Effects of neuronal magnetic fields on MRI: numerical analysis with axon and dendrite models.

Whether the neuronal magnetic fields (NMFs) could cause measurable MRI signal changes in the human brain seems to be still controversial. In this study, we have numerically investigated the NMF effects on the MRI signal using two separate current source models for axons and dendrites. Since intracellular current distributions are different in axons and dendrites, the NMFs emanating from axons and dendrites are also very different from each other. Due to the quadripole configuration of the intracellular current flowing through an axon, the axonal magnetic field is bipolar causing virtually no changes in the MRI signal. On the contrary, the dendritic magnetic field is unipolar so that its effects can be accumulated during the echo time. The dendritic magnetic field has measurable effects on the MRI signal, but, it is necessary to differentiate the NMF effects from much bigger background BOLD effects to utilize the NMF effects for fMRI.