Physiological modeling of tumor-affected renal circulation.

International audienceOne way of gaining insight into what can be observed in medical images is through physiological modeling. For instance, anatomical and functional modifications occur in the organ during the appearance and the growth of a tumor. Some of these changes concern the vascularization. We propose a computational model of tumor-affected renal circulation that represents the local heterogeneity of different parts of the kidney (cortex, medulla). We present a simulation of vascular modifications related to vessel structure, geometry, density, and blood flow in case of renal cell carcinoma. We also use our model to simulate computed tomography scans of a kidney affected by the renal cell carcinoma, at two acquisition times after injection of a contrast product. This framework, based on a physiological model of the organ and physical model of medical image acquisition, offers an opportunity to help radiologists in their diagnostic tasks. This includes the possibility of linking image descriptors with physiological perturbations and markers of pathological processes

Modeling of tumor conspicuity in hepatic CT images: combined compartment and vascular models

International audienceThe aim of this work is to simulate dynamic CT scan of the liver, in normal tissue and in a hypervascular tumor. Two models are developed: a physiological vascular model for the main vessels, until arterioles and venules, and a compartment model for parenchyma enhancement. Combining these two models allows us to compute locally the contrast product concentration, all along the propagation, after injection in the hepatic artery and the portal vein. In the second step, a density representation of the organ is created and CT scans are simulated by using the standard reconstruction algorithm - filtered backprojection. As a final step, enhancement curves are extracted from the obtained images, showing very good agreement with real hepatic enhancement in CT

A physiologically based pharmacokinetic model of vascular-extravascular exchanges during liver carcinogenesis: application to MRI contrast agents.

This is a preprint of an article published in Contrast Media & Molecular Imaging Copyright © 2007 Wiley Periodicals, Inc. http://www.insterscience.wiley.comInternational audienceThe extraction of physiological parameters by non-invasive imaging techniques such as dynamic magnetic resonance imaging (MRI) or positron emission tomography requires a knowledge of molecular distribution and exchange between microvascularization and extravascular tissues. These phenomena not only depend on the physicochemical characteristics of the injected molecules but also the pathophysiological state of the targeted organ. We developed a five-compartment physiologically based pharmacokinetic model focused on hepatic carcinogenesis and MRI contrast agents. This model includes physical characteristics of the contrast agent, dual specific liver supply, microvessel wall properties and transport parameters that are compatible with hepatocarcinoma development. The evolution of concentrations in the five compartments showed significant differences in the distribution of three molecules (differentiated by their diameters and diffusion coefficients ranging, respectively, from 0.9 to 62 nm and from 68.10(-9) to 47.10(-7) cm(2) s(-1)) in simulated regeneration nodules and dysplastic nodules, as well as in medium- and poorly differentiated hepatocarcinoma. These results are in agreement with known vascular modifications such as arterialization that occur during hepatocarcinogenesis. This model can be used to study the pharmacokinetics of contrast agents and consequently to extract parameters that are characteristic of the tumor development (like permeability), after fitting simulated to in vivo data

Multiscale modeling and imaging: the challenges of biocomplexity

International audienceComputational modeling and imaging in biology and medicine are gaining more and more interest with the discovery of in-depth structural and functional knowledge at all space and time scales (molecule to proteins, cells to organs and organisms). The recursion between description levels for highly dynamical, interacting and complex systems, i.e the integrative approach, is a very challenging topic where formal models, observational tools and experimental investigations have to be closely designed, coupled and confronted together. Imaging techniques play a major role in this interdisciplinary attempt to elucidate this biocomplexity: they convey relevant information about the underlying mechanisms, depict the conformations and anatomical topologies and draw the biophysical laws they may follow. Furthermore, the basic image analysis tools (from calibration to segmentation, motion estimation and registration up to pattern recognition) are generic enough to be of value whatever the objects under consideration. The same comments apply when Computer Graphics or Virtual Reality techniques are concerned. This paper will survey the recent contributions dealing with both models, imaging data and processing frames. Examples ranging over different scales, from macro to nano, will be given in order to enhance the mutual benefits and perspectives that can be expected from this coupling

A new approach in combined modeling of MRI and blood flow: A preliminary study.

International audienceWe propose a computational model to simulate the physical processes implied in the Magnetic Resonance Images formation in vascularised tissues. A combined model of MRI acquisition and blood flow is presented. The blood flow patterns are modeled using the Lattice Boltzmann Method, and the magnetic resonance experiments follow the Bloch equation. A new algorithm has been developed to compute the local magnetizations transport during the excitation, precession and relaxation steps. First results were compared to theoretical values of phase flow accumulation and amplitude attenuation. Next, the proposed algorithm is applied to simulate MR images in a simple stenosed vessel and in bifurcations. Characteristic flow artefacts are observed