Reporter gene imaging with PET/SPECT

Molecular imaging (MI) allows in vivo visualization of normal and abnormal cellular processes at the molecular and genomic levels, rather than at the anatomical level. MI is a relatively new biomedical discipline that enables cellular and subcellular biologic processes within living subjects to be visualized, characterized, and quantified. MI combines molecular biology and medical imaging and is increasingly attracting research attention in the molecular cell biology, chemistry, genetics, biomedical physics, engineering, and medical fields. It can be used to study genomics, proteomics, metabolomics, various intracellular processes, and cell–cell interactions. A major focus of MI is genetic imaging, that is, “molecular–genetic imaging, ” and imaging reporter genes are set to play a leading role in molecular–genetic imaging.Conventionally, gene expression levels can be determined by assaying reporter gene expression. To achieve this, a recombinant plasmid is constructed that expresses simultaneously a gene of interest and a reporter gene in a correlated manner, then it is transfected into target cells. When transcription and translation of the gene of interest and reporter gene occur simultaneously, by assaying reporter protein activity, gene expression can be indirectly evaluated in transfected cells. Conventional reporter genes include β-galactosidase, alkaline phosphatase, luciferases, and green fluorescent protein, but the conventional techniques of assaying them often required tissue sampling. More recent techniques with imaging reporter genes allow noninvasive and repetitive determination of transgene expression studies in living animals.