Methods and compositions are disclosed that lower the uptake of the radiopharmaceutical FDG, a glucose analog, by brown adipose tissue and the myocardium in FDG-PET/CT scans. The composition is substantially carbohydrate free and includes high levels of lipids. The method uses the composition and doses at particular times before the scan. The method has an advantage over fasting methods since it reduces the uptake by brown adipose tissue and/or myocardium that can be mistaken for cancer on FDG-PET or PET//CT scans or obscures sites of cancer adjacent to the heart. In addition, this permits the identification, monitoring and treatment of coronary artery disease on PET or PET/CT scans.