Quantification of Human and Rodent Brown Adipose Tissue Function Using 99mTc-Methoxyisobutylisonitrile SPECT/CT and 18F-FDG PET/CT

For brown adipose tissue (BAT) to be effective at consuming calories, its blood flow must increase enough to provide sufficient fuel to sustain energy expenditure and also transfer the heat created to avoid thermal injury. Here we used a combination of human and rodent models to assess changes in BAT blood flow and glucose utilization. Methods: 99mTc-methoxyisobutylisonitrile (MIBI) SPECT (n 5 7) and SPECT/CT (n 5 74) scans done in adult humans for parathyroid imaging were reviewed for uptake in regions consistent with human BAT. Site-directed biopsies of sub-cutaneous and deep neck fat were obtained for electron micros-copy and gene expression profiling. In mice, tissue perfusion was measured with 99mTc-MIBI (n 5 16) and glucose uptake with 18F-FDG (n 5 16). Animals were kept fasting overnight, anesthetized with pentobarbital, and given intraperitoneally either the b3-adrenergic receptor agonist CL-316,243, 1 mg/kg (n 5 8), or sa