[{"from": "human", "value": "Please give me some details about this molecule. [C][=N][C][=C][Branch1][=N][N][Ring1][Branch1][C][C][C][Branch1][Ring1][C][O][C][18F][N][=C][Branch1][=Branch1][N][C][Ring1][=C][=O][N]"}, {"from": "gpt", "value": "The molecule is a fluorine-18-labeled acycloguanosine derivative substrate for herpes simplex virus type-1 thymidine kinase (HSV1-tk). 18F-FHBG is used as a reporter probe to image the expression of the herpes simplex virus type-1 thymidine kinase (HSV1-tk) gene in gene transfer therapy. HSV1-tk and HSV1-tk-metabolized 18F-FHBG co-localize, allowing positron emission tomography (PET) localization of HSV1-tk gene-transfected tissue and the assessment of gene transfer efficiency."}]