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PubMed1998

Adaptive local regularization methods for the inverse ECG problem.

One of the fundamental problems in theoretical electrocardiography can be characterized by an inverse problem. We present new methods for achieving better estimates of heart surface potential distributions in terms of torso potentials through an inverse procedure. First, we outline an automatic adaptive refinement algorithm that minimizes the spatial discretization error in the transfer matrix, increasing the accuracy of the inverse solution. Second, we introduce a new local regularization procedure, which works by partitioning the global transfer matrix into sub-matrices, allowing for varying amounts of smoothing. Each submatrix represents a region within the underlying geometric model in which regularization can be specifically 'tuned' using an a priori scheme based on the L-curve method. This local regularization method can provide a substantial increase in accuracy compared to global regularization schemes. Within this context of local regularization, we show that a generalized version of the singular value decomposition (GSVD) can further improve the accuracy of ECG inverse solutions compared to standard SVD and Tikhonov approaches. We conclude with specific examples of these techniques using geometric models of the human thorax derived from MRI data.

Algorithms↗
PubMedDate not supplied

Self-motion perception: assessment by computer-generated animations.

The goal of this research is more precise description of adaptation to sensory rearrangements, including microgravity, by development of improved procedures for assessing spatial orientation perception. Thirty-six subjects reported perceived self-motion following exposure to complex inertial-visual motion. Twelve subjects were assigned to each of 3 perceptual reporting procedures: (a) animation movie selection, (b) written report selection and (c) verbal report generation. The question addressed was: do reports produced by these procedures differ with respect to complexity and reliability? Following repeated (within-day and across-day) exposures to 4 different "motion profiles," subjects either (a) selected movies presented on a laptop computer, or (b) selected written descriptions from a booklet, or (c) generated self-motion verbal descriptions that corresponded most closely with their motion experience. One "complexity" and 2 reliability "scores" were calculated. Contrary to expectations, reliability and complexity scores were essentially equivalent for the animation movie selection and written report selection procedures. Verbal report generation subjects exhibited less complexity than did subjects in the other conditions and their reports were often ambiguous. The results suggest that, when selecting from carefully written descriptions and following appropriate training, people may be better able to describe their self-motion experience with words than is usually believed.

Aerospace Medicine↗
PubMed1999

Training astronauts using three-dimensional visualisations of the International Space Station.

Recent advances in personal computer technology have led to the development of relatively low-cost software to generate high-resolution three-dimensional images. The capability both to rotate and zoom in on these images superposed on appropriate background images enables high-quality movies to be created. These developments have been used to produce realistic simulations of the International Space Station on CD-ROM. This product is described and its potentialities demonstrated. With successive launches, the ISS is gradually built up, and visualised over a rotating Earth against the star background. It is anticipated that this product's capability will be useful when training astronauts to carry out EVAs around the ISS. Simulations inside the ISS are also very realistic. These should prove invaluable when familiarising the ISS crew with their future workplace and home. Operating procedures can be taught and perfected. "What if" scenario models can be explored and this facility should be useful when training the crew to deal with emergency situations which might arise. This CD-ROM product will also be used to make the general public more aware of, and hence enthusiastic about, the International Space Station programme.

Astronauts↗
PubMed1993

Computerized analysis of the instrumentation of the root canal system.

A method is proposed for a three-dimensional visualization of the root canal system before and after the cleaning and shaping procedure to analyze the relationships of the root canal walls. The first part of the study provided cross-sections of the root perpendicular to the root canal. A system for remounting the sections of the root before and after instrumentation was set up. Micrographs of the sections were transferred to a graphics computer which rebuilt and elaborated the sections, providing a three-dimensional model of the root with the image of the root canal system before and after instrumentation. This experimental computerized model enables sections of all kinds to be produced, with great possibilities for measurement and analysis.

Computer Simulation↗
PubMed2001

Optimisation and evaluation of an asynchronous transfer mode teleradiology co-operative system: the experience of the EMERALD and the BONAPARTE projects.

This paper describes the work carried out to optimise and evaluate in clinical routine a multimedia telemedicine application for co-operative imaging diagnosis. This research has been attained within the framework of two European research projects, namely the EMERALD [1] and the BONAPARTE [2]. A user-centred telemedicine application was developed on an existing advanced broadband multimedia teleradiology platform to exploit the possibilities offered by Asynchronous Transfer Mode (ATM) technology to support real-time teleconsultation services for medical imaging. The evaluation of this telemedicine system in both projects has been performed with the aim of (1) characterising and optimising the ATM teleradiology platform, minimising the bandwidth requirements without degrading the quality of service offered to users and (2) evaluating the telemedicine system usability to improve the fulfillment of user's needs. The assessment outcomes have provided insights into technical limitations of broadband multimedia technologies for an optimum usage of a teleradiology co-operative diagnosis systems and the organisational difficulties and limitations involved in setting-up these new advanced telemedicine services to achieve the expected clinical benefits.

