title: MRI contrasts in high rank rotating frames.
abstract: OBJECTIVE
  MRI relaxation measurements are performed in the presence of a fictitious magnetic field in the recently described technique known as RAFF (Relaxation Along a Fictitious Field). This method operates in the 2(nd) rotating frame (rank n = 2) by using a nonadiabatic sweep of the radiofrequency effective field to generate the fictitious magnetic field. In the present study, the RAFF method is extended for generating MRI contrasts in rotating frames of ranks 1 ≤ n ≤ 5. The developed method is entitled RAFF in rotating frame of rank n (RAFFn).
  
  
  METHODS
  RAFFn pulses were designed to generate fictitious fields that allow locking of magnetization in rotating frames of rank n. Contrast generated with RAFFn was studied using Bloch-McConnell formalism together with experiments on human and rat brains.
  
  
  RESULTS
  Tolerance to B0 and B1 inhomogeneities and reduced specific absorption rate with increasing n in RAFFn were demonstrated. Simulations of exchange-induced relaxations revealed enhanced sensitivity of RAFFn to slow exchange. Consistent with such feature, an increased grey/white matter contrast was observed in human and rat brain as n increased.
  
  
  CONCLUSIONS
  RAFFn is a robust and safe rotating frame relaxation method to access slow molecular motions in vivo.
authors: A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.
authors: Timo
authors: T
authors: Liimatainen
authors: A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.
authors: Hanne
authors: H
authors: Hakkarainen
authors: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, USA.
authors: Silvia
authors: S
authors: Mangia
authors: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
authors: Janne M J
authors: JM
authors: Huttunen
authors: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, USA.
authors: Christine
authors: C
authors: Storino
authors: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, USA.
authors: Djaudat
authors: D
authors: Idiyatullin
authors: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, USA.
authors: Dennis
authors: D
authors: Sorce
authors: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, USA.
authors: Michael
authors: M
authors: Garwood
authors: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, USA.
authors: Shalom
authors: S
authors: Michaeli
mesh_terms: D000465:Algorithms; D000818:Animals; D001921:Brain / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D012399:Rotation; D012680:Sensitivity and Specificity
keywords: MRI; brain; contrast; grey matter; rotating frames; white matter