[Methodological approach to assessing the accuracy and reliability of computational equations for the approximate safe levels of substances].
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Environmental Exposure↗
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Orbital and maxillofacial computer aided surgery: patient-specific finite element models to predict surgical outcomes.
This paper addresses an important issue raised for the clinical relevance of Computer-Assisted Surgical applications, namely the methodology used to automatically build patient-specific finite element (FE) models of anatomical structures. From this perspective, a method is proposed, based on a technique called the mesh-matching method, followed by a process that corrects mesh irregularities. The mesh-matching algorithm generates patient-specific volume meshes from an existing generic model. The mesh regularization process is based on the Jacobian matrix transform related to the FE reference element and the current element. This method for generating patient-specific FE models is first applied to computer-assisted maxillofacial surgery, and more precisely, to the FE elastic modelling of patient facial soft tissues. For each patient, the planned bone osteotomies (mandible, maxilla, chin) are used as boundary conditions to deform the FE face model, in order to predict the aesthetic outcome of the surgery. Seven FE patient-specific models were successfully generated by our method. For one patient, the prediction of the FE model is qualitatively compared with the patient's post-operative appearance, measured from a computer tomography scan. Then, our methodology is applied to computer-assisted orbital surgery. It is, therefore, evaluated for the generation of 11 patient-specific FE poroelastic models of the orbital soft tissues. These models are used to predict the consequences of the surgical decompression of the orbit. More precisely, an average law is extrapolated from the simulations carried out for each patient model. This law links the size of the osteotomy (i.e. the surgical gesture) and the backward displacement of the eyeball (the consequence of the surgical gesture).
Algorithms↗
Parallel simulation of accretive growth and form in three dimensions.
A geometric model for diffusion-limited radiate accretive growth is used to simulate the emergence of growth and form of a certain class of organisms and crystals. In the model, layered structures are generated by the construction of new layers on top of the previous ones, the local growth velocities are determined by the local nutrient concentration gradients. The simulation of nutrient-limited growth in three dimensions (3D) is computationally very expensive. This paper presents a methodology to formulate the geometrical problem in terms of a 3D Laplace solver and maps this solver on a parallel platform. The aim of this paper is to demonstrate that this hybrid method is capable of simulating two typical properties of radiate accretive growth: (1) the indeterminateness of the growth process; and (2) the strong impact of the physical environment on the growth process.
Animals↗
A computer-administered neurobehavioral evaluation system for occupational and environmental epidemiology. Rationale, methodology, and pilot study results.
To facilitate the conduct of epidemiologic studies of populations at risk for or suffering from central nervous system (CNS) dysfunction due to environmental agents, a computer-administered neurobehavioral evaluation system has been developed. The system includes a set of testing programs designed to run on a microcomputer and questionnaires to facilitate interpretation of results. Standard tasks evaluating memory, psychomotor function, verbal ability, visuospatial ability, and mood were selected and adapted for computer presentation following the recommendation of an expert committee of the World Health Organization and the National Institute for Occupational Safety and Health. In two pilot surveys, test performance was found to be influenced by age, education level, and socioeconomic status in ways consistent with prior research findings. Performance on tests of short-term memory and reaction time was negatively correlated with intensity of organic solvent exposure among industrial painters. In view of the ease of administration and data handling, high subject acceptability, and sensitivity to the effects of known neurotoxic agents, computer-based assessment of CNS function holds promise for future epidemiologic research.
Central Nervous System↗
[Computed tomography of pneumoconioses].
Thoracic computed tomography is now used in the assessment of occupational diseases. Coal miner's pneumoconiosis, silicosis and benign asbestosis constitute the principal indications. The specific contribution of computed tomography techniques, their methodology and their signs are presented.
Asbestosis↗
Computational studies of the H-cluster of Fe-only hydrogenases: geometric, electronic, and magnetic properties and their dependence on the [Fe4S4] cubane.
The active sites of Fe-only hydrogenases (FeHases) feature an unusual polynuclear iron-sulfur cluster, known as the H-cluster, that consists of a [Fe4S4] cubane linked to a di-iron subunit (the [2Fe]H component) via a bridging cysteine ligand (SCys). While previous computational studies of FeHases employed H-cluster models that only included the [2Fe]H component, we have utilized density functional theory (DFT), in conjunction with the broken-symmetry (BS) approach, to explore the geometric, electronic, and magnetic properties of the entire H-cluster. These calculations have allowed us to evaluate, for the first time, the influence of the [Fe4S4] cubane on the [2Fe]H component of the H-cluster in its active (Hox) and CO-inhibited (Hox-CO) states, both of which are paramagnetic (S=1/2). Our results reveal that the presence of the cubane tunes both the position and the donor strength of the SCys ligand, which, in turn, modulates the internal geometric and electronic structures of the [2Fe]H subcluster. Importantly, the BS methodology provides an accurate description of the exchange interactions within the H-cluster, permitting insight into the electronic origin of the changes in magnetic properties observed experimentally upon conversion of Hox to Hox-CO. Specifically, while the unpaired spin density in the Hox state is localized on the distal Fe center, in the Hox-CO state, it is delocalized over the [2Fe]H component, such that the proximal Fe center acquires significant spin density (where distal and proximal refer to the positions of the Fe centers relative to the cubane). To validate our H-cluster models on the basis of experimental data, two DFT-based approaches and the semiempirical INDO/S method have been employed to compute electron paramagnetic resonance parameters for the H-cluster states. While most computations yield reasonably accurate g values and ligand hyperfine coupling constants (i.e., A values) for the Hox and Hox-CO states, they fail to reproduce the isotropic 57Fe A tensors found experimentally. Finally, extension of the computational methodology employed successfully for the Hox and Hox-CO states to the metastable Hoxphoto state, generated by irradiation of the Hox-CO state at cryogenic temperatures, has allowed us to discriminate between proposed structural models for this species.
Computer Simulation↗
Functional and anatomical brain imaging: impact on schizophrenia research.
A group of related new technologies has made it possible to study the brain's regional changes in metabolism, blood flow, electrical activity, and neurochemistry. Positron emission tomography (PET) produces slice images of radioisotope density--brain metabolism or receptor concentration can be quantitated. Studies in schizophrenia have indicated relative metabolic underactivity of the frontal lobes of schizophrenics. Decreased activity in the basal ganglia, which can be reversed with neuroleptic treatment, is also seen in schizophrenia. PET studies are in the early stages; standard methodology for isotope selection, task during tracer uptake, and quantitative analysis is still developing. Cerebral blood flow studies have shown similar patterns in the cortical surface. The electroencephalogram provides a short time resolution approach which can assess attention and arousal, but lacks some of the anatomic exactness and depth capabilities of PET. Magnetic resonance imaging furnishes anatomical images of gray and white matter previously unavailable with x-ray computed tomography. Advances in methodology and clinical studies with imaging are making neuroanatomic theories of schizophrenia more directly testable than ever before.
Attention↗
Geometric reconstruction for computational mesh generation of arterial bifurcations from CT angiography.
A methodology for patient-specific model reconstruction and computational mesh generation of arterial bifurcations from angio-CT scans is presented. Three-dimensional models were reconstructed with a level set technique, analyzed with a skeletoning algorithm and automatically decomposed into branches. Cooper scheme was then employed to generate high quality hexahedral mesh. We successfully applied our technique to the carotid bifurcations of two patients affected by severe atherosclerotic plaques. The proposed technique is fast, accurate and reproducible, and can be a useful tool for the evaluation of arterial fluid dynamics within conventional computed tomography investigations.
Aged↗
A classification of health computer systems and how it could help in deciding investment requirements.
Investment in information technology by the NHS is reaching unprecedented levels. This is true throughout the service, from the highly publicized district information systems and hospital information support systems to the investment of GPs in microcomputers. To place all these system developments in context, Peter Cross considers the changes in the structure of health computing in the 1980s and sets out a methodology for assessing both the need for computer systems and their success.
Decision Making↗
Systems modeling in support of evidence-based disaster planning for rural areas.
The objective of this communication is to introduce a conceptual framework for a study that applies a rigorous systems approach to rural disaster preparedness and planning. System Dynamics is a well-established computer-based simulation modeling methodology for analyzing complex social systems that are difficult to change and predict. This approach has been applied for decades to a wide variety of issues of healthcare and other types of service capacity and delivery, and more recently, to some issues of disaster planning and mitigation. The study will use the System Dynamics approach to create computer simulation models as "what-if" tools for disaster preparedness planners. We have recently applied the approach to the issue of hospital surge capacity, and have reached some preliminary conclusions--for example, on the question of where in the hospital to place supplementary nursing staff during a severe infectious disease outbreak--some of which we had not expected. Other hospital disaster preparedness issues well suited to System Dynamics analysis include sustaining employee competence and reducing turnover, coordination of medical care and public health resources, and hospital coordination with the wider community to address mass casualties. The approach may also be applied to preparedness issues for agencies other than hospitals, and could help to improve the interactions among all agencies represented in a community's local emergency planning committee. The simulation models will support an evidence-based approach to rural disaster planning, helping to tie empirical data to decision-making. Disaster planners will be able to simulate a wide variety of scenarios, learn responses to each and develop principles or best practices that apply to a broad spectrum of disaster scenarios. These skills and insights would improve public health practice and be of particular use in the promotion of injury and disease prevention programs and practices.
Decision Making↗
A life-like virtual cell membrane using discrete automata.
A framework is presented that captures the discrete and probabilistic nature of molecular transport and reaction kinetics found in a living cell as well as formally representing the spatial distribution of these phenomena. This particle or agent-based approach is computationally robust and complements established methods. Namely it provides a higher level of spatial resolution than formulations based on ordinary differential equations (ODE) while offering significant advantages in computational efficiency over molecular dynamics (MD). Using this framework, a model cell membrane has been constructed with discrete particle agents that respond to local component interactions that resemble flocking or herding behavioural cues in animals. Results from simulation experiments are presented where this model cell exhibits many of the characteristic behaviours associated with its biological counterpart such as lateral diffusion, response to osmotic pressure gradients, membrane growth and cell division. Lateral diffusion rates and estimates for the membrane modulus of elasticity derived from these simple experiments fall well within a biologically relevant range of values. More importantly, these estimates were obtained by applying a simple qualitative tuning of the model membrane. Membrane growth was simulated by injecting precursor molecules into the proto-cell at different rates and produced a variety of morphologies ranging from a single large cell to a cluster of cells. The computational scalability of this methodology has been tested and results from benchmarking experiments indicate that real-time simulation of a complete bacterial cell will be possible within 10 years.
Cell Membrane↗
Power spectrum analysis of heart rate variability to assess the changes in sympathovagal balance during graded orthostatic tilt.
BACKGROUND: The powers of the low-frequency (LF) and high-frequency (HF) oscillations characterizing heart rate variability (HRV) appear to reflect, in their reciprocal relationship, changes in the state of the sympathovagal balance occurring during numerous physiological and pathophysiological conditions. However, no adequate information is available on the quantitative resolution of this methodology. METHODS AND RESULTS: We studied 22 healthy volunteers (median age, 46.5 years) who were subjected after a rest period to a series of passive head-up tilt steps randomly chosen from the following angles: 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees. From the continuous ECG, after appropriate analog-to-digital conversion, a personal computer was used to compute, with an autoregressive methodology, time and frequency domain indexes of RR interval variability. Spectral and cross-spectral analysis with the simultaneously recorded respiratory signal excluded its contribution to LF. Age was significantly correlated to variance and to the absolute values in milliseconds squared of very-low-frequency (VLF), LF, and HF components. The tilt angle was correlated to both LF and HF (expressed in normalized units [nu]) and to the LF-to-HF ratio (r = .78, -.72, and .68; respectively). Lower levels of correlation were found with HF (in ms2) and RR interval. No correlation was present between tilt angle and variance, VLF, or LF (in ms2). Individual analysis confirmed that the use of nu provided the greatest consistency of results. CONCLUSIONS: Spectral analysis of HRV, using nu or LF-to-HF ratio, appears to be capable of providing a noninvasive quantitative evaluation of graded changes in the state of the sympathovagal balance.
Adult↗
[Determination of effective atomic number and electronic density by computed tomography with dual energies. Application to the thalamus (author's transl)].
The authors have studied seven thalamic hyperdense lesions of five patients in managing, at the same level, successively two scans with a computer tomograph at two different energies. After they recall their methodology of testing their C.T. and computations, they have found the effective atomic number and the electron density of these lesions. All (one Fahr disease and six old hemorrhages) have both high effective atomic number and electron density. They discuss the limits of this technic but they emphasize the great interest to see the chemical aspects of the structures observed in C.T.
Brain Diseases↗
[The Parity technique as an example of an analytical approach to designing computerized psychological tests].
The new computer technique "Paritet" for studying the function of attention and visual perception was developed by the author in 1995. This technique has been tested in the combined experiment "ECOPSI-95". The study results reveal the differences in the visual perception of symmetric and nonsymmetric images, combined and separate elements of the image. For solution of the problem of developing the methodology of designing the computer tests it is suggested to develop the system of ranging the visual images to suit the complexity of perception.
Attention↗
Conceptual and methodological issues in public health performance measurement: results from a computer-assisted expert panel process.
As part of the developmental process for the National Public Health Performance Standards Program, the CDC convened a group of experts in the fields of public health practice and research to evaluate key conceptual and methodological issues involved in measuring the performance of public health organizations. Participants engaged in a nominal group process and an electronic polling exercise designed to elicit expert opinions about these issues. Results revealed broad consensus around the need for measurement systems that support quality improvement and accountability applications, with scientific investigation viewed as an important but secondary objective of measurement. Substantial variation was observed in perceptions about the importance of specific measurement concepts and methods. Results highlight the need for performance measurement systems to reflect multiple organizational perspectives in their design and implementation.
Health Planning Councils↗
Free-energy analysis of enzyme-inhibitor binding: aspartic proteinase-pepstatin complexes.
Expeditious in silico determinations of the free energies of binding of a series of inhibitors to an enzyme are of immense practical value in structure-based drug design efforts. Some recent advances in the field of computational chemistry have rendered a rigorous thermodynamic treatment of biologic molecules feasible, starting from a molecular description of the biomolecule, solvent, and salt. Pursuing the goal of developing and making available a software for assessing binding affinities, we present here a computationally rapid, albeit elaborate, methodology to estimate and analyze the molecular thermodynamics of enzyme-inhibitor binding with crystal structures as the point of departure. The complexes of aspartic proteinases with seven inhibitors have been adopted for this study. The standard free energy of complexation is considered in terms of a thermodynamic cycle of six distinct steps decomposed into a total of 18 well-defined components. The model we employed involves explicit all-atom accounts of the energetics of electrostatic interactions, solvent screening effects, van der Waals components, and cavitation effects of solvation combined with a Debye-Huckel treatment of salt effects. The magnitudes and signs of the various components are estimated using the AMBER parm94 force field, generalized Born theory, and solvent accessibility measures. Estimates of translational and rotational entropy losses on complexation as well as corresponding changes in the vibrational and configurational entropy are also included. The calculated standard free energies of binding at this stage are within an order of magnitude of the observed inhibition constants and necessitate further improvements in the computational protocols to enable quantitative predictions. Some areas such as inclusion of structural adaptation effects, incorporation of site-dependent amino acid pKa shifts, consideration of the dynamics of the active site for fine-tuning the methodology are easily envisioned. The present series of studies, nonetheless, creates potentially useful qualitative information for design purposes on what factors favor protein-drug binding. The net binding free energies are a result of several competing contributions with 6 of the 18 terms favoring complexation. The nonelectrostatic contributions (i.e., the net van der Waals interactions) and the differential cavitation effects favor binding. Electrostatic contributions show considerable diversity and turn out to be favorable in a consensus view for the seven aspartic proteinase-inhibitor complexes examined here. Implications of these observations to drug design are discussed.
Aspartic Acid Endopeptidases↗
Desiderata for an adequate evaluation of cancer screening.
Three main problems in the evaluation of mass screening are obtaining reliable estimates of the impact of cancer screening on morbidity and mortality, taking account of the large number of factors that together determine the impact of cancer screening, and dealing adequately with all three stages (explanation, prediction, and planning) of evaluation. Mathematical models, implemented in computer programs, should preferably be used for the evaluation. Fourteen desiderata for adequate model-based evaluation of mass screening are formulated; they concern the model, the computer program, and the methodology used. Satisfying these desiderata is essential in overcoming the three main problems mentioned. As yet, no evaluation research group is close to fulfilling all 14 desiderata. Sticking to one model only should thus be avoided.
Computers↗
The TEAM methodology for the evaluation of information systems in biomedicine.
The TEAM evaluation methodology for information systems in biomedicine (Total Evaluation and Acceptance Methodology) is a unifying methodology for any computer-based information system based on a three dimensional framework; these dimensions being Role, Time and Structure. The theory is derived from how the information system relates to the general system where it should operate, the properties of information flow within a general system and the relation between a system and its models. As a system can in theory be modelled from many perspectives, a perspective to be modelled is built up by formulating criteria relevant to that perspective which can be evaluated by quantitative and qualitative assessment methods. Key characteristics of the methodology include the insistence on a global rather than partial approach to the evaluation of information systems, also the dynamic nature of an information system which is continually in modification as it more successfully deals with the inherent complexity of the environment in which it is operating. The role dimension identifies four main categories, designer, specialist user, end user and stakeholder from which several sub-categories may be identified. The time dimension has four main phases towards relative stability of the information system. The structural dimension distinguishes strategic, tactical or organisational and operational levels that often are confused together with risk of dilution in current approaches. It is believed that this framework and methodology can provide a basis for future standardisation of evaluation methodologies.
Evaluation Studies as Topic↗