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At least 1,027 records · Page 57Linked to original sources
PubMed1999

Three-dimensional computer-simulated prostate models: lateral prostate biopsies increase the detection rate of prostate cancer.

OBJECTIVES: Urologists routinely use the systematic sextant needle biopsy technique to detect prostate cancer. However, recent evidence suggests that this technique has a significant sampling error. We developed a novel three-dimensional (3D) computer-assisted prostate biopsy simulator based on whole-mounted step-sectioned radical prostatectomy specimens to compare the diagnostic accuracy of various prostate needle biopsy protocols. METHODS: We obtained digital images of 201 step-sectioned whole-mounted radical prostatectomy specimens. 3D computer simulation software was developed to accurately depict the anatomy of the prostate and all individual tumor foci. Additional peripheral devices were incorporated into the system to perform interactive prostate biopsies. We obtained 18 biopsies of each prostate model to determine the detection rates of various biopsy protocols. RESULTS: The 10- and 12-pattern biopsy protocols had a 99.0% detection rate; the traditional sextant biopsy protocol rate was only 72.6%. The 5-region biopsy protocol had a 90.5% detection rate and the 14-pattern, which includes all the biopsies used in the patterns above, only added 1 additional positive case (99.5%). Transitional zone and seminal vesicle biopsies did not result in a significantly increased detection rate when added to the patterns above. Only one positive model was obtained when the transitional zone biopsies were added. The lateral sextant pattern had a detection rate of 95.5%, and the 4-pattern lateral biopsy protocol had a 93.5% detection rate. CONCLUSIONS: Our results suggest that all the biopsy protocols that use laterally placed biopsies based on the 5-region anatomic model are superior to the routinely used sextant prostate biopsy pattern. Lateral biopsies in the mid and apical zones of the gland are the most important.

Biopsy, Needle↗
PubMed1996

The cell sectioning model. Nuclear/cytoplasmic ratio studied by computer simulation.

OBJECTIVE: Stereologic analysis can be supported using methods of modeling and simulation. To illustrate the use of a mathematical cell sectioning model (CSM) in predicting two-dimensional (2-D) measurement characteristics of sectioned cells by means of computer-assisted simulation, the present study was performed. STUDY DESIGN: Computer software based on the CSM was developed to simulate 2-D nuclear/cytoplasmic (N/C) ratio distributions and to test the sensitivity of the parameter to several factors. Simulations were performed with the following feature set for cells of simulated populations: (1) size, shape (approximated by an ellipsoid of rotation) and orientation of the cell, and (2) size, shape and intracellular position of the nucleus. RESULTS: The computer tests showed that the value of the 2-D N/C ratio depends upon many factors; the real three-dimensional N/C ratio is only one. Statistical characteristics of a 2-D N/C ratio sample were found to be sensitive to changes in (1) the nuclear position inside the cell, (2) cell shape, and (3) orientation of the asymmetric cell with respect to a cutting plane. CONCLUSION: CSM tests demonstrated the model validity of and potentials for using it as an algorithm for morphometry software. Taking into account the sensitivity of the 2-D N/C ratio parameter to various factors, great care must be used in interpreting its observations.

Animals↗
PubMed2004

Computational simulation of therapeutic parent artery occlusion to treat giant vertebrobasilar aneurysm.

We applied computational fluid dynamics (CFD) analysis to assess 3D digital subtraction angiography findings in a patient with a giant vertebrobasilar aneurysm to simulate and compare the consequences of left and right vertebral artery occlusion. The balloon occlusion test suggested that occlusion of the right vertebral artery is the better way to treat this patient's aneurysm from the point of view of aneurysmal thrombosis and isolation from the circulation. The computer simulation supported this conclusion, at the same time indicating that from the point of view of pressure distribution on the wall of the aneurysm, the right vertebral occlusion may be also accompanied by an undesirable effect. A high-pressure area on the aneurysm wall in systole was revealed. This high pressure potentially could lead to subsequent aneurysmal growth, which indeed occurred, as was revealed by a follow-up examination 6 months later. This study is a good example of possible future applications of CFD in patients with cerebrovascular disease before therapeutic intervention.

