Magnetic resonance imaging of ionic currents in solution: The effect of magnetohydrodynamic flow

Abstract

Purpose 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. Theory 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. Conclusion These results provide experimental support for the MHD flow hypothesis. Furthermore, MHD-driven cerebrospinal fluid flow could provide a novel fMRI contrast mechanism.