title: Myelin water mapping by spatially regularized longitudinal relaxographic imaging at high magnetic fields.
abstract: OBJECTIVE
  Magnetic resonance T1 -weighted images are routinely used for human brain segmentation, brain parcellation, and clinical diagnosis of demyelinating diseases. Myelin is thought to influence the longitudinal relaxation commonly described by a mono-exponential recovery, although reports of bi-exponential longitudinal relaxation have been published. The purpose of this work was to investigate if a myelin water T1 contribution could be separated in geometrically sampled Look-Locker trains of low flip angle gradient echoes.
  
  
  METHODS
  T1 relaxograms from normal human brain were computed by a spatially regularized inverse Laplace transform after estimating the apparent inversion efficiency.
  
  
  RESULTS
  With sufficiently long inversion-time sampling (ca. 5 × T1 of cerebrospinal fluid), the T1 relaxogram revealed a short-T1 peak (106-225 ms). The apparent fraction of this water component increased in human brain white matter from 8.3% at 3 T, to 11.3% at 4 T and 15.0% at 7 T. The T2 * of the short-T1 peak at 3 T was shorter, 27.9 ± 13.0 ms, than that of the long-T1 peak, 51.3 ± 5.6 ms.
  
  
  CONCLUSIONS
  The short-T1 fraction is interpreted as the water resident in myelin. Its detection is facilitated by longer T1 of axoplasmic water at higher magnetic field.
authors.affiliation: Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany; Laboratoire de Spectrométrie Ionique et Moléculaire, Université Claude-Bernard, Lyon, France; Faculty of Physics and Earth Sciences, University of Leipzig, Leipzig, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Labadie
authors.forename: Jing-Huei
authors.initials: JH
authors.lastname: Lee
authors.forename: William D
authors.initials: WD
authors.lastname: Rooney
authors.forename: Silvia
authors.initials: S
authors.lastname: Jarchow
authors.forename: Monique
authors.initials: M
authors.lastname: Aubert-Frécon
authors.forename: Charles S
authors.initials: CS
authors.lastname: Springer
authors.forename: Harald E
authors.initials: HE
authors.lastname: Möller
mesh_terms: D000328:Adult; D001834:Body Water / Q000737:chemistry*; D001923:Brain Chemistry; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D057054:Molecular Imaging / Q000379:methods*; D009186:Myelin Sheath / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: inverse Laplace transform; longitudinal relaxation; myelin water; regularization