Technical Notes

Patient preparation for FDG PET scanning is very important. Hyperglycemia from poorly controlled diabetes is the most common cause of poor-quality FDG PET scans. The elevated glucose levels alter the FDG uptake of both normal tissues and tumors. The excess glucose competes with the FDG for access to the GLUT receptors on the cell membranes. Glucose levels over 200 mg/dl lessen the ability of FDG PET to detect small and subtle cancer foci.

All patients referred for a PET scan must be questioned to determine if they are diabetic and if medications are required to control their diabetes. Diet controlled diabetics require no special preparation. All patients should fast six hours prior to a PET scan, whether they are diabetic not. Since diabetic control is best in the morning, diabetic patients are scheduled in the early to mid morning. It is important to warn the diabetic patient that their fingerstick blood sugar will be checked as one of the first things that is done and that the goal is a blood sugar less than 150 mg/dl.

Diabetic patients on oral medications should be maintained on those oral medications regardless of the type of medication. Patients taking insulin should receive one half to sometimes three-fourths of their long-acting insulin in the morning, but no regular insulin. No regular insulin should be given within two hours of the PET scan or it will drive the FDG into muscle tissue. After the patients have their uptake period of thirty-five to forty-five minutes, they receive one or more glasses of orange juice so that they do not become hypoglycemic during the actual scanning period. This is always performed whether the patient is taking oral medicines or insulin.

If one carefully follows the regimen of identifying the diabetics, specifically providing instructions for them, warning them that their blood sugar will be checked and that there are repercussions to their blood sugar being too high, adjusting their insulin and giving them orange juice before their scan, one can obtain high-quality PET images even in some of the more poorly controlled diabetics. My goal is diabetic control for one day for one PET scan.