Demonstration of full tensor current density imaging using ultra-low field MRI

Area of Science:

• Biophysics
• Neuroimaging
• Magnetic Resonance Imaging

Background:

• Direct imaging of electrical currents in biological tissues can enhance neuroimaging techniques.
• Ultra-low field (ULF) magnetic resonance imaging (MRI) operating at microtesla (µT) Larmor fields is a potential modality for current density imaging (CDI).

Purpose of the Study:

• To investigate the measurable impact of magnetic fields generated by impressed currents on MR signals for CDI.
• To develop and demonstrate a ULF MRI system capable of probing the full tensor of the current-induced magnetic field (B_J).

Main Methods:

• Utilized specialized MR sequences to probe the magnetic field (B_J) generated by impressed current density (J).
• Developed a ULF MRI system using a superconducting quantum interference device (SQUID) with a noise level of 380 fT/√Hz.
• Implemented zero-field encoding for probing the full B_J tensor without external magnetic fields.
• Demonstrated 3D CDI on phantoms with currents of ~2 mA (0.45–8 A/m²).

Main Results:

• Successfully demonstrated 3D CDI on phantoms, visualizing current densities.
• The ULF MRI system allowed for the derivation of the full B_J tensor without subject rotation.
• Achieved zero-field encoding by probing B_J in the absence of other magnetic fields.

Conclusions:

• The developed ULF MRI system and zero-field encoding method enable direct imaging of electrical currents within biological tissues.
• The study provides insights into necessary improvements for signal-to-noise ratio for in vivo applications.
• This technique holds promise for advancing electro-magnetic neuroimaging by providing conductivity information.