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

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@article{25cbec43d49040749e34d4a6bfccdcd3,
title = "The stray magnetic fields in Magnetic Resonance Current Density Imaging (MRCDI)",
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.",
keywords = "Cable currents, Magnetic Resonance Current Density Imaging, Magnetic resonance electric impedance tomography, Physiological noise, Artifacts, Signal-To-Noise Ratio, Magnetic Resonance Imaging/instrumentation, Magnetic Fields, Phantoms, Imaging",
author = "Cihan G{\"o}ksu and Klaus Scheffler and Siebner, {Hartwig R} and Axel Thielscher and Hanson, {Lars G}",
note = "Copyright {\textcopyright} 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.",
year = "2019",
month = mar,
day = "8",
doi = "10.1016/j.ejmp.2019.02.022",
language = "English",
volume = "59",
pages = "142--150",
journal = "Physica Medica",
issn = "1120-1797",
publisher = "Elsevier Ltd",

}

RIS

TY - JOUR

T1 - The stray magnetic fields in Magnetic Resonance Current Density Imaging (MRCDI)

AU - Göksu, Cihan

AU - Scheffler, Klaus

AU - Siebner, Hartwig R

AU - Thielscher, Axel

AU - Hanson, Lars G

N1 - Copyright © 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

PY - 2019/3/8

Y1 - 2019/3/8

N2 - 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.

AB - 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.

KW - Cable currents

KW - Magnetic Resonance Current Density Imaging

KW - Magnetic resonance electric impedance tomography

KW - Physiological noise

KW - Artifacts

KW - Signal-To-Noise Ratio

KW - Magnetic Resonance Imaging/instrumentation

KW - Magnetic Fields

KW - Phantoms, Imaging

UR - http://www.scopus.com/inward/record.url?scp=85062399226&partnerID=8YFLogxK

U2 - 10.1016/j.ejmp.2019.02.022

DO - 10.1016/j.ejmp.2019.02.022

M3 - Journal article

C2 - 30853265

VL - 59

SP - 142

EP - 150

JO - Physica Medica

JF - Physica Medica

SN - 1120-1797

ER -

ID: 56812087