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

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 \<30 mL/min/1.73m²), severe hepatic disease, or other severe endocrine disorders 6. Pregnancy or breastfeeding 7. Severe psychiatric illness or cognitive impairment precluding informed consent 8. Contraindication to MRI (pacemaker, cochlear implant, non-MRI-compatible implants) 9. Severe claustrophobia