Abstract: The energy substrate environment in body (the level of plasmaglucose and free fat acid et al) during the ¹⁸F-FDG imaging significantly affects the uptake of ¹⁸F-FDG in the tissues of tumor, myocardium and brain. It will further influence the quality of image, the clinical analysis of the image and the clinical judgement based on the ¹⁸F-FDG imaging. So during the ¹⁸F-FDG study,reasonably controlling of energy substrate environment according to the clinical study purpose is the basis of improving the quality of image and making correct analysis of the image.