title: Quantitative assessment of fat infiltration in the rotator cuff muscles using water-fat MRI.
abstract: OBJECTIVE
  To evaluate a chemical shift-based fat quantification technique in the rotator cuff muscles in comparison with the semiquantitative Goutallier fat infiltration classification (GC) and to assess their relationship with clinical parameters.
  
  
  METHODS
  The shoulders of 57 patients were imaged using a 3T MR scanner. The rotator cuff muscles were assessed for fat infiltration using GC by two radiologists and an orthopedic surgeon. Sequences included oblique-sagittal T1-, T2-, and proton density-weighted fast spin echo, and six-echo gradient echo. The iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) was used to measure fat fraction. Pain and range of motion of the shoulder were recorded.
  
  
  RESULTS
  Fat fraction values were significantly correlated with GC grades (P < 0.0001, κ >0.9) showing consistent increase with GC grades (grade = 0, 0%-5.59%; grade = 1, 1.1%-9.70%; grade = 2, 6.44%-14.86%; grade = 3, 15.25%-17.77%; grade = 4, 19.85%-29.63%). A significant correlation between fat infiltration of the subscapularis muscle quantified with IDEAL versus 1) deficit in internal rotation (Spearman Rank Correlation Coefficient [SRC] = 0.39, 95% confidence interval [CI] 0.13-0.60, P < 0.01) and 2) pain (SRC coefficient = 0.313, 95% CI 0.049-0.536, P = 0.02) was found but was not seen between the clinical parameters and GC grades. Additionally, only quantitative fat infiltration measures of the supraspinatus muscle were significantly correlated with a deficit in abduction (SRC coefficient = 0.45, 95% CI 0.20-0.60, P < 0.01).
  
  
  CONCLUSIONS
  An accurate and highly reproducible fat quantification in the rotator cuff muscles using water-fat magnetic resonance imaging (MRI) techniques is possible and significantly correlates with shoulder pain and range of motion.
authors.affiliation: Musculoskeletal and Quantitative Imaging Research, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Nardo
authors.forename: Dimitrios C
authors.initials: DC
authors.lastname: Karampinos
authors.forename: Drew A
authors.initials: DA
authors.lastname: Lansdown
authors.forename: Julio
authors.initials: J
authors.lastname: Carballido-Gamio
authors.forename: Sonia
authors.initials: S
authors.lastname: Lee
authors.forename: Roberto
authors.initials: R
authors.lastname: Maroldi
authors.forename: C Benjamin
authors.initials: CB
authors.lastname: Ma
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Link
authors.forename: Roland
authors.initials: R
authors.lastname: Krug
mesh_terms: D000273:Adipose Tissue / Q000473:pathology / Q000503:physiopathology*; D050154:Adiposity; D000293:Adolescent; D000328:Adult; D000368:Aged; D001834:Body Water / Q000378:metabolism*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D017006:Rotator Cuff / Q000473:pathology / Q000503:physiopathology*; D000070636:Rotator Cuff Injuries; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: fat quantification; magnetic resonance imaging (MRI); rotator cuff; shoulder; water-fat imaging