Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Computer Graphics”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,441 records · Page 80Linked to original sources
PubMed1997

Distributed system for processing 3D medical images.

Three-dimensional (3D) image data generated by radiological imaging modalities such as CT and MRI can provide detailed structural insight. Automating the analysis of these images can improve the consistency of the results and reduce user interaction time, but introduces a tremendous computational burden. To address this problem, we have designed a distributed processing environment for the rapid processing of 3D medical images. Our system allows a user to perform automatic 3D filtering, segmentation, and measurement on a 3D image using a heterogeneous network of processors and the PVM protocol.

Computer Communication Networks↗
PubMed1997

The assignment of velocity profiles in finite element simulations of pulsatile flow in arteries.

In this paper we present a new method for the assignment of pulsatile velocity profiles as input boundary conditions in finite element models of arteries. The method is based on the implementation of the analytical solution for developed pulsatile flow in a rigid straight tube. The analytical solution provides the fluid dynamics of the region upstream from the fluid domain to be investigated by means of the finite element approach. In standard fluid dynamics finite element applications, the inlet developed velocity profiles are achieved assuming velocity boundary conditions to be easily implementable-such as flat or parabolic velocity profiles-applied to a straight tube of appropriate length. The tube is attached to the inflow section of the original fluid domain so that the flow can develop fully. The comparison between the analytical solution and the traditional numerical approach indicates that the analytical solution has some advantages over the numerical one. Moreover, the results suggest that subroutine employment allows a consistent reduction in solving time especially for complex fluid dynamic model, and significantly decreases the storage and memory requirements for computations.

Algorithms↗
PubMed1998

A 3D deformable surface model for segmentation of objects from volumetric data in medical images.

In this paper we present a new 3D discrete dynamic surface model. The model consists of vertices and edges, which connect adjacent vertices. Basic geometry of the model surface is generated by triangle patches. The model deforms by internal and external forces. Internal forces are obtained from local geometry of the model and are related to the local curvature of the surface. External forces, on the other hand, are based on the image data and are calculated from desired image features. We also present a method for generating an initial volume for the model from a stack of initial contours, drawn by the user on cross sections of the volumetric data.

Algorithms↗
PubMed1988

Evolutionary and functional relationships between the basic and acidic beta-crystallins.

beta-Crystallins are complex oligomers composed of many related subunits. In order to understand their interactions we have built molecular models of several bovine beta-crystallins, based on their sequence similarity to the well-defined gamma-II crystallin structure, using interactive computer graphics techniques. Their common origin with gamma-crystallin is displayed in both the retention of four-fold sequence repeats of critical residues involved with stabilizing a folded beta-hairpin and the conservation of core-filling hydrophobic side-chains. The beta-crystallins have been built as bilobal molecules with each domain composed of two 'Greek key' motifs which associate about an approximate two-fold axis to form beta-sheets. The beta-crystallin sequences have previously been shown to comprise two families, the basic and acidic subunits, which have extensions of sequence. The three-dimensional models show how the two families appear to stabilize the folded beta-hairpin in the N- and C-terminal domains in ways which suggest that they have diverged from a common ancestor in different ways. Acidic beta-crystallins, like gamma-crystallins, have a regular array of charges on their N-terminal domain which has been interrupted in basic beta-crystallins by hydrophobic residues which may be related to the presence of a C-terminal extension. beta-Crystallins are more highly charged than gamma-crystallins although their charge density is higher in certain regions of the N-terminal domain, particularly in beta B1-crystallin. beta-crystallins also differ from gamma-crystallins in the virtual absence of core-filling sulphydryl groups whereas they have numerous sulphur-containing side-chains together with tryptophan and histidine rings protruding from the globular domains, particularly in the acidic subunits. The burial of these residues in subunit contacts is consistent with their spectroscopic and electrostatic properties. Protein subunit aggregation commonly occurs through hydrophobic interaction or beta-sheet extension. Analysis of the subunit surfaces has identified an N-terminal hydrophobic region common to beta B1 and beta B2 whereas a C-terminal hydrophobic loop region is common to beta B1 and beta A1 and may be correlated with their association properties. It is suggested that the polar C-terminal domain of beta B2 contributes towards the solubility of higher aggregates by interactions involving beta-sheet structure.

Amino Acid Sequence↗
PubMed1999

Crystal structure of the alpha1beta1 integrin I-domain: insights into integrin I-domain function.

The alpha1beta1 integrin is a major cell surface receptor for collagen. Ligand binding is mediated, in part, through a 200 amino acid inserted 'I'-domain contained in the extracellular part of the integrin alpha chain. Integrin I-domains contain a divalent cation binding (MIDAS) site and require cations to interact with integrin ligands. We have determined the crystal structure of recombinant I-domain from the rat alpha1beta1 integrin at 2.2 A resolution in the absence of divalent cations. The alpha1 I-domain adopts the dinucleotide binding fold that is characteristic of all I-domain structures that have been solved to date and has a structure very similar to that of the closely related alpha2beta1 I-domain which also mediates collagen binding. A unique feature of the alpha1 I-domain crystal structure is that the MIDAS site is occupied by an arginine side chain from another I-domain molecule in the crystal, in place of a metal ion. This interaction supports a proposed model for ligand-induced displacement of metal ions. Circular dichroism spectra determined in the presence of Ca2+, Mg2+ and Mn2+ indicate that no changes in the structure of the I-domain occur upon metal ion binding in solution. Metal ion binding induces small changes in UV absorption spectra, indicating a change in the polarity of the MIDAS site environment.

Animals↗
PubMed1990

Characterization of the binding sites of protein L11 and the L10.(L12)4 pentameric complex in the GTPase domain of 23 S ribosomal RNA from Escherichia coli.

Ribonuclease and chemical probes were used to investigate the binding sites of ribosomal protein L11 and the pentameric complex L10.(L12)4 on Escherichia coli 23 S RNA. Protein complexes were formed with an RNA fragment constituting most of domains I and II or with 23 S RNA and they were investigated by an end-labelling method and a reverse transcriptase procedure, respectively. The results demonstrate that the two protein moieties bind at adjacent sites within a small RNA region. The L11 binding region overlaps with those of the modified peptide antibiotics thiostrepton and micrococcin and is constrained structurally by a three-helix junction while the L10.(L12)4 site is centred on an adjacent internal loop. The secondary structure of the whole region was determined in detail by the phylogenetic sequence comparison method, and the results for the L11 binding region, together with the experimental data, were used in a computer graphics approach to build a partial RNA tertiary structural model. The model provides insight into the topography of the L11 binding site. It also provides a structural rationale for the mutually co-operative binding of protein L11 with the antibiotics thiostrepton and micrococcin, and with the L10.(L12)4 protein complex.

Base Sequence↗
PubMed1986

Calculation of the conformation of glycosphingolipids. 2. GM1- and GM2-gangliosides.

The conformations of GM1- and GM2-gangliosides have been predicted by energy minimization techniques including an orbital force field approach. The global energy minimum conformers for these two gangliosides show marked differences, particularly in the relative orientation of the sugar rings. The predicted structures are compared with those postulated from NMR spectroscopy in relation to the formation of a cation-binding site. The minimum energy conformer of GM2-ganglioside is able to form this binding site whereas this conformer of GM1-ganglioside is not. The nature of the specific interaction of gangliosides with activator proteins is discussed.

Carbohydrate Conformation↗
PubMed1988

Movable Finite Automata (MFA) models for biological systems. I: Bacteriophage assembly and operation.

A new class of models, called Movable Finite Automata (MFA) models, is introduced. MFA models are physically realistic, but still share some of the features of cellular automata that make the latter easy to handle mathematically and computationally. They are found to be quite versatile in modeling the self-organization of biological systems. Their use in simulating the interaction of protein molecules in the self-assembly and operation of the T4 bacteriophage is described. The results of these simulations carried out on a microcomputer, are given.

Bacteriophages↗
PubMed1998

The effect of ventricular volume reduction surgery in the dilated, poorly contractile left ventricle: a simple finite element analysis.

