A Radio Telemetry Device for Monitoring Cartilage Surface Pressures in the Human Hip

A miniaturized radio telemetry device has been developed which can monitor the magnitude and distribution of pressure generated between the cartilage-covered surface of the human hip socket and the surface of a hip prosthesis which replaces the spherical head of the femur in the hip. The pressure distribution is sensed by an array of 14 pressure transducers mounted inside the hollow ball of the prosthesis, and the signals from the transducers are transmitted to external receiving and recording equipment by a radio telemetry device also located inside the hollow ball.     

Postarthroplasty Examination Using X-Ray Images

Arthroplasty, the implantation of prostheses into joints, is a surgical procedure that is affecting a larger and larger number of patients over time. As a result, it is increasingly important to develop imaging techniques to noninvasively examine joints with prostheses after surgery, both statically and dynamically in 3-D. The static problem is considered here, with the aim to create a 3-D shape model of the bone as well as the prosthesis using a set of 2-D X-rays from various viewpoints. The most important challenge to be addressed is the lack of texture, the most common feature to recover shape from multiple views. In order to overcome this limitation, we reformulate the problem using a novel multiview segmentation approach where an active contours 3-D surface evolution with level-set implementation is used to recover the shape of bones and prostheses in postoperative joints. The recovered shape may then be used to track 3-D motions in dynamic X-ray sequences to obtain kinematic information.      

Shear Modulus Decomposition Algorithm in Magnetic Resonance Elastography

Magnetic resonance elastography (MRE) is an imaging modality capable of visualizing the elastic properties of an object using magnetic resonance imaging (MRI) measurements of transverse acoustic strain waves induced in the object by a harmonically oscillating mechanical vibration. Various algorithms have been designed to determine the mechanical properties of the object under the assumptions of linear elasticity, isotropic and local homogeneity. One of the challenging problems in MRE is to reduce the noise effects and to maintain contrast in the reconstructed shear modulus images. In this paper, we propose a new algorithm designed to reduce the degree of noise amplification in the reconstructed shear modulus images without the assumption of local homogeneity. Investigating the relation between the measured displacement data and the stress wave vector, the proposed algorithm uses an iterative reconstruction formula based on a decomposition of the stress wave vector. Numerical simulation experiments and real experiments with agarose gel phantoms and human liver data demonstrate that the proposed algorithm is more robust to noise compared to standard inversion algorithms and stably determines the shear modulus.     

Microwave drilling of bones

This paper presents a feasibility study of drilling in fresh wet bone tissue in vitro using the microwave drill method [Jerby et al, 2002], toward testing its applicability in orthopaedic surgery. The microwave drill uses a near-field focused energy (typically, power under approximately 200 W at 2.45-GHz frequency) in order to penetrate bone in a drilling speed of approximately 1 mm/s. The effect of microwave drilling on mechanical properties of whole ovine tibial and chicken femoral bones drilled in vitro was studied using three-point-bending strength and fatigue tests. Properties were compared to those of geometrically similar bones that were equivalently drilled using the currently accepted mechanical rotary drilling method. Strength of mid-shaft, elastic moduli, and cycles to failure in fatigue were statistically indistinguishable between specimen groups assigned for microwave and mechanical drilling. Carbonized margins around the microwave-drilled hole were approximately 15% the hole diameter. Optical and scanning electron microscopy studies showed that the microwave drill produces substantially smoother holes in cortical bone than those produced by a mechanical drill. The hot spot produced by the microwave drill has the potential for overcoming two major problems presently associated with mechanical drilling in cortical and trabecular bone during orthopaedic surgeries: formation of debris and rupture of bone vasculature during drilling.     

SAM扫描器件芯/焊结合空洞的失效分析

超声无损检测是70种无损探伤技术的最热点。扫描声学显微镜(SAM)的原理是声阻抗成像,要求缺陷尺度大于超声波的波长。结合SAM技术中的A-扫描波形分析和C-扫描特征成像,针对由封装引入的分层和空洞缺陷进行失效分析。研究发现:分层定位的关键是A-扫描波形分析中对各界面处反射波的时间位置的判断;基于分层定位的芯/焊结合空洞缺陷的判别,关键是C-扫描图像中灰阶色带的区分(反射率差值)。     

