Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Ionization-induced annealing in silicon upon dual-beam irradiation

Equipex GENESISInternational audienceSilicon single crystals were irradiated at room temperature (RT) with single and dual low-velocity (i.e., 900 keV I) and high-velocity (i.e., 27 MeV Fe or 36 MeV W) ion beams in order to study synergistic effects between nuclear and electronic energy losses in semiconductors. The damage created by irradiation was quantified by using Rutherford backscattering spectrometry in the channeling mode and Raman spectroscopy, and it was visualized using transmission electron microscopy. Whereas single low-velocity ion irradiation leads to amorphization of the surface layer of Si crystals, the use of a dual low- and high-velocity ion beam prevents this phase transformation. However, a remaining disorder exists, the level of which depends on the ratio of the high- to low-velocity ion fluxes. The higher the ratio (1.6 in the present case), the lower the disorder level, with a 30% integrated disorder instead of 100% upon single low-energy irradiation. These results provide evidence that ionization-induced disorder annealing can occur at RT in Si

Ionization-induced thermally activated defect-annealing process in SiC

International audienceIonizing events can lead to panoply of irradiation effects, and in silicon carbide (SiC), they drastically modify the defect production rate or the initial density. To better understand this phenomenon, 6H-SiC single crystals were first predamaged using low-velocity 100-keV Fe+ ions at three fluences in the range of 1014cm−2 to induce three different initial disorder levels peaking at values between ∼0.8 and 1 (1 corresponding to full amorphization). Crystals were then submitted to swift heavy ion irradiation in the 1013cm−2 fluence range at both low (∼100 K) and high (∼770 K) temperature. Rutherford backscattering spectrometry in channeling conditions revealed that swift ions allow annealing part of the initial damage, the recovery efficiency increasing with the irradiation temperature and reaching 75% in initially severely disordered crystals. This temperature effect has been qualitatively predicted by molecular dynamics simulations. Transmission electron microscopy allowed imaging both the recovery and the difference in the microstructure of the layers irradiated at low or high temperature. Recovery cross sections are found to lie in the range of a few square nanometers, consistent with previously reported values. A scenario for a general, two-step annealing mechanism referred to as an ionization-activated, thermally assisted defect-annealing (IATADA) process is proposed. This mechanism rationalizes the diverse descriptions reported so far in the literature

Comparison of Flow Measurement by 4D Flow Magnetic Resonance Imaging and by Particles Image Velocimetry on Phantom of Abdominal Aortic Aneurysm

International audiencePredicting the rupture of Aortic Aneurysms is a complex problem that interests, from several decades, many researchers. The works on this issue are very complex, involving both the study of mechanical behavior of the artery as the flow of blood. The Magnetic Resonance Imaging (MRI) technique allows to obtain anatomic information of the arteries, than the flow inside thereof. The goal of this study is an inter comparison betweenflow data from MRI and those obtained by Particle Image Velocimetry (PIV). An experimental device simulating hemodynamic circulation is used. Initially in order to validate the device, the flow in a cylindrical glass tube is measured by these two techniques and then compared to a theoretical model. Secondly, the flow in a phantom in silicone, with an axisymmetric aneurysm, is evaluated with 4D flow MRI sequences and the easurements are compared with those obtained by PIV with good agreement. The ability of the MRI technique to measure the flow thus makes an essential device for the study of cardiovascular diseas

Validation of aortic in-vitro strain measurement by Magnetic Resonance Imaging with realistic abdominal aortic aneurism phantom

International audienceIntroduction: Preoperative diagnostic protocols of abdominal aortic aneurysm (AAA) are today mainly based on the measurement of the aortic maximum diameter. This measurement is insufficient because the diameter is not a discriminant variable for predicting the rupture of the aorta. Recent works show the importance of determining the wall stress both due to the aortic shape, the pressure and the blood flow. The problem is very complex and requires the implementation of sophisticated models taking into account the heterogeneity of tissues and the complexity of flow. Then it is essential to validate the capacity of existing medical imaging systems to provide reliable measurements that will be introduced in these models., Method: The aim of this study is to verify the MRI's ability to provide reliable measurements, firstly for the deformation of the aortic wall, and secondly for the blood flow. Cine MRI acquisitions (SSFP sequence) enabled to accurately determine the geometry and deformation of the aneurysm and 4D flow MRI measurements (thanks to a 3D PC-MRI sequence) were used to quantify the velocities of the fluid. Measurements were carried out in vitro with an experimental device that simulated hemodynamic circulation on a realistic AAA phantoms in silicone that have properties closest as possible as the actual physiological conditions. The sequences were prospectively gated with the pressure signal given by a pressure sensor. The deformations of the phantom wall were then determined through solid modeling with Abaqus software in which the geometry and internal stresses determined by CFD modeling (pressure, Wall Shear Stress) were introduced (see Fig. 1). The deformations were compared with measurement made by stereovision. Moreover, blood flow estimation with MRI was compared with the fluid modelling performed with ANSYS software., Results: The obtained deformations with MRI are close to those obtained by stereovision with relative deviations less than 15% (see Fig.2). The comparison pixel to pixel between 4D Flow IRM and CFD is difficult because the spatial discretizations are different for the both technics. However the results of the mean instantaneous velocities are very similar between the two approaches throughout the cycle. Conclusion Our approach makes it possible to validate the ability of MRI to perform deformation measurements on phantom carried out with homogeneous materials and having complex geometries in which complex flow circulate. The first results showed the performance of the MRI to provide reliable raw data that can be included in the theoretical models., Figure 1. The different steps of the strain calculation, Figure 2. Maximal main strain comparison between stereovision and modelling obtained from IRM measurement, (C) 2016European Society of Cardiolog

Validation of the Strain Assessment of a Phantom of Abdominal Aortic Aneurysm: Comparison of Results Obtained From Magnetic Resonance Imaging and Stereovision Measurements

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MRI Assessment of the Bi-Leaflet Mechanical Heart Valve: Investigating the EOA Using the Acoustic Source Term Method

International audienceBackground: This work aims at defining the Effective Orifice Area (EOA) derived from the acoustic source term (AST) method from 4D Phase-Contrast MRI data to provide a reference for the assessment of MRI valvular prostheses as part of a comprehensive cardiac exam. Methods: Three different Bileaflet Mechanical Heart Valves (BMHV) and a dysfunctional BMHV were tested in-vitro using 4D Phase-Contrast MRI and a numerical design of the experimental study was performed, including the influence of internal diameter, stroke volume, and heart rate. The EOA AST was computed based on the MRI 4D Phase-Contrast acquisition. Results: EOAAST values vary by 15 mm from the BMHV center and should be computed between 8 to 10 mm after the metallic “blurring” artefact (ranging from 18.9 to 23.4 mm from the BMHV). EOAAST values were found to be lower compared with numerical results in the appropriate plane. Detection of the BMHV dysfunction by continuity equation computed from 4D flow acquisition is limited based on EOAAST computations, while EOAc and velocities after the valves could more directly highlight a blocked leaflet. Conclusion: This multi-disciplinary study demonstrates the suitability of the EOA AST method to assess BMHV function using MRI. Translation to the clinic is feasible using an optimized 2D Phase-Contrast flow stack or a 4D Phase-Contrast minimal volume based on the recommendations provided

Validation of the strain assessment of an abdominal phantom aortic aneurysm: comparison of results obtained from magnetic resonance imaging measurements and stereovision measurements

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In situ characterization of ion-irradiation enhanced creep of third generation Tyranno SA3 SiC fibers

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Monitoring of the recovery of ion-damaged 4H-SiC with in situ synchrotron X-ray diffraction as a tool for strain-engineering

International audienceIn situ thermal annealing (673-1273 K) during X-ray diffraction synchrotron measurements was performed to monitor the strain level as a proxy to follow the recovery of 300 keV Ar ion irradiated 4H-SiC single crystals. Results show that, when exposed to Ar ions at a fluence of 6.7 $\times$ 10$^{14}$ ions/cm$^2$ (0.7 dpa), the material suffers a maximum strain of 12$\%$ that reduces to 2$\%$ after the final anneal at 1273 K. In the same time, the disorder derived from the XRD data also demonstrates a thermal recovery of the crystalline structure. Hence, this work presents ion irradiation as a means to induce specific crystalline order and depth-controlled strain states within a few 100 s of nm window in 4H-SiC.[graphic not available: see fulltext][graphic not available: see fulltext