Imaging bicistronic gene expression. MicroPET imaging of the pCMV-D2R-IRES-tkm C6 tumors in a nude mouse. Three C6 cell lines stably transfected with pCMV-D2R-IRES-sr39tk (labeled A, B, C) and the C6 parental cell line (labeled D) were injected into four separate sites in a single mouse. After 10 days, when each tumor was at least 6 mm in diameter, the mouse was imaged with 2-[18F]-2-fluoro-deoxyglucose (FDG), followed 24 h later with [18F]-fluoroethylspiperone (FESP), followed 24 h later with 8-[18F]-fluoropenciclovir (FPCV). The FDG (whole body) image represents the average of all coronal (horizontal) planes and therefore the four tumors are not well visualized. The FDG (section) image taken from a set of planar images passing through all four tumors shows accumulation of FDG in all four tumors. Correlated signal intensity is observed between the FESP and FPCV images for each tumor. There is a high correlation between FESP and FPCV microPET signals. Br, Brain; Bl, bladder; R, rectum; %ID/g, percent injected dose per gram of tissue.