SEARCH · PubMed Health

Results for “Computer Graphics”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources

PubMedDate not supplied

Computerised biofeedback games: a new method for teaching stress management and its use in irritable bowel syndrome.

OBJECTIVES: To develop and test a computer biofeedback game designed to teach deep relaxation to patients with a stress related disorder and to assess whether relaxation can improve symptomatic episodes. STUDY DESIGN AND SETTING: An open, prospective, single centre study. Department of Gastroenterology, Royal Free Hospital, London. SUBJECTS: Forty patients with irritable bowel syndrome refractory to conventional medical treatment. MAIN OUTCOME MEASURES: Development of a computer aided biofeedback apparatus directed at the gut for teaching relaxation to patients with irritable bowel syndrome. The patients' ability to complete a computer game involving biofeedback modulated by a physiological loop that related changes in stress (monitored by electrodermal activity) to animated computer graphics. The degree to which deep relaxation was achieved was measured numerically by a progressive reduction in the sensitivity level of the biofeedback loop. The success of relaxation in ameliorating physical symptoms of irritable bowel syndrome was assessed by daily diaries in which global and weighted bowel symptom scores were entered. RESULTS: A computer biofeedback game based on animated gut imagery was successfully developed. Most patients learned to achieve progressively deeper levels of relaxation after four 30 minute biofeedback sessions (mean difference in sensitivity level 2.0 (95% confidence interval 0.96 to 2.93), p < 0.001). Use of 'dosed' relaxation when bowel symptoms were troublesome was helpful in 50% of patients. It reduced the global symptom score (mean difference 0.5 (0.02 to 0.32), p < 0.04) and the bowel symptom score (mean difference 0.8 (0.04 to 1.58), p < 0.04). At long term follow up, 64% of patients who had been helped by dosed relaxation continued to use the technique, although they had had no further contact with the hospital. CONCLUSIONS: This computer biofeedback game taught deep relaxation rapidly and effectively. Half the patients with refractory irritable bowel syndrome found the technique helpful on most occasions on which it was used. Computer biofeedback games may offer a simple, inexpensive strategy for managing other stress related medical disorders.

Adult↗

PubMed1991

The use of confocal microscopy and STERECON reconstructions in the analysis of sea urchin embryonic cell division.

A laser scanning confocal microscope has been used to investigate the development of the sea urchin embryo. The samples were fixed in Carnoy's solution at various developmental stages, stained for DNA with the Feulgen reaction, and optically sectioned with a BioRad MRC-500 confocal microscope. Computer-generated stereographic projection images and a three-dimensional contour tracing and reconstruction system were employed to investigate the cleavage pattern during the 6th cleavage division. Cell division is found to be asynchronous during the 6th cleavage, with macromere derivatives completing division first, followed by mesomeres, and finally by the outer quartet of micromeres (which begins division only after macromeres and mesomeres have completed their respective divisions). Sixth cleavage produces an embryo comprising 60 cells. Asynchronous division was also observed within individual tiers of blastomeres. Variations in the orientations of cell division axes within individual tiers of cells were also observed. The utility of computer-graphics reconstruction techniques for both quantitative and qualitative developmental analysis are discussed.

Animals↗

PubMed1990

Cat and monkey cortical columnar patterns modeled by bandpass-filtered 2D white noise.

A simple algorithm based on bandpass-filtering of white noise images provides good quality computer reconstruction of the cat and monkey ocular dominance and orientation column patterns. A small number of parameters control the frequency, orientation, "branchedness", and "regularity" of the column patterns. An oriented (anisotropic) bandpass filter followed by a threshold operation models the macaque ocular dominance column pattern and cat orientation column system. An unoriented (isotropic) bandpass filter models the cat ocular dominance column pattern and the macaque orientation column system. The resemblance of computer graphic simulations produced by this algorithm and histological pattern data, is strong. Since this algorithm is very fast, we have been able to extensively explore its parameters space in order to determine filter parameters which closely match the structure of the various cortical systems. In particular, we have applied spectral analysis to our recent computer reconstruction of the macaque ocular dominance column system, and the model produced by the present algorithm is in close agreement with this detailed data analysis.

Algorithms↗

PubMedDate not supplied

Use of CAD/CAM system to fabricate dental prostheses. Part 1: CAD for a clinical crown restoration.

The development of a computer-aided design system for a clinical crown restoration is reported. Initially, the shape of the standard crown was deformed and adapted on the die depending on the shape of the margin. Then, the measured occlusal record data were taken in the computer graphics, and the adapted crown was adjusted with these data to obtain the centric occlusion. The occlusal data were replaced with data obtained using a functionally generated path record and the occlusal interferences eliminated. The ends of the adapted crown were connected with the margin. Thus, the entire crown was efficiently designed using the computer program developed.

Computer-Aided Design↗

PubMed1994

A single mutation at lysine 426 of human placental S-adenosylhomocysteine hydrolase inactivates the enzyme.

S-Adenosylhomocysteine (AdoHcy) hydrolase catalyzes the conversion of AdoHcy to adenosine (Ado) and homocysteine (Hcy), as well as the reverse reaction, through a mechanism involving an NAD(+)-dependent oxidation of the 3'-hydroxyl group of AdoHcy (3'-oxidative activity), followed by elimination of Hcy to form 3'-keto-4',5'-didehydro-5'-deoxy-Ado. The addition of water at the 5'-position (5'-hydrolytic activity) of this tightly bound intermediate, followed by an NADH-dependent reduction, results in the formation of Ado. Based on a computer graphics model of the active site of this enzyme, it was hypothesized that amino acid residues at the carboxyl-terminal end of the protein reside in the active site of the enzyme and could play a role in catalyzing the 5'-hydrolytic reaction (Yeh, J. C., Borchardt, R. T., and Vedani, A. (1991) J. Comput. Aided Mol. Des. 5, 213-234). Using site-directed mutagenesis, we show here that lysine 426 is essential for the catalytic activity of the enzyme and that it appears to play a crucial role in the 5'-hydrolytic activity and/or stability of the quaternary structure of the human placental enzyme. Mutation of Lys-426 to arginine (K426R) produces a stable tetrameric enzyme that lacks overall catalytic activity and that was isolated predominantly as its NADH form containing tightly bound 3'-keto-Ado, suggesting that the K426R mutant has oxidative activity, but lacks 5'-hydrolytic activity, preventing it from completing the entire catalytic cycle. Mutations of Lys-426 to glutamic acid (K426E) and alanine (K426A) produce enzymes that exist primarily as monomers, do not bind NAD+ or NADH, and lack catalytic activity. The results of the Lys-426 mutations suggest that this lysine residue is crucial for the 5'-hydrolytic activity of the enzyme and/or stabilizing the quaternary structure of the enzyme.

Adenosylhomocysteinase↗

PubMed1993

Computer-assisted three-dimensional planning in craniofacial surgery.

Three-dimensional surface reconstruction from computed tomographic (CT) data has been used to plan craniofacial operations. Cephalometric and anthropometric databases were integrated with three-dimensional CT reconstructions to quantitate the skeletal deformity and to assist in the design of the surgical procedure. Interactive techniques were developed to simulate osteotomies and skeletal movements in three dimensions on the computer-generated surface images. The ocular globes were referenced to position the orbital segments; i.e., the osteotomized segments were transposed into normal anatomic relationship with respect to the eyes. The measurements from the computer graphic simulation were used intraoperatively to establish the correct position of the skeletal segments.

Adolescent↗

PubMed1985

Animal studies and prediction of human tumors can be aided by graphical sorting of animal data: neoplastic risk from B(a)P, benzene, benzidine, and chromium.

