Alessandro Chiabrera

Computational methods for ultrasonic bone assessment

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.

Relationship between plain radiographic patterns and three- dimensional trabecular architecture in the human calcaneus.

Abstract: 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 μm 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, R3D, 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 Rx-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, R3D, ranged from 1.38 to 2.54 with a mean of 1.88. The anisotropy of the 2D summated patterns, Rx-ray, ranged from 1.35 to 2.18 with a mean of 1.71. The linear correlation of the 3D trabecular architecture, R3D, with the radiographic trabecular architecture, Rx-ray, was 0.99 (p<0.0001). 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.

From the Langevin-Lorentz to the Zeeman model of electromagnetic effects on ligand-receptor binding

Abstract This paper attempts to elucidate the mechanism of action of electromagnetic exposure on ligand-receptor binding. The classical Langevin-Lorentz model, which can be used to describe the adsorption process of a messenger ion, is reviewed and discussed. We conclude that low intensity exposure does not affect appreciably the ion dynamics in the presence of background thermal white noise. A more realistic evaluation of the endogenous field present in a binding site leads to a quantum model based on weak Zeeman-Stark effects. The case of the Zeeman effect is studied in detail assuming a three-state binding site. The density operator method is used, introducing suitable lifetimes which model the thermal bath interaction. The closed form expression for the binding probability is found, as a function of the ligand-receptor parameters and of the electromagnetic sinusoidal exposure.

Diffraction effects in insertion mode estimation of ultrasonic group velocity

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.<<ETX>>

The Role of the Magnetic Field in the EM Interaction with Ligand Binding

Low-intensity magnetic induction fields (<(10 mT) can affect bioelectrochemical processes directly through the magnetic component of the Lorentz force, provided that some specific conditions are fulfilled1. This conclusion has been drawn after that an international consensus about the need for re-evaluating the role played by the magnetic fields was reached during the NATO Advanced Research Workshop “Interactions Between Electromagnetic Fields and Cells”, held at the E. Majorana Centre for Scientific Culture at Erice (Italy) in September 1984. Notwhitstanding the leading action of A.R. Liboff, his suggestion to study the motion of a charged particle (ion) in a constant magnetic field inside a helical membrane channel2 remains rather qualitative and has not yet reached the maturity of a mathematical model. The attempt to offer some quantitative basis for Liboff’s ideas turned out to be a failure3, as the related paper contains several theoretical pitfalls.

Effect of lifetimes on ligand binding modelled by the density operator

Abstract This paper addresses the problem of evaluating theoretically the effects of electromagnetic (EM) exposure on biological systems. EM fields can affect the chemical activity of ions while they interact with the membrane receptors of a cell during a binding process. A coulombic three-state Zeeman model for the binding site is proposed, and the ion adsorption under low-frequency magnetic exposure is described by means of the density operator. The system interactions with the thermal bath are accounted for by a suitable set of lifetime parameters. The limits of a first-order perturbation approach, which allows us to find a closed-form expression for the ion-binding probability, are discussed. The biological effectiveness of a Helmholtz coil exposure system is rather small if computed according to the simplifying assumptions of the paper.

Fokker–Planck analysis of the Langevin–Lorentz equation: Application to ligand-receptor binding under electromagnetic exposure

The statistical properties of the solution of the Langevin–Lorentz equation are analyzed by means of the Fokker–Planck approach. The equation describes the dynamics of an ion that is attracted by a central field and is interacting with a time-varying magnetic field and with the thermal bath. If the endogenous force is assumed to be elastic, then a closed-form expression for the probability density of the process can be obtained, in the case of constant magnetic exposure and, for the time-varying case, at least asymptotically. In the general case, a numerical integration of the resulting set of differential equations with periodically time-varying coefficients has been implemented. A framework for studying the possible effects of low-frequency, low-intensity electromagnetic fields on biological systems has been developed on the basis of the equation. The model assumes that an exogenous electromagnetic field may affect the binding of a messenger attracted by the endogenous force field of its receptor protei...

Interaction mechanism between electromagnetic fields and ion adsorption: endogenous forces and collision frequency

Abstract The adsorption of an ion messenger at a cell receptor is a potential target of electromagnetic exposure, which may affect the binding rate coefficient. The role of the endogenous field force experienced by an ion approaching the binding site is of paramount importance. In order to evaluate the effects of the exogenous field, the endogenous force obtained from the protein data bank has been approximated as a central field by means of a linear restoring force (“spring-like”) and by means of an inverse square field (“coulombic-like”). The first approximation is used in the classical Langevin-Lorentz model and the second in the quantum Zeeman-Stark model. The ion losses due to “collisions” near the binding site are modelled in the classical approach by a viscous collision frequency and in the quantum approach by a set of suitable inverse collision frequencies (lifetimes). In the case of collisions with solvent dipolar molecules (e.g. water), it is shown that the number of colliding solvent dipoles can be very small owing to the large gradients of the endogenous electric field. On the contrary, a binding site is, by definition, a spatial domain finite in size, where colliding molecules move in the Knudsen (ballistic) regime. As a consequence, the mean free path cannot exceed the domain dimension, irrespective of the low concentration of colliding molecules. It is concluded that the ion collision frequency (i.e. in classical terms, the effective viscosity of a binding site) can be many orders of magnitude lower than in the bulk solvent (lifetimes are longer in the quantum model), so that electromagnetic bioeffects may occur at low intensities of the exogenous fields.

Physical limits of integration and information processing in molecular systems

A review of the evolution of electronic information processing from small-scale integration to ultra-large-scale integration and beyond is presented recalling the milestones achieved in the development of electronic hardware. Physical principles which limit the size and performances of electronic circuits and the rate of information processing are discussed. In order to explore the new courses offered by organic molecular materials towards atomic-scale integration, the elementary computational capabilities of molecules are discussed by casting the quantum dynamic equations in the framework of system theory. Bond dynamics in polymeric networks is considered, thus showing the possibility of obtaining molecular probabilistic circuits.

Effect of ELF electromagnetic exposure on precipitation of barium oxalate

Abstract Studies on the effects of low-intensity, low-frequency electromagnetic fields on processes, such as nucleation and precipitation in living matter, have to face rather complex experimental conditions due to the large number of variables to be taken into account. Similar problems are usually associated with many bioelectromagnetic reactions. Inorganic systems where the same phenomena occur are more suitable for investigating the fundamental mechanisms involved. In this paper, we deal with the effect of ELF electromagnetic fields on the nucleation and precipitation of barium oxalate from aqueous solutions of barium nitrate. The effect of ELF electromagnetic fields on nucleation and on crystal growth kinetics lies in the production of fewer nuclei, which grow faster. It is shown that low-intensity ELF fields induce changes in the interfacial energy, which in turn increases both the total apparent free energy of activation for the nucleation process and the subsequent crystal growth kinetics.