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At least 1,531 records · Page 85Linked to original sources
PubMed1997

Micro-tomographic imaging for the nondestructive evaluation of trabecular bone architecture.

The structural properties of trabecular bone have been shown to vary significantly with age, anatomic location, and metabolic condition. Micro-computed tomography (microCT) is an emerging technique for the nondestructive assessment and analysis of the three-dimensional trabecular bone architecture. Within the framework of the European Union BIOMED I project "Assessment of Bone Quality in Osteoporosis," a total of 350 bone biopsies from five different anatomical locations were harvested post mortem from 70 donors (aged 23 to 92 years). These biopsies were measured using a newly devised compact micro-tomographic system, also referred to as desk-top microCT. Samples with a diameter from a few millimeters to a maximum of 18 mm and a length of up to 55 mm can be measured. For this study fresh, untreated bone biopsies with a diameter of 8 mm were measured micro-tomographically with a nominal isotropic resolution of 14 microns. For all samples, the volumes of interest (4 x 4 x 4 mm3) were binarized using a uniform threshold. Subsequently, standard structural indices such as bone volume density (BV/TV), bone surface density (BS/BV), trabecular plate number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp) and the degree of anisotropy (DA) were computed for all specimens incorporating mean intercept length (MIL) measurements. Regression analysis was used to estimate the correlations of single structural parameters with age or with a second parameter and also among different measurement sites. The nondestructive microCT measurements allowed not only to perform quantitative bone morphometry but also to assess other important microstructural features in the determination of the mechanical integrity of trabecular bone such as the incidence and prevalence of microcallus formations. The findings from the BIOMED I study are expected to improve our understanding of the relative importance of bone architecture, damage accumulation, and bone mineralization in the characterization of bone quality in the progress of age- and disease-related bone loss.

Adult↗
PubMed1993

Virtual reality in medicine.

Virtual reality (VR), as part of computer science, allows computer-based models of the real world to be generated, and provides humans with a means to interact with these models through new human-computer interfaces and, thus, to nearly realistically experience these models. This contribution explores the technical requirements for VR, describes technological advances and deficits, and analyzes the framework for future technological research and development. Although some non-medical applications are discussed, this contribution focuses primarily on medical applications of VR and outlines future prospects of medical VR applications. Finally, possible hazards arising from the use of VR are discussed. The authors recommend an interdisciplinary approach to technology assessment of VR.

Computer Graphics↗
PubMed1994

Fast wavelet transformation of EEG.

Wavelet transforms offer certain advantages over Fourier transform techniques for the analysis of EEG. Recent work has demonstrated the applicability of wavelets for both spike and seizure detection, but the computational demands have been excessive. We compare the quality of feature extraction of continuous wavelet transforms using standard numerical techniques, with more rapid algorithms utilizing both polynomial splines and multiresolution frameworks. We further contrast the difference between filtering with and without the use of surrogate data to model background noise, demonstrate the preservation of feature extraction with critical versus redundant sampling, and perform the analyses with wavelets of different shape. Comparison is made with windowed Fourier transforms, similarly filtered, at different data window lengths. We here report a dramatic reduction in computational time required to perform this analysis, without compromising the accuracy of feature extraction. It now appears technically feasible to filter and decompose EEG using wavelet transforms in real time with ordinary microprocessors.

Brain↗
PubMed2002

A comparative genomic method for computational identification of prokaryotic translation initiation sites.

The ever growing number of completely sequenced prokaryotic genomes facilitates cross-species comparisons by genomic annotation algorithms. This paper introduces a new probabilistic framework for comparative genomic analysis and demonstrates its utility in the context of improving the accuracy of prokaryotic gene start site detection. Our frame work employs a product hidden Markov model (PROD-HMM) with state architecture to model the species-specific trinucleotide frequency patterns in sequences immediately upstream and downstream of a translation start site and to detect the contrasting non-synonymous (amino acid changing) and synonymous (silent) substitution rates that differentiate prokaryotic coding from intergenic regions. Depending on the intricacy of the features modeled by the hidden state architecture, intergenic, regulatory, promoter and coding regions can be delimited by this method. The new system is evaluated using a preliminary set of orthologous Pyrococcus gene pairs, for which it demonstrates an improved accuracy of detection. Its robustness is confirmed by analysis with cross-validation of an experimentally verified set of Escherichia coli K-12 and Salmonella thyphimurium LT2 orthologs. The novel architecture has a number of attractive features that distinguish it from previous comparative models such as pair-HMMs.