This work is a graphical study of all known dose-response data for neoplasia induced by B(a)P, benzene, benzidine, and chromium administered to test animals. Doses are put in units of lifetime intake given in micromoles of chemical per kilogram body weight, and responses are in percent increased effect per unit dose. Space limitations do not permit experiment-by-experiment critiques; however, computer graphics have been used to compare the relationship of any individual dose-response point estimate to other such point estimates for the chemical of interest. Graphics are also used to study variability resulting from different experimental parameters such as species, route of intake, number of treatments, pathological classification of neoplasia, etc. Graphical sorting, according to various physical and biological classification parameters, permits one to judge, from visual inspection, such questions as whether mice as a species are more sensitive than rats as a species, whether intravenous injection is generally more effective than inhalation, whether a single well-defined dose-response function, which ignores these classification parameters, can be evaluated numerically from the composite data base deriving from all oncogenic studies with a given chemical, etc.

Animals↗

PubMed1985

Molecular interactions of toxic chlorinated dibenzo-p-dioxins and dibenzofurans with thyroxine binding prealbumin.

The interactions of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds with prealbumin, a model for the nuclear thyroid hormone receptor, have been studied with use of computer graphics and predictions made regarding relative binding affinities for such structures. These modeling predictions were tested by experimentally measuring the binding affinities of dioxin and furan analogues. The results were in general agreement with the modeling predictions and demonstrated that such compounds could be effective competitive binding ligands for thyroxine-specific binding sites in prealbumin. The computer modeling work also demonstrates the importance of lateral chlorine substitution in the binding of these toxic compounds. The prealbumin interaction model should be of use in investigating the structure-toxicity relationships of these classes of toxic compounds. Thus, if prealbumin is a model for the nuclear thyroid hormone receptor, this work would also have major implications bearing on the mechanism of dioxin toxicity and the potential of these compounds to function as potent and persistent thyroxine agonists. A new cooperative receptor mechanism for dioxin toxic action is proposed.

Benzofurans↗

PubMed1985

A simple hidden line removal algorithm for serial section reconstruction.

A simple and efficient program for removing the hidden lines from the computer graphics display of a three-dimensional structure has been developed. The algorithm is optimized for serial section reconstruction, that is, for three-dimensional structures composed of a series of stacked planar outlines. Using the algorithm, an anatomist can generate a realistic static picture of a reasonably complex reconstruction in about 20 s on a small laboratory computer.

Anatomy↗

PubMed1985

Reactivation of tritonated models of human polymorphonuclear leukocytes (PMNs): a computer-assisted analysis.

The orientation (chemotaxis) and locomotion (chemokinesis) of human polymorphonuclear leukocytes (PMNs) are generated by an internal movement mechanism that involves active cytoplasmic movement; they are influenced by external environmental and ionic conditions. We have studied the degree to which the orientation and movement mechanisms of PMNs are self-contained within the cell and the degree to which they are under membrane control. PMNs were partially and selectively demembranated by treatment with the non-ionic detergent, octyl-phenoxyl-polyethoxyethanol (commercially known as Triton X-100) under controlled conditions. The tritonated PMNs (referred to in the literature as models) were non-motile and non-locomotory. Addition of ATP/Mg++ with a trace amount of Ca++ to the medium was followed by reactivation of the tritonated PMN models to move again as motile cells. Although these reactivated PMN models actively locomoted, they could no longer orient to chemoattractants. Thus, the reactivation process restored the physical self-contained movement parameters but could not reestablish the orientation capacity (chemotactic responsiveness) that was characteristic of live PMNs. The demembranation process apparently destroyed the chemotactic receptors and/or eradicated the coordination function of the membrane. Videotapes of normal (control) as well as reactivated PMN movement were analyzed for movement characteristics. These characteristics were objectively analyzed with a newly designed computer-assisted micro-image-processing technique whereby the videotapes were digitized and quantified and the actual PMN movement printed out in computer-graphics and tracings (Freeman codes) for confirmation of orientation and movement arising as a result of reactivation.

Adenosine Triphosphate↗

PubMed1990

Conformational and helicoidal analysis of the molecular dynamics of proteins: "curves," dials and windows for a 50 psec dynamic trajectory of BPTI.

