title: Objective measurement of minimal fat in normal skeletal muscles of healthy children using T2 relaxation time mapping (T2 maps) and MR spectroscopy.
abstract: BACKGROUND
  Various skeletal muscle diseases result in fatty infiltration, making it important to develop noninvasive biomarkers to objectively measure muscular fat.
  
  
  OBJECTIVE
  We compared T2 relaxation time mapping (T2 maps) and magnetic resonance spectroscopy (MRS) with physical characteristics previously correlated with intramuscular fat to validate T2 maps and MRS as objective measures of skeletal muscle fat.
  
  
  METHODS
  We evaluated gluteus maximus muscles in 30 healthy boys (ages 5-19 years) at 3 T with T1-weighted images, T2-W images with fat saturation, T2 maps with and without fat saturation, and MR spectroscopy. We calculated body surface area (BSA), body mass index (BMI) and BMI percentile (BMI %). We performed fat and inflammation grading on T1-W imaging and fat-saturated T2-W imaging, respectively. Mean T2 values from T2 maps with fat saturation were subtracted from T2 maps without fat saturation to determine T2 fat values. We obtained lipid-to-water ratios by MR spectroscopy. Pearson correlation was used to assess relationships between BSA, BMI, BMI %, T2 fat values, and lipid-to-water ratios for each boy.
  
  
  RESULTS
  Twenty-four boys completed all exams; 21 showed minimal and 3 showed no fatty infiltration. None showed muscle inflammation. There was correlation between BSA, BMI, and BMI %, and T2 fat values (P < 0.05), and between BMI and BMI %, and lipid-to-water ratios (P < 0.05). There was strong correlation between T2 fat values and lipid-to-water ratios (P < 0.0001, r = 0.83).
  
  
  CONCLUSIONS
  T2 maps and MR spectroscopy correlate with physical characteristics associated with fatty infiltration of skeletal muscles, even in microscopic amounts, and validate each other. Both techniques might enable detection of minimal pathological fatty infiltration in children with skeletal muscle disorders.
authors.affiliation: Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA, Hee.Kim@cchmc.org.
authors.forename: Hee Kyung
authors.initials: HK
authors.lastname: Kim
authors.forename: Suraj
authors.initials: S
authors.lastname: Serai
authors.forename: Arnold C
authors.initials: AC
authors.lastname: Merrow
authors.forename: Lily
authors.initials: L
authors.lastname: Wang
authors.forename: Paul S
authors.initials: PS
authors.lastname: Horn
authors.forename: Tal
authors.initials: T
authors.lastname: Laor
mesh_terms: D050154:Adiposity / Q000502:physiology*; D000293:Adolescent; D000465:Algorithms; D002648:Child; D002675:Child, Preschool; D006801:Humans; D050356:Lipid Metabolism / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D009820:Ohio; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult