Variations in T₂* and fat content of murine brown and white adipose tissues by chemical-shift MRI

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• 作者：Houchun H. Hu^a ; ^{houchunh@usc.edu} ; ^{hhu@chla.usc.edu} ; Catherine D.G. Hines^b ; ^d ; Daniel L. Smith Jr.^c ; Scott B. Reeder^d ; ^e ; ^f ; ^g
• 关键词：Brown adipose tissue ; White adipose tissue ; T2* relaxation ; Fat fraction
• 刊名：Magnetic Resonance Imaging
• 出版年：2012
• 出版时间：April 2012
• 年：2012
• 卷：30
• 期：3
• 页码：323-329
• 全文大小：661 K

文摘

Purpose

The purpose was to compare T₂* relaxation times and proton density fat-fraction (PDFF) values between brown (BAT) and white (WAT) adipose tissue in lean and ob/ob mice.

Materials and Methods

A group of lean male mice (n=6) and two groups of ob/ob male mice placed on similar 4-week (n=6) and 8-week (n=8) ad libitum diets were utilized. The animals were imaged at 3 T using a T₂*-corrected chemical-shift-based water-fat magnetic resonance imaging (MRI) method that provides simultaneous estimation of T₂* and PDFF on a voxel-wise basis. Regions of interest were drawn within the interscapular BAT and gonadal WAT depots on co-registered T₂* and PDFF maps. Measurements were assessed using analysis of variance, Bonferroni-adjusted t test for multigroup comparisons and the Tukey post hoc test.

Results

Significant differences (P<.01) in BAT T₂* and PDFF were observed between the lean and ob/ob groups. The ob/ob animals exhibited longer BAT T₂* and greater PDFF than lean animals. However, only BAT PDFF was significantly different (P<.01) between the two ob/ob groups. When comparing BAT to WAT within each group, T₂* and PDFF values were consistently lower in BAT than WAT (P<.01). The difference was most prominent in the lean animals. In both ob/ob groups, BAT exhibited very WAT-like appearances and properties on the MRI images.

Conclusion

T₂* and PDFF are lower in BAT than WAT. This is likely due to variations in tissue composition. The values were consistently lower in lean mice than in ob/ob mice, suggestive of the former's greater demand for BAT thermogenesis and reflective of leptin hormone deficiencies and diminished BAT metabolic activity in the latter.