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Department of Radiology - Medical Physics

PD Dr. 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. While there are several innovative approaches to boosting the spatial resolution of MRI, these developments do not promise an image resolution better than of the order of a millimeter when considering MRI of large parts of the human body due to stringent physical and physiological limits on the measurements. Hence, the “mesoscopic” 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 mesoscopic 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, by combining gradient echo and spin echo signals, both acquired with 2-3 mm resolution.  

Obviously, not all cellular features survive such a massive averaging. In fact, most of the structural information about tissues at the cellular scale is lost. It is the aim of the mesoscopic MRI to establish which tissue properties can be “recovered” from the MR signal, and how to quantify them, with the ultimate goal of providing objective clinical biomarkers. This requires a new level of understanding how the measured MR signal originates at a cellular level, and how the mesoscopic structural features evolve upon averaging over a macroscopic voxel. Methods of modern theoretical physics, which have been originally developed within statistical and condensed matter physics to characterize complex media, prove invaluable in addressing this challenge.

I believe that the mesoscopic MRI approach holds tremendous promise for development of MRI towards 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 and neurodegenerative diseases.  


Prof. Dr. Dr. h.c. Jürgen Hennig

Scientific Director
Tel. +49 761 270-38360
Fax +49 761 270-38310

University Medical Center Freiburg
Dept. of Radiology · Medical Physics
Killianstrasse 5a       
79106 Freiburg, Germany

Laurence Haller
Assistant to the Scientific Director
Tel. +49 761 270-38350

For general inquiries: