611 research outputs found
Multidisciplinary and multiobjective design optimisation of coronary stents
No full textCoronary stents are tubular type scaffolds that are deployed, using an inflatable balloon on a catheter, most commonly to recover the lumen size of narrowed (diseased) arterial segments. Even though numerous stent designs, of varying geometrical and material complexity, are used in clinical practice today, the adverse biological responses post-stenting are not completely eliminated. In-stent restenosis (IR), reduction in lumen size due to neointima formation within 12 months of procedure, and stent thrombosis (ST), formation of a blood clot inside a stented vessel, are the two most common adverse responses to stents. Such adverse responses are multifactorial and their causes are not completely understood. However, the geometric design of a stent, which is a common differentiating factor between the numerous commercially available stents, is known to be a key factor influencing adverse responses. In light of the above, this thesis exploits stent geometry parameterisation in both constrained and multiobjective optimisation. Gaussian process surrogate modelling is used to cost effectively (a) understand the influence of stent geometry parameters on metrics indicating adverse response, and (b) obtain families of stent designs which are potentially more resistant to such responses.Various computational models are developed to evaluate the efficacy of a stent in terms of the factors influencing the adverse responses. In particular, two finite element analysis (FEA) models and two computational fluid dynamics (CFD) models are developed. The FEA models are used to simulate the balloon-expansion of stents in a representative coronary artery and bending of stents on application of bending moments. On the other hand, the CFD models simulate haemodynamic flow in the stented artery and the associated drug-release into the tissue. The expansion FEA models are validated against manufacturer provided pressure-diameter relationship and the flexibility FEA models are validated against the numerical studies found in literature. The numerical models are then used to extract metrics which are related to the adverse responses. Six metrics are formulated: (i) acute recoil, which measures the radial strength of the stent; (ii) volume average stress, which measures potential arterial injury caused by the stenting procedure; (iii) haemodynamic low and reverse index, which measures the haemodynamic alteration relevant to IR; (iv) volume average drug, which measures the amount of anti-proliferative drug delivered into the tissue; (v) drug deviation, which measures the uniformity of drug-distribution in the tissue; and (vi) flexibility metric, which measures the deliverability of the stent. These metrics are then used to compare the performance of different geometric stent designs. Two parameterisation techniques – one for a generic ring and link topology of stents, and one for the commercial CYPHER (Cordis corporation, Johnson & Johnson company) – are proposed to study the effect of geometrical variation in stent design on the formulated metrics of efficacy. These techniques are then combined with surrogate modelling to perform stent design optimisation studies and study the effect of stent geometry on the evaluation metrics. Finally, three paradigms to choose optimal stent designs from a set of non-dominated solutions, in terms of the evaluation metrics, are proposed, and optimal designs under such paradigms are identified.The last part of this thesis concerns surrogate assisted optimisation, and is not specific to the problem of stent design. Here, the use of analytically available gradient information in widely used Kriging predictors is explored. A search algorithm to locate all stationary points of a Krig, using a combination of an iterative sequence of the Krig derivative and a low-discrepancy sequence is proposed
Geometry parameterization and multidisciplinary constrained optimization of coronary stents
No full textCoronary stents are tubular type scaffolds that are deployed, using an inflatable balloon on a catheter, most commonly to recover the lumen size of narrowed (diseased) arterial segments. A common differentiating factor between the numerous stents used in clinical practice today is their geometric design. An ideal stent should have high radial strength to provide good arterial support post-expansion, have high flexibility for easy manoeuvrability during deployment, cause minimal injury to the artery when being expanded and, for drug eluting stents, should provide adequate drug in the arterial tissue. Often, with any stent design, these objectives are in competition such that improvement in one objective is a result