The development of in vivo imaging systems to study gene expression.

Imaging techniques are currently being developed to map the topography and level of gene expression following gene therapy. To date, two different imaging strategies have been investigated--using marker genes encoding either intracellular enzymes or cell-surface receptors. The first approach employs the ability of certain enzymes to modify imaging prodrugs, so that tissue accumulation of such drugs reflects the expression. The second approach utilises cell-surface expression of a ligand-binding receptor that can be detected using imaging tracers. In this review, we discuss nuclear-and magnetic-resonance-image techniques that have been developed to detect gene expression.