METHODS FOR QUANTITATIVE ASSESSMENT OF TI SSUE MICROCIRCULATION USINGDYNAMIC CONTRAST-ENHANCED MR-IMAGING

The development of rapid magnetic resonance imaging (MRI) sequences ma kes it possible to detect the fast kinetics of tissue response after i ntraveneous administration of paramagnetic contrast media (CM), reflec ting the status of tissue microcirculation. In this paper, the basic p hysical and tracer kinetic principles of dynamic relaxivity and suscep tibility contrast MRI techniques are reviewed. The quantitative analys is of the acquired dynamic image data is broken up into an MR specific part, in which the observed signal variations are related to the CM c oncentration in the tissue, and an MR independent part, in which the c omputed concentration-time-courses are analyzed by tracer kinetic mode ling. The purpose of the applied models is to describe the underlying physiological processes in mathematical terms and thus to enable the e stimation of tissue specific parameters from measured dynamic image se ries. Whereas the capillary permeability can be estimated from dynamic relaxivity contrast enhanced MRI studies, the regional blood volume a s well as the regional blood flow can be determined from dynamic susce ptibility contrast enhanced image series. However, since there are no intravascular but only diffusible CM available at present, the applica tion of the susceptibility technique is currently restricted to brain tissues with intact blood brain barrier. The practical realization of both dynamic MRI techniques is demonstrated by case studies.