# MRI contrast agents

Metal complexes, and particulary Gadolinium complexes, of tetraazacycloalkanes are used as contrast agents for magnetic resonance imaging (MRI).

# PET and SPECT contrast agents

Macrocyclic complexes of radiometals are used as contrast agent for Positron Emission Tomography and Single-Photon Emission Computed Tomography. Generally, theses applications require the synthesis of bifunctional chelating agents in order to connect the radiometal complexe to a biomolecule such as monoclonal antibodies or peptides.