Computer Graphics↗
PubMed2003

MOLVIE: an interactive visualization environment for molecular structures.

A Molecular visualization interactive environment (MOLVIE), is designed to display three-dimensional (3D) structures of molecules and support the structural analysis and research on proteins. The paper presents the features, design considerations and applications of MOLVIE, especially the new functions used to compare the structures of two molecules and view the partial fragment of a molecule. Being developed in JAVA, MOLVIE is platform-independent. Moreover, it may run on a webpage as an applet for remote users. MOLVIE is available at http://www.cs.ucsb.edu/~mli/Bioinf/software/index.html.

Amino Acid Sequence↗
PubMed2003

A flexible software for tracking of markers used in human motion analysis.

In this work, we present a software for the tracking of markers used in human motion analysis. This software is based mainly on image sequences captured by video cameras and on image processing and computer vision tools. Unlike the optoelectronic systems, which record only the coordinates of the markers, a video-based system offers more visual information and flexibility which can be exploited in different applications. However, it needs a more complex tracking procedure concerned with the extraction and identification of the used markers. The tracking module presented here is divided into the following three procedures: segmentation, matching and prediction. The segmentation consists in extracting the objects of interest (markers). The matching is used to find the correspondence between the extracted objects in two consecutive frames. The prediction is important to limit the region of processing, thus reducing the execution time. Some results of the automatic tracking are presented together with their application in human motions analysis.

Algorithms↗
PubMed1996

Qualitative process modeling of cell-cell-pathogen interactions in the immune system.

We present a general cell behavior modelling system for immune functions, based on qualitative process theory. Model system heuristics integrate known characteristics and processes of cells, pathogens, antibodies, antigens, and cytokines. The system generates qualitative simulations of primary immune responses to bacterial and viral infections. Model heuristics can be mapped to a free-running cellular automata-like simulation that demonstrates quantitative behaviors of actor populations. This system serves as a tool for testing assumptions about cellular functions in immunity, as well the basis for a qualitative discovery system that may infer new process heuristics based on evaluation of experimental data.

Artificial Intelligence↗
PubMed1996

Sequential and parallel molecular mechanics calculations.

This article describes a gradient algorithm for the computational optimization of model molecular structures, and discusses the various compromises inherent in the practical expression of the algorithm in a Fortran computer program (VULCAN) for both sequential and parallel computers. Details are given of some previously undiscussed properties of gradient algorithms; various acceleration techniques are compared; and some traps for the unwary are highlighted.

Algorithms↗
PubMed1996

Molecular dynamics simulations of silicon-fluorine etching.

Molecular dynamics simulations of the reactions between gaseous fluorine atoms and (SiFx)n adsorbates on the Si(100) - (2 x 1) surface are performed using the SW potential and compared to simulations with the WWC reparameterization of the SW potential. Theoretical and experimental work has demonstrated that the reactive fluorosilyl layer during silicon-fluorine etching is composed of tower-like adspecies of SiF, SiF2 and SiF3 groups. The objective of the simulations is to determine how the chemical composition, mechanism of formation, and energy distribution of the etched gas-phase products depend on the identity of the reacting adsorbate, the incident kinetic energy, and the parameterization of the potential energy function. Three reactions are simulated: F(g) + SiF3(a), F(g) + SiF2-SiF3(a), and F(g) + SiF2-SiF2-SiF3(a). SiF4 is the major product and Si2F6 and Si3F8 are minor products. In Si2F6 and Si3F8, the silicon-fluorine bond that is formed is stronger than the silicon-silicon bond in the molecule and, therefore, the majority of these products have enough energy to dissociate and will fragment before reaching the detector. An SN2-like mechanism is the primary mechanism responsible for the formation of SiF4, Si2F6, and Si3F8. In addition, at higher energies, the simulations have discovered a previously unknown mechanism for the formation of SiF4, which involves an insertion between a silicon-silicon bond. The results of the simulations with the two potentials differ quite substantially in their prediction of the reactivity of the adsorbates. The SW potential predicts a 2- to 3-eV lower energy threshold for reaction and a much higher reaction cross-section, especially for the SiF4 product. These results are explained in terms of the differences in the potential energy functions used to describe the silicon-fluorine interactions. In addition, the results are compared to experimental data on silicon-fluorine etching.

Computer Graphics↗