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At least 451 records · Page 25Linked to original sources
PubMed2000

Augmented reality simulator for training in two-dimensional echocardiography.

In two-dimensional echocardiography the sonographer must synthesize multiple tomographic slices into a mental three-dimensional (3D) model of the heart. Computer graphics and virtual reality environments are ideal to visualize complex 3D spatial relationships. In augmented reality (AR) applications, real and virtual image data are linked, to increase the information content. In the presented AR simulator a 3D surface model of the human heart is linked with echocardiographic volume data sets. The 3D echocardiographic data sets are registered with the heart model to establish spatial and temporal congruence. The heart model, together with an animated ultrasound sector represents a reference scenario, which displays the currently selected two-dimensional echocardiographic cutting plane calculated from the volume data set. Modifications of the cutting plane within the echocardiographic data are transferred and visualized simultaneously and in real time within the reference scenario. The trainee can interactively explore the 3D heart model and the registered 3D echocardiographic data sets by an animated ultrasound probe, whose position is controlled by an electromagnetic tracking system. The tracking system is attached to a dummy transducer and placed on a plastic puppet to give a realistic impression of a two-dimensional echocardiographic examination.

Computer Graphics↗
PubMed2001

Knee surgery assistance: patient model construction, motion simulation, and biomechanical visualization.

We present a new system that integrates computer graphics, physics-based modeling, and interactive visualization to assist knee study and surgical operation. First, we discuss generating patient-specific three-dimensional (3-D) knee models from patient's magnetic resonant images (MRIs). The 3-D model is obtained by deforming a reference model to match the MRI dataset. Second, we present simulating knee motion that visualizes patient-specific motion data on the patient-specific knee model. Third, we introduce visualizing biomechanical information on a patient-specific model. The focus is on visualizing contact area, contact forces, and menisci deformation. Traditional methods have difficulty in visualizing knee contact area without using invasive methods. The approach presented here provides an alternative of visualizing the knee contact area and forces without any risk to the patient. Finally, a virtual surgery can be performed. The constructed 3-D knee model is the basis of motion simulation, biomechanical visualization, and virtual surgery. Knee motion simulation determines the knee rotation angles as well as knee contact points. These parameters are used to solve the biomechanical model. Our results integrate 3-D construction, motion simulation, and biomechanical visualization into one system. Overall, the methodologies here are useful elements for future virtual medical systems where all the components of visualization, automated model generation, and surgery simulation come together.

Biomechanical Phenomena↗
PubMed1996

Interaction of human leukocyte elastase with a N-aryl azetidinone suicide substrate: Conformational analyses based on the mechanism of action of serine proteinases.

The three-dimensional interaction of the enzyme-activated (suicide) inhibitor AA 231-1 [N-(2-chloromethyl)-3, 3-difluoro-azetidin-2-one] with human leukocyte elastase has been studied using computer graphics and molecular mechanics. Systematic conformational analyses and energy minimizations have been performed for the inhibitor AA 231-1 and its presumed complexes formed during the enzymatic process of inactivation, i.e., the Michaelis complex, the acyl-enzyme, and the inactivated enzyme with the covalently bound inhibitor. The beta-lactam ring characteristics of modeled AA 231-1 were in agreement with crystallographic data of related structures. Lowest energy conformations were found when the angle between the planes of the beta-lactam ring and that of its phenyl substituent was about -60 or 60 degrees. To study the interaction with the enzyme, the enzyme-inhibitor complexes were constructed by docking the inhibitor in the active site using enzyme coordinates from an X-ray crystallographic structure. The whole enzyme structure was used for conformational analyses and energy mechanics. Favorable conformations for the Michaelis complex have been obtained in which the carbonyl oxygen of the inhibitor was located in the oxyanion hole and the hydroxyl of Ser195 was in position to interact with the beta-lactam carbonyl carbon on the alpha face of AA 231-1. Simulations of the approach of the benzylic carbon by the nucleophilic amino acid His40 or His57 through an SN2 displacement on the halomethyl group of AA 231-1 were performed. The results agreed with the alkylation of the imidazole nitrogen N epsilon 2 of His57 leading to the inactivated enzyme (bis-adduct form).

Azetidines↗
PubMed2001

[Modeling corneal topography with a subdivision scheme in keratoconus].

