A new approach to planning in vitro and in vivo experiments for cardiovascular stents. (1) Fundamentals of design procedures

Copyright @ 2000 Pacini Editore SpAWhile the use of cardiovascular stents is internationally widespread re-stenosis remains a common problem. There are a number of different designs, and this project seeks for design improvements leading to a reduction in re-stenosis rates. The haemodynamics of the stent as used in a patient is viewed as one of the major concerns, and the authors have already applied Computational Fluid Dynamics in investigating this. In this more comprehensive study, however, the novel approach of applying two formal engineering design procedures is used, namely Genetic Algorithms (GA) and Robust Engineering Design (RED). In this paper, the two procedures are explained and compared in the context of their application to the design of stents

A new approach to planning in vitro and in vivo experiments for cardiovascular stents. (2) Planning of experiments

Copyright @ 2000 Pacini Editore SpAWithin our overall project to improve the design of stents in terms of reduced rates of re-stenosis, there are three main methods, namely computer simulation and in vitro and in vivo experiments. These methods are closely integrated using contemporary design procedures described below, especially to accommodate patient-to-patient variation. Clinical experience shows that a small variation has considerable effects on flow characteristics of stents and in engineering terms may be described as a ‘geometric risk factor’. The Robust Engineering Design procedure readily incorporates this factor which may thus become a component feature in our experimental planning. We envisage that this approach could be applied to other invasive implants with a view to enhancing their quality

A new approach to planning in vitro and in vivo experiments for cardiovascular stents – II. Planning of experiment (abstract)

Within our overall project to improve the design of stents in terms of reduced rates of re-stenosis, there are three main methods, namely computer simulation and in vitro and in vivo experiments. These methods are closely integrated using contemporary design procedures described below, especially to accommodate patient-to-patient variation. Clinical experience shows that a small variation has considerable effects on flow characteristics of stents and in engineering terms may be described as a ‘geometric risk factor’. The Robust Engineering Design procedure readily incorporates this factor which may thus become a component feature in our experimental planning. We envisage that this approach could be applied to other invasive implants with a view to enhancing their quality

Computational fluid dynamics benchmark dataset of airflow in tracheas

Computational Fluid Dynamics (CFD) is fast becoming a useful tool to aid clinicians in pre - surgical planning through the ability to provide inform ation that could otherwise be extremely difficult if not impossible to obtain. However, in order to provide clinically relevant metrics, the accuracy of the computational method must be sufficiently high. There are many alternative methods employed in the process of performing CFD simulations within the airways, including different segme ntation and meshing strategies, as well as alternative approaches to solving the Navier - Stokes equations. However, as in vivo validation of the simulated flow patter ns within the airways is not possible, little exists in the way of validation of the various simulation techniques. The data presented here consists of very highly resolved flow data. The degree of resolution is compared to the highest necessary resolution s of the Kolmogorov length and time scales. Therefore this data is ideally suited to act as a benchmark case to which cheaper comput ational methods may be compared. A dataset and solution setup for one such more efficient method, large eddy simulation (LES ), is also presented

Voxel-based modeling of airflow in the human nasal cavity

This paper describes the simulation of airflow in human nasal airways using voxel-based modeling characterized by robust, automatic, and objective grid generation. Computed tomography scans of a healthy adult nose are used to reconstruct 3D virtual models of the nasal airways. Voxel-based simulations of restful inspiratory flow are then performed using various mesh sizes to determine the level of granularity required to adequately resolve the airflow. For meshes with close voxel spacings, the model successfully reconstructs the nasal structure and predicts the overall pressure drop through the nasal cavity

Realistic numerical simulations of diffusion tensor cardiovascular magnetic resonance: the effects of perfusion and membrane permeability

Purpose To study the sensitivity of diffusion tensor cardiovascular magnetic resonance (DT-CMR) to microvascular perfusion and changes in cell permeability. Methods Monte Carlo (MC) random walk simulations in the myocardium have been performed to simulate self-diffusion of water molecules in histology-based media with varying extracellular volume fraction (ECV) and permeable membranes. The effect of microvascular perfusion on simulations of the DT-CMR signal has been incorporated by adding the contribution of particles traveling through an anisotropic capillary network to the diffusion signal. The simulations have been performed considering three pulse sequences with clinical gradient strengths: monopolar stimulated echo acquisition mode (STEAM), monopolar pulsed-gradient spin echo (PGSE), and second-order motion-compensated spin echo (MCSE). Results Reducing ECV intensifies the diffusion restriction and incorporating membrane permeability reduces the anisotropy of the diffusion tensor. Widening the intercapillary velocity distribution results in increased measured diffusion along the cardiomyocytes long axis when the capillary networks are anisotropic. Perfusion amplifies the mean diffusivity for STEAM while the opposite is observed for short diffusion encoding time sequences (PGSE and MCSE). Conclusion The effect of perfusion on the measured diffusion tensor is reduced using an increased reference b-value. Our results pave the way for characterization of the response of DT-CMR to microstructural changes underlying cardiac pathology and highlight the higher sensitivity of STEAM to permeability and microvascular circulation due to its longer diffusion encoding time