Imaging of Shear Waves Induced by Lorentz Force in Soft Tissues

This study presents the first observation of elastic shear waves generated in soft solids using a dynamic electromagnetic field. The first and second experiments of this 5 study showed that Lorentz force can induce a displacement in a soft phantom and that this displacement was detectable by an ultrasound scanner using speckle-tracking algorithms. For a 100 mT magnetic field and a 10 ms, 100 mA peak-to-peak electrical burst, the displacement reached a magnitude of 1 um. In the third experiment, we showed that Lorentz force can induce shear waves in a phantom. A physical model 10 using electromagnetic and elasticity equations was proposed. Computer simulations were in good agreement with experimental results. The shear waves induced by Lorentz force were used in the last experiment to estimate the elasticity of a swine liver sample

Antimicrobial resistance patterns among Acinetobacter baumannii isolated from burn intensive care unit in Tripoli, Libya

Background: Acinetobacter baumannii is a troublesome and increasingly problematic healthcare-associated pathogen, especially in critical care unit. These organisms have a capacity for long-term survival in the hospital environment. Aim: This study aimed to investigates the drug resistance patterns of Acinetobacter baumannii strains isolated from burn ICU (BICU). Method: The antibiotic susceptibility of 176 isolates to imipenem, meropenem, gentamicin, ciprofloxacin, fusidic acid, amikacin, trimethoprim, cefepime, ceftazidime, ceftriaxone, cefotaxime, and amoxicillin-calvulanic acid was determined by disk agar diffusion test. Findings: The overall proportion of A. baumannii isolates among all clinical isolates has increased slightly throughout the study from 3.5% to 4.2%. Carpabenem remained the antimicrobial most active antibiotic against A. braumannii isolates compared with other antibiotics, during the two years there was an increase in resistance from 50.6% to 71.3% to imipenem (P<0.01), and meropenem from 50.6% to 74.5% (P<0.01). ICU isolates exhibited significantly higher level of resistance to imipenem (71.6%) and meropenem (73.4%) compared with non-ICU strains (42.6% and 44.6% respectively) (P<0.01). Conclusion: In conclusion, the high prevalence of multidrug resistance A. baumannii (97.7%) and increased resistance to imipenem and meropenem in our unit might be due to long hospital stay, intubation, surgery and previous antibiotic prescription. It would seem that practices to prevent cross-transmission are more important in controlling resistance

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Elastographie passive : application à la tomographie et la caractérisation mécanique des tissus biologiques

The aim of this thesis was the development of a new approach called passive elastography. This approach is inspired from noise correlation methods well developed in seismology and time reversal technics in acoustics. Passive elastography uses shear waves naturally induced in the human body to extract its mechanical properties of soft tissue. The feasibility of this method was tested in several applications. First in ultrasound, slow frame rate ultrasound scanner was used to monitor high intensity focused ultrasound treatment on porcine pancreas. Then, an ultrafast ultrasound scanner was used to retrieve shear wave speed map in a calibrated phantom and in-vivo. Second, Magnetic resonance elastography was implemented to image natural motion in the brain of healthy volunteers and conduct shear wavelength tomography. Third, of ophthalmological and dermatological applications, optical coherence passive elastography was tested in a phantom and a cornea of healthy mouse. Also, a fully optical setup was established to image surface wave for elastography applications. Finally, the resolution limit of elastography was measured using and ultrasound ultrafast scannerLes travaux menés lors de cette thèse portent sur le développement d'une approche passive d'Elastographie, l'imagerie de l'élasticité des tissus mous. Inspirée des techniques de corrélation de bruit sismique développée en séismologie, et du retournement temporel en acoustique. L'Elastographie passive utilise des ondes de cisaillement naturellement présentent dans le corps humain pour extraire les propriétés mécaniques des tissues biologiques. La faisabilité de cette approche passive est démontrée pour divers applications. En ultrason, un échographe à cadence lente ont été utilisés pour le guidage du traitement par ultrason à haut intensité dans une étude préclinique. Puis l'utilisation d'un échographe ultra-rapide pour la reconstruction des cartes de vitesses dans des gels calibrés ainsi que in-vivo. L'Elastographie passive par résonnance magnétique a été également mise en place pour imager les mouvements naturels dans le cerveau d'un volontaire sain et la réalisation d'une tomographie de longueurs d'ondes. En optique pour des applications en ophtalmologie ou en dermatologie, la faisabilité de l'Elastographie passive par cohérence optique a été démontrée dans un gel puis in-vivo dans l'œil d'une souris pour des. Puis une preuve du concept d'un dispositif d'imagerie d'ondes de surfaces complètement optique été testé dans des gels plan, courbé, isotrope ou anisotrope. Finalement, la limite de la résolution de l'Elastographie passive par ultrason est évalué

