Brown Fat Uptake on FDG PET

B. Brown adipose tissue (BAT) activation — FDG-avid brown fat is activated by cold temperature and beta-adrenergic stimulation

Brown adipose tissue (BAT) is highly metabolically active, using glucose oxidation to generate heat (non-shivering thermogenesis). It is activated by cold temperature or anxiety/adrenergic stimulation and shows intense FDG uptake on PET. BAT is typically distributed bilaterally and symmetrically in the supraclavicular, cervical, axillary, and paramediastinal/paravertebral regions — a pattern that can mimic lymphoma. Preventive measures include: warming the patient (heated blanket) before and during injection; a warm waiting area; sometimes propranolol (beta-blocker) premedication. Recognizing this bilateral symmetric distribution as BAT is critical to avoid false-positive cancer diagnoses.