Tissues which are rapidly dividing, such as cancer cells, have increased metabolic rates,
and subsequently an increased uptake of
glucose which provides the
fuel for
metabolism. Therefore, cancer cells usually show increased activity in a PET scan because of increased glucose uptake. However, some normal body tissues, like the bone marrow or the intestinal mucosal lining, are also actively dividing or have high metabolic rates and may also show activity in PET.