Abstract
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Objectives Brown Adipose Tissue(BAT) is present in a significant number of adult humans and can be activated by exposure to cold. Precise estimates of active BAT volume are desirable for determining the efficacy of treatments which activate BAT. The reproducibility of measurements of BAT presence/activity under controlled conditions have not been fully studied.
Methods 8 female volunteers had baseline and follow up FDG PET/CT performed under conditions of a cold intervention to activate brown fat. The cold intervention involved the participant placing their feet on a cold block of ice while sitting in a cooled room. A repeat study was performed under the same conditions within a target two weeks. Whole body scans were assessed qualitatively on a 0-4 point scale for the presence/intensity as well as the extent of BAT. SUV max and total BAT metabolic volume were determined using PERCIST 1.0 liver +2SD threshold values
Results Qualitative assessments of BAT were generally well-correlated in test-re test studies. 5 patients had intense BAT uptake at baseline (>or=3). All of these 5 had BAT activity on follow up scans. Max BAT SUV was only weakly correlated in test re-test studies , r=.33. Mean SUV baseline was 3.0 +/- 1.68 (SD) while follow up Mean SUV was 7.27 +/- 9.19 (SD) (p=.18). MTV of active BAT varied widely between test and re-test in some cases by over a factor of 20.
Conclusions FDG PET/CT can detect BAT under conditions of controlled cold intervention in humans. While qualitative presence of BAT appears reasonably correlated between test and re test imaging, quantitative assessments of SUV and BAT MTV vary substantially. The considerable variation in test re-test estimates of BAT with FDG PET imply sample sizes will need to be large in studies quantifying physiological changes in BAT volumes and metabolic activity related to treatment and support the highly dynamic character of this tissue.
Research Support NIH R21DK09078