Experimental evaluation of stent retrievers' mechanical properties and effectiveness.

BACKGROUND: Five randomized controlled trials recently appeared in the literature demonstrating that early mechanical thrombectomy in patients with acute ischemic stroke is significantly related to an improved outcome. Stent retrievers are accepted as the most effective devices for intracranial thrombectomy. OBJECTIVE: To analyze the mechanical properties of stent retrievers, their behavior during retrieval, and interaction with different clots and to identify device features that might correlate with the effectiveness of thrombus removal. MATERIALS AND METHODS: All stent retrievers available in France up to June 2015 were evaluated by mechanical and functional tests aimed at investigating the variation of their radial force and their behavior during retrieval. Devices were also tested during in vitro thrombectomies using white and red experimental thrombi produced with human blood. Functional tests and in vitro thrombectomies were conducted using a rigid 3D printed vascular model. RESULTS: Mechanical tests showed a variation in radial force during retrieval for each stent. A constant radial force during retrieval was related to continuous cohesion over the vessel wall and a higher rate of clot removal efficacy. All stent retrievers failed when interacting with white large thrombi (diameter ≥6 mm). CONCLUSIONS: None of the tested devices were effective in removing white clots of large diameter (≥6 mm). Constant radial force during retrieval allows constant cohesion to the vessel wall and pressure over the clot; such features allow for a higher rate of clot removal.

The pressure reduction coefficient: A new parameter to assess aneurysmal blood stasis induced by flow diverters/disruptors.

Background and purpose Pore density (PD), surface metal coverage (SMC) and the number of wires are all different parameters which can influence the efficacy of a flow disruptor/diverter. Nevertheless, the relative importance of a parameter to induce intra-aneurysmal blood stasis is still poorly evaluated. Therefore, comparison between devices based on a unique value is not reliable. The aim of this study was to propose a new bench top parameter (the pressure reduction coefficient (PRC; ξ)) in order to assess the global haemodynamic effect of each flow diverter/disruptor to slow flow. Methods Eight devices were tested in vitro during three different flow conditions. For the eight devices, the PRC was computed at different volumetric flow rates to characterise flow reduction. Comparison was made with SMC, PD and the number of wires. Results The PRC obtained for flow disruptors was on average 1.5 times more efficient in reducing flow compared to flow diverters. PD (mm2) ranged from 24 to 38 for flow diverters and did not independently correlate with the PRC. The SMC of flow diverters ranged from 25% to 70%, and ranged from 20% to 100% for flow disruptors, without independent correlation to the PRC. The number of wires ranged from 48 to 96 for the flow diverters and did not correlate independently to the PRC. Conclusion There were no direct correlations between individual device characteristics and the PRC, suggesting a multifaceted and interrelating association of the overall design of each implant. Hence, the PRC could be used as a simple, reliable parameter to assess the overall capacity of flow disruptors/diverters to induce intra-aneurysmal blood stasis.

Virtual Sculpting and 3D Printing for Young People with Disabilities.

The SHIVA project was designed to provide virtual sculpting tools for young people with complex disabilities, allowing them to engage with artistic and creative activities that they might otherwise never be able to access. Their creations are then physically built using 3D printing. To achieve this, the authors built a generic, accessible GUI and a suitable geometric modeling system and used these to produce two prototype modeling exercises. These tools were deployed in a school for students with complex disabilities and are now being used for a variety of educational and developmental purposes. This article presents the project's motivations, approach, and implementation details together with initial results, including 3D printed objects designed by young people with disabilities.

Space-Time Transfinite Interpolation of Volumetric Material Properties.

The paper presents a novel technique based on extension of a general mathematical method of transfinite interpolation to solve an actual problem in the context of a heterogeneous volume modelling area. It deals with time-dependent changes to the volumetric material properties (material density, colour, and others) as a transformation of the volumetric material distributions in space-time accompanying geometric shape transformations such as metamorphosis. The main idea is to represent the geometry of both objects by scalar fields with distance properties, to establish in a higher-dimensional space a time gap during which the geometric transformation takes place, and to use these scalar fields to apply the new space-time transfinite interpolation to volumetric material attributes within this time gap. The proposed solution is analytical in its nature, does not require heavy numerical computations and can be used in real-time applications. Applications of this technique also include texturing and displacement mapping of time-variant surfaces, and parametric design of volumetric microstructures.

MR derived volumetric flow rate waveforms of internal carotid artery in patients treated for unruptured intracranial aneurysms by flow diversion technique.

Little is known about the hemodynamic disturbances induced by the cerebral aneurysms in the parent artery and the effect of flow diverter stents (FDS) on these latter. A better understanding of the aneurysm-parent vessel complex relationship may aid our understanding of this disease and to optimize its treatment. The ability of volumetric flow rate (VFR) waveform to reflect the arterial compliance modifications is well known. By analyzing the VFR waveform and the pulsatility in the parent vessel, this study aimed to test the hypotheses that (1) intracranial aneurysms might disrupt the blood flow of the parent vessel and (2) the treatment by FDS might have measurable corrective effect on these changes. Ten patients followed for unruptured intracranial aneurysms treated by FDS and ten healthy volunteers as control group were included in this study. Two-dimensional quantitative phase-contrast magnetic resonance imaging (MRI) was performed on each patient on the ICA artery upstream and downstream to the aneurysm, and on each volunteer at similar locations. The aneurysms altered significantly the parent vessel pulsatility and this effect was correlated to their volume. The aneurysms treatment by FDS allowed for the restoration of a normally modulated flow and pulsatility correction in the parent vessel.