Aged↗
PubMed1991

Computer simulation of Boophilus cattle tick (Acari: Ixodidae) population dynamics.

A comprehensive computer model was developed for simulation of the population dynamics of the cattle ticks, Boophilus microplus (Canestrini) and B. annulatus (Say). The model is deterministic and based on a dynamic life table with weekly time steps. The model simulates the effects of major environmental variables, such as ambient temperature, saturation deficit, precipitation, type of pasture, type of cattle, and cattle density on Boophilus cattle tick population dynamics. General validity of the model is established by comparing simulated and observed yearly densities of standard female ticks/host/day. B. microplus population comparisons were made for a series of years using weekly weather data from two locations in Queensland, Australia. The model also produced acceptable values for initial population growth rate, generation time, and 3-yr population density when historical weather at 7 locations in Australia and 23 locations in the Americas were used. This model provides a framework for the study of Babesia transmission by Boophilus ticks, and can be used to study the effects of control technologies and to develop more efficient and environmentally acceptable eradication strategies for Boophilus ticks.

Animals↗
PubMed1999

Computational simulation of flows in an entire centrifugal heart pump.

A prototype computational code to numerically simulate the blood flows in an entire centrifugal heart pump has been developed. The unsteady incompressible Navier-Stokes equations are solved on a parallel computer, the Cray T3E. By domain decomposition, the whole flow space is decomposed to a number of subdomains for each of which a structured algebraic grid is assigned. The grids for the inlet eye and blade regions are on the rotating frame while grids for other regions are on the nonrotating frame, and the edge of the rotating grids slides over the edge of the nonrotating frame, and the edge of the rotating grids slides over the edge of the nonrotating grids. The code is able to simulate the flows in the rotor, volute, and diffuser as well as to find pump performance indicators. The present paper presents an overview of the code and describes a study on the effect of volute width.

Algorithms↗
PubMed1994

A computer simulation of the hypothalamic-pituitary-adrenal axis.

This paper describes the construction of a computer model that simulates the hypothalamic-pituitary-adrenal axis (HPA axis) regulation of cortisol production. It is presented to illustrate the process of physiological modeling using standard "off the shelf" technologies. The model simulates components of the HPA axis involved in the continuous secretion and elimination of cortisol, adrenocorticotropin (ACTH), and corticotropin releasing hormone (CRH). The physiological relations of these component pieces were modeled based on the current knowledge of their functioning. Rate constants, half lives, and receptor affinities were assigned values derived from the experimental literature. At its current level of development the model is able to accurately simulate the timing, magnitude and decay of the ACTH and cortisol concentration peaks resulting from the ovine-CRH stimulation test in normal and hypercortisolemic patients. The model will be used to predict the effects of lesions in different components of the HPA axis on the time course of cortisol and ACTH levels. We plan to use the model to explore the experimental conditions required to distinguish mechanisms underlying various disorders of the HPA axis, particularly depression. Efforts are currently underway to validate the model for a large variety of normal and pathological perturbations of the HPA axis.

Adrenocorticotropic Hormone↗
PubMed1991

Real time computer simulation of transmission electron microscope images with tilted illumination: grain boundary applications.

Computer programs have been developed to simulate electron microscope images from digitized graphically represented model structures. Via a television rate image processing system, these programs allow real time, interactive modification of the microscope objective lens parameters, incident beam inclination, and incident beam energy. In addition to explaining the computational methods, the need for using tilted beam illumination is explored to extend microscope resolution. For this study, the subject of grain boundary imaging is analyzed for a copper sigma = 5, 36.9 degrees, (310) tilt boundary with a [001] common rotation axis. The Cu [200] lattice spacings of approximately 1.8A on both sides of the interface cannot be reliably resolved under axial illumination conditions in a 200 kV microscope. Therefore, either tilted beam modes or higher incident beam energies were explored and the types of image features correlated with atomic position data through the digital frame store system.

Computer Simulation↗
PubMed2001

[Computer simulation for infrared spectra of pollution clouds with FTIS remote detection].

