Séminaires

  • 2020
    1st July

    "Cryogenic hyperpolarization of molecular agents for Magnetic Resonance Imaging"

    4:00 pm
    Location: Visioconférence

    Mohsine Mekhfi stagiaire Master BioMaps

    Magnetic resonance imaging (MRI) is a well established tool to visualize biological tissues in a non-invasive manner, generally based on the detection of Hydrogen nuclei (1H).The signal that could be detected is naturally very small, but this is often compensated by a high amount or high density of nuclei, as it is the case of water molecules (H2O) in human body. Other species than 1H such as 13C, 19F, or 17O have also a great interest in imaging  as they are implicated in a set of biological processes  (e.g. cellular respiration), and therefore, they  are an important tool to understand human physiology, establish proper diagnostic and test new treatment. Unfortunately, these nuclei cannot usually be detected due to their low concentration in biological tissues. The aim of this project is to increase the sensibility of MRI toward these low concentration atoms, and to do so, the idea is to prepare solution containing 13C for example (marked to a bio-molecules of interest) by exposing  them to a high magnetic field/ very low temperature, also known as brute force hyperpolarization. Once the equilibrium is eventually reached, the solution is ready to be administered prior to imaging metabolic process.

  • 2020
    17th June

    "Incertitude en reconstruction TEP"

    4:00 pm
    Location: Visioconférence

    Marina Filipovic-Pierucci post-doctorante BioMaps

    En imagerie TEP, les données acquises sont peu nombreuses et contiennent plusieurs types de bruit au sens large. Par conséquent, quand on veut reconstruire une image de la répartition du traceur dans le corps du patient à partir de ces données, il est judicieux de prendre en compte l'incertitude statistique des données. D'habitude, on modélise tout le processus d'imagerie (la relation entre l'image et les données acquises, le bruit) et on utilise des algorithmes d'optimisation pour estimer une image "optimale" qui correspondrait aux données acquises. On aimerait savoir à quel point on peut faire confiance à cette image estimée et aux valeurs de concentration du traceur obtenues pour les différentes régions dans le corps. Souvent, on a tendance à mettre sous le tapis l'incertitude et les imperfections de nos estimations, parce qu'on ne sait pas comment les gérer, alors que de nombreuses approches statistiques ont été développées spécifiquement pour cela.

TEP "optimale" axiale, qui présente une tumeur au niveau du tronc cérébral. L'unité de l'intensité des voxels est le SUV.
Image d'incertitude. L'intensité de voxel représente la déviation standard associée à chaque voxel.
  • 2020
    10th June

    "Multi-frequency MRE for absolute quantitation and optimal tissue discrimination: a multi-platform phantom study"

    4:00 pm
    Location: Visioconférence

    Fatiha Andoh doctorante BioMaps

    The knowledge of the viscoelastic parameters of biological tissues can provide valuable insights in pathophysiology, clinical diagnosis, staging and classification, therapeutic monitoring and interventional support for many diseases because most of pathological processes are generally accompanied by changes in the mechanical properties. Magnetic Resonance Elastography (MRE) makes it possible to map these mechanical properties of biological tissues by recording the displacement fields generated by a mechanical wave travelling trough them. In spite of successful applications in the clinic, the spread of MRE is undermined by the lack of accuracy and precision of the extracted measurement on a voxel basis. This seminar will be the opportunity to highlight recent results allowing to assess MRE repeatability, reproducibility and robustness over the extracted shear velocity and elastic moduli.

