title: Comparison of two quantitative proton density mapping methods in multiple sclerosis.
abstract: OBJECTIVE
  Proton density (PD) mapping requires correction for the receive profile (RP), which is frequently performed via bias-field correction. An alternative RP-mapping method utilizes a comparison of uncorrected PD-maps and a value ρ(T1) directly derived from T1-maps via the Fatouros equation. This may be problematic in multiple sclerosis (MS), if respective parameters are only valid for healthy brain tissue. We aimed to investigate whether the alternative method yields correct PD values in MS patients.
  
  
  METHODS
  PD mapping was performed on 27 patients with relapsing-remitting MS and 27 healthy controls, utilizing both methods, yielding reference PD values (PDref, bias-field method) and PDalt(alternative method).
  
  
  RESULTS
  PDalt-values closely matched PDref, both for patients and controls. In contrast, ρ(T1) differed by up to 3 % from PDref,and the voxel-wise correlation between PDrefand ρ(T1) was reduced in a patient subgroup with a higher degree of disability. Still, discrepancies between ρ(T1) and PDrefwere almost identical across different tissue types, thus translating into a scaling factor, which cancelled out during normalization to 100 % in CSF, yielding a good agreement between PDaltand PDref.
  
  
  CONCLUSIONS
  RP correction utilizing the auxiliary parameter ρ(T1) derived via the Fatouros equation provides accurate PD results in MS patients, in spite of discrepancies between ρ(T1) and actual PD values.
authors.affiliation: Department of Neurology, Goethe University, Frankfurt/Main, Germany. Rene-Maxime.Gracien@kgu.de.|Brain Imaging Center, Goethe University, Frankfurt/Main, Germany. Rene-Maxime.Gracien@kgu.de.
authors.forename: René-Maxime
authors.initials: RM
authors.lastname: Gracien
authors.affiliation: Department of Neurology, Goethe University, Frankfurt/Main, Germany.|Brain Imaging Center, Goethe University, Frankfurt/Main, Germany.
authors.forename: Sarah C
authors.initials: SC
authors.lastname: Reitz
authors.affiliation: Department of Neuroradiology, Goethe University, Frankfurt/Main, Germany.|Brain Imaging Center, Goethe University, Frankfurt/Main, Germany.
authors.forename: Marlies
authors.initials: M
authors.lastname: Wagner
authors.affiliation: Department of Neurology, Goethe University, Frankfurt/Main, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Mayer
authors.affiliation: Brain Imaging Center, Goethe University, Frankfurt/Main, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Volz
authors.affiliation: Department of Neurology, Goethe University, Frankfurt/Main, Germany.|Brain Imaging Center, Goethe University, Frankfurt/Main, Germany.
authors.forename: Stephanie-Michelle
authors.initials: SM
authors.lastname: Hof
authors.affiliation: Department of Neurology, Johannes Gutenberg University, Mainz, Germany.|Neuroimaging Center (NIC) of the Focus Program Translational Neuroscience (FTN), Johannes Gutenberg University, Mainz, Germany.
authors.forename: Vinzenz
authors.initials: V
authors.lastname: Fleischer
authors.affiliation: Department of Neurology, Johannes Gutenberg University, Mainz, Germany.|Neuroimaging Center (NIC) of the Focus Program Translational Neuroscience (FTN), Johannes Gutenberg University, Mainz, Germany.
authors.forename: Amgad
authors.initials: A
authors.lastname: Droby
authors.affiliation: Department of Neurology, Goethe University, Frankfurt/Main, Germany.
authors.forename: Helmuth
authors.initials: H
authors.lastname: Steinmetz
authors.affiliation: Department of Neurology, Johannes Gutenberg University, Mainz, Germany.|Neuroimaging Center (NIC) of the Focus Program Translational Neuroscience (FTN), Johannes Gutenberg University, Mainz, Germany.
authors.forename: Sergiu
authors.initials: S
authors.lastname: Groppa
authors.affiliation: Department of Neuroradiology, Goethe University, Frankfurt/Main, Germany.|Brain Imaging Center, Goethe University, Frankfurt/Main, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Hattingen
authors.affiliation: Department of Neurology, Goethe University, Frankfurt/Main, Germany.|Brain Imaging Center, Goethe University, Frankfurt/Main, Germany.|Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
authors.forename: Johannes C
authors.initials: JC
authors.lastname: Klein
authors.affiliation: Brain Imaging Center, Goethe University, Frankfurt/Main, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Deichmann
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging* / Q000473:pathology; D001931:Brain Mapping / Q000379:methods; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000000981:diagnostic imaging*; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results
keywords: Fatouros equation; Proton density; Quantitative MRI; Relapsing-remitting multiple sclerosis