A computer model of radiometric scene simulation for simulated spectra for pollution clouds in complicated environment is proposed. The model is used to introduce the effects of an actual hazardous pollution clouds, such as (CH3)2CHO(CH3)FPO or (CLCH2CH2)2S, into exiting measured background spectra by passive Fourier transform infrared spectrometer (FTIS). The simulated results agree well with the experimental results.

Air Pollutants↗
PubMed1994

Computer simulation for teaching synaptic potential.

An interactive simulation of neuronal synaptic potential is presented. The set-up comprises of two synaptic terminals and one postsynaptic membrane from which the intracellular potential is recorded. Certain parameters are interactively changeable by the user. For example, each synaptic terminal may cause changes in the membrane conductance to sodium, potassium, or chloride ions, or some combinations of them. One synaptic terminal may be turned on/off to allow study of the spatio-temporal summation of postsynaptic potentials with adjustable delay. The postsynaptic membrane may also be set at various values in order to study the effects of membrane potentials on the direction and magnitude of postsynaptic potentials. This simulation has been used with some success as an aid for teaching cellular neurophysiology.

Computer Simulation↗
PubMed1990

Optimization of an isocratic reversed phase liquid chromatographic system for the separation of fourteen steroids using factorial design and computer simulation.

An optimization strategy for an isocratic reversed phase high performance liquid chromatographic system (RP-HPLC) is described. Factorial design and a computer program are used to predict the retention time and resolution of fourteen steroids. An optimized rapid (less than 25 min) isocratic RP-HPLC system for the satisfactory separation of cortisone, cortisol, corticosterone, 11-deoxycortisol, 11-deoxycorticosterone, 17 alpha-hydroxyprogesterone, progesterone, androstenedione, testosterone, estrone, estradiol, estriol, prednisone acetate and dexamethasone acetate has been developed using this strategy through eight experiments.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Computer simulation of fluid resuscitation in trauma. I. Description of an extensive pathophysiological model and its first validation.

Computer-based 'patient simulators' are of a potential value in diagnosis, monitoring and therapy of the severely ill patient with trauma. An extensive pathophysiological model is described and documented in full detail. The model makes it possible to calculate and predict clinically important state variables on the basis of fluid input and fluid losses. Sample runs are presented for illustrations in hemorrhage, fluid and salt loading.

Animals↗
PubMed1994

Computer simulated evolution of a network of cell-signaling molecules.

We have trained a computer model of a simple cell-signaling pathway to give specified responses to a pulse of an extracellular ligand. The pathway consists of two initially identical membrane receptors, each of which relays the concentration of the ligand to the level of phosphorylation of an intracellular molecule. Application of random "mutational" changes to the rate constants of the pathway, followed by selection in favor of certain outputs, generates a variety of wave forms and dose-response curves. The phenotypic effect of mutations and the frequency of selection both affect the efficiency with which the pathway achieves its target. When the pathway is trained to give a maximal response at a specific concentration of the stimulating ligand, it gives a consistent pattern of changes in which the two receptors diverge, producing a high-affinity form with excitatory output and a low-affinity form with inhibitory output. We suggest that some high- and low-affinity forms of receptors found in present-day cells might have originated by a similar process.

Algorithms↗
PubMed2000

Computer simulation and geometric design of endarterectomized carotid artery bifurcations.

The main goal of this computational study is to establish surgical guidelines for optimal geometries of carotid endarterectomy reconstructions that may measurably reduce postoperative complications, that is, thrombosis, stroke, and/or restenosis. The underlying hypotheses are that nonuniform hemodynamics, or "disturbed flows," are linked to arterial diseases and consequently that minimization of "disturbed flow" indicators leads to geometric bifurcation designs that lower postoperative complication rates. Considering transient 3-D laminar blood flow in partially occluded, in-plane, rigid-wall carotid artery bifurcations, the results presented include time-averaged indicators of "disturbed flow", such as the wall shear stress, spatial wall shear stress gradient, and wall shear stress angle deviation. In addition, trajectories and deposition patterns of critical blood particles (i.e., monocytes) are shown and evaluated. Within given physiological constraints, the vessel geometry was then changed in order to reduce the magnitudes of key indicators associated with thrombosis (i.e., blood clot formation) or restenosis (e.g., renewed atherosclerosis and/or hyperplasia). The quantitative results and knowledge base generated will be crucial for future clinical trials.

