单脉冲激励的超声导波在长骨中传播时,信号的衰减大,导致接收信号的幅度很小,且噪声严重。Barker码激励能有效增大接收信号幅度,提高信噪比(SNR)。将其应用到超声导波长骨检测中,进行仿真和长骨实验,得到的信号分别用加权匹配滤波器和有限冲激响应-最小均方误差(FIR-LS)逆滤波器进行压缩,并与单脉冲激励的结果进行了对比。结果表明,对于13位的Barker码,采用加权匹配滤波器进行解码时,压缩信号幅度是单脉冲激励接收信号的13倍;而FIR-LS逆滤波器则达到-63.59 dB的峰值旁瓣水平(PSL),更好地抑制噪声。说明可以将Barker码激励超声导波应用于长骨的检测中。      

Quantification of guided mode propagation in fractured long bones

Guided modes propagation in intact, fractured and healing long bone has drawn significant research interests. However, mode quantifications for the direct comparison are still necessary to address. The aim of the study is to analyze the mode interaction with a notch-fracture in the long bone and find quantitative ultrasound parameters sensitive to depth and width variation of the fracture. We analyzed the impacts of the partially and completely diaphyseal osteotomy on fundamental guided modes propagation using the two-dimension finite-difference time-domain (2D-FDTD) simulations. The long bones were built as three layer models by a cortical plate embedded between overlying soft tissue and inner-coated marrow. Narrowband low-frequency sinusoids (100 kHz) were employed to only excite two fundamental guided modes. The mode amplitude variations were investigated as functions of the gap-breakage width and depth. It is found that the transverse fractures have strong influences on the anti-symmetric mode A0 transmission and reflection, whereas amplitudes of the symmetric mode S0 are not sensitive to the fracture degree. The quantitative results consistently indicate that reflection energy and transmission coefficients of the S0 and A0 modes can be used to quantify the mode interaction in the fractured long bone and further to evaluate long bone fracture status. Future study is needed to investigate the physical experiments on realistic fractured long bone and to insure that the proposed ultrasound parameters can be used to quantitatively evaluate the long bone fracture in clinical application.     

Three-dimensional finite element modeling of guided ultrasound wave propagation in intact and healing long bones

The use of guided waves has recently drawn significant interest in the ultrasonic characterization of bone aiming at supplementing the information provided by traditional velocity measurements. This work presents a three-dimensional finite element study of guided wave propagation in intact and healing bones. A model of the fracture callus was constructed and the healing course was simulated as a three-stage process. The dispersion of guided modes generated by a broadband 1-MHz excitation was represented in the time-frequency domain. Wave propagation in the intact bone model was first investigated and comparisons were then made with a simplified geometry using analytical dispersion curves of the tube modes. Then, the effect of callus consolidation on the propagation characteristics was examined. It was shown that the dispersion of guided waves was significantly influenced by the irregularity and anisotropy of the bone. Also, guided waves were sensitive to material and geometrical changes that take place during healing. Conversely, when the first-arriving signal at the receiver corresponded to a nondispersive lateral wave, its propagation velocity was almost unaffected by the elastic symmetry and geometry of the bone and also could not characterize the callus tissue throughout its thickness. In conclusion, guided waves can enhance the capabilities of ultrasonic evaluation.     

A hybrid FDTD-Rayleigh integral computational method for the simulation of the ultrasound measurement of proximal femur

The development of novel quantitative ultrasound (QUS) techniques to measure the hip is critically dependent on the possibility to simulate the ultrasound propagation. One specificity of hip QUS is that ultrasounds propagate through a large thickness of soft tissue, which can be modeled by a homogeneous fluid in a first approach. Finite difference time domain (FDTD) algorithms have been widely used to simulate QUS measurements but they are not adapted to simulate ultrasonic propagation over long distances in homogeneous media. In this paper, an hybrid numerical method is presented to simulate hip QUS measurements. A two-dimensional FDTD simulation in the vicinity of the bone is coupled to the semi-analytic calculation of the Rayleigh integral to compute the wave propagation between the probe and the bone. The method is used to simulate a setup dedicated to the measurement of circumferential guided waves in the cortical compartment of the femoral neck. The proposed approach is validated by comparison with a full FDTD simulation and with an experiment on a bone phantom. For a realistic QUS configuration, the computation time is estimated to be sixty times less with the hybrid method than with a full FDTD approach.     

采用超声导波特征参量的骨质疏松识别方法

骨质的定期检测对骨质疏松的防治至关重要。本文研究了骨质疏松对超声导波在人体长骨中传播的影响。提出采用多尺度小波变换方法对接收到的导波信号进行处理,通过分析在不同传播距离下高阶小波细节分量所占信号总能量的变化,来判断是否患有骨质疏松症。在13位志愿者的小腿胫骨上进行超声测量,得到导波信号。经多尺度小波变换方法的分析处理结果显示在13位志愿者中,有7位志愿者的超声导波信号随着传播距离的改变,其主要频率成分发生了明显的变化,显示这7位志愿者患有骨质疏松症。这一诊断结果与X射线技术诊断结果相比,准确率可以达到92.3%,表明本文所提出的利用小波多尺度变换方法对长骨进行超声诊断具有较好的潜力。      

Guided circumferential waves in orthotropic cylindrical curved plate and the mode conversion by the end-reflection

In ultrasonic nondestructive inspection of large-diameter pipes and curved plate, longitudinal cracks are detected more efficiently by using guided circumferential waves. In the present, the study of guided circumferential waves and their application in detecting longitudinal defect were relative adequate when pipe material is isotropic. Based on linear three-dimensional elasticity, an orthogonal polynomial series expansions approach is used for determining the guided circumferential waves dispersion curves in homogeneous infinitely long orthotropic hollow cylinders. Results are compared with those published earlier and with the finite element simulation to check up the accuracy and range of applicability of this polynomial approach. Through the analysis of the displacements distributions and finite element simulation, the mode conversion of guided circumferential waves by end-reflection in cylindrical curved plate is discovered.