Cardiology
Coronary arteries (CA) and coronary stents
Despite its two-dimensional nature, X-ray angiography (XRA) has served as the gold standard imaging technique in the interventional cardiology for over five decades. Accordingly, demands for tools that could increase efficiency of the XRA procedure for the quantitative analysis of coronary arteries (CA) are constantly increasing.
The aim of this study was to propose a novel procedure for three-dimensional modeling of CA from uncalibrated XRA projections. A comprehensive mathematical model of the image formation was developed and used with a robust genetic algorithm optimizer to determine the calibration parameters across XRA views. The frames correspondences between XRA acquisitions were found using a partial-matching approach. Using the same matching method, an efficient procedure for vessel centerline reconstruction was developed. Finally, the problem of meshing complex CA trees was simplified to independent reconstruction and meshing of connected branches using the proposed nonuniform rational B-spline (NURBS)-based method.
Because it enables structured quadrilateral and hexahedral meshing, our method is suitable for the subsequent computational modelling of CA physiology (i.e. coronary blood flow, fractional flow reverse, virtual stenting and plaque progression). Extensive validations using digital, physical, and clinical datasets showed competitive performances and potential for further application on a wider scale.
Despite a lot of progress in the fields of medical imaging and modeling, problem of estimating the risk of in-stent restenosis and monitoring the progress of the therapy following stenting still remains. The principal aim
of this paper was to propose architecture and implementation details of state of the art of computer methods for a
follow-up study of disease progression in coronary arteries stented with bare-metal stents. The 3D reconstruction
of coronary arteries was performed by fusing X-ray angiography and intravascular ultrasound (IVUS) as the most
dominant modalities in interventional cardiology. The finite element simulation of plaque progression was performed
by coupling the flow equations with the reaction–diffusion equation applying realistic boundary conditions at
the wall. The alignment of baseline and follow-up data was performed automatically by temporal alignment of IVUS
electrocardiogram-gated frames.
The assessment was performed using three six-month follow-ups of right coronary artery. Simulation results were compared with the ground truth data measured by clinicians. In all three data sets, simulation results indicated the right places as critical. With the obtained difference of 5.89 ± ~4.5 % between the clinical measurements and the results of computer simulations, we showed that presented framework is suitable for tracking the progress of coronary disease, especially for comparing face-to-face results and data of the same artery from distinct time periods.
Computational Assessment of Stent Durability Using Fatigue to Fracture Approach
Stents are metal scaffold devices used to maintain lumen and restore blood flow of diseased artery. Despite they brought care of coronary diseases to a new level of efficacy, problem of stent fracture remains unclear even after global needs reached number of 5.106 devices yearly. For projected work-life of 10 years, rate of fracture occurrence in
stents varies from 5% up to 25% for different designs. Analysis of such miniature devices and long-term events in realistic in vivo conditions remains impossible while experimental in vitro measurements provide limited results consuming much time and expensive equipment.
The principal aim of this study was to propose procedure for numerical estimation of coronary stents durability assuming the hyperphysiological pulsatile pressure conditions. The hypothesis was whether the stent durability would be achieved safely for the projected work-life of 10 yr? The procedure was carried out within three phases: (a) initial fatigue analysis based on S-N approach; (b) fatigue lifetime assessment based on fatigue crack growth simulation using Paris power law, and (c) safe-operation, i.e., nofatigue failure (based on Kitagawa–Takahashi diagram) as well as immediate predictions of the fracture event in the stent. For considered generic stent design, results showed that the stent durability would be achieved safely. Since special diagrams were used, the fatigue risk assessment was clearer compared to the conventional fatigue lifetimes. Moreover, it was found that crack growth was stable for both small and large scale sizes of the crack. Besides the fact that the presented procedure was shown as suitable for numerical assessment of the generic stent durability under hyperphysiological pulsatile pressure conditions, it was concluded that it might be applied for any other design as well as loading conditions. Moreover, it could be efficiently combined with experimental procedures during the process of the stent design validation to reduce manufacturing and testing costs.