J-based Magnetic Resonance Conductivity Tensor Imaging (MRCTI) at 3 T

Sadighi, Mehdi; Göksu, Cemil; Eyüboğlu, B. Murat

doi:10.1109/embc.2014.6943796

Cited by 5 publications

(8 citation statements)

References 13 publications

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“…Up to now, successful MRCDI and MREIT recordings have been demonstrated in phantoms, animal models and in-vivo in human limbs (Birgül et al, 2003;Eyüboğlu, 2006c;Han et al, 2010;Ider and Birgül, 1998;Jeon et al, 2009;Jeong et al, 2010;Kim et al, 2009Kim et al, , 2008Kim et al, , 2011Meng et al, 2012;Oh et al, 2005Oh et al, , 2003Sadighi et al, 2014;Sadleir et al, 2005;Seo and Woo, 2011;Woo and Seo, 2008).…”

Section: Introductionmentioning

confidence: 99%

Human in-vivo brain magnetic resonance current density imaging (MRCDI)

et al. 2018

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Magnetic resonance current density imaging (MRCDI) and MR electrical impedance tomography (MREIT) are two emerging modalities, which combine weak time-varying currents injected via surface electrodes with magnetic resonance imaging (MRI) to acquire information about the current flow and ohmic conductivity distribution at high spatial resolution. The injected current flow creates a magnetic field in the head, and the component of the induced magnetic field ΔB parallel to the main scanner field causes small shifts in the precession frequency of the magnetization. The measured MRI signal is modulated by these shifts, allowing to determine ΔB for the reconstruction of the current flow and ohmic conductivity. Here, we demonstrate reliable ΔB measurements in-vivo in the human brain based on multi-echo spin echo (MESE) and steady-state free precession free induction decay (SSFP-FID) sequences. In a series of experiments, we optimize their robustness for in-vivo measurements while maintaining a good sensitivity to the current-induced fields. We validate both methods by assessing the linearity of the measured ΔB with respect to the current strength. For the more efficient SSFP-FID measurements, we demonstrate a strong influence of magnetic stray fields on the ΔB images, caused by non-ideal paths of the electrode cables, and validate a correction method. Finally, we perform measurements with two different current injection profiles in five subjects. We demonstrate reliable recordings of ΔB fields as weak as 1 nT, caused by currents of 1 mA strength. Comparison of the ΔB measurements with simulated ΔB images based on FEM calculations and individualized head models reveals significant linear correlations in all subjects, but only for the stray field-corrected data. As final step, we reconstruct current density distributions from the measured and simulated ΔB data. Reconstructions from non-corrected ΔB measurements systematically overestimate the current densities. Comparing the current densities reconstructed from corrected ΔB measurements and from simulated ΔB images reveals an average coefficient of determination R of 71%. In addition, it shows that the simulations underestimated the current strength on average by 24%. Our results open up the possibility of using MRI to systematically validate and optimize numerical field simulations that play an important role in several neuroscience applications, such as transcranial brain stimulation, and electro- and magnetoencephalography.

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Section: Introductionmentioning

confidence: 99%

Human in-vivo brain magnetic resonance current density imaging (MRCDI)

et al. 2018

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“…Here, we performed Biot-Savart simulations for the cables as described in the theory section while subdividing each linear segment into 1000 pieces. The field changes due to a wire segment that was orthogonal to the main field and placed d = [4][5][6][7][8][9][10][11][12][13][14][15][16] cm away along the z-direction from the imaging region were calculated. We also simulated the field changes due to misalignment by θ = [0-40] degrees of the cable segments that are ideally parallel to the main field (Fig.…”

Section: ) Simulations Of the Stray Fields Due To The Cable Currentsmentioning

confidence: 99%

“…The current induces a magnetic field, and the component ∆B z,c that is parallel to the scanner field modulates the phase of the acquired MR signal accordingly. Therefore, the currentinduced magnetic field ∆B z,c can be determined from MR measurements, and the current flows and ohmic conductivities can be derived by means of recently developed reconstruction techniques [7][8][9][10][11][12][13]. However, accurate current flow and conductivity reconstructions require sensitive ∆B z,c measurements with high accuracy and precision.…”

Section: Introductionmentioning

confidence: 99%

“…Biot-Savart simulations of the cable-current-induced stray fields. (a) The desired ∆B z,cimage without stray fields (left) is compared with ∆B z,c images with stray fields for four different simulations in which the wire segment is placed d =[4,8,12,16] cm away from the imaging region (first row). ∆B z,c images for cable misalignments θ y =[10,20,30] degrees in y-direction (second row)…”

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confidence: 99%

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

Göksu¹,

Scheffler²,

Siebner³

et al. 2019

Physica Medica

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“…MRCDI and MREIT aim to measure these phase modulations to gain insight into the strength and spatial distribution of the current-induced magnetic field for informing reconstructions of the current flow and conductivity distributions. The approach has been successfully demonstrated in phantoms, animals and human limbs in-vivo (7,9,(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28), but it is particularly challenging for the human brain because the current-induced magnetic field stays below 1 to 2 nT in that case. This is caused by the low maximal current strength that is tolerable and safe (1-2 mA) (29) and the "shielding" effect of the low-conductive skull that results in part of the current to be shunted through the scalp.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity and resolution improvement for in-vivo magnetic resonance current density imaging (MRCDI) of the human brain

Göksu

Scheffler

Gregersen

et al. 2021

Preprint

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Purpose: Magnetic resonance current density imaging (MRCDI) combines MR brain imaging with the injection of time-varying weak currents (1-2 mA) to assess the current flow pattern in the brain. However, the utility of MRCDI is still hampered by low measurement sensitivity and poor image quality. Methods: We recently introduced a multi-gradient-echo-based MRCDI approach that has the hitherto best documented efficiency. We now advanced our MRCDI approach in three directions and performed phantom and in-vivo human brain experiments for validation: First, we verified the importance of enhanced spoiling and optimize it for imaging of the human brain. Second, we improved the sensitivity and spatial resolution by using acquisition weighting. Third, we added navigators as a quality control measure for tracking physiological noise. Combining these advancements, we tested our optimized MRCDI method by using 1 mA transcranial electrical stimulation (TES) currents injected via two different electrode montages in five subjects. Results: For a session duration of 4:20 min, the new MRCDI method was able to detect magnetic field changes caused by the TES current flow at a sensitivity level of 84 pT, representing in a twofold increase relative to our original method. Comparing both methods to current flow simulations based on personalized head models demonstrated a consistent increase in the coefficient of determination of ∆R2=0.12 for the current-induced magnetic fields and ∆R2=0.22 for the current flow reconstructions. Interestingly, some of the simulations still clearly deviated from the measurements despite of the strongly improved measurement quality. This suggests that MRCDI can reveal useful information for the improvement of head models used for current flow simulations. Conclusion: The advanced method strongly improves the sensitivity and robustness of MRCDI and is an important step from proof-of-concept studies towards a broader application of MRCDI in clinical and basic neuroscience research.

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J-based Magnetic Resonance Conductivity Tensor Imaging (MRCTI) at 3 T

Cited by 5 publications

References 13 publications

Human in-vivo brain magnetic resonance current density imaging (MRCDI)

Human in-vivo brain magnetic resonance current density imaging (MRCDI)

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

Sensitivity and resolution improvement for in-vivo magnetic resonance current density imaging (MRCDI) of the human brain

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