In preparation for F18 fluorodeoxyglucose (FDG) imaging, patients are required to fast to:

Fasting prior to F18 fluorodeoxyglucose (FDG) imaging is essential primarily to maximize tumor uptake. When patients fast, the insulin levels in their bloodstream decrease, which helps to ensure that glucose levels are also low. This is significant because FDG is a glucose analog; when glucose is diminished, tumors, which often have a higher metabolic demand and thus higher glucose uptake, will have increased accumulation of FDG. Enhanced tumor uptake allows for clearer imaging and better evaluation of cancerous tissues compared to normal tissues, which will uptake less FDG when the body is in a fasting state.

Maintaining this fasting state is critical for achieving an accurate representation of the metabolic activity of tumors during the imaging process, thereby improving diagnostic accuracy. Additionally, other physiological factors such as the avoidance of insulin release further support a higher relative uptake in malignant tissues versus normal tissues, primarily benefiting the imaging results.