Sensitivity analysis of magnetic field measurements for magnetic resonance electrical impedance tomography (MREIT)

Göksu, Cihan; Scheffler, Klaus; Ehses, Philipp; Hanson, Lars G.; Thielscher, Axel

doi:10.1002/mrm.26727

Cited by 15 publications

(39 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1b). Details of the sequences can be found in (Göksu et al, 2017). In short, we selected MESE because of its high SNR for the magnitude images and its robustness to field inhomogeneity (Nam and Kwon, 2010), and SSFP-FID for its high phase sensitivity (Lee et al, 2016;Scheffler et al, 2006).…”

Section: Mri Sequences For Mrcdimentioning

confidence: 99%

“…where γ is the gyromagnetic ratio of protons, and T ES the echo spacing. The measurement is performed twice with opposite current injection profiles, and M n ∠ + and M n ∠ − are the phases of the acquired complex MR images for the positive and negative current directions for the n th echo (Göksu et al, 2017;Nam and Kwon, 2010;Scott et al, 1992). The final ∆B z,c image is determined as the weighted sum of the n c z, ∆B images of the single echoes, with the weightings being proportional to the inverse of the variances of the images (Göksu et al, 2017).…”

Section: Mri Sequences For Mrcdimentioning

confidence: 99%

“…is the phase sensitivity to magnetic field changes (Göksu et al, 2017). We calculated it via spin simulations based on 3D rotation and relaxation matrices (Jaynes, 1955), and it depends on the sequence and tissue relaxation parameters.…”

Section: Mri Sequences For Mrcdimentioning

confidence: 99%

“…Given the higher efficiency of SSFP-FID compared to MESE (Göksu et al, 2017), we focused on SSFP-FID in the rest of the study. The sequence parameters were T R = 120 ms, N meas = 24 (T tot ≈ 9 mins) and N GE = 7.…”

Section: Experiments 3: Correction Of Cable-induced Stray Magnetic Fieldsmentioning

confidence: 99%

“…Using comprehensive theoretical analyses and phantom measurements, we have previously optimized the sensitivity of two MRI sequences for in-vivo MRCDI and MREIT measurements in the human brain (Göksu et al, 2017). We explored multi-echo spin echo (MESE) and steady-state free precession free induction decay (SSFP-FID) sequences, and derived optimized parameters to maximize their efficiency for measuring current-induced phase changes, given relaxation parameters of brain tissue at 3 T. Here, we validate the performance of the optimized sequences for in-vivo brain imaging and improve their robustness to artifacts that are of concern in an in-vivo setting, in order to ensure the validity of the results.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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

et al. 2018

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Mri Sequences For Mrcdimentioning

confidence: 99%

Section: Mri Sequences For Mrcdimentioning

confidence: 99%

Section: Mri Sequences For Mrcdimentioning

confidence: 99%

Section: Experiments 3: Correction Of Cable-induced Stray Magnetic Fieldsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

et al. 2018

Self Cite

View full text Add to dashboard Cite

show abstract

General principle and optimization of magneto‐acousto‐electrical tomography based on image distortion evaluation

Chen

Guo

et al. 2023

Medical Physics

View full text Add to dashboard Cite

Background: As a novel non-invasive multi-physics imaging methodology, the magneto-acousto-electrical (MAE) technology is capable of detecting electric conductivity changes for biological tissues, exhibiting prosperous perspectives in medical applications. However, the acoustic beam was often simplified to a straight line or a focused one, being perpendicular to layered boundaries of tissues in previous studies. Linear-scanning measurements were carried out to reconstruct B-mode MAE images for layered models without considering the radiation pattern of transducers. Obvious image distortions in both shape and brightness were observed in experiments without any reasonable explanation. Purpose: This study aims to establish a general physical model for MAE measurements and solve the problem of B-mode image distortion, and hence provide theoretical and technical supports for the improvement of MAE imaging in practical applications. Methods: By considering the radiation pattern of actual transducers and the inclined angle of electric conductivity boundaries, a general principal of MAE measurements applicable for objects of arbitrary shapes is proposed based on the theories of acoustic radiation, Hall Effect and electrical detection. The influences of inclined conductivity boundaries and transducer directivities are numerically analyzed with Matlab programming and also demonstrated by experimental measurements. To evaluate the degree of B-mode image distortion, the deformation length (3 dB amplitude decrease) of approximate straight lines for a circular model is defined as L = dtan(β m /2), with d and β m being the measurement distance and the half radiation angle of the main-lobe, respectively. The rotary-scanning-based MAE tomography (MAET) is employed to reduce the image distortion, and the rotation angle step is further optimized based on the criterion of the boundary radius fluctuation coefficient <0.01 mm. Results:The experimental results of MAE signals and B-mode images as well as MAETs show good agreements with simulations. It is demonstrated that, as the increase of the inclined angle, the MAE decreases rapidly with an extended time interval and reaches the 20 dB amplitude decrease when the angle exceeds 12 • . Meanwhile, the deformation length of B-mode MAE imaging increases with the increase of the radiation angle for the transducer with a weaker radiation pattern, and hence results in a more serious image distortion. A smaller rotation angle step should be adopted to the MAET system with a longer deformation length, and the optimized maximum angle step of 12 • is also achieved for the omnidirectional radiation of point sources with a long deformation length.

show abstract

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

Göksu

Scheffler

Gregersen

et al. 2021

Magnetic Resonance in Med

Self Cite

View full text Add to dashboard Cite

show abstract

Sensitivity analysis of magnetic field measurements for magnetic resonance electrical impedance tomography (MREIT)

Abstract: The efficiencies observed with the optimized sequence parameters will likely render in-vivo human brain MREIT feasible. Magn Reson Med 79:748-760, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Cited by 15 publications

References 32 publications

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

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

General principle and optimization of magneto‐acousto‐electrical tomography based on image distortion evaluation

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

Contact Info

Product

Resources

About