title: Rapid measurement of brain macromolecular proton fraction with transient saturation transfer MRI.
abstract: To develop an efficient MRI approach to estimate the nonwater proton fraction (f) in human brain.
  
  
  
  We implement a brief, efficient magnetization transfer (MT) pulse that selectively saturates the magnetization of the (semi-) solid protons, and monitor the transfer of this saturation to the water protons as a function of delay after saturation.
  
  
  
  Analysis of the transient MT effect with two-pool model allowed robust extraction of f at both 3 and 7 T. This required estimating the longitudinal relaxation rate constant (R1,MPand R1,WP) for both proton pools, which was achieved with the assumption of uniform R1,MPand R1,WPacross brain tissues. Resulting values of f were approximately 50% higher than reported previously, which is partly attributed to MT-pulse efficiency and R1,MPbeing higher than assumed previously.
  
  
  
  Experiments performed on human brain in vivo at 3 and 7 T demonstrate the ability of the method to robustly determine f in a scan time of approximately 5 min. Magn Reson Med 77:2174-2185, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: van Gelderen
authors.affiliation: Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Xu
authors.initials: X
authors.lastname: Jiang
authors.affiliation: Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Jeff H
authors.initials: JH
authors.lastname: Duyn
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D046911:Macromolecular Substances / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D057054:Molecular Imaging / Q000379:methods; D009186:Myelin Sheath / Q000378:metabolism*; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014018:Tissue Distribution
chemical_list: D046911:Macromolecular Substances
keywords: T1 relaxation; brain tissue; macromolecular proton fraction; magnetization transfer; myelin; white matter