ORIGINAL ARTICLE Seasonal variation in the effect of constant ambient temperature of 24°C in reducing FDG uptake by brown adipose tissue in children Katherine A. Zukotynski & Frederic H. Fahey & Stephen Laffin & Royal Davis & S. Ted Treves & Frederick D. Grant & Laura A. Drubach Received: 12 January 2010 / Accepted: 18 April 2010 / Published online: 27 May 2010 # Springer-Verlag 2010 Abstract Purpose It has been shown that warming patients prior to and during 18 F-FDG uptake by controlling the room temperature can decrease uptake by brown adipose tissue (BAT). The aim of this study is to determine if this effect is subject to seasonal variation. Methods A retrospective review was conducted of all patients referred for whole-body 18 F-FDG PET between December 2006 and December 2008. After December 2007, all patients were kept in the PET injection room at a constant 24°C for 30 min before and until 1 h following FDG administration. Patients over 22 years of age and those who received pre-medication known to reduce FDG uptake by BAT were excluded. One hundred and three patients were warmed to 24°C prior to scanning. The number of patients showing uptake by BAT in this group was compared to a control group of 99 patients who underwent PET prior to December 2007 when the injection room temperature was 21°C. Results Uptake by BAT occurred in 9% of studies performed after patient warming (24°C), compared to 27% of studies performed on the control group (21°C) (p <0.00001). The effect of warming on decreasing FDG accumulation in BAT was statistically significant in the winter (p <0.005) and summer (p <0.001). However, in the spring and autumn, though the effect of warming on decreasing FDG accumulation in BAT was evident, it was not statistically significant (p >0.05). Conclusion Maintaining room temperature at a constant 24°C for 30 min prior to and 1 h after IV tracer administration significantly decreases FDG uptake by BAT in children. This effect is greatest in the summer and winter. Keywords Seasonal variation . 18 F-FDG uptake . Brown adipose tissue . Children Introduction Brown adipose tissue (BAT) was first described by Gessner in 1551 [1] and is associated with increased energy expenditure, insulin sensitivity, and decreased susceptibility to weight gain [2–6]. Present in approximately 5% of the adult population, it is more commonly found in women, thin patients, and children [7–9]. Thought to play a thermogenic role, brown adipocytes may be metabolically activated by sympathetic stimulation following exposure to cold [10–13]. 18 F-fluorodeoxyglucose ( 18 F-FDG) is a radioactive glu- cose analog taken up by metabolically active BAT and may be seen on positron emission tomography (PET) [14, 15]. Sites of FDG-avid BAT on PET include the neck, medias- tinum, paravertebral region, and retroperitoneum [15, 16]. The intensity of radiotracer uptake is variable and may depend on seasonal variation in ambient temperature [12, 13]. Physiologic radiotracer accumulation in metabolically active F. H. Fahey : S. Laffin : R. Davis : S. T. Treves : F. D. Grant : L. A. Drubach (*) Department of Radiology, Division of Nuclear Medicine/PET, Children’ s Hospital Boston, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA e-mail: laura.drubach@childrens.harvard.edu K. A. Zukotynski Department of Imaging, Division of Nuclear Medicine, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA e-mail: kzukotynski@partners.org Eur J Nucl Med Mol Imaging (2010) 37:1854–1860 DOI 10.1007/s00259-010-1485-2