These two methods are being used at Julich Plant Phenotyping Centre (Germany) to investigate root/shoot systems growing in sand or soil, with respect to their structures, transport routes and the translocation dynamics of recently fixed photoassimilates labelled with the short lived radioactive carbon isotope 11C. Quantitative MRI and PET data will help not only to study the differences between species, but also in phenotyping of cultivars or plant lines in which growth pattern, water relations or translocation properties are important traits with respect to plant performance (Jahnke et al. 2009). Therefore, MRI-PET combination can provide new insights into structure-function relationships of intact plants. It also allows monitoring of dynamic changes in plant properties, which has not been possible to assess systematically until now to understand plant performance such as resource use efficiency or biomass production.