Design, x-ray image guidance and flow characterization of new asymmetric vascular stents
Ionita, Ciprian N
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Recent advances of x-ray imaging techniques have made possible improvement and development of new minimally invasive image guided interventions (IGI). Capabilities such as real-time, high special resolution image guidance with down to sub-millimeter precision, enabled a large increase in the number of the new minimally invasive treatments using x-ray guidance. One such treatment is a new method we are developing to treat intracranial aneurysms (ICA) using a new device, the asymmetric vascular stent (AVS). The present work deals with the physical aspects of the development and evaluation of this new device. In general, stents are specially designed vascular prosthesis similar to a uniform porous wire cylinder. Unlike current stents, the new devices have a low porous region which creates an asymmetry, hence the name we use for the device. The treatment of an intracranial aneurysm using AVSs is done by placing the low porous part over the aneurysm neck. By doing so, the flow in the aneurysm is modified and conditions for the thrombosis are created. The research on the device consisted of three parts: (i) design and fabrication of the device, (ii) flow evaluation and (iii) accurate of localization of the device during x-ray IGI. The first part involved the process design and fabrication of the stents using laser micro-welding. The second part was dedicated to flow evaluation and flow characterization of the AVS. The characterization of the flow parameters of the stent were done based on physical aspects of the flow and the structure geometry. Theoretical or empirical models were evaluated experimentally in order to verify if they were appropriate for our device. We verified the effects that stents have on flow in aneurysms using methods such as Particle Image Velocimetry (PIV) and x-ray video-densitometric measurements. The last part involved the development of a marking technique using x-ray radio-opaque markers. We verified the accuracy of placement of the stent when different marker configurations were used. We also built a micro cone-beam CT machine for nondestructive evaluation of the position of the stents in aneurysms samples. The results of this work indicate that treatment of intracranial aneurysms using AVSs can offer an alternative to current methods of treatment. In comparison with these methods, the method we propose will reduce the invasiveness and will mitigate some of the problems with current methods.