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At least 1,063 records · Page 59Linked to original sources
PubMed2004

Construction of realistic branched, three-dimensional arteries suitable for computational modelling of flow.

Routinely performed biplane digital coronary angiograms were used to construct a three-dimensional model of the coronary arteries. The technique took the images and automatically picked the centreline and radii in each. By reading the information contained in the DICOM format, the rotation angle between the two images could be ascertained, and the centreline in three dimensions could be determined. Once the centreline and radii had been calculated, a finite volume mesh of the artery was constructed that could be used as input into a fluid dynamics package that solves Navier-Stokes equations. A four-section method was adopted for constructing the mesh, utilising three tubular segments and a small junction section. The tubes were constructed automatically, and the junction procedure was semi-automated, maximising user-control over this region. A structured mesh was used for the tubes, and an unstructured mesh was used to model accurately the irregular shape of the junction. The accuracy of the reconstruction method was established by projection of a mesh onto an independent image of the same artery and the use of a coronary phantom. These tests, along with calibration of the edge detection, established an error of less than 2% in the model.

Coronary Angiography↗
PubMed1991

How do geometric factors influence epidural spinal cord stimulation? A quantitative analysis by computer modeling.

Effects of both anatomic and electrode geometry on the recruitment of rostrocaudal fibers in the spinal cord were investigated by computer simulation of epidural spinal cord stimulation. A three-dimensional model was used, representing the geometry and electrical conductivity of the spinal cord and surrounding tissues, in combination with a model representing the electrical properties of a myelinated nerve fiber. Recruitment contours in the dorsal columns were calculated at various spinal geometries as a function of electrode position, combination and area. Cathodal position appeared to be most significant. Recruitment areas resulting from different contact combinations of a mediodorsal array were almost identical. It was shown that perception threshold largely depends on both dorsal cerebrospinal fluid width and fiber size. The usual bipolar contact separation appeared to approximate the theoretically optimal value, resulting in maximum fiber recruitment at minimum stimulus.

Analgesia, Epidural↗
PubMed1997

CELSS-3D: a broad computer model simulating a controlled ecological life support system.

CELSS-3D is a dynamic, deterministic, and discrete computer simulation of a controlled ecological life support system (CELSS) focusing on biological issues. A series of linear difference equations within a graphic-based modeling environment, the IThink program, was used to describe a modular CELSS system. The overall model included submodels for crop growth chambers, food storage reservoirs, the human crew, a cyanobacterial growth chamber, a waste processor, fixed nitrogen reservoirs, and the atmospheric gases, CO, O2, and N2. The primary process variable was carbon, although oxygen and nitrogen flows were also modeled. Most of the input data used in CELSS-3D were from published sources. A separate linear optimization program, What'sBest!, was used to compare options for the crew's vegetarian diet. CELSS-3D simulations were run for the equivalent of 3 years with a 1-h time interval. Output from simulations run under nominal conditions was used to illustrate dynamic changes in the concentrations of atmospheric gases. The modular design of CELSS-3D will allow other configurations and various failure scenarios to be tested and compared.

Atmosphere↗