Schematic illustrating a reporter gene approach. An imaging reporter gene has to be introduced into the cell, which is driven by a promoter of choice. Transcription of the imaging reporter gene with subsequent translation of the mRNA leads to an enzyme. This enzyme can selectively trap an imaging reporter probe. The imaging reporter probe will not be trapped in those cells in which there is no expression of the imaging reporter gene. Note that it is also possible for the imaging reporter gene to encode for an intracellular and/or cell surface receptor. This receptor would then bind the imaging reporter probe (a ligand). Levels of the trapped probe can be related to levels of imaging reporter gene expression in either approach.