The stray magnetic fields in Magnetic Resonance Current Density Imaging (MRCDI)

Cihan Göksu, Klaus Scheffler, Hartwig R. Siebner, Axel Thielscher, Lars G. Hanson*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

45 Downloads (Pure)

Abstract

Purpose: MR Current Density Imaging (MRCDI) involves weak current-injection into the head. The resulting magnetic field changes are measured by MRI. Stray fields pose major challenges since these can dominate the fields caused by tissue currents. We analyze the sources and influences of stray fields. Methods: First, we supply validation data for a recently introduced MRCDI method with an unprecedented noise floor of ∼0.1 nT in vivo. Second, we assess the accuracy limit of the method and our corresponding cable current correction in phantoms ensuring high signal-to-noise ratio (SNR). Third, we simulate the influence of stray fields on current flow reconstructions for various realistic experimental set-ups. Fourth, we experimentally determine the physiological field variations. Finally, we explore the consequences of head positioning in an exemplary head coil, since off-center positioning provides space for limiting cable-induced fields. Results: The cable correction method performs well except near the cables. Unless correcting for cable currents, the reconstructed current flow is easily misestimated by up to 45% for a realistic experimental set-up. Stray fields dominating the fields caused by tissue currents can occur, e.g. due to a wire segment 20 cm away from the imaged region, or due to a slight cable misalignment of 3°. The noise is increased by 40% due to physiological factors. Minor patient movements can cause field changes of ∼40 nT. Off-centered head positioning can locally reduce SNR by e.g. 30%. Conclusions: Quantification of stray fields showed that MRCDI requires careful field correction. After cable correction, physiological noise is a limiting factor.

Original languageEnglish
JournalPhysica Medica
Volume59
Pages (from-to)142-150
ISSN1120-1797
DOIs
Publication statusPublished - 2019

Keywords

  • Cable currents
  • Magnetic Resonance Current Density Imaging
  • Magnetic resonance electric impedance tomography
  • Physiological noise

Fingerprint Dive into the research topics of 'The stray magnetic fields in Magnetic Resonance Current Density Imaging (MRCDI)'. Together they form a unique fingerprint.

Cite this