The influence of textile vascular prosthesis crimping on graft longitudinal elasticity and flexibility.

Textile vascular prostheses are the principal substitute for the replacement of large vascular arteries. These prostheses undergo a thermal treatment of crimping inducing a wavy shape of the graft wall. Today mechanical properties of crimped vascular prostheses are not well known. After implantation, vascular prostheses are exposed to several longitudinal forces due to blood pressure, inducing their deformation during the cardiac cycle. In arteries that undergo large bending deformation, the flexibility is a necessary feature of vascular prostheses. In the present work, a longitudinal tensile model and a bending model of woven vascular prosthesis are numerically simulated. The obtained results provide a better understanding of the impact of the crimping parameters on the longitudinal elasticity and the bending stiffness of the textile vascular prosthesis. Mathematical predictive models of longitudinal elasticity and bending stiffness of the textile prosthesis have been developed, allowing relating the prosthesis elasticity and flexibility with the crimping parameters.

Improved localization of coronary stents based on image enhancement.

Stent thrombosis remains a life threatening complication of percutaneous coronary interventions. The angiographic result of stent implantation is a high predictive factor of stent thrombosis. Nevertheless accurate placement of stents is hindered by the fact that most stents are only slightly radiopaque and hence difficult to see in typical coronary X-ray images. In this work, we propose a simple image guidance approach, making it easier to achieve optimum and complete intracoronary stent deployment. The main idea is to enhance the visibility of stents using an iterative landmark-based registration. After frame averaging over the series of registered frames, the resultant stent image is post processed to increase the contrast visibility. Preliminary simulation results show that despite its low computational cost, our method significantly improves the visibility of stent edge struts.

Influence of crimping textile polyester vascular prostheses on the fluid flow kinetics. Groupe Européen de Recherche sur les Prothèses appliquées à la Chirurgie Vasculaire.

OBJECTIVES: to characterise the impact of the crimping of polyester prostheses on the fluid flow kinetics. DESIGN: an experimental in vitro study. MATERIALS AND METHODS: we investigated four models of polyester vascular prostheses in a continuous laminar flow circuit. The flow velocity was 80 ml/s for all experiments. We studied two fluids of different viscosity within the circuit. The speed of the particles was measured by a laser Doppler anemometer 2 to 52 mm from the prosthetic interface. We first established a calibrated flow-velocity profile corresponding to the study of the support inside the circuit without any prosthesis. We measured the velocity profiles for each prosthesis corresponding to four crimp densities obtained by stretching the grafts. RESULTS: the crimping of PET textile prostheses led to a decrease of flow velocity especially closer to the prosthetic surface. The decrease of flow velocity was dependent on the model of prosthesis. This decrease of flow velocity is described by the following negative exponential law: DeltaV=a times b(-x)where (a) is the crimp density and (b) the fluid viscosity. CONCLUSIONS: flow velocity near a prosthetic surface is influenced by the morphology of the crimping. The impact of crimping on the flow velocity in a vascular prosthesis can be predicted by computer simulation models. This may provide the optimal shape of crimping for each prosthesis.