9.1 - THE DIAGNOSTIC IMPORTANCE OF FACTORS THAT INTERFERE WITH [F-18] FDG BIODISTRIBUTION.

Etchebehere ECSC, Vítola JV, Ramos CD, Barros FB, Santos AO, Lima MCL, Camargo EE. Division of Nuclear Medicine, Campinas State University (UNICAMP), Campinas, Brazil.

[F-18]FDG, an analog of glucose, is a metabolic tracer which is trapped in the cell after its conversion into FDG-6-PO4 by hexoquinase. Tissues with high levels of glucose-6-phosphatase such as the liver, kidneys, intestines and muscles, accumulate FDG-6-PO4. The purpose of this study is to demonstrate the normal distribution of [F-18] FDG and its variations. Whole body images were performed after an intravenous injection of [F-18]FDG in 5 patients after fasting for 6 hours and in 1 patient after insulin clamp. Studies were analyzed visually and semi-quantitatively. Whole body, brain, heart, liver and muscle counts were obtained in the anterior projection. In the patients studied in the fasting state the following [F-18]FDG distribution was observed: muscles (54,4%), brain (11,7%), liver (9,7%) and heart (1,9%). In the patient submitted to insulin clamp there was a significant change in [F-18]FDG distribution : muscles (75,2%), liver (4,4%), heart (3,7%) and brain (2,8%). The marked change in concentration in muscles, brain, liver and to a lesser extent in the heart when fasting is compared to insulin clamp should be taken into consideration when planning these studies. For example, myocardial concentration must be minimized when one searches for lung metastases; liver concentration must be minimized when one searches for liver metastases; muscle concentration must be minimized when searching for skin metastases. Besides insulin there are other factors that interfere with [F-18]FDG uptake. In these patients, [F-18]FDG was present in other normal structures such as kidneys, bladder and intestines. There are also reports that demonstrate increased [F-18]FDG uptake in increased muscular activity, sites of inflammation, bladder diverticulum, breasts while feeding, thymus, etc.