An artificial dielectric slab for ultra high-field MRI: proof of concept

High-permittivity dielectric pads, i.e., thin, flexible slabs, usually consisting of mixed ceramic powders and liquids, have been previously shown to increase the magnetic field at high and ultra high-fields in regions of low efficiency of transmit coils, thus improving the homogeneity of images. However, their material parameters can change with time, and some materials they contain are bio incompatible. This article presents an alternative approach replacing ceramic mixtures with a low-cost and stable artificial dielectric slab. The latter comprises a stack of capacitive grids realized using multiple printed-circuit boards. Results in this article show that the proposed artificial dielectric structure can obtain the same increase in the local transmit radiofrequency magnetic field distribution in a head phantom at 7 T as the conventional dielectric pad. (C) 2020 The Authors. Published by Elsevier Inc.Radiolog

No Efficacy of the Combination of Lopinavir/Ritonavir Plus Hydroxychloroquine Versus Standard of Care in Patients Hospitalized With COVID-19: A Non-Randomized Comparison

Objectives: No specific treatment has been approved for COVID-19. Lopinavir/ritonavir (LPV/r) and hydroxychloroquine (HCQ) have been used with poor results, and a trial showed advantages of combined antiviral therapy vs. single antivirals. The aim of the study was to assess the effectiveness of the combination of antivirals (LPV/r and HCQ) or their single use in COVID-19 hospitalized patients vs. standard of care (SoC). Methods: Patients ≥18 years with SARS-CoV-2 infection, defined as positive RT-PCR from nasal/oropharyngeal (NP/OP) swab or positive serology, admitted at L. Spallanzani Institute (Italy) were included. Primary endpoint: time to invasive ventilation/death. Secondary endpoint: time to two consecutive negative SARS-CoV-2 PCRs in NP/OP swabs. In order to control for measured confounders, a marginal Cox regression model with inverse probability weights was used. Results: A total of 590 patients were included in the analysis: 36.3% female, 64 years (IQR 51-76), and 91% with pneumonia. Cumulative probability of invasive ventilation/death at 14 days was 21.2% (95% CI 17.6, 24.7), without difference between SOC, LPV/r, hydroxychloroquine, HCQ + LPV/r, and SoC. The risk of invasive ventilation/death in the groups appeared to vary by baseline ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2). Overall cumulative probability of confirmed negative nasopharyngeal swabs at 14 days was 44.4% (95% CI 38.9, 49.9), without difference between groups. Conclusion: In this retrospective analysis, we found no difference in the rate of invasive ventilation/death or viral shedding by different strategies, as in randomized trials performed to date. Moreover, even the combination HCQ + LPV/r did not show advantages vs. SoC

Effect of a Near Fault on the Seismic Response of a Base-Isolated Structure with a Soft Storey

This study focuses on the soft-storey behavior of RC structures with lead core rubber bearing (LRB) isolation systems under near and far-fault motions. Under near-fault ground motions, seismic isolation devices might perform poorly because of large isolator displacements caused by large velocity and displacement pulses associated with such strong motions. In this study, four different structural models have been designed to study the effect of soft-storey behavior under near-fault and far-fault motions. The seismic analysis for isolated reinforced concrete buildings is carried out using a nonlinear time history analysis method. Inter-story drifts, absolute acceleration, displacement, base shear forces, hysteretic loops and the distribution of plastic hinges are examined as a result of the analysis. These results show that the performance of a base isolated RC structure is more affected by increasing the height of a story under nearfault motion than under far-fault motion

Seismic vibration control using a novel inerto-elastic damper

The use of advanced structural control devices is an effective engineering solution to reduce earthquake induced damages to structures. Owing to rapid advancement in technology and persistent research efforts, a variety of control devices have been developed and successfully implemented. Quite recently, a new passive damper, called inerter has been introduced, which is capable of developing a fictive mass. This study presents a novel inerto-elastic damper, which combines the inerter devices with classical elastic springs, and demonstrates the effectiveness of these devices in achieving seismic response reduction. The inerto-elastic device employs the inerter and elastic spring in parallel to control the seismic structural response. The effectiveness of the inerto-elastic dampers has been demonstrated through the response of a multi-degree of freedom system subjected to seismic excitations. The results of the analysis show a significant reduction in the response of the structure with novel inerto-elastic damper, as compared to those of structures with normal elastic spring as well as no dampers. The response quantities of interest, considered for this study are top floor displacement, inter-storey drift and base shear. The study also underlines optimal parameters for the inerter fictive mass and the elastic spring stiffness on the basis of the results obtained

Seismic vibration control using a novel inerto-elastic damper

The use of advanced structural control devices is an effective engineering solution to reduce earthquake induced damages to structures. Owing to rapid advancement in technology and persistent research efforts, a variety of control devices have been developed and successfully implemented. Quite recently, a new passive damper, called inerter has been introduced, which is capable of developing a fictive mass. This study presents a novel inerto-elastic damper, which combines the inerter devices with classical elastic springs, and demonstrates the effectiveness of these devices in achieving seismic response reduction. The inerto-elastic device employs the inerter and elastic spring in parallel to control the seismic structural response. The effectiveness of the inerto-elastic dampers has been demonstrated through the response of a multi-degree of freedom system subjected to seismic excitations. The results of the analysis show a significant reduction in the response of the structure with novel inerto-elastic damper, as compared to those of structures with normal elastic spring as well as no dampers. The response quantities of interest, considered for this study are top floor displacement, inter-storey drift and base shear. The study also underlines optimal parameters for the inerter fictive mass and the elastic spring stiffness on the basis of the results obtained

A practical realization of an artificial magnetic shield for preclinical birdcage RF coils

In the most of magnetic resonance imaging (MRI) systems, a conventional radiofrequency (RF) electric shield is typically placed around an RF volume coil to avoid the interaction with the other components of the system. Disadvantageously metal shields reduce the transmit efficiency of the RF coil as well as its receive sensitivity due to out-ofphase reflection of electromagnetic waves. In contrast, an ideal magnetic shield having high surface impedance provides in-phase reflection, which can be promising for improvement of RF coil's performance. In this work, we propose an artificial magnetic shield based on a cylindrical miniaturized corrugated structure to improve characteristics of a small-animal birdcage coil at 7T. The coil was simulated in the presence of the metal and ideal magnetic shield as well as the proposed structure. The results demonstrate enhancement of the coil's performance in the presence of the proposed shield, which is comparable with an ideal one.Peer reviewe

A metamaterial-inspired MR antenna independently tunable at two frequencies

International audienc

Optical properties of metamaterials: Influence of electric multipoles, magnetoelectric coupling, and spatial dispersion

International audienc

Hybridized eigenmodes of periodic wire arrays and their application in radiofrequency coils for preclinical MRI

International audienc