Mechanical and physical properties of aluminised E-glass fibre reinforced unsaturated polyester composites

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

High frequency elastic wave propagation in micro-elastography

International audienceWe recently proposed an alternative elasticity measurement technique based on elastic wave propagation within a single cell. At this scale, waves at a frequency never reached in the field of elastography (15kHz), are captured using an ultrafast camera and a microscope. This technique is based on the local measurement of the speed of a shear wave, a type of elastic wave. By assuming an infinite and homogeneous elastic medium with respect to the wavelength, the shear modulus μ (elasticity) is estimated. These latter assumptions are discussed through experiments conducted in controlled elastic solids at micro-scale. The conclusion is that wave guide effects as well as viscosity are crucial for quantitative mapping of elasticity

Improving Ventricular Arrhythmias Treatment Monitoring using Ultrafast Ultrasound

International audience<b>Context:</b> Ventricular arrhythmias are heart rhythm disorders triggered by specific regions of the ventricles. In most severe cases, these regions must be electrically isolated using radiofrequency (RF) thermal ablation. Catheter-based mapping techniques are used for RF treatment planning and control but they remain invasive, time-consuming and based on indirect assessments, amongst other limitations. Ultrafast ultrasound offers various possibilities which could be used in real-time to improve RF ablation monitoring, namely Electromechanical Wave Imaging (EWI) and Passive Elastography (PE). Here, we demonstrate that EWI can be used to identify arrhythmogenic foci on isolated perfused heart models and that PE can monitor thermal lesion formation on cardiac tissue samples. <b>Methods:</b> Two isolated perfused swine heart models were set up to mimic cardiac electrophysiological behavior. Pacing electrodes were screwed on the left ventricle to simulate arrhythmogenic foci. 54 EWI acquisitions were performed in a single cardiac cycle (4000 fps, 15MHz ultrasound probe). 6 thermal lesions were achieved in veal heart wall samples. Shear wave field was created in the tissue with a vibrator on sweep mode. PE acquisitions (600 fps, during 1s, 3MHz ultrasound probe) were performed before and after ablation to visualize elasticity modification induced by thermal lesions in the tissue. <b>Results/Discussion:</b> In this study, ultrafast ultrasound was used in two different ways which could help improve arrhythmias treatment monitoring. EWI allows visualizing propagation of the electromechanical wave in the heart, which could help define ablation target with high precision. By analyzing cardiac activation pattern with EWI, three blind readers were able to accurately retrieve cardiac electrical activation in 78% of the cases. PE demonstrated a local tissue stiffening after lesion formation on 83% of the cases. Transmural lesions were also visualized using PE and confirmed by gross pathology. PE could have the potential to directly monitor RF lesion formation in real-time

Ultrafast imaging of cell elasticity with optical microelastography

International audienceElasticity is a fundamental cellular property that is related to the anatomy, functionality and pathological state of cells and tissues. However, current techniques based on cell deformation, acoustic force microscopy or Brillouin scattering are rather slow and do not always accurately represent cell elasticity. Here, we have developed an alternative technique by applying shear wave elastography to the micrometer scale. Elastic waves were mechanically induced in live mammalian oocytes using a vibrating micropipette. These audible frequency waves were observed optically at 200,000 frames per second and tracked with an optical flow algorithm. Whole cell elasticity was then mapped using an elastography method inspired by the seismology field. Using this approach, we show that the elasticity of mouse oocyte is decreased when the oocyte cytoskeleton is disrupted with cytochalasin B. The technique is fast (less than 1 ms for data acquisition), precise (spatial resolution of a few micrometers), able to map internal cell structures, robust, and thus represents a tractable novel option for interrogating biomechanical properties of diverse cell types

Myocardial Thermal Ablation with a Transesophageal High-Intensity Focused Ultrasound Probe: Experiments on Beating Heart Models

International audienc