title: UTE bi-component analysis of T2* relaxation in articular cartilage.
abstract: OBJECTIVE
  To determine T2* relaxation in articular cartilage using ultrashort echo time (UTE) imaging and bi-component analysis, with an emphasis on the deep radial and calcified cartilage.
  
  
  METHODS
  Ten patellar samples were imaged using two-dimensional (2D) UTE and Car-Purcell-Meiboom-Gill (CPMG) sequences. UTE images were fitted with a bi-component model to calculate T2* and relative fractions. CPMG images were fitted with a single-component model to calculate T2. The high signal line above the subchondral bone was regarded as the deep radial and calcified cartilage. Depth and orientation dependence of T2*, fraction and T2 were analyzed with histopathology and polarized light microscopy (PLM), confirming normal regions of articular cartilage. An interleaved multi-echo UTE acquisition scheme was proposed for in vivo applications (n = 5).
  
  
  RESULTS
  The short T2* values remained relatively constant across the cartilage depth while the long T2* values and long T2* fractions tended to increase from subchondral bone to the superficial cartilage. Long T2*s and T2s showed significant magic angle effect for all layers of cartilage from the medial to lateral facets, while the short T2* values and T2* fractions are insensitive to the magic angle effect. The deep radial and calcified cartilage showed a mean short T2* of 0.80 ± 0.05 ms and short T2* fraction of 39.93 ± 3.05% in vitro, and a mean short T2* of 0.93 ± 0.58 ms and short T2* fraction of 35.03 ± 4.09% in vivo.
  
  
  CONCLUSIONS
  UTE bi-component analysis can characterize the short and long T2* values and fractions across the cartilage depth, including the deep radial and calcified cartilage. The short T2* values and T2* fractions are magic angle insensitive.
authors.affiliation: Department of Radiology, Shanghai Tenth People's Hospital, Tongji University School of Medicine, Shanghai 200072, China; Department of Radiology, University of California, San Diego, San Diego, CA 92103, USA.
authors.forename: H
authors.initials: H
authors.lastname: Shao
authors.affiliation: Department of Radiology, University of California, San Diego, San Diego, CA 92103, USA; Radiology Service, VA San Diego Healthcare System, San Diego, CA 92161, USA.
authors.forename: E Y
authors.initials: EY
authors.lastname: Chang
authors.affiliation: Department of Molecular and Experimental Medicine, The Scripps Research Institute, LA Jolla, CA, USA.
authors.forename: C
authors.initials: C
authors.lastname: Pauli
authors.affiliation: Department of Radiology, University of California, San Diego, San Diego, CA 92103, USA.
authors.forename: S
authors.initials: S
authors.lastname: Zanganeh
authors.affiliation: Department of Radiology, University of California, San Diego, San Diego, CA 92103, USA.
authors.forename: W
authors.initials: W
authors.lastname: Bae
authors.affiliation: Department of Radiology, University of California, San Diego, San Diego, CA 92103, USA; Radiology Service, VA San Diego Healthcare System, San Diego, CA 92161, USA.
authors.forename: C B
authors.initials: CB
authors.lastname: Chung
authors.affiliation: Department of Radiology, Shanghai Tenth People's Hospital, Tongji University School of Medicine, Shanghai 200072, China.
authors.forename: G
authors.initials: G
authors.lastname: Tang
authors.affiliation: Department of Radiology, University of California, San Diego, San Diego, CA 92103, USA. Electronic address: jiangdu@ucsd.edu.
authors.forename: J
authors.initials: J
authors.lastname: Du
mesh_terms: D000328:Adult; D002102:Cadaver; D002114:Calcinosis / Q000473:pathology*; D002358:Cartilage, Articular / Q000473:pathology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008859:Microscopy, Polarization; D008875:Middle Aged; D010329:Patella
keywords: Bi-component analysis; Deep radial and calcified cartilage; T2*; UTE