Poor Patient Preparation
Optimizing Pre-Scan Glucose and Insulin Levels:
As endogenous glucose competes with FDG at the cellular level, excess glucose will decrease FDG uptake in target tissues. Additionally, elevated blood glucose will stimulate insulin production, driving glucose (and FDG) into skeletal muscle. This results in decreased available FDG for tumor uptake and potential masking of tumor by surrounding hypermetabolic muscle activity.
- Patients are asked to fast for 5 hours prior to the exam. If fasting blood sugar prior to FDG injection is greater than 200 mg/dL, the examination is rescheduled (a blood sugar of less than 150 mg/dL is considered optimal).
- Diabetic Patients: While there are currently no universally accepted preparation guidelines for diabetic patients, we ask these patients refrain from their diabetes medications for 5 hours prior to their scan time. We typically schedule these diabetic patients for early morning, asking the patients to stop their medications by midnight the night prior to imaging.
- Low Carbohydrate Diet: Some radiologists recommend a low carbohydrate diet for the 24-hour period before the exam. This serves to decrease normal myocardial uptake, which can mask adjacent disease.
- Hydration: Patients are advised to drink at least a liter of water the day of the exam (they may drink right up until the time of the exam).
No Strenuous Exercise for 24-Hours Prior to Exam:
Exercise drives glucose (and FDG) into skeletal muscles, both decreasing available FDG for tumor uptake, and potentially masking pathologic uptake by the surrounding muscle activity.
After injection of FDG, patients are also asked to refrain from talking (to prevent laryngeal muscle uptake) and reading (to prevent extra-ocular muscle uptake).
Void Just Prior To Exam:
As the urinary bladder will fill with radiotracer, potentially masking adjacent disease, patients are asked to empty their bladder just prior to imaging.
Patient Instruction Sheet:
Each patient either receives a copy of this pre-scan instruction sheet or is read these instructions over the phone.
