Brown adipose tissue: metabolic role and non-invasive quantification in humans

The role of brown adipose tissue in humans is still a matter of debate: Does it play a substantial role in metabolic diseases, or not? The settling of this discussion requires clinical trials, generally including noninvasive imaging techniques, in order to assess the metabolic activity of brown adipose tissue. In this section we provide an overview of the (historical) importance of brown adipose tissue and explain the different imaging techniques. We explain the different imaging techniques that are available at the moment, with a focus on metabolic imaging with either PET or Single Photon Emission Computed Tomography as these can show a specific metabolic aspect with high specificity and sensitivity. There are a number of tracers (classes) which are additionally explained. Finally, we discuss the potential clinical impact of (quantifying) brown adipose tissue activity. We show that although there are currently multiple possibilities to visualize and quantify aspects of brown adipose tissue, these do not yet reach a convincing impact that is translatable to human clinical routine. There is clear evidence of brown adipose tissue in humans, there is also clear evidence that its activity is dependent on a number of factors—but the correlation to the overall health status still needs further investigation. Much research is still going on however, increasing our knowledge about brown adipose tissue evermore, and the techniques that were developed may prove to be useful for other metabolically relevant tissues as well.