Objective: Brown adipose tissue is a powerful organ metabolizing vast amounts of circulating lipoproteins and glucose. Here we visualise and analyse the delivery of lipophilic nutrients to brown and brown-in-white (“brite”) adipocytes in vivo. We use state-of-the-art multi-modal imaging technologies based on lipoprotein Trojan horses engineered with superparamagnetic or fluorescent nanocrystals. Methods:All experiments with mice as well as their sacrifice afterwards were conducted under anaesthesia (intraperitoneal injection of 90mg/kg xylazine and 1.28 mg/kg ketamine). Magnetic resonance imaging (MRI) was performed using a clinical 7T scanner with FVB wild-type mice. Real-time intravital imaging was performed using a confocal fluorescence microscope equipped with a resonant scanner with mice expressing green fluorescent protein under control of the Uncoupling protein-1 (Ucp1) promoter. Results: Using MRI we could detect lipoprotein catabolism non-invasively in brown adipose tissue as well as in brite adipocytes in inguinal white adipose tissue for the first time, indicated by a strong increase in T2* contrast. Using intravital imaging we could visualize lipoprotein and lipid uptake into brown adipocytes in real-time. This process comprised a two-step mechanism: initial binding followed by endocytosis. Interestingly, in electron microscopy studies we detected nanocrystals labelling the lipoproteins in endocytic vesicles of endothelial cells. When analysing brite adipocytes in inguinal white adipose tissue, only brite but not their neighbouring white adipocytes display endocytosis. This finding was supported by intravital imaging where only brite but not white adipocytes are characterized by lipoprotein accumulation at their access site to the capillary. Conclusion: In this project we were able to non-invasively image and quantify the activity of brown but also of brite adipocytes for the first time using MRI. Our mechanistic studies using intravital imaging and electron microscopy suggest that brown as well as brite adipocytes are able to manipulate their endothelial microenvironment, resulting in increased local influx of lipoproteins and nutrients for combustion or storage.