Algorithms↗
PubMed1992

A man-machine vision interface for sensing the environment.

This study describes a computer vision approach for sensing the environment with the intent of helping people with a visual impairment. The principal goal in applying computer vision is to exploit, in an optimal fashion, the information acquired by the camera(s) to yield useful descriptions of the viewed environment. The objective is to seek efficient and reliable guidance cues in order to improve the mobility needs of individuals with a visual impairment. In this research direction, the following problems are identified and addressed: 1) the vision system design; 2) establishment of the mapping principles between the two-dimensional (2-D) camera images and the three-dimensional (3-D) real world; 3) development of appropriate imaging techniques for the interpretation of the 2-D images; and, 4) establishment of a communication link between the vision system and the user. The soundness of this research direction is assessed by means of a theoretical framework and experimental evaluations.

Algorithms↗
PubMed1981

Quantitation in positron emission computed tomography: 4. Effect of accidental coincidences.

Accidental coincidences (ACs) and methods of compensation for ACs were investigated in terms of their effect on quantitation in positron emission computed tomography (ECT). Formulations of basic expressions describing the physical factors, which cause true coincidences or ACs, are presented to provide a framework of contrasting the two phenomena. Correction of image data for attenuation of the annihilation radiation or nonuniformities in detector efficiency is shown to amplify errors caused by the presence of ACs in the data. It was shown that failure to compensate for ACs caused overestimates in measurements of isotope concentrations from image data and that in many cases the overestimate was significant for relatively modest percentages of ACs in the data. Three methods of compensation for ACs were evaluated as to their accuracy and effect on statistical noise in images. It was found that nonuniform detector efficiencies could cause prominent image artifacts if an inadequate method was employed in the determination and subtraction of ACs from image data. The additional statistical noise produced in images by subtraction of ACs from total coincidence data demonstrates the advisability of minimizing AC rates in spite of an ability to adequately measure and compensate for their presence in the data.

Copper↗
PubMed2002

A kinetic framework for a mammalian RNA polymerase in vivo.

We have analyzed the kinetics of assembly and elongation of the mammalian RNA polymerase I complex on endogenous ribosomal genes in the nuclei of living cells with the use of in vivo microscopy. We show that components of the RNA polymerase I machinery are brought to ribosomal genes as distinct subunits and that assembly occurs via metastable intermediates. With the use of computational modeling of imaging data, we have determined the in vivo elongation time of the polymerase, and measurements of recruitment and incorporation frequencies show that incorporation of components into the assembling polymerase is inefficient. Our data provide a kinetic and mechanistic framework for the function of a mammalian RNA polymerase in living cells.

Animals↗
PubMed1985

A topological model of cell division: structure of the computer program.

The general structure of a computer program (CD3D) simulating division in a sheet of cells is presented. The program is based on a topological representation of cell division previously developed by the authors, and the biological background to the model is discussed. The computer modelling of the various elements of the model (i.e. vertices, edges and meshes) is described, and an annotated description of the subroutines making up the program is given in an Appendix. Although the program and model are specifically designed to represent cell division processes, the graph framework may have applicability in other biological subject areas where dynamic relationships between elements are involved.

Animals↗
PubMed2005

Predictive fine granularity successive elimination for fast optimal block-matching motion estimation.

Given the number of checking points, the speed of block motion estimation depends on how fast the block matching is. In this paper, a new framework, fine granularity successive elimination (FGSE), is proposed for fast optimal block matching in motion estimation. The FGSE features providing a sequence of nondecreasing fine-grained boundary levels to reject a checking point using as little computation as possible, where block complexity is utilized to determine the order of partitioning larger sub-blocks into smaller subblocks in the creation of the fine-grained boundary levels. It is shown that the well-known successive elimination algorithm (SEA) and multilevel successive elimination algorithm (MSEA) are just two special cases in the FGSE framework. Moreover, in view that two adjacent checking points (blocks) share most of the block pixels with just one pixel shifting horizontally or vertically, we develop a scheme to predict the rejection level for a candidate by exploiting the correlation of matching errors between two adjacent checking points. The resulting predictive FGSE algorithm can further reduce computation load by skipping some redundant boundary levels. Experimental results are presented to verify substantial computational savings of the proposed algorithm in comparison with the SEA/MSEA.

Algorithms↗
PubMed2005

Characteristics of fluent skills in a complex, dynamic problem-solving task.

We examined critical characteristics of fluent cognitive skills, using the Georgia Tech Aegis Simulation Program, a tactical decision-making computer game that simulates tasks of an anti-air-warfare coordinator. To characterize learning, we adopted the unit-task analysis framework, in which a task is decomposed into several unit tasks that are further decomposed into functional-level subtasks. Our results showed that learning at a global level could be decomposed into learning smaller component tasks. Further, most learning was associated with a reduction in cognitive processes, in which people make inferences from the currently available information. Eye-movement data also revealed that the time spent on task-irrelevant regions of the display decreased more than did the time spent on task-relevant regions. In sum, although fluency in dynamic, complex problem solving was achieved by attaining efficiency in perceptual, motor, and cognitive processes, the magnitude of the gains depended on the preexisting fluency of the component skills. These results imply that a training program should decompose a task into its component skills and emphasize those components with which trainees have relatively little prior experience. Actual or potential applications of this research include learning and training of complex tasks as well as evaluation of performance on those tasks.

Aviation↗
PubMed1998

Extending contemporary decision support system designs to patient-oriented systems.

Decision support systems for patients can benefit from adopting knowledge engineering-based architectures. In this paper, we describe how decision support systems for patients differ from decision support systems for health professionals and knowledge engineering principles that can be used to improve the efficiency of developing patient support systems. We discuss a five-step process model for patient-computer dialogue and its incorporation into an architecture based on knowledge engineering ontologies. The architecture's components are grouped into transient and persistent application layers that support a general framework for patient decision support. The implementation of the object-based model using a relational database management system is also discussed.

Artificial Intelligence↗
PubMed2004

A molecular thermodynamic view of DNA-drug interactions: a case study of 25 minor-groove binders.

Developing a molecular view of the thermodynamics of DNA recognition is essential to the design of ligands for regulating gene expression. In a first comprehensive attempt at sketching an atlas of DNA-drug energetics, we present here a detailed thermodynamic view of minor-groove recognition by small molecules via a computational study on 25 DNA-drug complexes. The studies are configured in the MMGBSA (Molecular Mechanics-Generalized Born-Solvent Accessibility) framework at the current state of the art and facilitate a structure-energy component correlation. Analyses were conducted on both energy minimized structures of DNA-drug complexes and molecular dynamics trajectories developed for the purpose of this study. While highlighting the favorable role of packing, shape complementarity, and van der Waals and hydrophobic interactions of the drugs in the minor groove in conformity with experiment, the studies reveal an interesting annihilation of favorable electrostatics by desolvation. Structural modifications attempted on the ligands point to the requisite physico-chemical factors for obtaining improved binding energies. Hydrogen bonds predicted to be important for specificity based on structural considerations do not always turn out to be significant to binding in post facto analyses of molecular dynamics trajectories, which treat thermal averaging, solvent, and counterion effects rigorously. The strength of the hydrogen bonds retained between the DNA and drug during the molecular dynamics simulations is approximately 1kcal/mol. Overall, the study reveals the compensatory nature of the diverse binding free energy components, possible threshold limits for some of these properties, and the availability of a computationally viable free energy methodology which could be of value in drug-design endeavors.

Binding Sites↗
PubMed1987

The potential for community level evaluations based on loop analysis.

In this paper we present results obtained with a computer simulation in which a community, described by Levins in his presentation of loop analysis (Levins, R., 1975, Evolution in communities near equilibrium, in: Ecology and Evolution of Communities, M.L. Cody and J.M. Diamond (eds) (Harvard University Press, Cambridge, Mass.) pp. 16-50), is analysed. We show how our simulation accurately reproduces Levins' calculations and further, (i) how our simulation can be used to answer questions raised by Levins but never answered, (ii) how the simulation can be used to dissect a community in order to analyse the roles played by the various entities, and (iii) how predictions relating to the evolution of this community, proposed by Levins, can be analysed with some interesting and unexpected results. In particular, it becomes clear that discussion of the type of selection that may take place needs to be done in the framework of the community in which it occurs.

