Ultrasound and the biomechanical competence of bone

Ultrasound is a mechanical wave and consequently has a unique potential to characterize the mechanical properties of bone. In some applications, such as determination of the anisotropic elastic constants of cortical bone specimens, this potential has been realized. In other applications, including the hugely important field of clinical measurements, current ultrasonic techniques struggle to provide information directly relating to mechanical properties. This article reviews the successes and shortcomings of ultrasound as a tool for determination of bone mechanical properties and highlights those new developments likely to bring progress in the future.     

Ultrasound monitoring of the setting of calcium-based bone cements

In this study, the setting of calcium-sulphate (CS) and -phosphate (CP) based bone cements (BCs) was monitored by ultrasound. The objective was to link acoustic and material properties of ceramic-based BCs from the early stages of the cement curing process. The powder phase of the CS-cement consisted of CS hemihydrate; the CP-cement was a mixture of alpha-tricalcium phosphate, CS dihydrate and hydroxyapatite. For the CS-cement, the acoustic impedance z (c)(t), the speed of sound c (c)(t) and the density ρ(c)(t) were measured at the interval of liquid-to-powder ratios LPRs from 0.20 to 3.00?ml/g. For the CP-cement, the acoustic characteristics obtained were the z (c)(t) and the reflection coefficient R (p,c)(t), and the LPRs ranged from 0.30 to 0.40?ml/g. The resulting acoustic properties indicated that CP- and CS-cements exhibited distinctly different curing behaviour; while CS-cement expanded, CP-cement shrank with time.     

Ultrasound simulation of complex flow velocity fields based on computational fluid dynamics

In this work, a simulation environment for the development of flow-related ultrasound algorithms is presented. Ultrasound simulations of realistic Doppler signals require accurate modeling of blood flow. Instead of using analytically described flow behavior, complex blood movement can be derived from velocity fields obtained with computational fluid dynamics (CFD). By further modeling blood as a collection of point scatterers, resulting RF-signals can be efficiently retrieved using an existing ultrasound simulation model. The main aim of this paper is to elaborate on creating CFD-based phantoms for ultrasound simulations. The coupling of a computed flow field with an ultrasound model offers flexible control of flow and ultrasound imaging parameters, beneficial for improving and developing imaging algorithms. The proposed method was validated in a straight tube with a stationary parabolic velocity profile and further demonstrated by an eccentrically stenosis carotid bifurcation. The estimated flow velocities are in good agreement with the CFD reference, both for color flow imaging and pulsed-wave doppler simulations. The presented method can also be extended to include wall mechanics simulations in future work.     

Finite element simulation of anisotropic damage accumulation and creep in acrylic bone cement

Acrylic bone cement is used to fixate hip replacement implants into the bone. Creep and fatigue failure of the cement promote failure of the implant. For the purpose of implant testing, we derived a finite element algorithm that simulates creep and damage accumulation in acrylic bone cement. The simulation combines a Maxwell creep model, with a 3-D continuum damage mechanics approach modeling anisotropic damage accumulation. The technical details of the simulation are described. In a first application tensile fatigue tests on tubular cement specimens are simulated. The creep elongation and fatigue life of the specimens, as predicted by the simulations, are successfully correlated to the experimental results. In a second application, the simulation is used to predict creep and fatigue failure of the cement mantle around two hip implants with different clinical outcomes. It is shown how the simulation is able to predict the locations of cement damage around the implants, and the amounts of implant migration attributable to creep.     

Finite element simulation of bone remodelling in the human mandible surrounding dental implant

Dental implant is a biocompatible titanium device surgically placed into the jaw bone to support a prosthetic tooth crown in order to replace missing teeth. However, placement of an implant changes the normal mechanical environment of jawbone, which causes the bone density to redistribute and adapt to the new environment by remodelling. This study aims to predict the density distribution in human jawbone surrounding a dental implant. Based on some popular yet distinctive theories for bone remodelling, a new algorithm is proposed that takes into account both the ??lazy zone?? effect and the self-organizational control process. The proposed algorithm is first verified by a two-dimensional (2D) plate model simulating bone tissue, then, a 2D finite element model of implant and jawbone is studied. The effects of two parameters, viz the reference value of strain energy density (SED) and the ??lazy zone?? region, on density distribution are also investigated. The proposed algorithm is proven to be effective, and the predicted density distribution patterns correlate well with clinical observations. This study has demonstrated that consideration of the lazy zone is less important than consideration of the stress and strain (quantified as SED) induced within the bone.     

Modeling and simulation of osteoporosis and fracture of trabecular bone by meshless method

Osteoporosis is a skeletal disease characterized by a decrease in bone strength as a result of a decrease of bone mass and a deterioration of bone microstructure. In this work, the imaging data of a CT scanned human femoral neck trabecular bone is directly converted into a meshless model. A model is developed to analyze osteoporosis process. A fracture criterion and the corresponding post-failure are proposed for trabecular bone. The fracture process is modeled and simulated. The simulations show that the fracture stress is not a monotonically decreasing function in the process of fracture, and the microstructure of trabecular bone has a positive effect in preventing progressive failure. The approach in this work may be used to understand the osteoporosis-related fracture and the bone density–strength relationship, and to serve as a way for prognosis of osteoporosis.     

