Table 1.

Commonly used MRI reporter genes.

Gene/Protein	Contrast Mechanism	Observed Change	Test System	Ref.
Ferritin	Sequesters iron from labile intracellular iron pool and acts as an intracellular SPIO analog	T2 changes from 45 to 20 ms with 30 µg Ferritin expressed per mg of total protein (14 T)	Cell culture; viral-mediated transfection in mouse brain	[16]
Transferrin receptor (TfR)	Transferrin-conjugated SPIO particles are internalized by ectopically expressed TfR on transfected cells	50% change in T2-weighted MRI signal (3 mg iron injected per mouse, 7.1 T)	Mice implanted with TfR-expressing gliosarcoma cells	[17]
Tyrosinase (TYR)	TYR produces melanin to chelate metal ions (Fe3+)	37% increase in T1-weighted MRI signal (1.5 T)	Transfected mouse fibroblasts and HEK cells	[18]
β-galactosidase	Expressed β-gal cleaves a caged synthetic Gd3+ compounds	60% T1-weighted signal increase (3.2 nmol per frog embryo, 12 T)	Xenopuslaevisembryos transfected withLacZ	[19]
Lysine rich-protein (LRP)	Chemical exchange saturation transfer (CEST)	134% signal increase (6 days after 5 × 104 cells transplanted into the striatum of NOD-SCID male mice, 11.7 T)	Mice implanted with LRP and EGFP expressing xenografts respectively in opposite hemispheres	[20]