title: MRI relaxation in the presence of fictitious fields correlates with myelin content in normal rat brain.
abstract: OBJECTIVE
  Brain myelin plays an important role in normal brain function. Demyelination is involved in many degenerative brain diseases, thus quantitative imaging of myelin has been under active investigation. In previous work, we demonstrated the capability of the method known as Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n (RAFFn) to provide image contrast between white and gray matter in human and rat brains. Here, we provide evidence pointing to myelin being the major source of this contrast.
  
  
  METHODS
  RAFFn relaxation time constant (TRAFFn) was mapped in rat brain ex vivo. TRAFFn was quantified in 12 different brain areas. TRAFFn values were compared with multiple other MRI metrics (T1, T2 , continuous wave T1ρ, adiabatic T1ρ and T2ρ, magnetization transfer ratio), and with histologic measurements of cell density, myelin and iron content.
  
  
  RESULTS
  Highest contrast between white and grey matter was obtained with TRAFFn in the rotating frames of ranks n = 4 and 5. TRAFFn values correlated strongly with myelin content, whereas no associations between TRAFFn and iron content or cell density were found.
  
  
  CONCLUSIONS
  TRAFFn with n = 4 or 5 provides a high sensitivity for selective myelin mapping in the rat brain.
authors: A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.
authors: Hanne
authors: H
authors: Hakkarainen
authors: A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.
authors: Alejandra
authors: A
authors: Sierra
authors: Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
authors: Silvia
authors: S
authors: Mangia
authors: Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
authors: Michael
authors: M
authors: Garwood
authors: Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
authors: Shalom
authors: S
authors: Michaeli
authors: A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.
authors: Olli
authors: O
authors: Gröhn
authors: A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.|Imaging Center, Kuopio University Hospital, Kuopio, Finland.
authors: Timo
authors: T
authors: Liimatainen
mesh_terms: D000465:Algorithms; D000818:Animals; D001921:Brain / Q000648:ultrastructure*; D005260:Female; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009186:Myelin Sheath / Q000648:ultrastructure*; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: brain; contrast imaging; fictitious field; myelin; relaxation; rotating frame
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