A feasibility study was carried out for the determination of blood perfusion based on arterial spin labelling (ASL) with flow alternating inversion recovery (FAIR) in the interscapular brown adipose tissue (iBAT). iBAT consists of brown adipocytes (fat cells) containing numerous lipid droplets and a high concentration of mitochondria which give rise to the primary function of iBAT as to generate body heat without shivering. A dense network of micro vessels support the oxygen needed for the thermogenesis process, therefore iBAT blood perfusion is a parameter of relevance for iBAT functional analysis and phenotyping. So far, iBAT perfusion has been investigated using near infrared fluorescence imaging [1] or through MRI blood pool contrast agent administration [2]. In this study, quantitative ASL based blood perfusion was measured in iBAT and skeletal muscle of C57BL/6 wildtype mice (n = 4) and in addition, total iBAT blood consumption was estimated based on the perfusion rate and iBAT volumetry.Measurements were carried out on a 7 T preclinical MRI platform with 640 mT/m gradient strength and a 2 CH T/R cryo surface coil. Instead of echo planar imaging (EPI), rapid acquisition with relaxation enhancement (RARE) was chosen as imaging readout of the FAIR perfusion sequence in order to prevent off-resonant distortions arising from the high lipid content of iBAT and the difficult to shim morphology of the interscapular area. The used surface coil array covered the heart and the lungs in order to ensure inversion of the inflowing blood through the global adiabatic pulse of the FAIR sequence. Two consecutive captured sagittal slices covered the left and right iBAT lobe as well as the back (skeletal) muscle. The slice positions (Fig. 1) were chosen orthogonal to the iBAT vascular system based on an a priori acquired time of flight angiography (parameters: TR/TE = 17/3.8 ms, α = 50°, matrix = 256x256, 70 coronal slices, ~80 µm in-plane at a slice thickness of 0.15 mm, Taq = 4:5 min:s). Measuring 12 inversion time delays within the range of [50..1000] ms guaranteed good coverage of the short background T1 (~400..500 ms) of iBAT and a TR of 10 s was used for total spin relaxation. With a RARE factor of 16, one slice was acquired within two shots. Other parameters were: total Taq/slice: 8:20 min:s; TE = 36 ms; matrix: interpolated 128x64 for ~240 µm in-plane resolution at a slice thickness of 1.5 mm. Perfusion rate was calculated as in [3], estimated blood T1 = 2300 ms [4] and assumed tissue blood participation coefficient λ = 0.83 [5]. For iBAT volumetry, T1 weighted RARE acquisitions with the following parameters were used: TR/TE = 800/6.5 ms, RARE factor = 2, matrix = 256x192, 15 slices, ~100 µm in-plane at a slice thickness of 1 mm, Taq = 57 s. iBAT volumes were determined by manual segmentation of the interscapular BAT region within the acquired axial image slices. Animals were measured at an age of 11 weeks and anesthetized with isoflurane under body temperature control (37°C) with isoflurane concentration kept at a minimum (< 1.5 % in 1 l/min O2) in dependence of animals breath-rate (target: 80-100 bpm).The high iBAT perfusion (Fig. 2b) is a result of a dense vessel network supplying the iBAT with blood (Fig. 2a). Measured perfusion rates are summarized in Fig. 3. The blood perfusion of skeletal muscle in WT mice was determined with an average mean (left/right slice) of f_muscle = 82.3 ± 17.7 ml/100g/min by contrast to the perfusion of interscapular BAT of f_iBAT = 518.0 ± 132.3 ml/100g/min. Segmentation of the total iBAT volumes resulted in 119.6 ± 5.8 µl and, assuming a tissue density of 1 g/ml, total blood flow into iBAT was determined to be 546 ± 186 µl/min.The perfusion values acquired from the back muscle of wildtype mice are in good agreement with literature [6] and justify the applied in vivo measurement setup. The perfusion rate in iBAT is comparable to numbers known from well perfused myocardial tissue [3] indicating a high grade of blood perfusion even in the thermoneutral state the animals had been kept in during measurement. However, at this point it is important to mention that different studies reported that isoflurane anesthesia, which has a vasodilatory effect, modulates blood perfusion in various tissue types [6, 7]. In addition, the absolute perfusion values in iBAT presented here underlie an uncertainty arising from the assumed participation coefficient of blood, actually derived for myocardial tissue [6].Quantitative blood perfusion was demonstrated in the interscapular brown adipose tissue. Future work should clarify the impact of anesthesia to the observed perfusion rates and future measurements will investigate iBAT blood perfusion during cold-induced activated iBAT thermogenesis.