title: Histological correlation of 7 T multi-parametric MRI performed in ex-vivo Achilles tendon.
abstract: BACKGROUND
  The goal of this in vitro validation study was to investigate the feasibility of biochemical MRI techniques, such as sodium imaging, T₂ mapping, fast imaging with steady state precession (FISP), and reversed FISP (PSIF), as potential markers for collagen, glycosaminoglycan and water content in the Achilles tendon.
  
  
  METHODS
  Five fresh cadaver ankles acquired from a local anatomy department were used in the study. To acquire a sodium signal from the Achilles tendon, a 3D-gradient-echo sequence, optimized for sodium imaging, was used with TE=7.71 ms and TR=17 ms. The T₂ relaxation times were obtained using a multi-echo, spin-echo technique with a repetition time (TR) of 1200 ms and six echo times. A 3D, partially balanced, steady-state gradient echo pulse sequence was used to acquire FISP and PSIF images, with TR/TE=6.96/2.46 ms. MRI parameters were correlated with each other, as well as with histologically assessed glycosaminoglycan and water content in cadaver Achilles tendons.
  
  
  RESULTS
  The highest relevant Pearson correlation coefficient was found between sodium SNR and glycosaminoglycan content (r=0.71, p=0.007). Relatively high correlation was found between the PSIF signal and T2 values (r=0.51, p=0.036), and between the FISP signal and T₂ values (r=0.56, p=0.047). Other correlations were found to be below the moderate level.
  
  
  CONCLUSIONS
  This study demonstrated the feasibility of progressive biochemical MRI methods for the imaging of the AT. A GAG-specific, contrast-free method (sodium imaging), as well as collagen- and water-sensitive methods (T₂ mapping, FISP, PSIF), may be used in fast-relaxing tissues, such as tendons, in reasonable scan times.
authors.affiliation: Center of Excellence for High Field MR, Department of Radiology, Medical University of Vienna Waehringer Guertel 18-20, A-1090, Vienna, Austria.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Juras
authors.forename: Sebastian
authors.initials: S
authors.lastname: Apprich
authors.forename: Christina
authors.initials: C
authors.lastname: Pressl
authors.forename: Stefan
authors.initials: S
authors.lastname: Zbyn
authors.forename: Pavol
authors.initials: P
authors.lastname: Szomolanyi
authors.forename: Stephan
authors.initials: S
authors.lastname: Domayer
authors.forename: Jochen G
authors.initials: JG
authors.lastname: Hofstaetter
authors.forename: Siegfried
authors.initials: S
authors.lastname: Trattnig
mesh_terms: D000125:Achilles Tendon / Q000033:anatomy & histology* / Q000737:chemistry*; D001834:Body Water / Q000737:chemistry*; D002102:Cadaver; D003094:Collagen / Q000032:analysis*; D005240:Feasibility Studies; D005260:Female; D006025:Glycosaminoglycans / Q000032:analysis*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D057054:Molecular Imaging / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic
chemical_list: D006025:Glycosaminoglycans; D003094:Collagen