Methods for quantitative assessment of tissue microcirculation using dynamic contrast-enhanced MR imaging

The development of rapid magnetic resonance imaging (MRI) sequences makes it possible to detect the fast kinetics of tissue response after intraveneous administration of paramagnetic contrast media (CM), reflecting the status of tissue microcirculation. In this paper, the basic physical and tracer kinetic principles of dynamic relaxivity and susceptibility contrast MRI techniques are reviewed. The quantitative analysis 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 concentration in the tissue, and an MR independent part, in which the computed concentration-time-courses are analyzed by tracer kinetic modeling. The purpose of the applied models is to describe the underlying physiological processes in mathematical terms and thus to enable the estimation of tissue specific parameters from measured dynamic image series. Whereas the capillary permeability can be estimated from dynamic relaxivity contrast enhanced MRI studies, the regional blood volume as well as the regional blood flow can be determined from dynamic susceptibility contrast enhanced image series. However, since there are no intravascular but only diffusible CM available at present, the application 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.