有限元法仿真LIPUS照射骨细胞的局部声场分布

低强度脉冲超声(Low-Intensity Pulsed Ultrasound,LIPUS)作为一种可用于治疗骨病的潜在物理疗法,可以有效避免药物的不良反应,且具有无创伤、无电离辐射等优点,因而有着广阔的应用前景。应用有限元法(Finite Element Method,FEM)仿真研究LIPUS照射骨细胞时的局部声场分布,从微观角度探究骨细胞与声场间的相互作用以及各超声参数和照射位置对于声场分布的影响。首先建立了骨细胞模型,然后在不同位置施加超声激励并改变超声的激励声压与频率,计算不同情况下的声场分布,最后对仿真结果进行综合分析与比较。结果表明,骨细胞会在一定程度上影响声场的分布,且超声的各个参数及照射位置均对声场有一定的影响。仿真结果从声压与能量的角度阐述了LIPUS治疗骨病的潜在物理机制,另一方面也为离体细胞实验中LIPUS的参数筛选和照射方式提供理论参考。     

Ultrasound in the process industries

The advantages of nondestructive ultrasonic methods for monitoring and speeding process reactions, measuring fluid flow, tomographic imaging etc., open up many applications for the methods in the process industries. This article represents an overview of an IEE colloquium on `Ultrasound in the process industry' held on 23rd September 1993     

Performance of bioactive PMMA-based bone cement under load-bearing conditions: an in vivo evaluation and FE simulation

In the past, bioactive bone cement was investigated in order to improve the durability of cemented arthroplasties by strengthening the bone-cement interface. As direct bone–cement bonding may theoretically lead to higher stresses within the cement, the question arises, whether polymethylmethacrylate features suitable mechanical properties to withstand altered stress conditions? To answer this question, in vivo experiments and finite element simulations were conducted. Twelve rabbits were divided into two groups examining either bioactive polymethylmethacrylate-based cement with unchanged mechanical properties or commercially available polymethylmethacrylate cement. The cements were tested under load-bearing conditions over a period of 7?months, using a spacer prosthesis cemented into the femur. For the finite element analyses, boundary conditions of the rabbit femur were simulated and analyses were performed with respect to different loading scenarios. Calculations of equivalent stress distributions within the cements were applied, with a completely bonded cement surface for the bioactive cement and with a continuously interfering fibrous tissue layer for the reference cement. The bioactive cement revealed good in vivo bioactivity. In the bioactive cement group two failures (33?%), with complete break-out of the prosthesis occurred, while none in the reference group. Finite element analyses of simulated bioactive cement fixation showed an increase in maximal equivalent stress by 49.2 to 109.4?% compared to the simulation of reference cement. The two failures as well as an increase in calculated equivalent stress highlight the importance of fatigue properties of polymethylmethacrylate in general and especially when developing bioactive cements designated for load-bearing conditions.     

Ultrasound enhanced geopolymerisation

The feasibility of using ultrasound to enhance the geopolymerisation of metakaolinite/sand and fly ash/metakaolinite mixtures was investigated. The introduction of ultrasonication into the geopolymerisation systems increased the compressive strength of the formed geopolymers and the strength increased with increased ultrasonication up to a certain time. The dissolution of metakaolinite and fly ash in alkaline solutions was enhanced by ultrasonication, hence releasing more Al and Si into the gel phase for polycondensation. SEM analysis demonstrated that ultrasonication improved the distribution of the gel phase in the geopolymeric matrices and strengthened the binding between the particle surfaces and the gel phases. XRD patterns showed that ultrasonication enhanced the formation of semi-crystalline to crystalline phases in the formed geopolymers. The ²⁷Al MAS-NMR spectra showed ²⁷Al chemical shifts at around 55 ppm for the geopolymers synthesised with and without ultrasonication, indicating that Al was tetrahedrally coordinated in the form of Al(4Si). ²⁹Si MAS-NMR studies showed that ultrasonication largely improved the interlinkage between Si and Al species, increased the concentrations of polysialate species and enhanced the ordering of the Si and Al tetrahedra in the gel phase in geopolymerisation. Both ²⁷Al and ²⁹Si MAS-NMR spectra indicated an increased extent of polymerisation between Al and Si species in the presence of ultrasonication. The thermal analysis indicated that ultrasonication improved the thermal stability of the formed geopolymers. The improved performance of the ultrasonically formed geopolymers in terms of compressive strength and thermal stability could be attributed to the accelerated dissolution of the Al—Si source materials, the strengthened bonds at the solid particle/gel phase interfaces, the enhanced polycondensation process and the increased semi-crystalline and crystalline phases.     

