The invention provides a composition of matter of the formula (I): V-L-R, where V is a vector moiety having affinity for an angiogenesis-related endothelias cell receptor, L is a linker moiety or a bond and R is a detectable moiety, characterised in that V is a non-peptidic organic group, or V is peptidic and R is a macromolecular or particulate species providing a multiplicity of labels detectable in in vivo imaging.