Imaging and targeted agents in gastrointestinal cancers: overview on perfusion- and diffusion-weighted magnetic resonance imaging and angiogenesis inhibitors

The advent of new antitumoral agents targeting tumoral vascularity require a change of diagnostic strategy. Imaging modalities should aim at detecting treatment-induced intratumoral changes as treatment success not necessarily leads to a substantial loss of tumor volume. The tumoral vasculature and cellular microstructure offer attractive diagnostic targets for functional magnetic resonance imaging (MRI)-techniques. Dynamic contrast-enhanced (DCE)-MRI demonstrates tissue perfusion and permeability and can be used as a pharmacodynamic indicator for the efficacy of antivascular treatment. Diffusion-weighted (DW)-MRI allows for tissue differentiation based on changes in tissular water mobility, acting as a surrogate marker for microstructural density. By its ability to differentiate intact tumoral tissue from necrosis, DW-MRI can be used for early assessment of tumor response to systemic treatment. The aim of this paper is to discuss the background, basic principles and potential applications of perfusion- and diffusion-MRI for follow-up of treatment with angiogenesis inhibitors.