NMR methods for imaging of transport processes in micro-porous systems

Magnetic resonance imaging (MRI) allows non-destructive and non-invasive measurement and visualisation of both static and dynamic water phenomena. Flow and transport processes can either be measured by following the local intensity in time-controlled sequential images, by mapping the effect of contrast agents or labelled molecules, or by mapping the (proton) displacement in a well known time interval directly. By a proper choice of methods, a time window ranging from milliseconds to weeks (or even longer) can be covered. Combining transport measurements with relaxation time information allows the discrimination of transport processes in different environments or of different fluids, even within a single picture element within an image. Here we present an overview of the principles of NMR imaging techniques to visualise and unravel complex, heterogeneous transport processes in porous systems. Applications and limitations will be discussed, based on results obtained in model and artificial soil systems. (C) 1997 Elsevier Science B.V.