Significant suppression of myocardial (18)F-fluorodeoxyglucose uptake using 24-h carbohydrate restriction and a low-carbohydrate, high-fat diet.

OBJECTIVES: (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) is a useful tool for evaluating inflammation. Because, myocardial-FDG uptake occurs with diverse physiology, it should be suppressed during evaluation of myocardial inflammation by FDG-PET/CT. Diets inducing fat-based metabolism, such as a low-carbohydrate, high-fat diet (LCHF), are used in uptake-suppression protocols. However, a complete suppression of myocardial-FDG uptake has not been established. Hence, we assessed the efficacy of 24-h carbohydrate restriction along with an LCHF diet compared to that of the conventional protocol in suppressing myocardial-FDG uptake and also compared fat and glucose metabolism between these protocols.

METHODS: Fourteen healthy volunteers agreed to undergo >24-h carbohydrate restriction (glucose, <10g) and drank an LCHF beverage an hour before FDG administration. A scan performed under conventional fasting protocol served as the control. The maximal standardized uptake values (SUVmax) of the left ventricular (LV) myocardium, and left atrium lumen (blood pool), liver, and lung fields as background, were measured. Blood sugar, free fatty acids (FFAs), insulin, and triglyceride concentrations were measured just before FDG injection and compared between the 2 protocols.

RESULTS: Global LV myocardial uptake was significantly lower with the diet-preparation protocol (SUVmax 1.31 [1.15-1.49] vs. 2.98 [1.76-6.43], p=0.001). Target-to-background ratios [myocardium-to-blood ratio (MBR), myocardium-to-lung ratio (MLR), and myocardium-to-liver ratio (MLvR)] were also significantly lower with the diet-preparation protocol [MBR: 0.75 (0.68-0.84) vs. 1.63 (0.98-4.09), p<0.001; MLR: 1.87 (1.53-2.47) vs. 4.54 (2.53-12.78), p=0.004; MLvR: 0.48 (0.44-0.56) vs. 1.11 (0.63-2.32), p=0.002]. Only insulin levels were significantly different between the subjects in each protocol group (11.3 [6.2-15.1] vs. 3.9 [2.9-6.2]).

CONCLUSION: Carbohydrate restriction together with an LCHF supplement administered 1h before FDG significantly suppressed myocardial-FDG uptake. FFAs and insulin might not directly affect myocardial-FDG uptake.