Sensitivity and resolution improvement for in vivo magnetic resonance current‐density imaging of the human brain

Göksu, Cihan; Scheffler, Klaus; Gregersen, Fróði; Eroğlu, Hasan; Heule, Rahel; Siebner, H. R.; Hanson, Lars G.; Thielscher, Axel

doi:10.1002/mrm.28944

Cited by 5 publications

(30 citation statements)

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“…They have also been used to understand individual variability in tDCS induced-electric fields combined with anatomical scans, to estimate the amount of current that can theoretically be injected into the skull and reach the cortex based on resistive properties of tissue, and to determine a proper dose of current depending on age differences (Ciechanski et al, 2018;Indahlastari et al, 2021). However, only a few studies have attempted to measure the actual current flow, or current induced magnetic field as a marker of the current flow, in the human brain in-vivo (Jog et al, 2016(Jog et al, , 2020(Jog et al, , 2021Kasinadhuni et al, 2017;Goksu et al, 2018Goksu et al, , 2021.…”

Section: Resultsmentioning

confidence: 99%

“…Previous in-vivo measurements of current flow in the brain make use of Ampere's law to infer the underlying current distribution from the magnetic field induced by the injected current (Kasinadhuni et al, 2017;Goksu et al, 2018Goksu et al, , 2021. When tDCS is performed within an MRI scanner, the resulting magnetic field perturbations in the head cause local proton off-resonance, which in turn alters the phase of the MRI signal as a function of local current magnitude and current flow direction in the brain region.…”

Section: Resultsmentioning

confidence: 99%

“…In practice, therefore, the MRI-based current mapping strategy is often inherently constrained by incomplete information. Previous studies have used predictions from computational modeling to fill in the two missing components (Kasinadhuni et al, 2017;Goksu et al, 2018Goksu et al, , 2021, but this method makes comparison of the outcome of computation models and actual experiment data circular.…”

Section: Resultsmentioning

confidence: 99%

“…The major limitation of this study is that it only measured the B z component of the induced magnetic field, which accounts for some of the missing current. Yet we declined to augment these measurements with models of the missing components to avoid biasing the results (Kasinadhuni et al, 2017;Goksu et al, 2018Goksu et al, , 2021. By repeating the scans twice while the head is tilted from its normal position, a complete picture of the magnetic field distribution can be obtained (Hernandez-Garcia et al, 2019), which would allow full characterization of the current flow.…”

Section: Limitations Of the Studymentioning

confidence: 99%

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Inconsistencies in mapping current distribution in transcranial direct current stimulation

Jwa¹,

Goodman²,

Glover³

2023

Front. Neuroimaging

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IntroductiontDCS is a non-invasive neuromodulation technique that has been widely studied both as a therapy for neuropsychiatric diseases and for cognitive enhancement. However, recent meta-analyses have reported significant inconsistencies amongst tDCS studies. Enhancing empirical understanding of current flow in the brain may help elucidate some of these inconsistencies.MethodsWe investigated tDCS-induced current distribution by injecting a low frequency current waveform in a phantom and in vivo. MR phase images were collected during the stimulation and a time-series analysis was used to reconstruct the magnetic field. A current distribution map was derived from the field map using Ampere's law.ResultsThe current distribution map in the phantom showed a clear path of current flow between the two electrodes, with more than 75% of the injected current accounted for. However, in brain, the results did evidence a current path between the two target electrodes but only some portion ( 25%) of injected current reached the cortex demonstrating that a significant fraction of the current is bypassing the brain and traveling from one electrode to the other external to the brain, probably due to conductivity differences in brain tissue types. Substantial inter-subject and intra-subject (across consecutive scans) variability in current distribution maps were also observed in human but not in phantom scans.DiscussionsAn in-vivo current mapping technique proposed in this study demonstrated that much of the injected current in tDCS was not accounted for in human brain and deviated to the edge of the brain. These findings would have ramifications in the use of tDCS as a neuromodulator and may help explain some of the inconsistencies reported in other studies.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Limitations Of the Studymentioning

confidence: 99%

See 2 more Smart Citations

Inconsistencies in mapping current distribution in transcranial direct current stimulation

Jwa¹,

Goodman²,

Glover³

2023

Front. Neuroimaging

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“…32,39,42,44 We corrected the combined ΔB z,c images for stray magnetic fields induced by cable currents. 41,42…”

Section: Measuring Current-induced Magnetic Fieldsmentioning

confidence: 99%

Volumetric measurements of weak current–induced magnetic fields in the human brain at high resolution

Göksu,

Gregersen,

Scheffler

et al. 2023

Magnetic Resonance in Med

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PurposeClinical use of transcranial electrical stimulation (TES) requires accurate knowledge of the injected current distribution in the brain. MR current density imaging (MRCDI) uses measurements of the TES‐induced magnetic fields to provide this information. However, sufficient sensitivity and image quality in humans in vivo has only been documented for single‐slice imaging.MethodsA recently developed, optimally spoiled, acquisition‐weighted, gradient echo–based 2D‐MRCDI method has now been advanced for volume coverage with densely or sparsely distributed slices: The 3D rectilinear sampling (3D‐DENSE) and simultaneous multislice acquisition (SMS‐SPARSE) were optimized and verified by cable‐loop experiments and tested with 1‐mA TES experiments for two common electrode montages.ResultsComparisons between the volumetric methods against the 2D‐MRCDI showed that relatively long acquisition times of 3D‐DENSE using a single slab with six slices hindered the expected sensitivity improvement in the current‐induced field measurements but improved sensitivity by 61% in the Laplacian of the field, on which some MRCDI reconstruction methods rely. Also, SMS‐SPARSE acquisition of three slices, with a factor 2 CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration) acceleration, performed best against the 2D‐MRCDI with sensitivity improvements for the and Laplacian noise floors of 56% and 78% (baseline without current flow) as well as 43% and 55% (current injection into head). SMS‐SPARSE reached a sensitivity of 67 pT for three distant slices at 2 × 2 × 3 mm3 resolution in 10 min of total scan time, and consistently improved image quality.ConclusionVolumetric MRCDI measurements with high sensitivity and image quality are well suited to characterize the TES field distribution in the human brain.

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SNR and total acquisition time analysis of multi-echo FLASH pulse sequence for current density imaging

Sadighi

Şişman

Eyüboğlu

2021

Journal of Magnetic Resonance

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Sensitivity and resolution improvement for in vivo magnetic resonance current‐density imaging of the human brain

Abstract: How to cite this article: Göksu C, Scheffler K, Gregersen F, et al. Sensitivity and resolution improvement for in vivo magnetic resonance currentdensity imaging of the human brain.

Cited by 5 publications

References 59 publications

Inconsistencies in mapping current distribution in transcranial direct current stimulation

Inconsistencies in mapping current distribution in transcranial direct current stimulation

Volumetric measurements of weak current–induced magnetic fields in the human brain at high resolution

SNR and total acquisition time analysis of multi-echo FLASH pulse sequence for current density imaging

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