Brown Adipose Tissue as a Mechanistic Determinant of Semaglutide Treatment Response in Obesity (BAT-Sema Study)

This study investigates whether the activity of brown adipose tissue (BAT) - a special type of fat that burns energy as heat - can predict how well individuals with obesity respond to semaglutide (Wegovy), a once-weekly injectable weight loss medication. Participants who are starting semaglutide treatment will undergo ¹⁸FDG-PET/CT imaging before and after 24 weeks of treatment. Prior to each PET/CT scan, participants will wear a water-circulating cooling vest to activate BAT. By measuring BAT activity at baseline and comparing it with the degree of weight loss and metabolic improvement at 24 weeks, the investigators aim to identify BAT as a predictive biomarker for personalized obesity treatment.

Inclusion Criteria: 1. Age 20-70 years at the time of enrollment 2. Initiating semaglutide (Wegovy) treatment for obesity (newly starting treatment) 3. BMI ≥ 27 kg/m² with at least one weight-related comorbidity: * Hypertension (SBP ≥130 or DBP ≥80 mmHg, or on antihypertensive medication) * Dyslipidemia (LDL-C ≥130, TG ≥150, or low HDL-C, or on lipid-lowering medication) * Non-alcoholic fatty liver disease (NAFLD/MASLD, confirmed by imaging or ALT/AST ≥1.5× ULN) * Obstructive sleep apnea (AHI ≥5/hr or clinically diagnosed) * Established cardiovascular disease (CAD, stroke, PAD) * Obesity-related osteoarthritis of knee or hip with functional impairment OR BMI ≥ 30 kg/m² (regardless of comorbidity) 4. Ability and willingness to provide written informed consent Exclusion Criteria: 1. Diagnosis of type 1 or type 2 diabetes mellitus 2. History of neck surgery or radiation therapy to the neck 3. Use of anti-obesity medications within 1 month prior to enrollment, or current use of beta-adrenergic blocking agents 4. Personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 (MEN2) 5. Active malignancy, severe renal disease (eGFR \