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Ultrasound has been proposed as a means to noninvasively assess bone and, particularly, bone strength and fracture risk. Although there has been some success in this application, there is still much that is unknown regarding the propagation of ultrasound through bone. Because strength and fracture risk are a function of both bone mineral density and architectural structure, this study was carried out to examine how architecture and density interact in ultrasound propagation. Due to the difficulties inherent in obtaining fresh bone specimens and associated architectural and density features, simulation methods were used to explore the interactions of ultrasound with bone. A sample of calcaneal trabecular bone was scanned with micro-CT and subjected to morphological image processing (erosions and dilations) operations to obtain a total of 15 three-dimensional (3-D) data sets. Fifteen two-dimensional (2-D) slices obtained from the 3-D data sets were then analyzed to evaluate their respective architectures and densities. The architecture was characterized through the fabric feature, and the density was represented in terms of the bone volume fraction. Computer simulations of ultrasonic propagation through each of the 15 2-D bone slices were carried out, and the ultrasonic velocity and mean frequency of the received waveforms were evaluated. Results demonstrate that ultrasound propagation is affected by both density and architecture, although there was not a simple linear correlation between the relative degree of structural anisotropy with the ultrasound measurements. This study elucidates further aspects of propagation of ultrasound through bone, and demonstrates as well as the power of computational methods for ultrasound research in general and tissue and bone characterization in particular.

We describe diffraction effects in ultrasonic group velocity estimation using an insertion technique. We characterize the estimation error produced by diffraction as a function of distance and nominal velocity values. A new method termed Group Velocity Diffraction Correction (GVDC) which corrects for the diffraction effect is presented. Experimental validation of the technique is also presented using measurements made with both 1 MHz and 500 kHz ultrasonic transducer pairs. The results demonstrate that diffraction effects on ultrasonic group velocity estimation are usually small, and may often be neglected. Significant improvement, up to about 50%, in the accuracy of the group velocity estimate can however be obtained using the method described here in those cases in which higher degrees of accuracy are required. >

The possibility of hysteretic behaviours in plane monolayers of electric dipoles is investigated. The basic tool for this study is a model where the electric dipoles can rotate around the nodes of a plane rhombic grid and the electric interactions among dipoles are properly simplified ( Union Jack approximation). In the ideal case of an infinitely extending monolayer, the model yields analytical solutions both for the spatially periodical equilibrium orientations of dipoles and for their stability under the influence of an external electric field. On this basis, a set of hysteresis cycles dealing with different physical situations is obtained and discussed. Then, the much more realistic and complex case of finite-size dipole monolayers is considered and the hysteresis cycles are obtained by computer calculations. The degree of similarity of these numerical results with the analytical ones of the corresponding infinitely extending monolayers puts into evidence the prediction capabilities of such simple model.

In this paper we present the results of an animal bone fracture study which attempts to relate the vibrational response of a healing limb to its mechanical stiffness. Tibial osteotomies are performed on nine rabbits which are sacrificed at different stages of healing. Vibrational measurements are acquired from the healing fractured limb and the contralateral intact limb. The frequency domain vibrational admittance function is estimated using an electromechanical shaker and force and acceleration transducers. A feature known as the energy ratio (ER) derived from the admittance function estimates of both the fractured and intact limbs is used to characterize the strength of the healing fracture relative to the intact value, obtained using a biomechanical torsional test. Results indicate a strong correlation between the ER and relative stiffness of the fractured to intact limb. Vibrational measurements from three human clinical fracture patients over several weeks is also presented. A feedforward neural network scheme is also described for classifying the vibrational data. INTRODUCTION Bone fractures are the most common injury treated by orthopaedic surgeons. Treatment typically consists of immobilization of the fracture site until normal weightbear- ing can resume, i.e., until return of normal stiffness and strength values. Techniques for assessment of bone fracture healing currently consist of radiographic and clinical evalua- tions. Uncertainty regarding the significance of radiological findings may result in unnecessarily long periods of immobiliz- ation. The challenge to develop a reliable bone strength measurement during fracture healing has led several inves- tigators to apply low frequency (50 Hz-2 kHz) vibrational energy techniques (1,21. These previous attempts have not. however, related the vibrational response to healing fractured bone strength, and thus have not achieved any degree of use in orthopaedic practice. The objective of the present study was to develop a vibrational fracture healing assessment method which could overcome limitations of previous approaches, and thus provide orthopedists with a clinical tool for accurate and quantitative strength estimates during fracture healing.

One of the key points for the development of molecular manipulation based technologies is the availability of techniques capable to operate in such a dimensional range. The Scanning Probe Microscopes as well as the Langmuir-Blodgett film deposition technology have always been the best candidates for such a task. In this paper the authors present a method that allows one to obtain controlled surface modifications of cadmium arachidate Langmuir-Blodgett multilayers through Scanning Force Microscopy. Variable depth permanent ablations at the submicron scale have been produced as a function of applied force and scanning speed. In view of an "organic microelectronics technology" this technique can be envisaged as the organic analog of the microelectronics lithographic techniques.

The purpose of this study was to determine the relationship between three-dimensional (3D) trabecular structure and two-dimensional plain radiographic patterns. An in vitro cylinder of human calcaneal trabecular bone was three-dimensionally imaged by micro-CT using synchrotron radiation, at 33.4 micrometer resolution. The original 3D image was processed using 14 distinct sequences of morphologic operations, i.e., of dilations and erosions, to obtain a total of 15 3D models or images of calcaneal trabecular bone. These 15 models had distinct densities (volume fractions) and architectures. The 3D structure of each calcaneal model was assessed using mean intercept length (fabric), by averaging individual fabric measurements associated with each medial-lateral image slice, and determining the relative anisotropy, R(3D), of the structure. A summated pattern or plain radiograph was also computed from the 3D image data for each calcaneal model. Each summated pattern was then locally thresholded, and the resulting two-dimensional (2D) binary image analyzed using the same fabric analysis as used for the 3D data. The anisotropy of the 2D summated pattern was denoted by R(x-ray). The volume fractions of the 15 models ranged from 0.08 to 0.19 with a mean of 0. 14. The medial-lateral anisotropies, R(3D), ranged from 1.38 to 2.54 with a mean of 1.88. The anisotropy of the 2D summated patterns, R(x-ray), ranged from 1.35 to 2.18 with a mean of 1.71. The linear correlation of the 3D trabecular architecture, R(3D), with the radiographic trabecular architecture, R(x-ray), was 0.99 (p0.0001). This study shows that the plain radiograph contains architectural information directly related to the underlying 3D structure. A well-controlled sequential reproducible plain radiograph may prove useful for monitoring changes in trabecular architecture in vivo and in identifying those individuals at increased risk of osteoporotic fracture.

Development of ultrasound nondestructive evaluation techniques (NDT) has involved a combination of both analytic and experimental methods. In contrast, relatively little work has been done on the use of computational methods for experimental design and analysis in NDT. This is due to the relative lack of availability of software for such computations. While computational methods and associated software implementations abound in the electromagnetic and structural analysis engineering communities, no such paradigm exists for ultrasound researchers and engineers. This paper demonstrates a software package, Wave2000, which computes the full solution to the 2D viscoelastic wave equation. 2D objects are represented by graphical images and are comprised of a number of solids and/or liquids. Each material is specified in terms of its material density, the first and second Lame constants, and the first and second viscosities. The program computers the displacement vector was a function of Cartesian coordinates x and y and of time t, and the solution includes effects of diffraction, scattering, reflection, and attenuation of the propagating wave. Wave2000 implements a finite difference solution on a standard personal computer running Microsoft Windows 95 or NT. Sources and receivers may be located anywhere in or on the surface of the object. The source waveform can be practically any temporal function desired, including data collected from an actual transducer, and the receiver data can be sorted in a data file for subsequent processing. Several examples of the use of Wave2000 are given, including simulations of scattering from cracks and propagation through layers of materials and fluid-filled porous structures. Results demonstrate that computational methods can play an important can play an important role in NDT specifically and in ultrasonics in general.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A physical system consisting of a lipid monolayer surrounded by a set of electrodes is defined and proposed as a plausible example of a molecular circuit for information processing. The lipid monolayer is characterized as a cellular array of electric dipoles, where each dipole lying on the monolayer plane represents the head of a lipid molecule. Each dipole experiences the effects of the electric field generated by both the surrounding dipoles and the electrodes. The electrodes’ contribution to the electric field is calculated through a proper discretization of their charge densities. According to this model the dipoles of the cellular array play the role of neurodes whose state is described by the dipole orientations on the plane, and a cellular automation can be defined once the orientation values have been properly discretized. The electrodes act as input‐ and output‐signal sources. it is shown that the simple system considered here, i.e., a two‐port system, is characterized by a nonlinear voltage tran...

Type I Gaucher disease is a genetic disorder afflicting between 5000 and 10,000 Ashkenazi Jews in the United States. It is characterized by the deficient activity of the lysosomal hydrolase, acid s-glucosidase. The progressive infiltration and replacement of the bone marrow by “Gaucher cells” (lipid-filled macrophages) lead sequentially to diffuse osteopenia, localized destruction, ischemic necrosis, and osteosclerosis. Degenerative changes in the skeleton are the leading cause of disability in patients with type I disease, and some degree of osteopenia and osteolysis occurs in virtually all patients. However, the extent of bone disease also is markedly variable, which makes it very difficult to predict the course of the disease once a diagnosis has been made.

The paper deals with a study of the spatially periodical dipole patterns that result from the interactions among polar lipid heads, whose tails are confined to a planar thin layer. The model is based on a continuous approach that assumes the dipole layer to be a planar region of infinitesimal thickness; according to this approach the dipole distributions are first represented through proper continuous functions, which are a normal dipole vector per unit area and a given surface charge density. Both of them must be periodical with respect to the coordinates of the plane, as they must be compatible with the periodic electric field configurations studied in this paper. It is shown that the periodical patterns associated to discrete dipoles can be derived from the afore-side continuous representation through the definition of “elementary cells” that contain a finite number of “subdomains” each of which corresponds to a single lipid molecule. A set of dipole patterns is obtained and discussed for the case of a square elementary cell. Results point out that both ferroelectric and antiferroelectric organizations of the dipole components on the layer plane do exist.

Non-invasive therapeutic treatment of bone in vivo using ultrasound in conjunction with application of a biochemical compound or bone growth factor is performed by subjecting bone to an ultrasound signal supplied to an ultrasound transducer placed on the skin of a bony member, and involving a repetitive finite duration signal consisting of plural frequencies that are in the ultrasonic range to 20 MHz. Concurrent with application of the ultrasound is the utilization of a bone growth factor applied to the skin of a bony member before stimulation with ultrasound. Ultrasonic stimulation is operative to transport the bone growth factor to the bone and then to synergistically enhance the interaction of the bone growth factor with the bone, whereby to induce healing, growth and ingrowth responses. In another embodiment, a vibrational or mechanical input together with a biochemical compound enhances both bone fracture healing and treats osteoporosis.

The first-order nonlinear analysis of IMPATT diodes is performed and a model is obtained in which the nonlinear effects due to avalanche are separated from the activity and transit-time effects. Such a mildly nonlinear model is suitable for CAD applications. The determination of the model parameters by means of small signal measurements is outlined, and the applicability of the proposed model is demonstrated on real devices.

The study of self-organized two-dimensional structures can furnish new ideas for future molecular devices, especially if the self-organization of the structures can be modulated by external agents, like an exogenous electric field.

A simplified theory of image formation in phase contrast microscopy is presented. It is shown that the phase shift induced in light (related to the refractive index) by the observed object can be reconstructed, point by point, from the phase-contrast digitally sampled image through an appropriate algorithm. This allows one to make quantitative observations on unstained, living cells.

It has been shown that low-power ultrasound (US) has a significant effect on the rate of fresh fracture healing in animals and humans. The action of US can involve a direct mechanical effect (microstrain) or an indirect electrokinetic effect. To test the electrokinetic hypothesis, a four-electrode measurement technique is used to evaluate the effects of externally applied US on cell membrane impedance. Results indicate that US significantly affects the membrane impedance in the frequency range predicted by electrochemical modeling to be relevant to specific absorption, 5-100 kHz. The action of US via an electrokinetic pathway implies the displacement of ions in the diffuse double layer via the local pressure wave. Results obtained with a chloride-ion-depleted solution showed a significant US modification of membrane impedance in a higher frequency range (50-300 kHz), which appears to confirm that the effect of US at the membrane surface is ion-dependent. >

The problem of simulating the observation of a ho- logram from an assigned point of view is considered. It is shown that there exists a simple transforma-tion between the angular spectra of the hologram and of the image seen by the observer.Introduction This work is a part of a general investigation (undertaken by the research group to which the au-thors belong) on the subject of three -dimensional imaging of microscopic biological objects. We areinvestigating various techniques, which use both coherent and incoherent light. Holographic methods, considered in this paper, essentially belong to the first class. As it is well known, an outstanding feature of holography is its ability to give three -dimensional images. This possibility is due to the fact that holograms contain (coded in some more or less di- rect form) information on both amplitude and phase of the light scattered by a given object. For example, in the well known Leith -Upatnieks set -up [lj holographic imaging works as follows:the object is placed between a source S of monochro-matic, plane waves (coherent light) and a photogra-phic film. The light scattered by the object inter-feres with the one coming again from S through