[A fluorine-18 labeled acycloguanosine derivative and a reporter probe with imaging activity. Used in conjunction with adenoviral gene transfer system containing report gene for herpes simplex virus type 1 thymidine kinase (HSV1-TK), 18F-FHBG can be phosphorylated by this enzyme, thereby accumulating in the adenoviral transfected cells. This allows for assessment of transfection tissue location and efficiency of gene transfer. ( NCI )] (UMLS (NCI) C0754974) 9-(4-18F-Fluoro-3-[hydroxymethyl]butyl)guanine; Reporter Probe 18F-FHBG; =Nucleic Acid, Nucleoside, or Nucleotide