title: Musculoskeletal MRI at 3.0 T and 7.0 T: a comparison of relaxation times and image contrast.
abstract: OBJECTIVE
  The purpose of this study was to measure and compare the relaxation times of musculoskeletal tissues at 3.0 T and 7.0 T, and to use these measurements to select appropriate parameters for musculoskeletal protocols at 7.0 T.
  
  
  METHODS
  We measured the T₁ and T₂ relaxation times of cartilage, muscle, synovial fluid, bone marrow and subcutaneous fat at both 3.0 T and 7.0 T in the knees of five healthy volunteers. The T₁ relaxation times were measured using a spin-echo inversion recovery sequence with six inversion times. The T₂ relaxation times were measured using a spin-echo sequence with seven echo times. The accuracy of both the T₁ and T₂ measurement techniques was verified in phantoms at both magnetic field strengths. We used the measured relaxation times to help design 7.0 T musculoskeletal protocols that preserve the favorable contrast characteristics of our 3.0 T protocols, while achieving significantly higher resolution at higher SNR efficiency.
  
  
  RESULTS
  The T₁ relaxation times in all tissues at 7.0 T were consistently higher than those measured at 3.0 T, while the T₂ relaxation times at 7.0 T were consistently lower than those measured at 3.0 T. The measured relaxation times were used to help develop high resolution 7.0 T protocols that had similar fluid-to-cartilage contrast to that of the standard clinical 3.0 T protocols for the following sequences: proton-density-weighted fast spin-echo (FSE), T₂-weighted FSE, and 3D-FSE-Cube.
  
  
  CONCLUSIONS
  The T₁ and T₂ changes were within the expected ranges. Parameters for musculoskeletal protocols at 7.0 T can be optimized based on these values, yielding improved resolution in musculoskeletal imaging with similar contrast to that of standard 3.0 T clinical protocols.
authors.affiliation: Department of Radiology, The Richard M. Lucas Center for Imaging, Stanford University, Stanford, CA 94305-5488, United States. cjordan@stanford.edu
authors.forename: Caroline D
authors.initials: CD
authors.lastname: Jordan
authors.forename: Manojkumar
authors.initials: M
authors.lastname: Saranathan
authors.forename: Neal K
authors.initials: NK
authors.lastname: Bangerter
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hargreaves
authors.forename: Garry E
authors.initials: GE
authors.lastname: Gold
mesh_terms: D000328:Adult; D000465:Algorithms; D001842:Bone and Bones / Q000033:anatomy & histology*; D002358:Cartilage, Articular / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007719:Knee Joint / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity