title: Feasibility of assessing bone matrix and mineral properties in vivo by combined solid-state 1H and 31P MRI.
abstract: OBJECTIVE
  To develop and evaluate an integrated imaging protocol for bone water and phosphorus quantification in vivo by solid-state 1H and 31P MRI.
  
  
  METHODS
  All studies were HIPAA-compliant and were performed with institutional review board approval and written informed consent. Proton (1H) ultra-short echo-time (UTE) and phosphorus (31P) zero echo-time (ZTE) sequences were designed and implemented on a 3 T clinical MR scanner to quantify bone water and mineral in vivo. The left tibia of ten healthy subjects (including both genders, 49±15 y/o) was examined with a custom-built 1H/31P dual-frequency extremity RF coil. Total bone water (TW), water bound to the collagen matrix (BW) and bone 31P were quantified from MR images with respect to reference samples of known 1H or 31P concentration, and pore water (PW) was subsequently determined from TW and BW. Porosity index (PI) was calculated as the ratio between UTE images acquired at two echo times. MRI parameters were compared with bone density measures obtained by high-resolution peripheral quantitative CT (HR-pQCT).
  
  
  RESULTS
  The total scan time for the bone water and 31P quantification protocol was about 50 minutes. Average TW, BW, PW and 31P concentrations were 13.99±1.26, 10.39±0.80, 3.34±1.41 mol/L and 7.06±1.53 mol/L for the studied cohort, respectively, in good agreement with previous results conducted ex vivo. Average intra-subject coefficients of variation were 3.47%, 2.60% and 7.50% for TW, BW and PW and 5.60% for 31P. Negative correlations were observed between PW and vBMD (p<0.05) as well as between PI and 31P (p<0.05), while bone mineral content (BMC) estimated from 31P MRI and HR-pQCT were strongly positively correlated (p<0.0001).
  
  
  CONCLUSIONS
  This work demonstrates the feasibility of quantifying bone water and mineral phosphorus in human subjects in a single MRI session with a clinically practical imaging protocol.
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, 1 Founders Building, MRI Education Center, Philadelphia, PA, United States of America.
authors.forename: Xia
authors.identifier: http://orcid.org/0000-0001-8108-6528
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, 1 Founders Building, MRI Education Center, Philadelphia, PA, United States of America.
authors.forename: Hee Kwon
authors.initials: HK
authors.lastname: Song
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, 1 Founders Building, MRI Education Center, Philadelphia, PA, United States of America.
authors.forename: Alan C
authors.initials: AC
authors.lastname: Seifert
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, 1 Founders Building, MRI Education Center, Philadelphia, PA, United States of America.
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.affiliation: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, 1 Founders Building, MRI Education Center, Philadelphia, PA, United States of America.
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D015519:Bone Density; D001842:Bone and Bones / Q000000981:diagnostic imaging*; D005240:Feasibility Studies; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*