穿孔机械阻抗板的吸声特性研究

为提高低频吸声性能,在机械阻抗板(MIP)上穿少量微孔形成穿孔机械阻抗板(MIPMP)吸声结构。对MIPMP结构吸声性能进行初步研究,建立计算模型,用驻波管测量吸声系数。结果表明,MIPMP结构的吸声为机械阻抗和微穿孔的共同作用。吸声曲线出现两个吸声峰:一个在200~300 Hz,由机械阻抗引起,吸声系数可达0.95;一个出现在300~600Hz,由微穿孔引起。计算模型与实验结果所示趋势一致:随穿孔率的增大,机械阻抗单元吸声峰值先增大后减小,向高频移动,微穿孔单元吸声峰值逐渐减小,带宽增大,向高频移动;随背腔的增厚,机械阻抗单元吸声峰值变大,频率基本不变,微穿孔单元吸声峰值略减小,向低频移动。MIPMP与微穿孔板(MPP)构成的复合吸声结构在200~1 600Hz有好的吸声性能。     

Gradient Array of Freely Suspended Nanomembranes

Freely suspended layer‐by‐layer nanomembranes have been transferred onto an array of circular openings of varying diameters (a gradient array). The mechanical behavior of these nanomembrane gradient arrays have been studied using both bulging tests and point‐load experiments. By using the gradient array, experimental statistics are significantly improved. The observed scale‐dependent mechanical properties, investigated in an efficient fashion, are evident in the trend of increasing elastic modulus with decreasing membrane diameter. The observed increase in bending rigidity with decreasing membrane diameter is satisfactorily described by the theoretical model of an elastic membrane under a point load.     

Trabecular Bone Analysis in CT and X-Ray Images of the Proximal Femur for the Assessment of Local Bone Quality

Currently, conventional X-ray and CT images as well as invasive methods performed during the surgical intervention are used to judge the local quality of a fractured proximal femur. However, these approaches are either dependent on the surgeon's experience or cannot assist diagnostic and planning tasks preoperatively. Therefore, in this work a method for the individual analysis of local bone quality in the proximal femur based on model-based analysis of CT- and X-ray images of femur specimen will be proposed. A combined representation of shape and spatial intensity distribution of an object and different statistical approaches for dimensionality reduction are used to create a statistical appearance model in order to assess the local bone quality in CT and X-ray images. The developed algorithms are tested and evaluated on 28 femur specimen. It will be shown that the tools and algorithms presented herein are highly adequate to automatically and objectively predict bone mineral density values as well as a biomechanical parameter of the bone that can be measured intraoperatively.     

Resolution Improvement of Scanning Acoustic Microscopy Using Sparse Signal Representation

Scanning acoustic microscopy is an imaging method in which the focused high frequency ultrasound is used to visualize the micro structures. The morphology and acoustic properties of the biological tissues can be evaluated using scanning acoustic microscope system. To determine thin tissues having micrometer thickness, the high acoustic frequency is required for conventional SAM. In practice the acoustic frequency is restricted by the penetration depth through the material. Characterization of thin sliced tissue is difficult, as the reflected signals from top and bottom are superimposed. In order to improve the axial resolution of conventional SAM, a technique based on sparse signal representation in overcomplete time–frequency dictionaries is investigated and among the great number of algorithms for finding sparse representation, we first apply matching pursuit (MP) and basis pursuit (BP) and then propose the orthogonal matching pursuit (OMP) and stagewise orthogonal matching pursuit (StOMP) algorithms to decompose the A-scan signal to an overcomplete Gabor dictionary. Different criteria are used for measuring the performance of these algorithms in C-scan imaging. The proposed method can separate closely space overlapping echoes beyond the resolution of conventional SAM systems and also the final results show that StOMP performs best overall in extracting the specific echo, since this algorithm is precise and fast.     

Direct investigations of the interface impedance of organic field-effect transistors with self-assembled-monolayer-modified electrodes

It has been demonstrated that the modification of electrodes with self-assembled monolayers (SAMs) reduces the contact resistance and improves the device performances of organic field-effect transistors (OFETs). However, it has been difficult to judge if the contact resistance was reduced by the change in the electronic properties or by the change in the morphology of the metal–organic interface caused by the SAM modification because they have been difficult to be separately assessed. We have directly investigated the local impedance and the potential difference at the electrode–channel interfaces of the OFETs with and without modification of the electrodes by a pentafluorobenzenethiol SAM using frequency-modulation scanning impedance microscopy (FM-SIM). The potential profile measurement and the FM-SIM measurement at the interface showed that the improvement of the field-effect mobility in the SAM-modified OFET was caused by the reduction of the energy level mismatch, namely, the hole injection barrier at the source–channel interface, presumably with the reduction of the hole trap sites at the source–channel interface.     

