MR properties of brown and white adipose tissues

Abstract

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.

Copyright © 2011 Wiley-Liss, Inc.

Figures

Figure 1

Representative white (left) and brown (right) adipose tissue MR spectrum at 3T (TR 5000 ms, TE 13 ms). Of the six fat peaks resolvable by spectroscopy at 3T, two peaks (peak 1 at 5.19–5.29 ppm and peak 2 at 4.2 ppm) are buried under the large water peak in BAT. The MRUI generated fit (dotted line) is also shown along with the residues of the fit.

Figure 2

Change in the white (left) and brown (right) adipose tissue MR spectrum (TR 5000 ms, TE 13 ms) with increasing TI (50, 100, 200, 300, 400, 600, 1000, 2000 and 4000 ms).

Figure 3

Change in the white (left) and brown (right) adipose tissue MR spectrum (TR 5000 ms) with increasing TE (13, 18, 23, 28, and 33 ms).

Figure 4

The inversion recovery behavior measured in the water peak in each of the samples of white (left) and brown (right) adipose tissue. The fully recovered water signal is normalized to 1000 AU to allow comparison of the different tissues.