A new procedure for the graphic analysis of molecular dynamics (MD) simulations on proteins is introduced, in which comprehensive visualization of results and pattern recognition is greatly facilitated. The method involves determining the conformational and helicoidal parameters for each structure entering the analysis via the method "Curves," developed for proteins by Sklenar, Etchebest, and Lavery (Proteins: Structure, Function Genet. 6:46-60, 1989) followed by a novel computer graphic display of the results. The graphic display is organized systematically using conformation wheels ("dials") for each torsional parameter and "windows" on the range values assumed by the linear and angular helicoidal parameters, and is present in a form isomorphous with the primary structure per se. The complete time evolution of dynamic structure can then be depicted in a set of four composite figures. Dynamic aspects of secondary and tertiary structure are also provided. The procedure is illustrated with an analysis of a 50 psec in vacuo simulation on the 58 residue protein, bovine pancreatic trypsin inhibitor (BPTI), in the vicinity of the local minimum on the energy surface corresponding to a high resolution crystal structure. The time evolution of 272 conformational and 788 helicoidal parameters for BPTI is analyzed. A number of interesting features can be discerned in the analysis, including the dynamic range of conformational and helicoidal motions, the dynamic extent of 2 degrees structure motifs, and the calculated fluctuations in the helix axis. This approach is expected to be useful for a critical analysis of the effects of various assumptions about force field parameters, truncation of potentials, solvation, and electrostatic effects, and can thus contribute to the development of more reliable simulation protocols for proteins. Extensions of the analysis to present differential changes in conformational and helicoidal parameters is expected to be valuable in MD studies of protein complexes with substrates, inhibitors, and effectors and in determining the nature of structural changes in protein-protein interactions.

Biological Evolution↗

PubMed2006

Enhancing the visual realism of hysteroscopy simulation.

Visualization is a very important part of a high fidelity surgical simulator. Due to modern computer graphics hardware, which offers more and more features and processing power, it is possible to extend the standard OpenGL rendering methods with advanced visualization techniques to achieve highly realistic rendering in real-time. For an easy and efficient use of these new capabilities, a stand-alone graphics engine has been implemented, which exploits these advanced rendering techniques and provides an interface in order to ensure the interoperability with a software framework for surgical simulators.

Computer Simulation↗

PubMed1989

[Use of digital technics in the display of electromyography signals].

The use of digital techniques for the display of electromyographic signals often introduces grave errors in the visualization of the high frequency signal components. The causes for this can be quantitatively deduced from the technical principles of the systems. In the digital storage oscilloscope, the accuracy of reproduction is determined by the sampling rate and the memory capacity. In addition, there may be a considerable loss of quality in the visual display of systems using computer graphics despite accurate signal acquisition. Based on the quantitative analysis recommendations as to the technical equipment and use of digital neurophysiological systems are given.

Analog-Digital Conversion↗

PubMed1996

Design of a 3-D surface scanner for lower limb prosthetics: a technical note.

A three-dimensional (3-D) noncontact optical surface range sensing imaging system that captures the entire circumferential and distal end surfaces of lower limb residua in less than 1 second has been developed. The optical surface scanner (OSS) consists of four charge injection device (CID) cameras and three white light projectors, mounted on a rigid frame surrounding the subject's residuum, allowing 360 degrees surface coverage of the lower residual limb. Anatomic 3-D computer graphics reconstruction of a residuum surface, recorded with the OSS imaging system, is used for visualization and measurement. One cubical and two spherical calibration test objects were used to obtain a system precision of less than 1 mm. In a study conducted with 13 persons with below knee (BK) amputation, the OSS system was compared to calipers, electromagnetic digitizer, and volumetric computed tomography with better than 1 mm precision on plaster positive casts and approximately 2 mm on the residual limbs.

Amputation, Surgical↗

PubMedDate not supplied

Visualization of MR angiographic data with segmentation and volume-rendering techniques.

