Gene therapy often uses viral vectors to insert a therapeutic gene into cells. It is necessary to develop molecular imaging techniques to safely monitor gene expression. We designed a strategy to image expression of a transgene using a genetically engineered CEST reporter. An adeno associated vector encoding for 150 L-arginine residues fused to a fluorophore was produced and injected in the mouse brain. Specific signals were observed in both CEST and fluorescence modalities, demonstrating the possibility to use CEST-based reporter genes to monitor transgene distribution and expression. Such noninvasive imaging modality could be valuable for further developments of gene therapy.