Present role of dynamic tests of thyroid function.

Abstract

<b>1365</b> <h3><b>Objectives</b></h3> The use of FDG PET/CT for detecting pathology of the small and large bowel is limited by the presence of normal physiologic FDG uptake. In order to suppress normal bowel uptake it is necessary to determine the origin of this uptake. In a prior study, we showed evidence that large bowel FDG uptake, seen on normal PET-CT scans, is intraluminal. The goal of this study is to determine the site of FDG secretion into the GI tract. <h3><b>Methods</b></h3> To confirm our hypothesis, patients with ileostomies were recruited for an IRB approved prospective study. Volunteers were asked to prepare for the FDG injection as they would for a clinical study. Ileostomy volunteers received 1.5 mCi of FDG and then emptied their ileostomy bags at predetermined times following injection. The samples collected were then imaged in a PET/CT scanner and SUVmean was recorded. <h3><b>Results</b></h3> Three ileostomy volunteers have been completed for the prospective study. Following low dose administration of FDG, ileostomy contents from all three volunteers showed high FDG activity (SUVmean &gt; 3) relative to blood (SUVmean = 1) at two-hours. These results indicate that FDG is secreted within the small bowel. In addition, since SUVmean of the samples were greatest at two-hours for all three volunteers, it appears that FDG activity peaks between one and four-hours post-FDG injection. <h3><b>Conclusions</b></h3> Although classic gastrointestinal physiology posits a one way transfer of glucose across the intestinal membrane into the blood, this study indicates that FDG, and presumably glucose, can also be transferred into the intestinal tract beginning in the small intestine, and is responsible for at least some of the uptake seen on PET/CT scans. Future studies are necessary to determine how FDG secretion and uptake in the small bowel correlates with the presence of physiologic FDG uptake in the colon