Biologization of Allogeneic Bone Grafts with Polyphosphate: A Route to a Biomimetic Periosteum

The physiological polyphosphate (polyP), released primarily from platelets after bone fractures, acts as a donor for metabolic energy and as a phosphate source for bone mineralization. In this study allogeneic, decellularized bone samples are biologized with a layer of inorganic polyP by submersion of human femur cortex slices into a solution of Na‐polyP. Then polyP coat is modified by exposure to CaCl₂, resulting in in situ formation of amorphous Ca‐polyP microparticles (Ca‐polyP‐MP; diameter of ≈155 nm). Energy dispersive X‐ray spectroscopy analysis of the Ca‐polyP‐MP coat reveals a Ca:P molar ratio of ≈0.78, while the nonmodified bone cortex is characterized by a Ca:P ratio of ≈1.52. An ionic shift promotes the strong binding of the polyP to the bone. While the polyP modification only insignificantly increases the hardness of the bone sample, without changing the elastic surface properties, the polyP‐modified bone provides a very favorable substrate for SaOS‐2 cells to attach and to mineralize. In the presence of medium/serum the polyP coat transforms to a functionally active coacervate. The cells, attached to the polyP coat, show a marked spreading behavior and became entrapped into the polyP‐coacervate. The results suggest that regenerative‐active polyP might be of potential use in healing of bone.     

Compensation of sound speed deviations in 3-D B-mode ultrasound for intraoperative determination of the anterior pelvic plane

An accurate determination of the pelvic orientation is inevitable for the correct cup prosthesis placement of navigated total hip arthroplasties. Conventionally, this step is accomplished by percutaneous palpation of anatomic landmarks. Sterility issues and an increased landmark localization error for obese patients lead to the application of B-mode ultrasound imaging in the field of computer-assisted orthopedic surgery. Many approaches have been proposed in the literature to replace the percutaneous digitization by 3-D B-mode ultrasound imaging. However, the correct depth localization of the pelvic landmarks could be significantly affected by the acoustic properties of the penetrated tissues. Imprecise depth estimation could lead to a miscalculation of the pelvic orientation and subsequently to a misalignment of the acetabular cup implant. But so far, no solution has been presented, which compensates for acoustic property differences for correct depth estimation. In this paper, we present a novel approach to determine pelvic orientation from ultrasound images by applying a hierarchical registration scheme based on patch statistical shape models to compensate for differences in speed of sound. The method was validated based on plastic bones and a cadaveric specimen.     

C-SAM sounds the warning for IC packaging defects

C-mode acoustic microscopy provides unique advantages over SLAM techniques in detecting microcracks, voids, and delaminations. The reliability of integrated circuit (IC) packages depends in many respects on their mechanical integrity. The effect of structural weaknesses caused by poor bonding, voids, microcracks or delaminations may not be evident in the electrical performance characteristics, but may cause premature failure. C-mode scanning acoustic microscopy (C SAM) is an excellent tool for non-destructive failure analysis of IC packages. It provides a rapid and comprehensive imaging of critical package defects and the location of these defects in three dimensions within the package     

Additive Manufacturing of Material Scaffolds for Bone Regeneration: Toward Application in the Clinics

Additive manufacturing (AM) allows the fabrication of customized bone scaffolds in terms of shape, pore size, material type, and mechanical properties. Combined with the possibility to obtain a precise 3D image of the bone defects using computed tomography or magnetic resonance imaging, it is now possible to manufacture implants for patient-specific bone regeneration. This paper reviews the state-of-the-art of the different materials and AM techniques used for the fabrication of 3D-printed scaffolds in the field of bone tissue engineering. Their advantages and drawbacks are highlighted. For materials, specific criteria, are extracted from a literature study: biomimetism to native bone, mechanical properties, biodegradability, ability to be imaged (implantation and follow-up period), histological performances, and sterilization process. AM techniques can be classified in three major categories: extrusion-based, powder-based, and vat photopolymerization. Their price, ease of use, and space requirement are analyzed. Different combinations of materials/AM techniques appear to be the most relevant depending on the targeted clinical applications (implantation site, presence of mechanical constraints, temporary or permanent implant). Finally, some barriers impeding the translation to human clinics are identified, notably the sterilization process.     

Processing and Characterization of Nanosilver Pastes for Die-Attaching SiC Devices

Screen/stencil-printable nanosilver pastes were processed and characterized for die-attaching SiC devices. The nanosilver pastes were made by mixing silver particles in diameter with an organic binder vehicle. For the die-attachment, the nanosilver pastes were printed onto silver-coated or gold-coated direct-bond-copper (DBC) substrates. After die-attaching the SiC devices, the assemblies were heated to 300 with a 40-min dwell time to develop bonding up to 40 MPa on the silver-coated substrates, which was comparable to that of the Pb37Sn63 solder die-attachment. Scanning acoustic microscopy (SAM) of the sintered silver die-attachment did not reveal any detectable voids, while scanning electron microscopy (SEM) showed the presence of uniformly distributed microscale pores. Because of the porous microstructure of the sintered silver and its low apparent elastic modulus, it could help relieve thermomechanical stresses in the die-attachment assembly. Finally, since silver die-attachment is almost pure in constituent (>99%), the die-attachment could enable packaging of wide bandgap semiconductors devices, such as SiC or GaN, for high-temperature operation.     

