Effects of a short interval carbohydrate free diet on tissue FDG uptake

Purpose: Tight glucose control is essential for 18-Fludeoxyglucose (18F-FDG) positron emission tomography (PET) imaging. A strategy to ensure appropriate glucose levels is to advise a carbohydrate free diet prior to scanning. This alters glucose metabolism which can have ramifications on tissue FDG biodistribution. The aim of this study is to evaluate the effects of advising a carbohydrate free diet for two days prior to PET scan on FDG uptake in the liver, heart, bone marrow, skeletal muscle and tumor. Materials and methods: All patients at an outpatient facility were advised to maintain a diet free of carbohydrates for two days prior to 18F- FDG PET/Computed tomography (CT) scanning to maintain glucose control at the time of the scan. Self reported adherence to the diet was recorded by the scheduling coordinator on the day of imaging. A retrospective analysis of 228 consecutive 18F-FDG PET/CT scans was performed in which the maximum standardized uptake value (max SUV) was recorded for the following six sites: right and left hepatic lobes, left ventricle of the heart, sacrum, thigh and tumor. The max SUV of the patients who adhered to the diet (n=144) were compared with those who did not (n=85). Results: The average max SUV for the right and left hepatic lobes and the left ventricle were 3.93±0.78, 3.70±0.76 and 6.34±5.12 for the adherent patients and 3.63±0.84, 3.41±0.80 and 6.98±4.69 for the non-adherent patients. The average max SUV in the hepatic lobes of the adherent group was statistically significantly higher by 8.2% in the right lobe and 8.8% in left lobe when compared with the non-adherent group ( p <0.003). The average max SUV in the heart of the adherent group was statistically significantly lower by 10% when compared with the non-adherent group ( p <0.040). No significant difference was observed in the remaining tissues, including tumor. Conclusions: Altering carbohydrate intake can significantly affect the metabolic milieu (FDG biodistribution in normal tissues). The liver max SUV in patients on a carbohydrate free diet prior to PET scanning was higher than those who were not. This difference should be kept in mind when defining a normal cut off threshold SUV in the liver.