What is the normal pattern of FDG uptake in the body?
High FDG uptake is observed in the gray matter of the brain. Also, high FDG activity is seen in the collecting systems, ureters, and bladder due to urinary excretion of FDG, which can be mitigated by patient hydration and voiding prior to image acquisition. Mild to moderate FDG uptake is usually seen in the tonsils, salivary glands, tongue, vocal cords, brown fat, bone marrow, liver, stomach, and large bowel. Mild FDG uptake is usually seen in the thyroid gland, esophagus, small bowel, spleen, and skeletal muscle. Minimal FDG uptake is seen in the lungs and pancreas. Variable FDG uptake is observed in the myocardium, as the heart uses glucose as well as fatty acids as sources of fuel. FDG uptake will generally be increased in the myocardium with a carbohydrate rich meal and decreased with a fatty rich meal prior to PET scanning.
Minimizing talking and patient movement as well as keeping the environment quiet and dimly lit during the FDG uptake period are methods to decrease FDG uptake in the normal tissues of the head and neck and skeletal muscles. In general, FDG uptake in bilaterally located organs should be symmetric, and up to 70% of unexpected findings detected on FDG PET are malignant or premalignant in nature.