In adult humans, brown adipose tissue (BAT) has been found to be metabolically active. However, the physiological relevance of BAT in adult humans is still imprecise and largely speculative. The study of oxidative metabolism of BAT during different physiological states can unravel the significance of BAT in whole-body energy metabolism; and meanwhile there is also a need to improve the characterisation of BAT using the existing non-invasive medical imaging methods. 

The aim of the doctoral work was to evaluate whether the oxygen consumption of BAT in adult humans, measured using positron emission tomography, is influenced by cold stress, and with the ingestion of a mixed meal. Cold-induced and meal-induced whole-body thermogenesis was also studied. Additionally, the utility of a non-invasive medical imaging method of x-ray computed tomography to provide metabolic information related to BAT was investigated. 

The results showed that cold stress, as well as ingestion of a mixed meal,increases the oxygen consumption of BAT. However, the overall capacity of BAT to contribute to cold-induced and meal-induced whole-body thermogenesis is limited. The x-ray computed tomography derived metrics of BAT has the potential to give an insight into underlying tissue composition and substrate metabolism, and this characteristic can be exploited to make a distinction between white adipose tissue and BAT.