SUN-670 - Brown Adipose Tissue and Systemic Glucose Metabolism: Insights from Whole Body Fluorodeoxyglucose Positron Emission Tomography with Computed Tomography

Brown adipose tissue (BAT) is a thermogenic organ primarily activated by cold exposure, this organ is most commonly detected using 18F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography with computed tomography (PET/CT). Interestingly, detectable ¹⁸F-FDG uptake by BAT at room temperature is associated with improved cardiometabolic health including in people with obesity, however the mechanisms underlying these benefits remain unclear. We hypothesised that adults with detectable BAT exhibit distinct organ-level glucose uptake patterns indicative of altered systemic metabolism compared with BAT-negative individuals.

Whole-body ¹⁸F-FDG PET/CT scans were analysed from 15 BAT-positive (aged 64.2 ± 13.9 years; BMI 25.0 ± 5.4 kg/m²) and 15 age-/sex-/BMI-matched BAT-negative (64.2 ± 14.4 years; 26.4 ± 5.1 kg/m²) patients who had undergone diagnostic scanning. For each scan, BAT was manually segmented according to BARCIST criteria and >140 tissues were segmented using the Multi-Organ Objective segmentation engine (MOOSE). Standardised uptake values (SUVs) from individual tissues were compared between groups using t-tests or Mann-Whitney tests with false discovery rate correction. Principal component analysis (PCA) was employed to identify the main drivers of variance, while an unsupervised network analysis based on Spearman correlations (>0.85) was used to explore inter-organ glucose uptake relationships.

Glucose uptake in key cardiometabolic tissues such as skeletal muscle, liver, white adipose tissue and heart were similar between BAT-positive and BAT-negative groups, and PCA indicated that skeletal and bone marrow tissues from the vertebrae were the primary contributors to systemic variance in glucose metabolism. Network analysis revealed marked differences in metabolic organisation, in BAT-positive participants, glucose uptake formed a larger, more integrated network, with the major component linking skeletal and marrow tissue with cardiovascular, metabolic and immune organs. In contrast, the BAT-negative group exhibited more isolated, organ-specific correlations.

In this thermoneutral cohort, detectable ¹⁸F-FDG uptake by BAT was not associated with organ-specific differences in glucose uptake, although BAT-positive participants showed a more integrated metabolic network. This study demonstrates the potential of total-body PET/CT with automated segmentation to explore systemic metabolism and inter-organ interactions.