ABSTRACT
Current understanding of in vivo human brown adipose tissue (BAT) physiology is limited by a reliance on positron emission tomography (PET)/computed tomography (CT) scanning, which has measured exogenous glucose and fatty acid uptake but not quantified endogenous substrate utilization by BAT. Six lean, healthy men underwent 18fluorodeoxyglucose-PET/CT scanning to localize BAT so microdialysis catheters could be inserted in supraclavicular BAT under CT guidance and in abdominal subcutaneous white adipose tissue (WAT). Arterial and dialysate samples were collected during warm (â¼25°C) and cold exposure (â¼17°C), and blood flow was measured by 133xenon washout. During warm conditions, there was increased glucose uptake and lactate release and decreased glycerol release by BAT compared with WAT. Cold exposure increased blood flow, glycerol release, and glucose and glutamate uptake only by BAT. This novel use of microdialysis reveals that human BAT is metabolically active during warm conditions. BAT activation substantially increases local lipolysis but also utilization of other substrates such as glutamate.
Subject(s)
Adipose Tissue, Brown/physiology , Cold Temperature , Lipolysis , Thermogenesis , Triglycerides/metabolism , Adipose Tissue, White/physiology , Adolescent , Adult , Aged , Cells, Cultured , Female , Glucose/metabolism , Glutamic Acid/metabolism , Glycerol/metabolism , Humans , Lactic Acid/metabolism , Male , Microdialysis/methods , Middle Aged , Thyroid Diseases/metabolismABSTRACT
PURPOSE: In order to locally validate the technique, a retrospective review of a cohort of randomly selected single-photon emission computed tomography (SPECT) bone scans reconstructed with ordered subsets expectation maximization (OSEM) and Evolution for Bone was undertaken. MATERIALS AND METHODS: Thirty consecutive bone SPECT patient data sets (17 spine, nine pelvis, and four spine and pelvis) were chosen. Poisson resampling was used to simulate reduced count data at 50, 75, and 100% of the original number of counts. Evolution for Bone applied resolution recovery to the reduced count images. All images were compared with the original OSEM images, currently used as the standard for clinical use. A qualitative blinded assessment was made by two independent observers, who assessed for noise, contrast, and resolution. RESULTS: Both radiologists saw an improvement in resolution (P = 0.776), noise (P = 0.007), and image quality with all data sets, compared with images processed purely with OSEM and viewed in Volumetrix. However, they completely disagreed on contrast, as the two radiologists scored contrast differently; however, the results are understandable. CONCLUSION: Images with 50, 75, and 100% of the original counts viewed using Evolution for Bone have improved image quality compared with images processed purely with OSEM and viewed in Volumetrix. Evolution for Bone therefore has great potential in departments for reducing either patient doses, waiting lists, or both.