OBJECTIVES: Ventricular volume reduction surgery has been proposed by Batista to improve cardiac function in patients with dilated cardiomyopathy. However, limited clinical data exist to determine the efficacy of this operation. A finite element simulation is therefore used to determine the effect of volume reduction surgery on left ventricular end-systolic elastance, diastolic compliance, stroke work/end-diastolic volume (preload recruitable stroke work), and stroke work/end-diastolic pressure (Starling) relationships. METHODS: End-diastole and end-systole were represented by elastic finite element models with different unloaded shapes and nonlinear material properties. End-systolic elastance, diastolic compliance, preload recruitable stroke work, and Starling relationships, as well as energy expenditure per gram of unresected myocardium, were calculated. Two different types of volume reduction surgery (apical and lateral) were simulated at 10% and 20% left ventricular mass reduction. RESULTS: Ventricular volume reduction surgery causes diastolic compliance to shift further to the left on the pressure-volume diagram than end-systolic elastance. Volume reduction surgery increases the slope of the preload recruitable stroke work relationship (dilated cardiomyopathy 0.006 J/mL; 20% lateral volume reduction surgery 0.009 J/mL) but decreases the slope of the Starling relationship (dilated cardiomyopathy 0.028 J/mm Hg; 20% lateral volume reduction 0.023 J/mm Hg). For a given amount of resection, lateral volume reduction has a greater effect than apical volume reduction. Ten-percent and 20% lateral volume reduction reduces energy expenditure by 7% and 17%, respectively. CONCLUSION: Ventricular volume reduction surgery shifts end-systolic elastance and diastolic compliance to the left on the pressure-volume diagram. The net effect on ventricular function is mixed. Volume reduction surgery increases the slope of preload recruitable stroke work, but increased diastolic compliance causes a small decrease in the Starling relationship (3 mm Hg difference between dilated cardiomyopathy and volume reduction surgery at stroke work = 0.5 J).

Adult↗
PubMed2002

Endoluminal ureteroileal anastomosis.

PURPOSE: We present an alternative technique used to complete the ureteroileal anastomosis during the formation of an ileal conduit or neobladder. MATERIALS AND METHODS: Using an intraoperative camera to produce digital images and with the aid of computer graphics a visual and descriptive method was used to illustrate the technique. It involves eversion of the proximal ileal segment with exteriorization of the ileal mucosa. RESULTS: This technique allows for direct visualization of the mucosa-to-mucosa ureteroileal anastomosis. With normal tissues it does not require ureteral stents postoperatively. We have been performing this technique for the last 20 years and have never observed symptomatic urinary leakage. CONCLUSIONS: We present an alternative technique for completing the ureteroileal anastomosis with direct visualization and minimal morbidity.

Anastomosis, Surgical↗
PubMed1990

Wide-field transesophageal echocardiographic tomography: feasibility study.

In this report, we describe our initial investigation of wide-field ultrasonic cardiothoracic tomography utilizing a transesophageal transducer. Examination included manual rotation of an esophageal transducer 180 to 360 degrees in order to visualize contiguous related structures. Consecutive sector views were photographed and then incorporated into a digital graphics computer for smoothing. This feasibility study introduces the concept of wide-field transesophageal cardiothoracic ultrasound tomography, which holds promise for tomographic depiction of cardiothoracic and mediastinal anatomy.

Aged↗
PubMed1997

Perceptual asymmetries in judgements of facial attractiveness, age, gender, speech and expression.

Lateralization of perception of various facial attributes (age, attractiveness, gender, lip-reading and expression) was studied using chimaeric faces in which the sides of the face differed along one dimension (e.g. the left side was male and the right side female). Computer graphics were used to eliminate naturally occurring physical asymmetries (e.g. those present in the mouth during speech and spontaneous smiles) and obvious vertical mid-line joins in the photo-realistic chimaeric stimuli. Following previous studies, we found that subjects' judgements of gender and expression were influenced more by the left than the right side of the face (viewer's perspective). This left of face stimulus bias extended to judgements about facial attractiveness and facial age. This was not true of lip-reading stimuli; for these stimuli subjects were influenced more by the right than the left side of the face. Thus using free fixation, it appears possible to demonstrate in normal subjects that brain processes underlying judgements of facial speech display different lateralization from the judgements of other facial dimensions.

