Does brown adipose tissue activation increase its density as measured by CT Hounsfield units?
CT Hounsfield units of brown adipose tissue increase during activation, likely due to lipid consumption, providing a potential imaging marker for BAT activity.
UNLABELLED: Brown adipose tissue (BAT) densities assessed as CT Hounsfield units (HUs) were evaluated in a rodent model and in patients to determine whether HUs changed in relation to BAT activity. METHODS: Serial (18)F-FDG PET/CT was performed on rats under both room temperature control conditions and after 4 h of cold-stimulation, which is known to activate BAT. The maximum standardized uptake values and CT HUs of BAT were measured, and tissues were examined in the laboratory. Image records from cancer patients who underwent PET/CT were reviewed, and 23 patients were identified who displayed both high and low (18)F-FDG uptake into BAT on serial (18)F-FDG PET/CT scans. The maximum standardized uptake values and CT HUs of BAT were compared in these scans. RESULTS: The mean (+/-SD) CT HUs of cold-activated BAT (-12.4 +/- 22.4) were significantly higher than those (-27.9 +/- 9.6) of the controls in the rat model. The CT HUs of BAT (-71.6 +/- 18.0) in the patients with high (18)F-FDG uptake were significantly higher than those (-104.4 +/- 16.8) of the patients with low (18)F-FDG uptake . A decrease in relative lipid content is seen in activated BAT in rats on histology. CONCLUSION: The CT HUs of BAT increased in activated conditions in both animals and patients, likely because of lipid consumption by activated BAT.
Baba et al. (2010) studied this question.