SYSTEME OPTOELECTRONIQUE « COMPATIBLE IRM-PRECLINIQUE » POUR L’IMAGERIE DIFFUSE RAPIDE

International audienceL’imagerie et la spectroscopie par résonance magnétique, des organes en mouvement chez le petit animal requierent des méthodes de compensation. On cherche alors à s’affranchir des perturbations de cohérence des signaux qui se traduisent par des artefacts en imagerie (flou cinétique, « ghosting », etc.) comme en spectroscopie (élargissement des raies, défaut de délimitation spatiale des voxels, etc.). Or si les méthodes de synchronisation retrospectives ne sont pas toujours d’implémentation aisée pour tous les types de séquences, les méthodes de synchronisation retrospectives souffrent parfois des limitations pratiques. Ainsi les dispositifs de mesure d’Electrocardiogramme pour l’IRM cardiaque révèlent parfois des difficultés de mise en oeuvre, liés à l’intervention de matériaux conducteurs et aux liaisions filaires. Particulièrement dans les situations cumulant de forts gradients de champs, un fort encombrement associé notamment aux tunnels à hauts champs actuels, ou encore une géométrie particulière d’antennes et de connexion, des dispositifs tout optique pourraient alors constituer des alternatives attrayantes, comme nous l’avons précédemment montré [1]. Non seulement les dispositifs à base de capteurs à fibres optiques ont l’avantage d’être intrinsèquement compatibles IRM, rapides à l’échelle temporelle des phénomènes physiologiques visés, mais ils peuvent aussi être disposés en réseau de façon à collecter des informations réparties sur le corps de l’animal [2].1. R. Sablong et al. IEEE Transactions on Biomedical Engineering, 65(1), 2014.2. JD Johansson et al, Biomed Opt Express, 7(2):481-98 2016

Protocole de caractérisation et de comparaison des bobines RF applicable aux systèmes d’IRM précliniques et cliniques

National audienceLe calcul théorique du profil de sensibilité et du rapport signal à bruit (SNR) des bobines RF peut se faire analytiquement [1-3] mais nécessite d'avoir une connaissance complète des caractéristiques du capteur ce qui n'est pas le cas pour les capteurs commerciaux. Le but de ce travail est de standardiser et de diffuser un protocole expérimental permettant de caractériser le SNR et le volume de sensibilité des bobines et capteurs RF adaptés à la fois aux systèmes IRM précliniques et cliniques. La première motivation est de comparer les performances des capteurs entre eux. Ce protocole peut également être utilisé pour suivre les équipements dans le cadre d'une démarche qualité

Transient MR elastography (t-MRE) using ultrasound radiation force: theory, safety, and initial experiments in vitro.

International audienceThe purpose of our study was to assess the feasibility of using ultrasound radiation force as a safe vibration source for transient MR elastography (t-MRE). We present a theoretical framework to predict the phase shift of the complex MRE signal, the temperature elevation due to ultrasound, and safety indicators (I(SPPA), I(SPTA), MI). Next, we report wave images acquired in porcine liver samples in vitro. MR thermometry was used to estimate the temperature elevation induced by ultrasound. Finally, we discuss the implications of our results with regard to the feasibility of using radiation force for t-MRE in a clinical setting, and a specific echo-planar imaging (EPI) MRE sequence is proposed

New trends in MRI of cartilage: Advances and limitations in small animal studies

International audienceDue to the actual interest for bioengineering in the osteoarthritis (OA) healing context, researchers need accurate qualitative and quantitative methodologies to evaluate in vivo the integration and functionality of their cartilage-like biomate-rials. As in clinical diagnostic strategies, advances in Magnetic Resonance Imaging (MRI) seem promising for non-vulnerant assessments of articular cartilage bio-architecture and morphology in small animal models. These experimental models are commonly used to monitor the physiopathology of OA and to evaluate therapeutic responses mediated by chondroprotective drugs or tissue engineering. Nowadays, the application of MR protocols to in vivo small animal cartilage imaging is achievable with the development of high magnetic fields and the adaptation of methodologies to reach the required spatial resolution and contrast. The purpose of this article is to summarize these current MRI strategies used for in vivo small animal articular cartilage assessments

PROTOCOLE DE CARACTERISATION DE CAPTEUR IRM

International audienceLes capteurs IRM jouent un rôle crucial dans la détection du signal. De ce fait, ils connaissent une évolution permanente pour augmenter leur efficacité. Aujourd'hui, il existe un grand nombre de capteurs différents et il peut être difficile de choisir celui qui est le plus adapté à un examen inhabituel. De plus, ce choix peut lourdement se complexifier lorsqu'on a accès à des systèmes IRM de différents fabricants et opérant à différents champs statiques. Le protocole de caractérisation que nous proposons ici a pour but de comparer les capteurs en terme de SNR et de volume uniforme. Il peut être utilisé pour comparer des systèmes IRM dans le cadre d’étude multicentrique ou encore comme un outil de contrôle qualité

SNR and volume characterization of RF coils: A simple procedure and an automatic post-processing tool for a straightforward comparison

International audienceTo choose the most suitable RF coil available for an MRI study, we propose a procedure which uses a calibrated phantom, a 3D gradient-echo sequence, and an automatic post-processing tool available on the web. This tool generates a report which contains the measurement of a SNR with uniform volumes located in the depth. The post-processing could be done on MR images acquired on most main MRI vendors (Siemens, GE, Philips and Bruker) with prior verification of applied scaling or filtering. RF coil characterization results performed on at 4.7T and 7T were compared. The tool can be used for quality control

Comparison of high-resolution magnetic resonance imaging and micro-computed tomography arthrography for in-vivo assessment of cartilage in non-human primate models

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Apparent Diffusion coefficient (ADC), T1 and T2 quantitative indexes of the myocardium in athletes before, during and after extreme mountain ultra-marathon: correlation with myocardial damages and inflammation biomarkers

International audienceBackground: previous MRI and US studies have shown the existence of functional and biochemical alterations in the myocardium after prolonged endurance exercise, demonstrating transient diastolic dysfunction [1]. Simultaneous transient increases of cTnT and NT-proBNP biomarkers have been reported [2, 3] without focal necrosis identified by delayed enhancement imaging, probably due to a cytosolic's dropping of biomarkers rather than destruction of myocytes. Inflammation, microstructural & functional modifications caused by extreme loading conditions, have never been explored using quantitative MRI.Methods: We prospectively studied 50 runners enrolled on the 2014 « Tor des Géants » edition (the most extreme mountain ultra-marathon (336 km length, 24000 m cumulative elevation), without clinical evidence of personal history of cardiac or pulmonary disease. Subjects were studied before, at arrival, and after 3 days recovery. Imaging protocol included global and regional LV function analysis and quantitative MRI : T1, T2 and ADC values were obtained using respectively a MOLLI sequence, a radial multi-echo sequence, a Stejskal-Tanner diffusion sequence [4]. T1, T2 and ADC values at 1.5T were compared with plasma levels of inflammation, myocardial stress and/or damage biomarkers including hs-TnT, NT-proBNP, Gal-3 (a carbohydrate binding lectin produced by macrophages, upregulated in hypertrophied heart, emerging as a mediator for fibrosis development and remodeling) and ST2 (a family member of IL-1 receptors known for its role in immunological processes, having a potential role in cardiac pathogenesis).Results: 27 finishers (54%) completed the longitudinal study.T2, T1 and ADC values significantly increased immediately after the race. ADC quickly normalized after recovery while T1, T2 markers remained higher than baseline (Figure 1). Significant correlations were found between myocardial MR biomarkers and blood (Gal3,ST2,NT-proBNP), plasmatic (CRP, CKs, hs-TNT) and cellular (WBC, lymphocytes, neutrophilis) ones (Figure 2).Conclusion: It is the first study investigating the role of quantitative MR diffusion to explore human acute stress in humans together. ADC, T1 and T2 were all able to identify changes in subjects and related to several plasmatic biomarkers and therefore appear as valuable MR biomarkers of myocardial inflammation at least for this specific type of acute stress. Prior to a deeper understanding of the impact of ultra-endurance, this study hightlights an added value of ADC, that differ from T1 and T2 markers, to scrutinize acute stress phenomena in the myocardium. ADC represents a novel information, revealing more about water redistribution leading to ultraexercise-induced reversible myocardial inflammation. Overal it illustrates the usefulness and complementary nature of ADC as an emerging cardiac biomarker, foreseen to be deployed at short-term in the evaluation of innovative therapeutic strategies targeting inflammation