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

Mechanisms of pressure-diuresis and pressure-natriuresis in Dahl salt-resistant and Dahl salt-sensitive rats

<p>Abstract</p> <p>Background</p> <p>Data on blood flow regulation, renal filtration, and urine output in salt-sensitive Dahl S rats fed on high-salt (hypertensive) and low-salt (prehypertensive) diets and salt-resistant Dahl R rats fed on high-salt diets were analyzed using a mathematical model of renal blood flow regulation, glomerular filtration, and solute transport in a nephron.</p> <p>Results</p> <p>The mechanism of pressure-diuresis and pressure-natriuresis that emerges from simulation of the integrated systems is that relatively small increases in glomerular filtration that follow from increases in renal arterial pressure cause relatively large increases in urine and sodium output. Furthermore, analysis reveals the minimal differences between the experimental cases necessary to explain the observed data. It is determined that differences in renal afferent and efferent arterial resistances are able to explain all of the qualitative differences in observed flows, filtration rates, and glomerular pressure as well as the differences in the pressure-natriuresis and pressure-diuresis relationships in the three groups. The model is able to satisfactorily explain data from all three groups without varying parameters associated with glomerular filtration or solute transport in the nephron component of the model.</p> <p>Conclusions</p> <p>Thus the differences between the experimental groups are explained solely in terms of difference in blood flow regulation. This finding is consistent with the hypothesis that, if a shift in the pressure-natriuresis relationship is the primary cause of elevated arterial pressure in the Dahl S rat, then alternation in how renal afferent and efferent arterial resistances are regulated represents the primary cause of chronic hypertension in the Dahl S rat.</p

Modèle de transport de molécules dans le foie (application à l'IRM dynamique)

L'analyse d'images est une méthode non invasive utilisée dans la définition du diagnostic des lésions du foie. En complément de l analyse visuelle effectuée par les radiologues, certaines méthodes quantitatives, telles que l'analyse de texture peuvent donner des résultats encourageants dans la caractérisation des tumeurs. Nous proposons de coupler un modèle bi-niveau du foie, prenant en compte des paramètres physiologiques et pathologiques, avec un modèle d'acquisition d'IRM, dans le but de comprendre certaines relations entre les caractéristiques de l'image et le développement tumoral. Un modèle pharmacocinétique basé physiologie (PBPK) distribué axialement et adapté au foie, permet de simuler la distribution de molécules d agents de contraste spécifiques au foie. Il est couplé à un modèle macroscopique de l organe et de sa vascularisation. Ce modèle multi-échelle permet la simulation de modifications d'ordre pathologique liées au développement du carcinome hépatocellulaire, et la simulation des images IRM correspondantes.Image analysis is a noninvasive technique used to define the diagnosis of liver lesions. In addition to the visual inspection brought by radiologists, some quantitative methods such as texture analysis can also give encouraging results regarding tumor characterization. We propose to couple a bi-level model of the liver, which takes into account some physiological and pathological parameters, with the simulation of dynamic MRI acquisition, in order to understand some relations between image characteristics and the tumor development. A new axially-distributed Physiologically-Based PharmacoKinetic (PBPK) model, adapted to the liver, enables the simulation of the distribution of liver-specific contrast agents. This model is coupled with a macroscopic model of the liver and of its vascularisation. The multiscale model allows for i) simulations of pathological modifications related to the development of the hepatocellular carcinoma, and ii) simulations of corresponding MR images.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Multiscale model of liver DCE-MRI towards a better understanding of tumor complexity.

International audienceThe use of quantitative imaging for the characterization of hepatic tumors in magnetic resonance imaging (MRI) can improve the diagnosis and therefore the treatment of these life-threatening tumors. However, image parameters remain difficult to interpret because they result from a mixture of complex processes related to pathophysiology and to acquisition. These processes occur at variable spatial and temporal scales. We propose a multiscale model of liver dynamic contrast-enhanced (DCE) MRI in order to better understand the tumor complexity in images. Our design couples a model of the organ (tissue and vasculature) with a model of the image acquisition. At the macroscopic scale, vascular trees take a prominent place. Regarding the formation of MRI images, we propose a distributed model of parenchymal biodistribution of extracellular contrast agents. Model parameters can be adapted to simulate the tumor development. The sensitivity of the multiscale model of liver DCE-MRI was studied through observations of the influence of two physiological parameters involved in carcinogenesis (arterial flow and capillary permeability) on its outputs (MRI images at arterial and portal phases). Finally, images were simulated for a set of parameters corresponding to the five stages of hepatocarcinogenesis (from regenerative nodules to poorly differentiated HepatoCellular Carcinoma)

Texture-based characterization of arterialization in simulated MRI of hypervascularized liver tumors.

International audienceThe use of quantitative imaging for the characterization of hepatic tumors in MRI can improve the diagnosis and therefore the treatment. However, image parameters remain difficult to interpret because they result from a mixture of complex processes related to pathophysiology and to acquisition. In particular, the lesion arterialization is prominent in the resulting contrast between normal and tumoral tissues in contrast-enhanced images. In order to identify this influence, we propose a multiscale model of liver dynamic contrast-enhanced MRI, consisting of a model of the organ coupled with a model of the image acquisition. A sensitivity analysis of the model to the arterial flow has enabled us to emphasize the existence of relationships between texture parameters in simulated arterial-phase MR images, and the arterialization phenomena involved in carcinogenesis

Effect of ageing on the cerebral hemodynamics in the marmoset monkey

International audienceAimCerebrovascular function declines during normal ageing and appears to be closely linked to brain functionalteration in the elderly. We adapted dedicated MRI sequences to analyze blood flow dynamics in arterial andvenous intracranial vessels, using a non-human primate model of significant interest for preclinical research, themarmoset monkey Callithrix jacchus.MethodsImaging sequences were acquired on a 7T MRI (Bruker Biospec, voxel size: 0,15x0,15X1mm3) on two groups ofmale and female marmosets: 10 young (4 years old) and 9 aged (9 years old). Internal carotid arteries, basilarartery, superior and inferior sagittal sinuses were first identified by Time Of Flight (TOF) sequences and flowvelocity in these different vessels was recorded by Phase Contrast (PC) MRI synchronized with ECG signal.ResultsThe main significant results show that during the cardiac cycle:-The blood flow peaks earlier in the basilary trunk than in the carotids.-The arterial flow peak occurs earlier in the aged than in the young marmoset brains.-The time interval between the arterial- and the venous flow peaks is shorter in old than in young marmosets.ConclusionsThese results reflect vessel rigidity and tissue compliance changes occurring during ageing in the vascularnetwork. They have not been shown in human studies, in which blood flow dynamics are usually synchronizedwith peripheral pulse measured on the fingertip. They suggest that the time courses of the different vascularflows could contribute as early markers of brain ageing and brain pathologies

Le singe marmouset comme modèle humain : Effet du vieillissement sur l'hémodynamique cérébrale.

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Diffeomorphic registration with self-adaptive spatial regularization for the segmentation of non-human primate brains

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Atlas statistique de la vascularisation cérébrale chez le singe marmouset

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Atlas statistique de la vascularisation cérébrale chez le singe marmouset

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