of trade-off in others. This study proposes a technique to parameterize stent geometry, by varying the shape of circumferential rings and the links, and assess performance by modelling the processes of balloon expansion and drug diffusion. Finite element analysis is used to expand each stent (through balloon inflation) into contact with a representative diseased coronary artery model, followed by a drug release simulation. Also, a separate model is constructed to measure stent flexibility. Since the computational simulation time for each design is very high (approximately 24 h), a Gaussian process modelling approach is used to analyse the design space corresponding to the proposed parameterization. Four objectives to assess recoil, stress distribution, drug distribution and flexibility are set up to perform optimization studies. In particular, single objective constrained optimization problems are set up to improve the design relative to the baseline geometry—i.e. to improve one objective without compromising the others. Improvements of 8, 6 and 15% are obtained individually for stress, drug and flexibility metrics, respectively. The relative influence of the design features on each objective is quantified in terms of main effects, thereby suggesting the design features which could be altered to improve stent performance. In particular, it is shown that large values of strut width combined with smaller axial lengths of circumferential rings are optimal in terms of minimizing average stresses and maximizing drug delivery. Furthermore, it is shown that a larger amplitude of the links with minimum curved regions is desirable for improved flexibility, average stresses and drug deliver
Multi-objective design optimisation of coronary stents
No full textThis study presents the first multi-objective and multi-disciplinary coronary stent design optimization study of its kind. Coronary stents are tubular, often mesh-.like, structures which are deployed in diseased (stenosed) artery segments to provide a scaffolding feature that keeps the arteries open (after the treatment of coronary artery disease). A novel three variable geometry parameterisation of a CYPHER (Cordis corp., Johnson & Johnson co.) type stent is proposed to explore the functionality of a sequence of circumferential rings connected by ‘n’ shaped links. The performance of each design is measured by six figures of merit (objectives/metrics) representing (i) acute recoil, (ii) tissue stresses, (iii) haemodynamic disturbance, (iv) drug delivery, (v) uniformity of drug distribution, and (vi) flexibility. These metrics are obtained from computational simulations of (i) structural deformation through balloon inflated expansion of a stent into contact with a stenosed vessel, (ii) pulsatile flow over the deformed stent embedded in the vessel wall, (iii) steady-state drug distribution into the tissue, and (iv) flexibility of a stent in response to an applied moment. Design improvement is obtained by a multi-objective surrogate modelling approach using a non-dominated sorting genetic algorithm (NSGA-II) to search for an optimal family of designs. A number of trade-offs between the different objectives are identified. In particular a conflict between pairs of the following objectives are shown – (a) volume average stress vs recoil, (b) volume average drug vs. volume average stress, (c) flexibility vs volume average stress, (d) flexibility vs. haemodynamic disturbance, (e) volume average drug vs. haemodynamic disturbance, and (f) uniformity of drug vs. volume average stress. Different paradigms to choose the optimal designs from the obtained Pareto fronts are presented and under each such paradigm, the optimal designs and there relative positions with respect to a representative CYPHER stent are show
The influence of strut-connectors in stented vessels: a comparison of pulsatile flow through five coronary stents
No full textThe design of coronary stents has evolved significantlyover the past two decades. However, they still face theproblem of in-stent restenosis, formation of neointima within12 months of the implant. The biological response after stentimplantation depends on various factors including the stentgeometry which alters the hemodynamics. This study takesfive different coronary stent designs, used in clinical practice,and explores the hemodynamic differences arising due to thedifference in their design. Of particular interest is the designof the segments (connectors) that connect two struts.Pulsatile blood flow analysis is performed for each stent,using 3-D computational fluid dynamics (CFD), and variousflow features viz. recirculation zones, velocity profiles, wallshear stress (WSS) patterns, and oscillatory shear indices areextracted for comparison. Vessel wall