Wide Range Control of Microstructure and Mechanical Properties of Carbon Nanotube Forests: A Comparison Between Fixed and Floating Catalyst CVD Techniques

Vertically aligned carbon nanotube (CNT) forests may be used as miniature springs, compliant thermal interfaces, and shock absorbers, and for these and other applications it is vital to understand how to engineer their mechanical properties. Herein is investigated how the diameter and packing density within CNT forests govern their deformation behavior, structural stiffness, and elastic energy absorption properties. The mechanical behavior of low‐density CNT forests grown by fixed catalyst CVD methods and high‐density CNT forests grown by a floating catalyst CVD method are studied by in situ SEM compression testing and tribometer measurements of force‐displacement relationships. Low‐density and small‐diameter CNT columns (fixed catalyst) exhibit large plastic deformation and can be pre‐deformed to act as springs within a specified elastic range, whereas high‐density and large‐diameter CNT columns (floating catalyst) exhibit significant elastic recovery after deformation. In this work the energy absorption capacity of CNT forests is tuned over three orders of magnitude and it is shown that CNT forest density can be tuned over a range of conventional foam materials, but corresponding stiffness is ～10× higher. It is proposed that the elastic behavior of CNT forests is analogous to open‐cell foams and a simple model is presented. It is also shown that this model can be useful as a first‐order design tool to establish design guidelines for the mechanical properties of CNT forests and selection of the appropriate synthesis method.     

The estimation of tube wall compliance using acoustic inputimpedance

An acoustic-electric analog and transmission line theory have been used to examine acoustic wave propagation in a tube with a compliant wall. The input impedance (i.e., input pressure-flow) has been simulated using a distributed element model. A relative minimum and maximum, denoted by fr and f2, respectively, that are independent of tube length have been identified theoretically and confirmed experimentally from input impedance measurements on a compliant tube. A method has been devised which uses measured values of fr and f2 to deduce the tube wall properties from the theoretical model. This method has been validated on a tube with known wall properties determined using standard methods. In practice, the input impedance is measured through a short section of rigid connecting pipe. In this case fr remains constant while f2 is reduced. This reduction can be accounted for by the volume compliance of the gas within the lumen of the rigid pipe. The theory could have useful applications such as estimating the wall properties of the airways from noninvasive measurements made through the mouth.     

Spectral composition of heart sounds before and after mechanicalheart valve implantation using a modified forward-backward Prony'smethod

This paper investigates the impact of the lung-thorax and heart-valve system on the overall spectral composition of the externally recorded heart sounds. The study concentrates on the case of the first and the second heart sounds for normal patients and patients before and after implantation of a mechanical valve in the mitral or aortic position. The analysis is performed using a modified forward-backward overdetermined Prony's method (MFBPM) which uses a forward-backward mean filter and a modified procedure for estimating the position of the signal poles. In terms of the normalized cross-correlation coefficient, this method has an average modeling accuracy of 99.62% for representing the first and second heart sounds and an average least square time-domain error of 0.43%. Results obtained from 40 subjects show that the condition of the native mitral or aortic valve affects mostly the distribution of the amplitudes of the spectral components, whereas the number of the spectral components or their respective relative energy remains more or less unchanged. It has been found that the amplitudes of frequency components in the range 120-250 Hz are more affected by abnormalities of native mitral valves. Furthermore, in the case of the second heart sound the region 250-400 Hz has been found to be more affected by abnormalities in the aortic valve. It has also been found that the mechanical prosthetic heart valve affects mostly the spectrum beyond 400 Hz. A clear difference has been observed in the frequency spectrum above 400 Hz between both normally and abnormally functioning native valves and normally functioning mechanical valves. Preliminary results in some malfunctioning cases of mechanical prosthesis suggest that spectral components beyond 400 Hz can be used to monitor the condition of these prostheses     

基于铂黑的微针电极阵列表面修饰方法

由于微针电极阵列尖端直径小,空间分辨率高,可以记录单个神经元的放电活动,已成为神经信号记录的首选.但商用微针电极阵列的阻抗较高,降低电极阻抗有利于提高信噪比,改善记录信号质量.采用超声电镀铂黑的方法对微针电极表面进行修饰.测试结果表明铂黑修饰后的微针电极电化学性能优异,1 kHz处阻抗约为2.5 kΩ,相比裸金电极降低...