title: Dixon-based MRI for assessment of muscle-fat content in phantoms, healthy volunteers and patients with achillodynia: comparison to visual assessment of calf muscle quality.
abstract: OBJECTIVE
  To quantify the muscle fat-content (MFC) in phantoms, volunteers and patients with achillodynia using two-point Dixon-based magnetic resonance imaging (2pt-MRIDIXON) in comparison to MR spectroscopy (MRS) and visual assessment of MFC.
  
  
  METHODS
  Two-point Dixon-based MRI was used to measure the MFC of 15 phantoms containing 0-100 % fat-content and calf muscles in 30 patients (13 women; 57 ± 15 years) with achillodynia and in 20 volunteers (10 women; 30 ± 14 years) at 1.5 T. The accuracy of 2pt-MRIDIXON in quantification of MFC was assessed in vitro using phantoms and in vivo using MRS as the standard of reference. Fat-fractions derived from 2pt-MRIDIXON (FFDIXON) and MRS (FFMRS) were related to visual assessment of MFC (Goutallier grades 0-4) and Achilles-tendon quality (grade 0-4).
  
  
  RESULTS
  Excellent linear correlation was demonstrated for FFDIXON with phantoms and with FFMRS in patients (p c = 0.997/0.995; p < 0.001). FFDIXON of the gastrocnemius muscle was significantly higher (p = 0.002) in patients (7.0 % ± 4.7 %) compared with volunteers (3.6 % ± 0.7 %), whereas visual-grading showed no difference between both groups (p > 0.05). FFMRS and FFDIXON were significantly higher in subjects with (>grade 1) structural damage of the Achilles-tendon (p = 0.01).
  
  
  CONCLUSIONS
  Two-point Dixon-based MRI allows for accurate quantification of MFC, outperforming visual assessment of calf muscle fat. Structural damage of the Achilles tendon is associated with a significantly higher MFC.
  
  
  CONCLUSIONS
  Two-point Dixon-based MRI allows accurate quantification of muscular fat content (MFC). Quantitative analysis outperforms visual analysis in the detection of elevated MFC. Achillodynia results in an increased MFC of the gastrocnemius muscles. Structural damage of the Achilles tendon further increases the MFC.
authors.affiliation: Radiology, University Hospital Balgrist, Forchstrasse 340, 8008, Zurich, Switzerland, michaelalexander.fischer@usz.ch.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Fischer
authors.forename: Christian W A
authors.initials: CW
authors.lastname: Pfirrmann
authors.forename: Norman
authors.initials: N
authors.lastname: Espinosa
authors.forename: Dimitri A
authors.initials: DA
authors.lastname: Raptis
authors.forename: Florian M
authors.initials: FM
authors.lastname: Buck
mesh_terms: D000125:Achilles Tendon / Q000473:pathology*; D000273:Adipose Tissue / Q000473:pathology*; D050154:Adiposity; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000473:pathology*; D019047:Phantoms, Imaging; D052256:Tendinopathy / Q000473:pathology*