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

Magn Reson Imaging. 2019 Jul:60:137-144. doi: 10.1016/j.mri.2019.03.010. Epub 2019 Mar 18.

Abstract

Direct imaging of impressed dc currents inside the head can provide valuable conductivity information, possibly improving electro-magnetic neuroimaging. Ultra-low field magnetic resonance imaging (ULF MRI) at μT Larmor fields can be utilized for current density imaging (CDI). Here, a measurable impact of the magnetic field BJ, generated by the impressed current density J, on the MR signal is probed using specialized sequences. In contrast to high-field MRI, the full tensor of BJ can be derived without rotation of the subject in the scanner, due to a larger flexibility in the sequence design. We present an ULF MRI setup based on a superconducting quantum interference device (SQUID), which is operating at a noise level of 380 aT Hz-1/2 and capable of switching all imaging fields within a pulse sequence. Thereby, the system enables zero-field encoding, where the full tensor of BJ is probed in the absence of other magnetic fields. 3D CDI is demonstrated on phantoms with different geometries carrying currents of approximately 2 mA corresponding to current densities between 0.45 and 8 A/m2. By comparison to an in vivo acquired head image, we provide insights to necessary improvements in signal-to-noise ratio.

Keywords: Current density imaging; Ultra-low field MRI; Zero-field encoding.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Computer Simulation
  • Equipment Design
  • Fourier Analysis
  • Head / diagnostic imaging*
  • Humans
  • Image Processing, Computer-Assisted / methods*
  • Imaging, Three-Dimensional / methods*
  • Magnetic Fields*
  • Magnetic Resonance Imaging*
  • Models, Anatomic
  • Phantoms, Imaging*
  • Rotation
  • Signal-To-Noise Ratio*