Adult↗
PubMed1997

The role of 3-D surface slope in a lightness/brightness effect.

Adelson has shown how two patches in a 5 by 5 array of grey patches can be perceived to consist of different shades, depending on whether they are represented at a 3-D horizontal or vertical ridge. Adelson interprets the illusion in terms of the orientation of the patches with respect to the inferred illuminant. We investigated: (1) the illusion in the vertical and horizontal stimuli and added a flat (ridgeless) control stimulus; (2) stimuli of varying ridge amplitudes to examine the effect more fully. 3-D renderings of real surfaces were modelled with computer graphics and displayed to observers who used a mouse to alter the brightness of a square to match patches indicated in the stimuli. Five observers were used for the vertical, flat and horizontal stimuli, while a larger group (n = 20) was used for an independent design when varying ridge amplitudes. A significant effect in the flat surface demonstrates that patches lying in the same plane can have their brightness altered without changes in their orientation. When the surface was seen as a 3-D ridge the size of the effect was a function of 3-D slope of the surface. By measuring each patch independently we have shown that the effect changes the brightness of the two patches to differing degrees. We offer an explanation of this based on a proposed qualitative shading rule for identifying reflectance and illumination edges.

Adult↗
PubMed1999

Human heading judgments and object-based motion information.

In four experiments, we explored observers' ability to make heading judgments from simulated linear and circular translations through sparse forests and with pursuit fixation on one tree. We assessed observers' performance and information use in both regression and factorial designs. In all experiments we found that observers used three sources of object-based information to make their judgments--the displacement direction of the nearest object seen (a heuristic), inward displacement towards the fovea (an invariant) and outward deceleration (a second invariant). We found no support for the idea that observers use motion information pooled over regions of the visual field.

Computer Graphics↗
PubMed1989

Mapping the distribution of thiamine monophosphatase, fluoride-resistant acid phosphatase, and substance P in the spinal cord with a personal computer compatible program.

Distribution of the marker enzymes fluoride-resistant acid phosphatase (FRAP) and thiamine monophosphatase (TMPase) as well as that of the marker neuropeptide substance P (SP) has been mapped by means of the semi-automatic computer program MUDH, in various experimental conditions, including degeneration, regeneration, and anti-Nerve Growth Hormone treatment of the sciatic nerve. The program is written in standard Pascal language; it is applicable to Commodore 64 and IBM compatible personal computers. Graphical illustration of values obtained in serial sections is a powerful and highly valuable contribution in the analysis of various biodynamic reactions related to transganglionic regulation of primary sensory neurons.

Acid Phosphatase↗
PubMed1999

Study of the functional share of lysosomal cathepsins by the development of specific inhibitors.

To analyze the functional share of individual cathepsins, we developed powerful and specific inhibitors for individual cathepsins using computer graphics of substrate binding pockets based on X-ray crystallography. These new inhibitors were named CLIK group. Epoxy succinate peptide derivatives, CLIK-066, 088, 112, 121, 148, 181, 185 and 187, are typical specific inhibitors for cathepsin L. Aldehyde derivatives CLIK-060 and CLIK-164 showed specific inhibition against cathepsin S and cathepsin K, respectively. We found that pyridoxal phosphate (PLP), a coenzyme form of vitamin B6, inhibits all cathepsins and also new artificially synthesized pyridoxal derivatives, CLIK-071 and -072, in which the phosphate esters of PLP were replaced by propionic acid, exhibited strong inhibition for cathepsins. Furthermore, CLIK-071 was easy to incorporate into cells and showed powerful inhibition for intracellular cathepsins. Using these selective inhibitors, the allotment of individual cathepsin functions in cells has been studied as follows. Cathepsin L and/or K participate in bone resorption based on bone type-1 collagen degradation and the L-type protease inhibitors suppressed the bone resorption. Cathepsins B and S participate in antigen presentations based on antigen processing and invariant chain degradation, respectively. Also cathepsin L participates in cell apoptosis mediated by caspase III activation.

Animals↗