Biological Evolution↗
PubMed1967

The future of scientific journals. A computer-based system will enable a subscriber to receive a personalized stream of papers.

Since many of the problems that beset readers, authors, and publishers of scientific journals are caused by the growth of science or by the frailties of human nature, we cannot hope for complete solutions. In an effort to make progress, within the framework of the possible, we propose that journals stop binding papers into issues and, instead, distribute to each subscriber a personalized stream of papers, abstracts, and titles. This type of distribution, which has been made possible by the advent of high-speed computers, would not affect the traditional roles of editors, referees, and libraries. We also propose that journals recognize the need for very rapid communication in certain fields, and meet the threat of public preprint-exchange systems in these fields by themselves publishing preprints in an appropriately limited manner.

Computers↗
PubMed1999

A task-specific evaluation of three-dimensional image interpolation techniques.

Image interpolation is an important operation that is widely used in medical imaging, image processing, and computer graphics. A variety of interpolation methods are available in the literature. However, their systematic evaluation is lacking. In a previous paper, we presented a framework for the task-independent comparison of interpolation methods based on certain image-derived figures of merit using a variety of medical image data pertaining to different parts of the human body taken from different modalities. In this work, we present an objective task-specific framework for evaluating interpolation techniques. The task considered is how the interpolation methods influence the accuracy of quantification of the total volume of lesions in the brain of multiple sclerosis (MS) patients. Sixty lesion-detection experiments coming from ten patient studies, two subsampling techniques and the original data, and three interpolation methods are carried out, along with a statistical analysis of the results.

Brain↗
PubMed1994

Computer vision approaches for the three-dimensional reconstruction of coronary arteries: review and prospects.

The objective of this article is to define the different stages involved in the 3D reconstruction of arteries and to review, from our experience and from the literature, the solutions already proposed. A full reconstruction framework includes the characterization of the imaging device (in terms of distortion and calibration), the specificity of the image acquisition process, the preprocessing that can be applied, the detection of the vascular structures, the 2D feature formation, the reconstruction itself, and the visualization aspects. They are examined according to a computer vision approach where two or three views are assumed to be available. Their generalization to temporal image sequences are also considered. Some of the material reported here is unpublished. The article allows the reader to identify the true critical issues that are not often clearly mentioned in the literature and the challenges that they convey. A final discussion presents a few perspectives in this area of research.

Artificial Intelligence↗
PubMed2004

Polygonal and polyhedral contour reconstruction in computed tomography.

This paper is about three-dimensional (3-D) reconstruction of a binary image from its X-ray tomographic data. We study the special case of a compact uniform polyhedron totally included in a uniform background and directly perform the polyhedral surface estimation. We formulate this problem as a nonlinear inverse problem using the Bayesian framework. Vertice estimation is done without using a voxel approximation of the 3-D image. It is based on the construction and optimization of a regularized criterion that accounts for surface smoothness. We investigate original deterministic local algorithms, based on the exact computation of the line projections, their update, and their derivatives with respect to the vertice coordinates. Results are first derived in the two-dimensional (2-D) case, which consists of reconstructing a 2-D object of deformable polygonal contour from its tomographic data. Then, we investigate the 3-D extension that requires technical adaptations. Simulation results illustrate the performance of polygonal and polyhedral reconstruction algorithms in terms of quality and computation time.

Algorithms↗
PubMed2005

Tensor voting for image correction by global and local intensity alignment.

This paper presents a voting method to perform image correction by global and local intensity alignment. The key to our modeless approach is the estimation of global and local replacement functions by reducing the complex estimation problem to the robust 2D tensor voting in the corresponding voting spaces. No complicated model for replacement function (curve) is assumed. Subject to the monotonic constraint only, we vote for an optimal replacement function by propagating the curve smoothness constraint using a dense tensor field. Our method effectively infers missing curve segments and rejects image outliers. Applications using our tensor voting approach are proposed and described. The first application consists of image mosaicking of static scenes, where the voted replacement functions are used in our iterative registration algorithm for computing the best warping matrix. In the presence of occlusion, our replacement function can be employed to construct a visually acceptable mosaic by detecting occlusion which has large and piecewise constant color. Furthermore, by the simultaneous consideration of color matches and spatial constraints in the voting space, we perform image intensity compensation and high contrast image correction using our voting framework, when only two defective input images are given.

Algorithms↗