Abstract
Currently, obesity is one of the leading causes death in the world. Shortly before 2000, researchers began describing metabolically active adipose tissue on cancer-surveillance 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in adult humans. This tissue generates heat through mitochondrial uncoupling and functions similar to classical brown and beige adipose tissue in mice. Despite extensive research, human brown/beige fat’s role in resistance to obesity in humans has not yet been fully delineated. FDG uptake is the de facto gold standard imaging technique when studying brown adipose tissue, although it has not been rigorously compared to other techniques. We, therefore, present a concise review of established and emerging methods to image brown adipose tissue activity in humans. Reviewed modalities include anatomic imaging with CT and magnetic resonance imaging (MRI); molecular imaging with FDG, fatty acids, and acetate; and emerging techniques. FDG-PET/CT is the most commonly used modality because of its widespread use in cancer imaging, but there are mechanistic reasons to believe other radiotracers may be more sensitive and accurate at detecting brown adipose tissue activity. Radiation-free modalities may help the longitudinal study of brown adipose tissue activity in the future.
Highlights
Obesity is caused by chronic excess of calories consumed relative to calories burned
Beta-Methyl-Iodophenyl-Pentadecanoic Acid (BMIPP) is a fatty acid tracer routinely used for cardiac SPECT/Computed tomography (CT) in Japan [61]
11 C-acetate K estimating CO production from the citric acid cycle [49,60], which may provide a better assessment of iBAT metabolic activity than other methods because it is sensitive to mobilization of intracellular energy stores
Summary
Obesity is caused by chronic excess of calories consumed relative to calories burned. One potential target for medical therapies aimed at reducing obesity and preventing associated metabolic dysfunction is metabolically active fat tissue. Resonance imaging allows for repeated scans without radiation and can take advantage of the intrasubject variability and iBAT cellular composition changes over time may limit the utility known difference in typical fat fraction andtechniques mitochondrial betweenoptoacoustic iBAT and white adipose of current. IBAT is does not directly provide any functional data, radiodensity, which in the case of adipose tissue is most often encountered in humans on CTs obtained during PET-CT studies in cancer patients. Obese individuals have lower mean Hus in typical location of iBAT as in the supraclavicular to supraclavicular depots, relatively high-attenuation fatincreases depots with in cervical, axillary, region consistent with greater lipid content, and mean HU weight loss [29]. Density in BAT compared to WAT in our experience (Figure 2) [32]
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