title: Measurement of T1relaxation time of osteochondral specimens using VFA-SWIFT.
abstract: OBJECTIVE
  To evaluate the feasibility of SWIFT with variable flip angle (VFA) for measurement of T1relaxation time in Gd-agarose-phantoms and osteochondral specimens, including regions of very short T2*, and compare with T1measured using standard methods METHODS: T1s of agarose phantoms with variable concentration of Gd-DTPA2-and nine pairs of native and trypsin-treated bovine cartilage-bone specimens were measured. For specimens, VFA-SWIFT, inversion recovery (IR) fast spin echo (FSE) and saturation recovery FSE were used. For phantoms, additionally spectroscopic IR was used. Differences and agreement between the methods were assessed using nonparametric Wilcoxon and Kruskal-Wallis tests and intraclass correlation.
  
  
  RESULTS
  The different T1mapping methods agreed well in the phantoms. VFA-SWIFT allowed reliable measurement of T1in the osteochondral specimens, including regions where FSE-based methods failed. The T1s measured by VFA-SWIFT were shifted toward shorter values in specimens. However, the measurements correlated significantly (highest correlation VFA-SWIFT versus FSE was r = 0.966). SNR efficiency was generally highest for SWIFT, especially in the subchondral bone.
  
  
  CONCLUSIONS
  Feasibility of measuring T1relaxation time using VFA-SWIFT in osteochondral specimens and phantoms was demonstrated. A shift toward shorter T1s was observed for VFA-SWIFT in specimens, reflecting the higher sensitivity of SWIFT to short T2* spins. Magn Reson Med 74:175-184, 2015. © 2014 Wiley Periodicals, Inc.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.|Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.|Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Mikko J
authors.initials: MJ
authors.lastname: Nissi
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.|Department of Neurobiology, A.I. Virtanen Institute for Molecular Medicine, University of Eastern Finland, Kuopio, Finland.
authors.forename: Lauri J
authors.initials: LJ
authors.lastname: Lehto
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Curtis A
authors.initials: CA
authors.lastname: Corum
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Djaudat
authors.initials: D
authors.lastname: Idiyatullin
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Jutta M
authors.initials: JM
authors.lastname: Ellermann
authors.affiliation: Department of Neurobiology, A.I. Virtanen Institute for Molecular Medicine, University of Eastern Finland, Kuopio, Finland.
authors.forename: Olli H J
authors.initials: OHJ
authors.lastname: Gröhn
authors.affiliation: Department of Diagnostic Radiology, Oulu University Hospital and University of Oulu, Oulu, Finland.|Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland.
authors.forename: Miika T
authors.initials: MT
authors.lastname: Nieminen
keywords: Gd-DTPA2-; SWIFT; T1 relaxation; bone; cartilage; variable flip angle
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