Displacement fields measured with MRE in a liver fibrosis calibration phantom on the Philips 1.5 T MRI system
  • 2020
    4th June

    "Soutenance de thèse: Dynamic PET/MRI integration for a new multiparametric approach of tumor heterogeneity in non-small cell lung cancer (NSCLC)"

    10:00 am
    Location: Visioconférence

    Florent Besson MCU-PH-doctorant BioMaps

    Tumor heterogeneity is an important factor of progression and resistance to treatment. Multiparametric PET-MRI imaging offers unique opportunities to characterize biological cellular processes, but has never been evaluated at the regional level in Non-Small Cell Lung Cancer (NSCLC), the leading cause of oncological death. A simultaneous dynamic multiparametric 18F-FDG PET-MRI approach has been developed to this end. This approach required the “in-house” implementation of the reference absolute PET quantitative method of glucose metabolism (Sokoloff's tri-compartmental model); the development of a method for correcting geometric distortions in diffusion weighted imaging, validated on phantom and clinically tested; the phantom validation of quantitative MRI methods (T1/T2 relaxometry), also clinically tested; and the "in-house" implementation of the Tofts compartmental model (extended version) for the evaluation of tumor vascularization by dynamic perfusion MRI. The results of our work, performed at the regional intratumor level, illustrate the heterogeneity of the regional interlinks between glucose metabolism and vascularization in NSCLC, two fundamental biological hallmarks of tumor progression, and show that an unsupervised tumor partitioning by Gaussian mixture model, integrating all the PET-MRI biomarkers of this project, individualizes 3 types of supervoxels, whose biological signature can be predicted with 97% accuracy by 4 dominant PET-MRI biomarkers, revealed by metaheuristic machine learning methods.

  • 2020
    3rd June

    "Nouvelle méthode de caractérisation non-linéaire d'antennes supraconductrices basée sur l'imagerie par résonance magnétique"

    4:00 pm
    Location: Visioconférence

    Aimé Labbé post-doctorant BioMaps

    L’imagerie par résonance magnétique à haute-résolution (~100 µm)³ comporte un intérêt considérable pour la recherche clinique et préclinique, mais souffre d’un important manque de sensibilité. Pour améliorer la sensibilité de l’expérience d’IRM, une approche est d’utiliser des antennes miniatures en céramique supraconductrice. Un enjeu important du développement de cette technologie porte sur le découplage de l’antenne supraconductrice (utilisée en réception) de l’antenne d’émission. La méthode de découplage développée au laboratoire exploite les propriétés non-linéaires des supraconducteurs afin de désactiver l’antenne pendant la phase d’émission. Une bonne caractérisation des propriétés électriques de l’antenne est donc essentielle. Au cours de ce séminaire confiné, nous allons décrire et illustrer par quelques résultats une nouvelle méthode de caractérisation exploitant les artéfacts d’imagerie causés par le couplage et permettant de remonter aux propriétés électriques non-linéaires de l’antenne : facteur de qualité et résistance en fonction de la puissance incidente.

Comparaison entre des images IRM expérimentales (gauche) et simulées (droite) pour des durées croissantes d’impulsions radiofréquences à puissance fixe. Les artéfacts observés dépendent continument de la durée d’impulsion et permettent de remontrer aux propriétés électriques de l’antenne. L’antenne est une référence en cuivre et l’échantillon est un fantôme d’eau de 1 ml.
  • 2020
    27th May

    "Caractérisation mécanique des tissus biologiques"

    4:00 pm
    Location: Visioconférence

    Steve Beuve post-doctorant BioMaps

    L’élastographie est une science qui vise à évaluer ou mesurer les propriétés mécaniques de tissus biologiques afin de détecter ou suivre l’évolution de pathologies.  La présentation du quatrième séminaire confiné présente deux modalités de mesure du module de cisaillement. Une première mesure globale dans le cas d’un champ d’onde complexe se propageant  dans un fantôme puis une seconde locale utilisant les méthodes d’élastographie passive dans le plan transverse de la thyroïde.

