Fig. 7: Detection of BAT thermogenic activity by absolute MR thermometry with hyperpolarized xenon.

a Hyperpolarized xenon (HPXe) NMR spectrum acquired during cold exposure at 8 s from the beginning of the breath hold, on a 25-30 y.o. female with a BMI of 24.1 kg/m². b Localized ¹H spectrum acquired right before the acquisition of the HPXe spectrum shown in (a) by using a single-voxel spectroscopy sequence from the 40 ×40 x 26 mm³ voxel centered within the supraclavicular fat depot and shown in yellow in (d), (e), and (g). The lipid-dissolved xenon (LDX) frequency, referenced to the CH₂ frequency, revealed active BAT with an average temperature of 39.6 \(\pm\) 0.8 °C. c Fused axial ¹⁸F-FDG-PET/CT image collected from the same participant two days prior to the collection of the MR images and spectra, showing enhanced glucose uptake in the supraclavicular fat depot. d Anatomical fat-only MR axial image, showing the location of the voxel from which the spectrum in (b) was acquired. e Low-resolution HPXe MR image collected from the same participant showing enhanced ¹²⁹Xe signal from the same shimmed region from which the CH₂ signal was acquired for temperature measurements. f Overlay of the HPXe image shown in (e) onto the corresponding anatomical fat-only image. g Coronal fat-only ¹H MR image acquired from the same participant showing the other dimension of the selected voxel from which the spectrum in (b) was acquired; h Second axial HPXe image acquired on the same participant on a different day. i Overlay of the HPXe MR image shown in figure (h) onto the corresponding anatomical fat-only ¹H image. Enhanced xenon signal is observed from the same region within the supraclavicular fossa.