Modeling direct effects of neural current on MRI.

Area of Science:

• Biophysics
• Neuroimaging
• Magnetic Resonance Imaging

Background:

• Neural activity generates magnetic fields.
• These fields can potentially influence Magnetic Resonance Imaging (MRI) signals.
• Understanding this interaction is crucial for advanced neuroimaging techniques.

Purpose of the Study:

• To investigate the impact of neural magnetic fields on MRI signal magnitude and phase.
• To develop an analytical approximation for MRI signals under neuromagnetic influence.
• To quantify the effects for different neural current strengths.

Main Methods:

• Developed a phenomenological parameter to describe neural current effects.
• Derived an analytic approximation for small neuromagnetically induced phases.
• Compared analytical results with numerical simulations.
• Constrained current strengths using magnetoencephalography (MEG) data.

Main Results:

• Phase shifts are first-order effects, while magnitude reduction is second-order.
• Excellent agreement between analytic approximation and simulations for weak currents.
• For typical neural activity (10 nAm dipole moment), MRI magnitude reduction is minimal (2x10^-5).
• Maximum phase shift is approximately 4x10^-3 under specific voxel displacement conditions.

Conclusions:

• Neural magnetic fields induce measurable phase shifts in MRI signals.
• Magnitude changes are significantly smaller than phase shifts for typical neural activity.
• The developed model provides insights into the neuromagnetic influence on MRI, though it may overestimate effects.