title: Variations in T(2)* and fat content of murine brown and white adipose tissues by chemical-shift MRI.
abstract: OBJECTIVE
  The purpose was to compare T(2)* relaxation times and proton density fat-fraction (PDFF) values between brown (BAT) and white (WAT) adipose tissue in lean and ob/ob mice.
  
  
  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 T(2)*-corrected chemical-shift-based water-fat magnetic resonance imaging (MRI) method that provides simultaneous estimation of T(2)* and PDFF on a voxel-wise basis. Regions of interest were drawn within the interscapular BAT and gonadal WAT depots on co-registered T(2)* 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 T(2)* and PDFF were observed between the lean and ob/ob groups. The ob/ob animals exhibited longer BAT T(2)* 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, T(2)* 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.
  
  
  CONCLUSIONS
  T(2)* 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.
authors.affiliation: Department of Radiology, Children's Hospital Los Angeles, Los Angeles, CA 90027, USA. houchunh@usc.edu
authors.forename: Houchun H
authors.initials: HH
authors.lastname: Hu
authors.forename: Catherine D G
authors.initials: CD
authors.lastname: Hines
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Smith
authors.forename: Scott B
authors.initials: SB
authors.lastname: Reeder
mesh_terms: D002001:Adipose Tissue, Brown / Q000033:anatomy & histology*; D052436:Adipose Tissue, White / Q000033:anatomy & histology*; D000704:Analysis of Variance; D000818:Animals; D016018:Least-Squares Analysis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051379:Mice; D008820:Mice, Obese