Dispositif de génération d’ondes de cisaillement dans un fantôme tissulaire. Spectre de la vitesse particulaire dans le fantôme lors du passage des ondes de cisaillement pour 6 fréquences f=[83 101 116 138 153 178] Hz.
  • 2020
    20th May

    "Dynamic PET"

    3:00 pm
    Location: Visioconférence

    Zacharias Chalampalakis doctorant BioMaps

    Dynamic PET allows quantification of kinetic parameters that describe functions of the body at the molecular level by use of probes/radiopharmaceuticals. Whole-body dynamic imaging can extend research and clinical studies to study functions over the whole body. But it also poses various problems, especially for creation of parametric images, caused by low count statistics and limitations from the PET systems axial field of view. Optimised acquisition protocols and novel reconstruction algorithms have been developed and tested on PET/MR dynamic whole-body protocols at SHFJ, to reduce quantification bias and improve image quality of parametric imaging. Results so far show significant improvement in image quality, comparable to single organ PET studies, with similar quantification accuracy.

  • 2020
    6th May

    "Flexible multi-turn multi-gap coaxial RF coils: design concept and implementation for Magnetic Resonance Imaging at 3 and 7 Tesla"

    2:00 pm
    Location: Visioconférence

    Lena Nohava doctorante BioMaps/Université de Vienne

    Multi-turn multi-gap coaxial coils (MTMG-CCs) are flexible, form-fitting radio frequency (RF) coils for MRI extending the concept of the single-turn single-gap CC. It is demonstrated that the design enables free choice of the coil diameter, and thus, optimizing it for the application to a certain anatomical site, while operating at the self-resonance frequency. An equivalent circuit for MTMG-CCs is modeled and electromagnetic simulations are used to investigate the functioning principle of the MTMG-CC. Standard copper wire loop coils and flexible CCs made from commercially available coaxial cable types with diameters between 4 and 15 cm were fabricated as receive-only coils for 3 T and transmit/receive coils at 7 T. SNR, transmit efficiency, and active detuning performance of CCs and standard loop coils were compared in bench tests and MR experiments. MTMG-CCs can be sized to optimize sensitivity, are flexible and lightweight, and could therefore enable the fabrication of wearable coils with improved patient comfort.

  • 2020
    29th April

    "Echographie multiparamétrique du diaphragme"

    2:00 pm
    Location: Visioconférence

    Thomas Poulard doctorant BioMaps/Institut de myologie

    Mesurer la pression générée par le diaphragme est un enjeu clinique majeur, qui repose cependant sur des techniques invasives et peu utilisées. A travers ce travail, nous étudions dans quelles mesures l'échographie multi-paramétrique permet d'évaluer la contractilité du diaphragme de manière non-invasive. Nos efforts se sont concentrés sur les techniques d'élastographie par ondes de cisaillement appliquée chez le patient en réanimation, ainsi qu'à l'échographie ultrarapide permettant d'observer le comportement du diaphragme lors de stimulations magnétiques.

  • 2020
    6th February

    "Pushing the physical limits of Shear Wave Elastography"

    11:00 am
    Location: Salle verte, SHFJ, Orsay

    Dr. Javier Brum Maître de conférence de l'Université de Montevideo, Uruguay 

    For medical diagnosis, many techniques were developed within the past two decades for the noninvasive assessment of the tissue shear elasticity μ. These techniques are commonly denominated shear wave elastography (SWE). To provide a quantitative estimation of μ, SWE uses shear wave propagation inside the tissue, because under the hypothesis of an elastic, isotropic homogenous medium, the shear wave speed cT is directly linked to μ. However, in several medical applications the above physical hypothesis are not valid: tissue is viscoelastic, anisotropic and inhomogeneous. During this talk I will present some of the work me and my collaborators have been doing to push the physical limits of SWE. First I will present shear wave propagation in boundary sensitive organs, where waves are guided showing velocity dispersion effects. Second I will show how it is possible to simultaneously measure the viscoelastic properties of tissue using Supersonic Imagine (SSI). Finally, I will present a new approach termed “passive elastography” which is based on physiological noise correlation and time reversal of shear waves. 

  • 2020
    27th January

    "Immuno-radiothérapie et imagerie"

    11:00 am
    Location: Salle verte, SHFJ, Orsay

    Pr. Eric Deutsch de l'Institut Gustave Roussy