Couplage d'un modèle vasculaire bi-niveau et d'un modèle d'acquisition d'images : application à la simulation d'IRM dynamique du Carcinome Hépatocellulaire

La modélisation physiologique permet de mieux comprendre les images médicales et de mettre en évidence, dans l'image, des marqueurs de la pathologie. Dans cet article, nous proposons de coupler un modèle de la vascularisation hépatique à un modèle d'acquisition d'Images de - Résonance Magnétique (IRM), et d'appliquer ces modèles à la simulation d'IRM dynamique du Carcinome Hépatocellulaire (CHC). Le modèle vasculaire intègre les propriétés anatomiques et fonctionnelles clos vaisseaux, modifiées au cours du développement tumoral (densité vasculaire, débits, perméabilité, etc). Il permet de simuler la propagation de différents produits de contraste, ou tenant compte de leurs principales propriétés physiques et magnétiques, aux niveaux macro- et micro-vasculaire. Les images simulées à clos temps d'acquisition différents (phase artérielle, phase portale) présentent clos contrastes proches de ceux observés sur clos images réelles

Application of texture analysis to muscle MRI: 1-What kind of information should be expected from texture analysis?

Several previous clinical or preclinical studies using computerized texture analysis of MR Images have demonstrated much more clinical discrimination than visual image analysis by the radiologist. In muscular dystrophy, a discriminating power has been already demonstrated with various methods of texture analysis of magnetic resonance images (MRI-TA). Unfortunately, a scale gap exists between the spatial resolutions of histological and MR images making a direct correlation impossible. Furthermore, the effect of the various histological modifications on the gray level of each pixel is complex and cannot be easily analyzed. Consequently, clinicians will not accept the use of MRI-TA in routine practice if TA remains a “black box” without clinical correspondence at a tissue level. A goal therefore of the multicenter European COST action MYO-MRI is to optimize MRI-TA methods in muscular dystrophy and to elucidate the histological meaning of MRI textures.info:eu-repo/semantics/publishedVersio

Editorial for "Noninvasive Assessment of APAP-Induced Hepatotoxicity Using Multiple MR Parameters in an Experimental Rat Model"

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Développements méthodologique en IRM dynamique (vers la caractérisation des états précancéreux et cancéreux du foie)

L'IRM dynamique du foie permet de caractériser la fibrose et les tumeurs hépatiques. Cependant cette méthode est exigeante en terme de rapport signal sur bruit et de temps d'acquisition, et particulièrement pour les modèle animaux comme le rat et la souris. Cette étude présente le développement de méthodes pour améliorer la quantification de T1 et de la concentration d'agent de contraste. Ces méthodes sont ensuite appliquées dans un protocole complet d'imagerie de perfusion in vivo.Dynamic MRI in the liver enable to characterize the liver fibrosis and liver tumors. Yet this method requires both good signal to noise ratio and short acquisition time to apply the DCE MRI on small animal models like mice and rats. Methods are proposed in this study to improve the quantification of T1 and the contrast agent concentration. Then those methods are applied in a complete in vivo protocol of perfusion imaging.RENNES1-BU Santé (352382103) / SudocSudocFranceF

Mapping of low flip angles in magnetic resonance.

International audienceErrors in the flip angle have to be corrected in many magnetic resonance imaging applications, especially for T1 quantification. However, the existing methods of B1 mapping fail to measure lower values of the flip angle despite the fact that these are extensively used in dynamic acquisition and 3D imaging. In this study, the nonlinearity of the radiofrequency (RF) transmit chain, especially for very low flip angles, is investigated and a simple method is proposed to accurately determine both the gain of the RF transmitter and the B1 field map for low flip angles. The method makes use of the spoiled gradient echo sequence with long repetition time (TR), such as applied in the double-angle method. It uses an image acquired with a flip angle of 90° as a reference image that is robust to B1 inhomogeneity. The ratio of the image at flip angle alpha to the image at a flip angle of 90° enables us to calculate the actual value of alpha. This study was carried out at 1.5 and 4.7 T, showing that the linearity of the RF supply system is highly dependent on the hardware. The method proposed here allows us to measure the flip angle from 1° to 60° with a maximal uncertainty of 10% and to correct T1 maps based on the variable flip angle method

SIMULATION OF HEPATOCELLULAR CARCINOMA IN MRI BY COMBINED MACROVASCULAR AND PHARMACOKINETIC MODELS

International audiencePhysiological modeling is a way to better understand medical images, and to find some image markers of pathology. As far as the main hepatic tumor is concerned (Hepatocellular Carcinoma), the changes we try to reveal in images are mainly vascular ones. These modifications can be seen in Magnetic Resonance Images, whose visual analysis is usually performed by radiologists in order to detect and characterize liver lesions. We propose to model i) the liver and its pathological vascular changes related to tumoral development and ii) the MRI acquisition after injection of contrast product. The hepatic vascularization is modeled from the main branches until capillaries, including several parameters characterizing the tumor. The output of this physiological model constitutes the input of the MRI simulator. This one is based on the Bloch equations and images depend on the acquisition parameters, the tissue properties (relaxation times, proton density) and the contrast product propagation

Effect of a vascular disruptive agent (DMXAA) on extracellular pH measured by 1H-MRS in a glioma model in mice.

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Suivi in vivo de nanomédecines par spectroscopie localisée de diffusion

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