Blood Flow Velocity↗
PubMed2004

Computer simulator training enhances the competency of gastroenterology fellows at colonoscopy: results of a pilot study.

OBJECTIVES: Computer-based colonoscopy simulation (CBCS) is being utilized in endoscopy training without supporting evidence that it improves patient-based colonoscopy performance. The goal of this pilot study was to determine if CBCS training improves gastroenterology (GI) fellows' patient-based colonoscopy skills. METHODS: Competency at colonoscopy among 4 novice GI fellows who completed a 6-h CBCS curriculum was compared with 4 novice fellows who were not CBCS-trained. Measurements of competency were rendered by supervising faculty by recording "insertion time,""depth of unassisted insertion,""independent procedure completion,""ability to identify endoscopic landmarks,""inserts in a safe manner,""adequately visualizes mucosa on withdrawal," and "responds appropriately to patient discomfort" with each colonoscopy. RESULTS: Simulator-trained fellows outperformed traditionally trained fellows during their initial 15 colonoscopies in all performance aspects except "insertion time" (pp < 0.05). Simulator-trained fellows inserted the endoscope significantly further and reached the cecum independently nearly twice as often during this early training period. Three parameters ("depth of insertion,""independent completion," and "ability to identify landmarks") demonstrated a continued advantage out to 30 colonoscopies. Beyond 30 procedures, there was no difference in the performance of the two groups. CONCLUSION: In this pilot study, a 6-h CBCS curriculum provides an early training advantage by enhancing competency at the early stages of patient-based colonoscopy. These advantages are negligible after approximately 30 patient-based procedures. CBCS-enhanced training may allow faculty to be more efficient with their colonoscopy practice.

Clinical Competence↗
PubMed1998

Effects of myocardial fiber orientation in echocardiography: quantitative measurements and computer simulation of the regional dependence of backscattered ultrasound in the parasternal short-axis view.

We measured the regional disparity in backscattered ultrasound by means of obtaining integrated backscatter images of 10 healthy subjects and placing a region of interest in 18 distinct positions. A computer model simulating the short-axis view was implemented on the basis of previously measured values for the anisotropic ultrasonic properties of myocardium. Measurements showed that the integrated backscatter value was greatest for the anterior septum and decreased by 15.9 +/- 3.5 dB for the lateral wall and 17.7 +/- 3.5 dB for the inferior septum. The value in the posterior wall was 8.1 +/- 3.8 dB below the value for the anterior septum. The regional variation of backscatter predicted with the simulation correlated well with the clinical measurements. These results suggested that analyses based on measurements of backscatter may require compensation for the inherent anisotropic properties of myocardium.

Adult↗
PubMed1996

Mathematical model for chemically induced lipid peroxidation in precision-cut liver slices: computer simulation and experimental calibration.

A biologically based pharmacodynamic (BBPD) model was developed in order to describe and simulate chemically induced lipid peroxidation in precision cut mouse liver slices. The model was written in Advanced Continuous Simulation Language (ACSL) and simulations were performed using SIMUSOLV software on a VAX/VMS mainframe computer. The BBPD model simulated formation of lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS) over time as a function of the amounts of cytochrome P450 (CYP)-activated chemical inducer and active antioxidants. The rate of peroxidation was controlled by lipid peroxidizability, destruction of CYP, autooxidation, and activity of glutathione peroxidase. The BBPD model was initially parameterized with the literature data for TBARS formation during lipid peroxidation, reported for rat liver slices induced with bromotrichloromethane and tert-butyl hydroperoxide (TBOOH). Then, the biochemical parameters were adjusted to reflect the physiology of the mouse liver, and the BBPD model was used to simulate TBARS formation during lipid peroxidation in precision cut mouse liver slices induced with TBOOH. The BBPD model predictions were in agreement with the experimental data.

Animals↗