title: Quantitative characterization of nuclear overhauser enhancement and amide proton transfer effects in the human brain at 7 tesla.
abstract: OBJECTIVE
  This study aimed to quantitatively investigate two main magnetization transfer effects at low B1: the nuclear Overhauser enhancement (NOE) and amide proton transfer in the human brain at 7 T.
  
  
  METHODS
  The magnetization transfer effects in the human brain were characterized using a four-pool proton model, which consisted of bulk water, macromolecules, an amide group of mobile proteins and peptides, and NOE-related protons resonating upfield. The pool sizes, exchange rates, and relaxation times of these proton pools were investigated quantitatively by fitting, and the net signals of amide proton transfer and NOE were simulated based on the fitted parameters.
  
  
  RESULTS
  The results showed that the four-pool model fitted the experimental data quite well, and the NOE effects in human brain at 7 T had a broad spectrum distribution. The NOE effects peaked at a B1 of ∼ 1-1.4 μT and were significantly stronger in the white matter than in the gray matter, corresponding to a pool-size ratio ∼ 2:1. As the amide proton transfer effect was relatively small compared with the NOE effects, magnetization transfer asymmetry analysis yielded an NOE-dominated contrast in the healthy human brain in this range of B1.
  
  
  CONCLUSIONS
  These findings are important to identify the source of NOE effects and to quantify amide proton transfer effects in human brain at 7 T.
authors.affiliation: State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; UCLA-Beijing Joint Center for Advanced Brain Imaging, Beijing, China and Los Angeles, California, USA; Graduate University, Chinese Academy of Sciences, Beijing, China.
authors.forename: Dapeng
authors.initials: D
authors.lastname: Liu
authors.forename: Jinyuan
authors.initials: J
authors.lastname: Zhou
authors.forename: Rong
authors.initials: R
authors.lastname: Xue
authors.forename: Zhentao
authors.initials: Z
authors.lastname: Zuo
authors.forename: Jing
authors.initials: J
authors.lastname: An
authors.forename: Danny J J
authors.initials: DJ
authors.lastname: Wang
mesh_terms: D000328:Adult; D000465:Algorithms; D000577:Amides / Q000378:metabolism*; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D046911:Macromolecular Substances / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D057054:Molecular Imaging / Q000379:methods*; D011522:Protons; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D055815:Young Adult
chemical_list: D000577:Amides; D046911:Macromolecular Substances; D011522:Protons