title: Quantification of abdominal fat depots in rats and mice during obesity and weight loss interventions.
abstract: OBJECTIVE
  Obesity is a leading healthcare issue contributing to metabolic diseases. There is a great interest in non-invasive approaches for quantitating abdominal fat in obese animals and humans. In this work, we propose an automated method to distinguish and quantify subcutaneous and visceral adipose tissues (SAT and VAT) in rodents during obesity and weight loss interventions. We have also investigated the influence of different magnetic resonance sequences and sources of variability in quantification of fat depots.
  
  
  METHODS
  High-fat diet fed rodents were utilized for investigating the changes during obesity, exercise, and calorie restriction interventions (N = 7/cohort). Imaging was performed on a 7T Bruker ClinScan scanner using fast spin echo (FSE) and Dixon imaging methods to estimate the fat depots. Finally, we quantified the SAT and VAT volumes between the L1-L5 lumbar vertebrae using the proposed automatic hybrid geodesic region-based curve evolution algorithm.
  
  
  RESULTS
  Significant changes in SAT and VAT volumes (p<0.01) were observed between the pre- and post-intervention measurements. The SAT and VAT were 44.22±9%, 21.06±1.35% for control, -17.33±3.07%, -15.09±1.11% for exercise, and 18.56±2.05%, -3.9±0.96% for calorie restriction cohorts, respectively. The fat quantification correlation between FSE (with and without water suppression) sequences and Dixon for SAT and VAT were 0.9709, 0.9803 and 0.9955, 0.9840 respectively. The algorithm significantly reduced the computation time from 100 sec/slice to 25 sec/slice. The pre-processing, data-derived contour placement and avoidance of strong background-image boundary improved the convergence accuracy of the proposed algorithm.
  
  
  CONCLUSIONS
  We developed a fully automatic segmentation algorithm to quantitate SAT and VAT from abdominal images of rodents, which can support large cohort studies. We additionally identified the influence of non-algorithmic variables including cradle disturbance, animal positioning, and MR sequence on the fat quantification. There were no large variations between FSE and Dixon-based estimation of SAT and VAT.
authors.affiliation: Laboratory of Molecular Imaging, Singapore Bioimaging Consortium, Agency for Science, Technology, and Research, Singapore, Singapore.
authors.forename: Bhanu Prakash
authors.initials: BP
authors.lastname: Kn
authors.affiliation: Laboratory of Molecular Imaging, Singapore Bioimaging Consortium, Agency for Science, Technology, and Research, Singapore, Singapore.
authors.forename: Venkatesh
authors.initials: V
authors.lastname: Gopalan
authors.affiliation: Laboratory of Molecular Imaging, Singapore Bioimaging Consortium, Agency for Science, Technology, and Research, Singapore, Singapore.
authors.forename: Swee Shean
authors.initials: SS
authors.lastname: Lee
authors.affiliation: Laboratory of Molecular Imaging, Singapore Bioimaging Consortium, Agency for Science, Technology, and Research, Singapore, Singapore.
authors.forename: S Sendhil
authors.initials: SS
authors.lastname: Velan
mesh_terms: D050153:Abdominal Fat / Q000473:pathology*; D000465:Algorithms; D000818:Animals; D050218:Body Fat Distribution; D059305:Diet, High-Fat; D008279:Magnetic Resonance Imaging; D051379:Mice; D009765:Obesity / Q000473:pathology*; D051381:Rats; D015203:Reproducibility of Results; D015431:Weight Loss