MR properties of brown and white adipose tissues

Purpose: To explore the MR signatures of brown adipose tissue (BAT) compared with white adipose tissue (WAT) using single‐voxel MR spectroscopy. Materials and Methods: 1 H MR STEAM spectra were acquired from a 3 Tesla clinical whole body scanner from seven excised murine adipose tissue samples of BAT (n = 4) and WAT (n = 3). Spectra were acquired at multiple echo times (TEs) and inversion times (TIs) to measure the T1, T2, and T2‐corrected peak areas. A theoretical triglyceride model characterized the fat in terms of number of double bonds (ndb) and number of methylene‐interrupted double bonds (nmidb). Results: Negligible differences between WAT and BAT were seen in the T1 and T2 of fat and the T2 of water. However, the water fraction in BAT was higher (48.5%) compared with WAT (7.1%) and the T1 of water was lower in BAT (618 ms) compared with WAT (1053 ms). The fat spectrum also differed, indicating lower levels of unsaturated triglycerides in BAT (ndb = 2.7, nmidb = 0.7) compared with WAT (ndb = 3.3, nmidb = 1.0). Conclusion: We have demonstrated that there are several key MR‐based signatures of BAT and WAT that may allow differentiation on MR imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.