Novel image processing and computer graphics techniques were developed to create three-dimensional (3D) models of vasculature from magnetic resonance (MR) angiographic images of the head or neck. Region growing was used to produce a mask that isolated the vascular signal in the MR angiographic data. The masked images were subjected to gradient-shaded volume rendering to create 3D views of the vasculature. The computer-derived model of intracranial vasculature was then merged with a 3D model of brain parenchyma derived from a set of MR images. The combined display of vascular and gyral anatomy may be useful for neurosurgical planning.

Brain↗

PubMed1991

Computer modeling 16 S ribosomal RNA.

A three-dimensional structure for 16 S RNA has been produced with a computer protocol that is not dependent on human intervention. This protocol improves upon traditional modeling techniques by using distance geometry to fold the molecule in an objective and reproducible fashion. The method is based on the secondary structure of RNA and treats the molecule as a set of double-stranded helices that are linked by flexible single-strands of variable length. Data derived from chemical cross-linking studies of 16 S RNA and tertiary phylogenetic relationships provide the constraints used to fold the molecule into a compact three-dimensional form. Possibly subjective evaluation of the input data are transformed into verifiable quantitative parameters. Relationships based on general locations within the 30 S subunit or on protein-RNA interactions have been specifically excluded. The resolution of the model exceeds that of electron micrographs and approaches that obtained in preliminary X-ray crystal structures. The model size of 245 x 190 x 140 A is compatible with that of the 30 S subunit as determined by electron microscopy. The volume of the model is 1.87 x 10(6) A which is similar to that of the small subunit in a preliminary X-ray crystal structure. The radius of gyration of the model structure of 76 A is intermediate to that seen for partially denatured and fully folded 16 S RNA. Computer graphics are used to display the results in a manner that maximizes the opportunities for human visual interpretation of the models. A format for displaying the structures has been developed that will make it possible for researchers who have not devoted themselves to ribosomal modeling to comprehend and make use of the information that the models embody. On this basis the computer-generated models are compared with models developed by other researchers and with structural data not included in the folding parameter data set.

Base Sequence↗

PubMed1990

Visual information processing of computed topographic electrical activity brain maps.

Effective display of computer-generated biomedical images draws on computer graphics and image processing, display technology and human factors, visual psychophysics and perception, cognitive psychology, and the new field of scientific data visualization. In converting from raw, acquired data to a visual display, developers need to know the limitations of the data and of the display technology. To obtain reliable inferences about the clinical or physiological state of the patient requires that the computer display be matched to the visual information-processing competence and limitations of human observers. The issues that should be considered by both developers and users of computer-based display technologies to enhance clinical performance in observation and diagnosis are surveyed with reference to electrical activity brain maps.

Brain↗

PubMed1983

Three-dimensional structure of the Mcg IgG1 immunoglobulin.

The three-dimensional structure of an IgG1(lambda) immunoglobulin from a patient (Mcg) with amyloidosis was determined at 6.5-A resolution with X-ray diffraction techniques. The protein crystallized from water in the space group C2221, with a = 87.8, b = 111.3 and c = 186.3 A; the crystallographic asymmetric unit was a half-molecule consisting of one light and one heavy chain. The structure was solved by the multiple isomorphous replacement method with five heavy-atom derivatives. Electron density maps were interpreted with the aid of a protein modeling system used in conjunction with an Evans and Sutherland Picture System II graphics station. IgG1 molecules were tightly packed in the crystal lattice, with numerous intermolecular contacts. The two-fold axis relating identical halves of each molecule was found to be parallel to the y crystallographic axis. Electron density modules collectively representing one molecule were identified as three lobes representing the two antigen-binding (Fab) arms and the Fc region. An interchain disulfide bond connecting the two CL domains was located on the molecular diad and used as a landmark in the interpretation of the electron density map. A computer graphics method was developed to produce a solid image model of the IgG1 molecule in any prescribed orientation.

Computers↗