regions with abnormalflow features, particularly low, reverse, and oscillating WSS,are usually more susceptible to restenosis. Unlike previousstudies, which have tried to study the effect of designparameters such as strut thickness and strut spacing onhemodynamics, this work investigates the differences in theflow arising purely due to differences in stent-shape, otherparameters being similar. Two factors, the length of theconnectors in the cross-flow direction and their alignmentwith the main flow, are found to affect the hemodynamicperformance. This study also formulates a design index(varying from 18.81% to 24.91% for stents used in thisstudy) that quantifies the flow features that could affectrestenosis rates and which, in future, could be used foroptimization studies
Scientometric Insights into Research Contributions of Govind Ballabh Pant University of Agriculture and Technology
No full textThis study evaluates the research productivity and impact of Govind Ballabh Pant University of Agriculture and Technology using Scopus data (2001–2021). A total of 4,897 publications receiving 53,059 citations were analyzed with scientometric indicators including AGR, RGR, DT, collaboration measures, authorship, citations, and keywords. Results show a gradual growth in research output, with peak productivity during 2017–2021 and Kumar, A. as the most prolific author (165 publications)
OpenAIRE Graph: dataset for research community in Virtual Human Twins
No full text<div>
<p>This dataset contains metadata records of publications, research data, software and projects relevant for the research community in Virtual Twins in health.<br>The dump contains the records available in the <a href="https://dth.openaire.eu/" target="_blank" rel="noopener">OpenAIRE Gateway on Digital Twins in Health</a> of the <a href="https://www.edith-csa.eu/" target="_blank" rel="noopener">EDITH CSA project </a>of the European Commission (grant agreement n. 101083771).</p>
<p>Records are identified via full-text mining and inference techniques applied to the <a href="https://graph.openaire.eu/">OpenAIRE Graph</a>.<br>The OpenAIRE Graph is one of the largest Open Access collections of metadata records and links between publications, datasets, software, projects, funders, and organizations, aggregating thousands of scholarly data sources world-wide.</p>
<p>The dump consists of a tar archive containing gzip files with one json per line.<br>Each json is compliant to the schema available at <a href="https://doi.org/10.5281/zenodo.10519297">https://doi.org/10.5281/zenodo.10519297</a>.</p>
<p> </p>
</div>
Some existence and uniqueness results for a solution of a system of equations
No full text[EN] This paper presents some existence and uniqueness results for a solution of a system of equations. Our results extend and generalize the well-known and celebrated results of Boyd and Wong [Proc. Amer. Math. Soc. 20 (1969)], Matkowski [Dissertations Math.(Rozprawy Mat.) 127 (1975)], Proinov [Nonlinear Anal. 64 (2006)], Ri [Indag. Math. (N. S.) 27 (2016)] and many others. We also present some illustrative examples to validate our results.The first author acknowledges the support from the URC/FRC fellowship, University of Johannesburg, South Africa.Khantwal, D.; Pant, R. (2024). Some existence and uniqueness results for a solution of a system of equations. Applied General Topology. 25(1):159-174. https://doi.org/10.4995/agt.2024.19798OJS15917425
OpenAIRE Graph: dataset for research community in Virtual Human Twins
No full text<div>
<p>This dataset contains metadata records of publications, research data, software and projects relevant for the research community in Virtual Twins in health.<br>The dump contains the records available in the <a href="https://dth.openaire.eu/" target="_blank" rel="noopener">OpenAIRE Gateway on Digital Twins in Health</a> of the <a href="https://www.edith-csa.eu/" target="_blank" rel="noopener">EDITH CSA project </a>of the European Commission (grant agreement n. 101083771).</p>
<p>Records are identified via full-text mining and inference techniques applied to the <a href="https://graph.openaire.eu/">OpenAIRE Graph</a>.<br>The OpenAIRE Graph is one of the largest Open Access collections of metadata records and links between publications, datasets, software, projects, funders, and organizations, aggregating thousands of scholarly data sources world-wide.</p>
<p>The dump consists of a tar archive containing gzip files with one json per line.<br>Each json is compliant to the schema available at <a href="https://doi.org/10.5281/zenodo.10519297">https://doi.org/10.5281/zenodo.10519297</a>.</p>
<p>The CSV file contains the links to the full-texts of the publications available in the gateway that OpenAIRE could download and use.</p>
<p> </p>
</div>
- …
