title: Selective in vivo bone imaging with long-T2suppressed PETRA MRI.
abstract: To design and evaluate an optimized PETRA (point-wise encoding time reduction with radial acquisition) sequence with long-T2suppression at 3 Tesla.
  
  
  
  An adiabatic inversion recovery-based scheme was used to null the long-T2signal. To minimize scan time, the signal was sampled multiple times after each inversion with variable excitation flip angles designed to yield constant short-T2signal amplitude. The excitation pulses were phase-modulated, allowing for increased flip angle and higher signal-to-noise ratio (SNR). A fast, noniterative image reconstruction algorithm was designed to minimize image artifacts due to nonuniform excitation profile.
  
  
  
  Phase-modulated pulse excitation, along with the noniterative reconstruction algorithm, allows the use of larger radiofrequency pulse flip angles, resulting in effective suppression of long-T2protons and improved image SNR without causing image artifacts. Midtibia images representative of collagen-bound water yielded SNR of 15 at 1-mm isotropic resolution in 6.5 minutes with a standard extremity coil. Further, the technology is shown to be suited for generating multi-angle projection images of bone akin to X-ray images displaying subtle anatomic detail.
  
  
  
  Optimized long-T2suppressed PETRA allows imaging of bone matrix water unencumbered by long-T2soft tissue and pore water protons, opening up new possibilities for anatomic bone imaging at isotropic resolution and quantification in clinically practical scan times. Magn Reson Med 77:989-997, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Jeremy F
authors.initials: JF
authors.lastname: Magland
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Xia
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Alan C
authors.initials: AC
authors.lastname: Seifert
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000328:Adult; D000465:Algorithms; D000818:Animals; D016477:Artifacts; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012756:Sheep; D012815:Signal Processing, Computer-Assisted; D013977:Tibia / Q000033:anatomy & histology*
keywords: image reconstruction; inversion recovery; long-T2 suppression; phase-modulated RF excitation; short T2; ultrashort echo time; zero echo time