title: Magnetic resonance imaging of ionic currents in solution: the effect of magnetohydrodynamic flow.
abstract: OBJECTIVE
  Reliably detecting MRI signals in the brain that are more tightly coupled to neural activity than blood-oxygen-level-dependent fMRI signals could not only prove valuable for basic scientific research but could also enhance clinical applications such as epilepsy presurgical mapping. This endeavor will likely benefit from an improved understanding of the behavior of ionic currents, the mediators of neural activity, in the presence of the strong magnetic fields that are typical of modern-day MRI scanners.
  
  
  BACKGROUND
  Of the various mechanisms that have been proposed to explain the behavior of ionic volume currents in a magnetic field, only one-magnetohydrodynamic flow-predicts a slow evolution of signals, on the order of a minute for normal saline in a typical MRI scanner.
  
  
  METHODS
  This prediction was tested by scanning a volume-current phantom containing normal saline with gradient-echo-planar imaging at 3 T.
  
  
  RESULTS
  Greater signal changes were observed in the phase of the images than in the magnitude, with the changes evolving on the order of a minute.
  
  
  CONCLUSIONS
  These results provide experimental support for the MHD flow hypothesis. Furthermore, MHD-driven cerebrospinal fluid flow could provide a novel fMRI contrast mechanism.
authors.affiliation: Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Mukund
authors.initials: M
authors.lastname: Balasubramanian
authors.affiliation: Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Robert V
authors.initials: RV
authors.lastname: Mulkern
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Wells
authors.affiliation: Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Padmavathi
authors.initials: P
authors.lastname: Sundaram
authors.affiliation: Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Darren B
authors.initials: DB
authors.lastname: Orbach
mesh_terms: D001921:Brain / Q000502:physiology*; D002555:Cerebrospinal Fluid / Q000502:physiology; D006801:Humans; D057446:Hydrodynamics; D007477:Ions / Q000378:metabolism; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010100:Oxygen / Q000378:metabolism; D019047:Phantoms, Imaging
chemical_list: D007477:Ions; D010100:Oxygen
keywords: BOLD; CSF; fMRI; ionic currents; magnetohydrodynamic flow; neuronal currents