Figure 2. In vivo use of a gadolinium based smart contrast agent to demonstrate gene transfection. When the enzyme -galactosidase is expressed in engineered cells, the -galactopyranose ring protecting the Gd³⁺ is cleaved allowing bulk water access to the paramagnetic gadolinium ion. The images labelled A and B are of Xenopus (African claw toed frog) embryos that express -galactosidase or not. The embryo labelled +mRNA is expressing -galactosidase and significantly more detail is seen in this embryo than the one labelled –mRNA. The bottom embryo is oriented upside down compared with the top one. Reproduced with permission [28].