Combination of BOLD-fMRI and VEP recordings for spin-echo MRI detection of primary magnetic effects caused by neuronal currents.

In the present paper, for the first time, the feasibility to detect primary magnetic field changes caused by neuronal activity in vivo by spin-echo (SE) magnetic resonance imaging (MRI) is investigated. The detection of effects more directly linked to brain activity than secondary hemodynamic-metabolic changes would enable the study of brain function with improved specificity. However, the detection of neuronal currents by MRI is hampered by such accompanying hemodynamic changes. Therefore, SE image acquisition, rather than gradient-echo (GE) image acquisition, was preferred in the present work since the detection of primary neuronal and not blood oxygenation level-dependent (BOLD)-related effects may be facilitated by this approach. First of all, a precise spatiotemporal synchronization of image acquisition with the neuronal event had to be performed to avoid refocusing of the dephasing phenomenon during the course of the SE sequence. At this aim, we propose the combined use of visual evoked potential (VEP) recordings and BOLD-fMRI measurements prior to SE MRI scanning. Moreover, we exemplify by theory and experimentation how the control of artefactual signal changes due to BOLD and movement effects may be further improved by the experimental design. Finally, results from a pilot study using the proposed combination of VEP recordings and MRI techniques are reported, suggesting the feasibility of this method.