BACKGROUND: Videokeratoscopy is often unable to obtain complete data sets in cases of irregular or asymmetric corneal topography. Subdivision schemes are very common in computer graphics for completion and smoothing of surfaces. Based on a network of triangular facets a smooth and complete surface in a standard coordinate system can be derived from topographic raw data. PATIENTS AND METHODS: We examined 88 patients with keratoconus and 40 normal controls. Polygons and polyhedra were defined from videokeratoscopic height data, and a surface was modeled using a modified butterfly subdivision scheme for a nonuniform sampled grid. To assess the model quality topographic raw data were changed to missing values centrally (at the apex of the cone) and in four midperipheral quadrants. The target value was the root mean square error, comparing the remodeled value of the subdivision scheme to the raw data at the position of the missing values for each group. RESULTS: Due to the nonuniform mesh of our Placido-based topographer we used a dynamic adaptive model and the governing dynamic differential equation. With a single missing value, no difference was detected between normals and patients with keratoconus. For a missing area consisting of 13 raw data points, the remodeling error was significantly higher in patients with keratoconus than in normals. With the neighborhood of 13 missing data points, the apex of the cone was remodeled in both groups of patients with less precision than with the peripheral missing data. CONCLUSION: The locality of the equation systems to be solved and the easy calculation of explicit formulas for the normals may simplify ray-tracing techniques and make subdivision attractive for large datasets in corneal topography even with irregular patterns.

Adult↗
PubMed1995

Analysis of action of the wobble adenine on codon reading within the ribosome.

Computer graphics simulation of the interaction between the codon-anticodon duplexes containing adenine in the first (wobble) position of the anticodons, and bound to the ribosomal A- and P-sites, was made. This demonstrated that widespread use of adenine in the wobble position in anticodons should lead to a low efficiency of ribosomal translation, since the wobble A of the P-site tRNA weakens the codon-dependent binding of aminoacyl-tRNA at the A-site via interduplex interaction. Besides the canonical partner U, the wobble A of aminoacyl-tRNA can recognize A, C, G in the third position of the codon by the formation of the propeller twist in the wobble pairs AA, AC, AG. The conversion of the wobble A into inosine improves its pairing with the codon bases (the pairs IA and IC, unlike AA and AC, should not form the propeller twist leading to the deformation of base-base hydrogen bonds) and should reduce an adverse effect of the P-site wobble adenine on the formation of the A-site duplex. The consequence of the interaction between the ribosomal P- and E-site duplexes has been formulated. According to this the E-site wobble A should enhance the probability of frameshifting. These properties of the wobble A and I could be a reason why A is very rarely observed in the first anticodon position and why evolutionary processes have developed the enzyme which modifies the wobble A to I. The results obtained can be subjected to direct experimental tests.

Adenine↗
PubMed1993

[A graphic presentation of the anesthesiologist's action pattern].

The action patterns of anesthesiologists are different among individuals. We have developed a graphic presentation system for anesthesiologists' action patterns using computer graphics. The resulting representation is called "thought map". Data were obtained from 6 anesthesiologists (4 certified instructors and 2 new doctors) with a time interval of 2 years, regarding the use of 3 drugs (enflurane, sevoflurane and isoflurane). The "maps" were compared among individuals, dates and drugs. The following results were obtained: 1) significant differences existed among individuals, 2) during the 2-year time interval, 2 new drugs were introduced and the practice pattern alterations were seen in the maps, 3) for the 2 new anesthesiologists, the maps show the process of professional knowledge acquisition. We propose an index ("immovable rate"), denoting the proportion of the map where concentration of the drug didn't change. This index is to be used for evaluating human thinking.

Anesthesia, Inhalation↗
PubMed1991

Reliability of cephalometric analysis using manual and interactive computer methods.

This study compares the results of cephalometric analyses using manual and interactive computer graphics methods. Results are statistically in favour of the interactive computer system. This study provides a basis for ongoing research into alternative methods of cephalometric analyses, such as digitization and automatic landmark identification using sophisticated computer vision systems.

Cephalometry↗
PubMed1993

Psyclops: an exploratory graphical system for clinical research and education.

We present Psyclops, an interactive computer graphic system designed to help address a growing information dilemma in the examination of individual psychiatric cases. Ever more information is needed to better understand conscious experience, interpersonal behavior, and the formation of psychiatric signs and symptoms, yet the information load already exceeds our usual methods of handling it. Psyclops consists of a suite of software modules, manual sections, and standards that have been developed according to guiding concepts intended to help one collect, organize, access, and explore complex data about a single subject for research, education, and ultimately, clinical care purposes. This document provides background in clinical information science and a description of the system; the reader interested in its application in clinical research theory development is referred to the companion paper in this issue (Horowitz et al., Pathological Grief: An Intensive Case Study).

Arousal↗
PubMed1988

The modelling of nucleophilic and electrophilic additions to organometallic complexes using molecular graphics techniques.

A new formalism has been developed in order to evaluate intermolecular interaction energies for inorganic and organometallic complexes in the framework of the extended Hückel method. In order to provide the shortest possible response time on an interactive computer graphics facility, this model should require the minimum amount of computer time, which explains why approximate procedures are used to evaluate electrostatic, charge transfer and exchange repulsion components. When applying this model to typical examples of electrophilic addition reactions to organometallic complexes, it is found that it is essential to take account of charge transfer interactions, the electrostatic component alone being not sufficient, even qualitatively, for a proper description of the reaction mechanism. The results, presented as color-coded dot molecular surfaces, show a very good agreement with experiment as to the site of attack, namely (i) on metal for the electrophilic attack on Fe(cp)2, Fe(CO)5 and X(cp)(CO)2, X = Co, Rh; (ii) on the cp ligand for the nucleophilic attack on Co(cp)2+ and Rh(cp)2+; (iii) on bz for the nucleophilic attack on Fe(cp)(bz)+. Finally, modellizations of the nucleophilic attack on a coordinated olefin and of the relation between structure and acidic properties of zeolites are presented and discussed.

Computer Graphics↗
PubMed2001

Multiscale computing.

Multiscale computing (MSC) involves the computation, manipulation, and analysis of information at different resolution levels. Widespread use of MSC algorithms and the discovery of important relationships between different approaches to implementation were catalyzed, in part, by the recent interest in wavelets. We present two examples that demonstrate how MSC can help scientists understand complex data. The first is from acoustical signal processing and the second is from computer graphics.

Computer Graphics↗
PubMed1984

Analyzing and comparing the performance of two real-time playback systems.

A technique used in animated computer graphics involves the use of real-time playback. This method is used when it is not possible to display frames of display code in real-time. Instead, frames are compiled in advance at non realtime rates, saved in secondary storage, and played back at desired realtime speeds. The basic design and operation of two such systems will be considered. The more powerful of the two is built upon an Evans and Sutherland picture System I and utilizes animated vector graphics. The other playback system is built upon a Terak micro computer display and represents an example of rudimentary raster graphics animation. The synchronization, buffering, blocking and man-machine interfaces of both systems are detailed thus spotlighting their operational behavior. A comparison of the two systems show: that similarities in the logical organization of each system exist; that both systems are input bound; and both require their image files to be built on other computer systems. The differences in the performance of the two systems can be attributed to technological differences between the two systems; the retrieval rates of their respective disk subsystems; and differences in the intent and purpose behind the design of each machine. The systems are demonstrated by applying them to chemical modeling. It is determined that playback is a useful technique for examining complicated sequential situations or for providing the concise and convenient representation of large amounts of data.

Computer Graphics↗
PubMed1996

The three-dimensional bone interface of an osseointegrated implant. II: A morphometric evaluation after three months of loading.

To clarify the three-dimensional bone structure around two plasma-sprayed hydroxyapatite-coated titanium implants loaded for 3 months in a monkey, computer graphic evaluation was performed after computer-assisted integration of 70 serial buccolingual sections at 75 microm intervals. Quantitative analysis of the bone contact ratio (BCR) was also conducted with programmed software. The graphics revealed the macroscopic bone structure. The BCR values varied in portions from the top to the bottom of the implant and in the buccolingual or mesiodistal directions. Because these two implants had more cortical bone at the top portion in the lingual direction, the BCR was greatest in the lingual direction. The BCR values at the bottom portion of the two implants were greater than those at the top portions along the horizontal plane, which suggested the effect of loading. The lowest BCR value was observed at the top portion of one implant at a site where moderate periimplant gingivitis was observed. The total surface BCR value for the implants was 69.3% and 64.5%. These results provide additional detailed information on the bone structure around the hydroxyapatite-coated implant after short-term loading.

Animals↗
PubMed1991

A veterinary digital anatomical database.

This paper describes the Veterinary Digital Anatomical Database Project. The purpose of the project is to investigate the construction and use of digitally stored anatomical models. We will be discussing the overall project goals and the results to date. Digital anatomical models are 3 dimensional, solid model representations of normal anatomy. The digital representations are electronically stored and can be manipulated and displayed on a computer graphics workstation. A digital database of anatomical structures can be used in conjunction with gross dissection in teaching normal anatomy to first year students in the professional curriculum. The computer model gives students the opportunity to "discover" relationships between anatomical structures that may have been destroyed or may not be obvious in the gross dissection. By using a digital database, the student will have the ability to view and manipulate anatomical structures in ways that are not available through interactive video disk (IVD). IVD constrains the student to preselected views and sections stored on the disk.

Anatomy, Veterinary↗