Exploring the relationship of brown adipose tissue to bone microarchitecture using 7T MRI and micro-CT

Brown adipose tissue (BAT) is involved both in energy production and bone metabolism. The purpose of this study was to analyze the relationship between BAT and microarchitecture at cancellous and cortical bone using Kunming mice and the methods of 7T magnetic resonance imaging (MRI) combined with micro-CT.

Twenty-four female Kunming mice were examined by 7T MRI and measured T2* relaxation time on the deep and superficial interscapular BAT (iBAT) and subcutaneous white adipose tissue (sWAT). Cancellous bone microarchitecture of the distal femur and cortical bone of the middle femur were examined by micro-CT. A paired t-test was used to analyze the differences in T2* values between iBAT and sWAT. The correlation between BAT T2* values and bone microstructure parameters were analyzed using Pearson's correlation.

T2* values of the deep and superficial iBAT (6.36±3.31 ms and 6.23±2.61 ms) were significantly shorter than those of sWAT (16.30±3.05 ms, t(deep) iBAT=-10.816), t(superficial) iBAT =-12.276, p<0.01). Deep iBAT T2* values were significantly and negatively correlated with bone volume, cancellous thickness, and bone thickness (Th) and trabecular thickness (Tb.Th) of the cancellous bone of femur. Deep iBAT T2* values were significantly and positively correlated with the structural model index of cancellous bone of femur. Deep iBAT T2* values were significantly and negatively correlated with bone mineral density of the cortical bone of femur.

MRI can distinguish the two adipose tissues from each other. T2* values of BAT were lower than WAT on MRI. BAT related bone remodeling was more correlated with the microstructure of cancellous bone than that of cortical bone.