Fig. 8. Hyperpolarized ¹²⁹Xe spectrum and image acquired on a 25-30 y.o. male with a BMI of 29.9 kg/m² that showed enhanced xenon uptake in non-glucose avid supraclavicular fat.

The ¹⁸F-FDG-PET/CT was performed in the winter months with an outside temperature averaging 4 °C. a Hyperpolarized xenon (HPXe) spectrum acquired during cold exposure, using the small, single-tuned, xenon surface coil. The ¹²⁹Xe NMR spectrum shows a large lipid-dissolved xenon peak at 193.2 ppm downfield from the gas phase peak. b Localized ¹H NMR spectrum, acquired from a 30 mm × 30 mm × 30 mm voxel centered within the supraclavicular fat pad, showing a small CH₂ peak at 1.3 ppm. The CH₂ peak is much smaller than the water peak, indicating a very hydrated BAT. The lipid-dissolved xenon frequency, referenced to the CH₂ frequency, revealed active BAT during cold exposure with a temperature of (39.5 $\mathit{\pm }$ ± 2.5) °C. c 3D MR volume rendering of the same participant showing the positioning of the small surface coil labeled with a circular tube containing CuSO₄-doped water; d HPXe axial MR image showing localized ¹²⁹Xe signal. e Overlay of the axial HPXe MR image shown in (d) onto the corresponding ¹H image confirming that the lipid-dissolved ¹²⁹Xe signal originates primarily from the supraclavicular fat pad. f ¹⁸F-FDG-PET maximum intensity projection-image, showing absence of glucose avid BAT in the supraclavicular region or other well-known BAT locations (axillary, paravertebral).