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Dynamic Contrast-Enhanced MRI (DCE-MRI) in Cerebral Tumors: Basics & Analysis
James R. Ewing, PhD
Henry Ford Health System, Dept. Neurology
Oakland University Dept. Physics – Wayne State University Dept. Neurology
DCE-MRI studies are an example of a long-employed class of methods in physiological measurements termed Indicator Dilution studies. In these studies, the behavior over time of an indicator in tissue is modeled in order to infer such physiological properties of the tissue as blood flow, vascular volume, vascular permeability and extracellular distribution volume. Conservation of mass is a first principle of the model formation, and a stationary two-port linear model is usually the underlying theoretical structure.
In the leaky vascular beds usually associated with cerebral pathologies, DCE-MRI studies may be able to produce a nearly complete description of the physiology of cerebral pathologies in the form of estimates of blood flow, plasma volume, vascular permeability-surface area product, and extracellular volume, subject to considerations of signal-to-noise. Models of the uptake and clearance of an MR contrast agent (MRCA) in tissue will be described, and an algorithm for model choice in cerebral tissue will be presented. Results of test-retest studies in rat models of cerebral tumors will be presented, and the short-term effects of standard therapies (radiotherapy, anti-angiogenic regimens) will be described. An ongoing cooperative study between the University of Florida and HFHS, consisting of a proposal to employ the experimental data produced by DCE-MRI to describe the mechanical and fluidic properties of embedded tumors will also be presented.
In all experiments, systematic errors undermine the utility of inferences. The systematic errors of DCE-MRI studies will be examined, as a cautionary tale of “tapering effects” in biological systems.
Dr. Ewing has functioned as an experimental physicist in a medical setting for the last half-century, leading the development and validation of methods for measuring vascular physiology in humans and animals, both in normal cerebral tissue, and in cerebral pathologies. Dr Ewing has over 120 peer-reviewed publications in these and related fields. His work of the last fifteen years has focused on measures of vascular physiology in cerebral tumors, where he has been principally concerned with making unbiased estimates of relevant physiological quantities (blood flow, extracellular volume, vascular volume and vascular permeability), and estimating the errors of those measures. In the field, both nationally and internationally, he has led, and continues to lead, an effort in Medical Physics to impose a rigorous and parsimonious analysis on dynamic MRI data for the production of robust and stable estimates of physiology, with a particular focus on cerebral tumors.