title: Morphological and Quantitative 7 T MRI of Hip Cartilage Transplants in Comparison to 3 T-Initial Experiences.
abstract: The aims of this study were to evaluate morphological and quantitative 7 T magnetic resonance imaging (MRI) hip sequences in patients after acetabular cartilage transplantation and to compare image quality with 3 T MRI.
  
  
  
  Following approval from the local institutional ethics committee and signing informed consent, 9 patients with history of autologous acetabular cartilage transplantation were imaged at 7 T and 3 T MRI. Sequences (3-dimensional dual echo steady state, 3-dimensional T1 volume interpolated breath-hold examination, sagittal proton density [PD] turbo spin echo and coronal fat-saturated PD turbo spin echo, sagittal T1 mapping in dual flip angle technique, and multiecho spin echo/gradient echo sequences for T2 and T2* mapping) were applied after the intravenous application of Gd-DTPA according to a protocol for delayed gadolinium-enhanced MRI of cartilage and manual B1 shimming at 7 T. Images were compared intraindividually regarding image quality and assessability of cartilage structures using 5-point scales (1 = 3 T clearly superior, 5 = 7 T clearly superior) in consensus with 2 radiologists. Contrast ratios were calculated between articular cartilage, joint fluid, and subchondral bone. An adapted MOCART (MR observation of cartilage repair tissue) score was assessed independently at 3 T and 7 T. Relaxation times were measured in the transplanted acetabular region and in 2 reference regions by 2 readers independently to calculate interreader reliability. Statistical significances of field strength comparisons were calculated using Student t test and t test for dependent measurements.
  
  
  
  A 7 T MRI was superior to 3 T MRI in the majority of the sequences regarding subjective ratings. Furthermore, 7 T yielded comparable or better contrast ratios compared with 3 T. The criteria of the MOCART score matched totally at 3 T and 7 T, apart from the signal intensity of the repair tissue in PDw, which was rated higher at 7 T in 5 patients. Interreader reliability of all relaxation times was excellent. T1 and T2* relaxation times were significantly shorter at 7 T compared with 3 T. T2 relaxation times were longer at 7 T compared with 3 T without statistical significance. No significant difference could be seen when comparing the relaxation ratios (relaxation times after standardization to reference regions) of the cartilage transplant between the 2 field strengths.
  
  
  
  This study shows the feasibility of morphological and quantitative 7 T hip MRI in patients after acetabular cartilage transplantation and its predominant superiority regarding image quality, assessment of cartilage transplants, and contrast over 3 T MRI. To compare relaxation times between the field strengths, the calculation of intraindividual ratios is recommended.
authors.affiliation: From the *Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen; †Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen; ‡High Field and Hybrid MR Imaging, University Hospital Essen, Essen; §Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg; ∥Facharztklinik Essen; and ¶Department of Orthopaedics, University Hospital Essen, Essen, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Lazik-Palm
authors.forename: Oliver
authors.initials: O
authors.lastname: Kraff
authors.forename: Sören
authors.initials: S
authors.lastname: Johst
authors.forename: Harald H
authors.initials: HH
authors.lastname: Quick
authors.forename: Mark E
authors.initials: ME
authors.lastname: Ladd
authors.forename: Christina
authors.initials: C
authors.lastname: Geis
authors.forename: Konrad
authors.initials: K
authors.lastname: Körsmeier
authors.forename: Stefan
authors.initials: S
authors.lastname: Landgraeber
authors.forename: Jens M
authors.initials: JM
authors.lastname: Theysohn
mesh_terms: D000328:Adult; D002358:Cartilage, Articular / Q000000981:diagnostic imaging* / Q000601:surgery; D003287:Contrast Media; D005069:Evaluation Studies as Topic; D005260:Female; D019786:Gadolinium DTPA; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D014182:Transplantation, Autologous; D055815:Young Adult
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA