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At least 883 records · Page 49Linked to original sources
PubMed2003

An advanced approach for computer modeling and prototyping of the human tooth.

This paper presents a systematic and practical method for constructing accurate computer and physical models that can be employed for the study of human tooth mechanics. The proposed method starts with a histological section preparation of a human tooth. Through tracing outlines of the tooth on the sections, discrete points are obtained and are employed to construct B-spline curves that represent the exterior contours and dentino-enamel junction (DEJ) of the tooth using a least square curve fitting technique. The surface skinning technique is then employed to quilt the B-spline curves to create a smooth boundary and DEJ of the tooth using B-spline surfaces. These surfaces are respectively imported into SolidWorks via its application protocol interface to create solid models. The solid models are then imported into Pro/MECHANICA Structure for finite element analysis (FEA). The major advantage of the proposed method is that it first generates smooth solid models, instead of finite element models in discretized form. As a result, a more advanced p-FEA can be employed for structural analysis, which usually provides superior results to traditional h-FEA. In addition, the solid model constructed is smooth and can be fabricated with various scales using the solid freeform fabrication technology. This method is especially useful in supporting bioengineering applications, where the shape of the object is usually complicated. A human maxillary second molar is presented to illustrate and demonstrate the proposed method. Note that both the solid and p-FEA models of the molar are presented. However, comparison between p- and h-FEA models is out of the scope of the paper.

Anatomy, Cross-Sectional↗
PubMed1984

[A computer model for the simulation of intra-arterial tumor therapy in the area of the external carotid artery].

The complex theoretical background of intra-arterial (i.a.) tumour therapy induced the installation of a computer assisted model based on the use of 7 variables, the most important factors being the blood flow of the infused organ and the clearance of the drug, as well as the tissue binding of the drug. Various relevant conditions of i.a. infusion are represented by simple but typical diagrams allowing quick orientation on the principles governing i.a. infusion even for those who are not very familiar with the theoretical background of i.a. infusion. The model represents an improvement in the individual planning of effective i.a. chemotherapy.

Antineoplastic Agents↗
PubMed1998

Aortic and hepatic contrast medium enhancement at CT. Part I. Prediction with a computer model.

PURPOSE: To develop a physiologic model of contrast medium enhancement by incorporating available physiologic data and contrast medium pharmacokinetics and to predict organ-specific contrast medium enhancement at computed tomography (CT) with various contrast medium injection protocols in patients of variable height and weight. MATERIALS AND METHODS: A computer-based, compartmental model of the cardiovascular system was generated by using human physiologic parameters and more than 100 differential equations to describe the transport of contrast medium. Blood volume, extracellular fluid volume, and regional blood flow were estimated from available data. Local structures were modeled mathematically to describe the distribution and dispersion of intravascularly administered iodinated contrast medium. A global model was formed by integrating regional circulation parameters with the models of local structures. Aortic and hepatic CT contrast-enhancement curves were simulated for three protocols and were compared with mean enhancement curves in three groups of 25-28 patients (80 patients total; 28 in one group, 25 in one group, and 27 in one group) receiving the same protocols. The percent difference in maximum enhancement between the simulated and empiric curves and the enhancement difference index (sum of the area difference between the simulated and empiric curves divided by the total area under the empiric curve) were computed. RESULTS: The simulated and empiric enhancement curves closely agreed in maximum enhancement (the mean percent difference in the aorta was 7.4%; liver, 4.8%) and in variation over time (mean enhancement difference index in the aorta was 11.6%; liver, 12.7%). CONCLUSION: A computer-based, physiologic model that may help predict organ-specific CT contrast medium enhancement for different injection protocols was developed. Such a physiologic model may have many clinical applications.

Adult↗
PubMed1998

Computer modeling of size and shape descriptors of alpha 1-adrenergic receptor antagonists and quantitative structure-affinity/selectivity relationships.

Computational chemistry and molecular modeling procedures allow us to define and compute ad hoc size and shape descriptors on the different prototropic forms assumed by drugs in biotest solutions. Together with experimental data measured on a well-identified target receptor, these descriptors are essential elements for obtaining simple, consistent, comparable, and easily interpretable theoretical quantitative structure-activity relationship (QSAR) models based on the ligand similarity-target receptor complementarity paradigm. In this context, quantitative size and shape affinity/subtype selectivity relationships have been modeled for a large set of very heterogeneous alpha 1a-, alpha 1b-, and alpha 1c-adrenergic receptor antagonists. The linear QSAR models generated have been validated by predicting both binding affinity and selectivity of a test set of noncongeneric antagonists. The satisfactory results obtained highlight both the simplicity and the versatility of the approach presented.

Adrenergic alpha-Antagonists↗
PubMed1989

Computer modeling of sheep reproduction: II. Accelerated reproduction in sheep.

A computer simulation program was written in SLAM (Simulation Language for Alternative Modeling) to simulate certain biological aspects involved in alternative systems of reproduction in sheep. Four fundamental lambing schemes, once a year, three times in 2 yr, twice a year and continuous schemes, along with modifications of these schemes, are simulated. Parameters of greatest effect in this simulation were the average spread of the estrous season (SA), the measure of asymmetry (SD) and the maximum proportion of ewes exhibiting estrus (MX). It was demonstrated that the greater the SA values (longer estrous seasons and shorter anestrous seasons), the more advantageous it was to breed frequently. The SD and MX parameters influenced to a lesser degree the lambing results obtained from these simulations. The relative merits of certain breeds and locations for out-of-season breeding were studied and evaluated for annual and seasonal fertility.

Algorithms↗
PubMed1996

The use of a computer model to simulate epithelial pathologies.

The complexity of the interactions of the many rules governing cell behaviour and the changes that lead to the pathological features seen in disease is such that linking cause and effect can be very difficult. However, the use of computers to model normal biological and pathological processes provides a powerful technique for studying the effects of the interactions of a variety of biological rules. Such an approach is strengthened by using a graphical display that simulates the organization of cells in a tissue. Skin, and specifically the epidermis, is characterized by a regular morphology and the ability to regenerate itself throughout adult life and there are considerable biological data available on the normal and pathological process that affect this organ. A model of normal skin has been developed which shows a structure similar to normal epidermis and is capable of healing itself if damaged. This paper describes the effects on the overall structure of introducing mutations to individual rules in the model. Changes that alter cell proliferation or differentiation are introduced and the effects that these produce are compared with epidermal pathologies. Even a simple model is capable of producing insights into the types of events that may occur in a variety of dermatopathological conditions.

Basement Membrane↗
PubMed1994

A computer model for simulating ultrasonic scattering in biological tissues with high scatterer concentration.

Scattering of ultrasonic waves by biological tissues at different scatterer concentrations is investigated using one- and two-dimensional computer simulation models. The backscattered power as a function of scatterer concentrations is calculated using two types of incident waves, a Gaussian shaped pulse and a continuous wave (CW). The simulation results are in good agreement with the Percus-Yevick packing theory within the scatterer concentrations, from 0% to 100% in one-dimensional (1D) space, and 0% to 46% in two-dimensional (2D) space. In all cases, the simulation results from a pulsed incident wave show a much smaller standard deviation (SD) than those from an incident CW. The simulation can serve as a useful tool to verify scattering theories, simulate different experimental conditions, and to investigate the interaction between the scatterer properties and the scattering of ultrasonic waves. More importantly, the 2D simulation procedure serves as an initial step toward the final realization of a true three-dimensional (3D) simulation of ultrasonic scattering in biological tissues.

Blood↗
PubMed2003

Interdependent effect of P-glycoprotein-mediated drug efflux and intracellular drug binding on intracellular paclitaxel pharmacokinetics: application of computational modeling.

Intracellular concentration of paclitaxel is determined by the extracellular drug concentration, the level of the mdr1 P-glycoprotein (Pgp), and binding to intracellular proteins including tubulins/microtubules. The present study used a computational method to examine the effects of these factors, singly and in combination, on intracellular paclitaxel pharmacokinetics. The study was performed using our previously described intracellular pharmacokinetic model. The parameters representing Pgp-mediated drug efflux and intracellular drug binding (i.e., number of Pgp and binding sites and binding affinity) were altered systematically and used to generate computer simulations depicting the intracellular paclitaxel pharmacokinetics at clinically relevant extracellular (e.g., plasma) drug concentrations. The simulation results indicate that all four factors played a role in determining the intracellular drug accumulation. The rank order of the importance of these parameters was extracellular drug concentration >> intracellular binding capacity > intracellular binding affinity > Pgp expression. The results further showed that omission of one or more of these factors in the experimental design would lead to erroneous conclusions on the importance of other factors, as simultaneous changes in more than one parameter altered the relative importance and offset the effects of other parameters. In summary, results of the present study demonstrate the use of computational modeling to depict the effects of biological parameters such as drug efflux transporters, drug binding sites, and binding affinity on intracellular accumulation and retention of drugs that bind to cellular components.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1984

A computer model simulating the intestinal absorption of bile acids.

Mathematical models were developed for assessment of the absorption kinetics of compounds passing down the length of a perfused intestinal segment. The models considered the intestinal segment as a cylinder composed of a large number of very small (infinitesimal) cylinders and described the concentration decline of the compound in situations with active, passive and combined active and passive transport. The maximal velocity of active transport, Vmax, the Michaëlis-Menten constant, Km, and the permeability coefficient, P, were calculated. A computer program was developed to operate the mathematical expressions. The models were validated by jejunal and ileal perfusions of various bile acids in six healthy volunteers. The fit between the mathematical models and the actually measured data showed an average standard deviation of 0.14 mmol/l (substrate infusion concentration ranging from 0.25 mmol/l to 3.0 mmol/l). It was concluded that the computer models were feasible for practical purposes. Moreover, the models reduced the number of perfusions necessary to determine the absorption kinetics of a given bile acid.

Adult↗