医用超声诊断仪超声源输出超声功率测量值的不确定度的评定

医用超声诊断仪超声源输出超声功率测量结果不确定度的评定与表示。     

超声功率测量现状及大功率超声测量研究进展

超声功率是超声设备的一项重要量化指标。本文首先介绍了目前国内外超声功率测量和国际比对现状,以及国内外有关大功率超声测量的研究水平。介绍新建立的大功率平面超声源和大功率聚焦超声源,测量并比较了几种吸收靶的吸声系数,利用研制的吸收靶对大功率平面超声源和大功率聚焦超声源进行了功率测量。实验表明,基于吸收靶的大功率超声测量是稳定的、可行的。     

Finite element simulation of adaptive bone remodelling: A stability criterion and a time stepping method

Adaptive bone remodelling simulations which use finite element analysis can potentially aid in the design of orthopedic implants and can provide examples which test specific bone remodelling hypotheses in a quantitative manner. By concentrating on remodelling algorithms in which the geometry is fixed but the tissue stiffness changes based on strain energy density, we have predicted stability conditions for bone remodelling and we have tested the applicability of these conditions using numerical simulations. The stability requirements arrived at using a finite element formulation are similar to the requirements arrived at in an earlier analytical study. In order to test the stability conditions, we have developed an Euler backward time stepping technique which uses the derivation for stability. These simulations arrived at solutions which were impossible using Euler forward time stepping as applied in this study. Cases in which a simplified version of the derived Euler backward method are unstable or marginally stable have also been seen, but when the Euler backward method is applied using the full derived matrices, no instabilities are apparent. The results of the stability tests indicate that the converged density distributions in the examples studied are stable. Although a priori conditions which ensure stability are not found, a test for stability is provided, given an assumed density distribution.     

Monte Carlo simulation of trabecular bone remodelling and absorbed dose coefficients for tritium and 14C

A Monte Carlo simulation of multiple trabecular bone cavities in adult bone was developed and the absorbed radiation dose factors evaluated for 3H and 14C. The model was developed to assess the dose from radionuclide uptake in quiescent bone, but also the effects of temporal changes in bone turnover by incorporating bone-modelling units (BMU). Absorbed dose fractions were calculated for target regions that include the endosteal layer where radiation-sensitive stem cells in bone marrow are considered to reside preferentially. There were large differences in the absorbed fractions for two types of bone surface, quiescent and forming. Tritium in quiescent bone results in a dose to the endosteum about 20 times that for the same activity in forming bone surface irradiating osteoblasts. When the quiescent bone surface source was extended from an infinitely thin layer to a more realistic 1 microm thick, the tritium absorbed fractions for endosteum and red marrow targets fell by more than 2-fold.     

CT技术的发展与其在医学上的应用

本文简要介绍了CT技术的原理以及其发展过程,并详细介绍了其在医学上的相关应用,可以给想要掌握CT领域现有技术的人群提供一定参考。     

Ultrasound holographic B-scan imaging

An ultrasound holographic B-scan (UHB) imaging apparatus comprising a minicomputer system, a data acquisition unit, and a special 64-element UHB transducer has been developed. Simulation studies and real experiments with a tissue-equivalent phantom show that lateral and longitudinal resolution (-6 dB) of about 1 mm was achieved in the entire image. Furthermore, results from clinical evaluation, including diagnostic and neurosurgical imaging, suggest that the UHB imaging method is operational and has some special advantages in patient diagnosis. Theoretically, the addition of phase information to the ultrasound images can result in enhanced tissue characterization, which is extremely important in tumor diagnosis and treatment.     

超声场作用下导电聚苯胺的合成

采用正相微乳液聚合法在超声波作用下制备导电聚苯胺,研究超声场强度的变化和作用时间的长短对导电聚苯胺的粒度和导电性能的影响。结果表明:与非超声场相比,采用超声场作用下正相微乳液聚合法制备的导电聚苯胺粉体的粒度显著降低,平均粒径从16.59μm减小到10.35μm。随着超声时间的增加,聚苯胺的电导率从5.230×10-2S/cm提高到1.923×10-1S/cm,提高了一个数量级。在超声波的作用下,聚苯胺粉体中分子间的偶极矩变化加强,超声作用产生的空化效应强化了十二烷基苯磺酸的掺杂和乳化作用。     

超声与微泡在血管病变治疗方面的应用

超声微泡属于"超声分子影像学"的范畴.将其携带上基因或药物后,超声与微泡不仅用于超声显像,还可用于疾病的治疗.本文现将其在血管病变治疗方面的应用作一简要综述.     

肘部超声显像

肘关节是上肢重要的关节,肘部超声检查的优点包括简单易行、多平面扫查以及能够动态检查关节结构.病人症状和触痛最明显的位置与影像结果有直接的相关性,易于与对侧进行对照.超声不仅能够检查关节周围的肌腱、韧带等结构,还可以显示关节积液、游离体和局限性囊肿和肿瘤.如果手法得当,超声检查必将是肘关节疾病诊断的一种有价值的影像学方法.