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apl. Prof. Dr. (Rus) Valerij G. Kiselev

Medical Physics
Department of Radiology
University Medical Center Freiburg

Killianstrasse 5a
79106 Freiburg

Tel.: +49 761 270 93880
Fax: +49 761 270 38310

It is all about the question “How to see the invisible?”, the invisible being biological cells, the fundamental structural units of living organisms. Magnetic resonance imaging (MRI) provides anatomical maps of living tissues with a “macroscopic” resolution, of about a millimeter. Hence, the microscopic cell size, typically of the order of a micrometer, is just about 1000x too fine for the clinical MRI. Consequently, the signal acquired with a coarse macroscopic resolution is a result of a massive averaging over contributions from millions of cells with their individual sizes, shapes, arrangement, membrane permeability and other physical and physiological properties.

The microstructural MRI aims at obtaining quantitative information about these properties in vivo using various MRI modalities at the typical resolution of clinical scanners. An example is the Vessel Size Imaging, a method developed for clinical applications in our group to evaluate the mean size of capillaries, which is of the order of 10 micrometers, using MRI with 2-3 mm spatial resolution. While keeping the same paradigm, the focus of modern development is shifted towards diffusion of water molecules in the complex cellular environment.

The insight in tissue microstructure is enabled by understanding physics of MRI signal formation. It is mainly methods of soft condensed matter physics that help to realize what cellular features survive the massive averaging by the coarse MRI resolution. In the environment of the University Hospital, physicists are tightly connected to medical doctors, which greatly help for mutual inspiration about new diagnostic methods.

I believe that the microstructural MRI holds tremendous promise for quantifying tissue structure far below the nominal MRI resolution. Its applications will help address fundamental problems in tissue physiology, as well as will be instrumental in early detection and diagnosis of tumors, stroke, neurodegenerative and other diseases.