Estimation of local magnetic fields in the rat brain based on multichannel potential recordings

Conventional functional magnetic resonance imaging (MRI) has a relatively low temporal resolution, because this method does not measure neuronal activity itself but observes blood flow. The detection of local magnetic fields in close proximity to the activating area leads to a novel functional MRI with ultrahigh temporal resolution. Magnetic fields arising from neuronal electrical activities are very weak. The aim of this study is to evaluate the feasibility of detecting neuronal magnetic fields using MRI. The threedimensional potential distribution in the rat brain was measured using a microelectrode array. Somatosensory evoked potentials were recorded during hind paw stimulation with a spatial resolution of 300 μm. The intensity of the magnetic flux density was calculated from the measured result, and was estimated at 2.84 pT. Estimation of the theoretical limit of MRI sensitivity suggested that the calculated magnetic flux density was within the detectable range of MRI.