Evaluating the Performance of Ultra-Low-Field MRI for in-vivo 3D Current Density Imaging of the Human Head

Peter Hömmen*, Antti J. Mäkinen, Alexander Hunold, René Machts, Jens Haueisen, Koos C.J. Zevenhoven, Risto J. Ilmoniemi, Rainer Körber

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Magnetic fields associated with currents flowing in tissue can be measured non-invasively by means of zero-field-encoded ultra-low-field magnetic resonance imaging (ULF MRI) enabling current-density imaging (CDI) and possibly conductivity mapping of human head tissues. Since currents applied to a human are limited by safety regulations and only a small fraction of the current passes through the relatively highly-resistive skull, a sufficient signal-to-noise ratio (SNR) may be difficult to obtain when using this method. In this work, we study the relationship between the image SNR and the SNR of the field reconstructions from zero-field-encoded data. We evaluate these results for two existing ULF-MRI scanners—one ultra-sensitive single-channel system and one whole-head multi-channel system—by simulating sequences necessary for current-density reconstruction. We also derive realistic current-density and magnetic-field estimates from finite-element-method simulations based on a three-compartment head model. We found that existing ULF-MRI systems reach sufficient SNR to detect intra-cranial current distributions with statistical uncertainty below 10%. However, the results also reveal that image artifacts influence the reconstruction quality. Further, our simulations indicate that current-density reconstruction in the scalp requires a resolution <5 mm and demonstrate that the necessary sensitivity coverage can be accomplished by multi-channel devices.

Original languageEnglish
Article number105
Number of pages13
JournalFrontiers in Physics
Volume8
DOIs
Publication statusPublished - 30 Apr 2020
MoE publication typeA1 Journal article-refereed

Keywords

  • current-density imaging
  • finite-element method
  • Monte-Carlo simulation
  • MRI simulation
  • signal-to-noise ratio
  • ultra-low-field MRI
  • zero-field encoding

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