This file was created by the Typo3 extension sevenpack version 0.7.14 --- Timezone: CET Creation date: 2018-12-12 Creation time: 08-57-50 --- Number of references 6 article GoksuHSEST2017 NeuroImage 2018 5 171 26-39 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 ΔBz,c 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 ΔBz,c for the reconstruction of the current flow and ohmic conductivity. Here, we demonstrate reliable ΔBz,c 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 ΔBz,c with respect to the current strength. For the more efficient SSFP-FID measurements, we demonstrate a strong influence of magnetic stray fields on the ΔBz,c 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 ΔBz,c fields as weak as 1 nT, caused by currents of 1 mA strength. Comparison of the ΔBz,c measurements with simulated ΔBz,c 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 ΔBz,c data. Reconstructions from non-corrected ΔBz,c measurements systematically overestimate the current densities. Comparing the current densities reconstructed from corrected ΔBz,c measurements and from simulated ΔBz,c images reveals an average coefficient of determination R2 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. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler https://www.sciencedirect.com/science/article/pii/S1053811917310996 10.1016/j.neuroimage.2017.12.075 cgoksuCGöksu LGHanson HRSiebner ehsesPEhses schefflerKScheffler thiekscherAThielscher article GoksuSEHT2017 Magnetic Resonance in Medicine 2018 2 79 2 748–760 Purpose Clinical use of magnetic resonance electrical impedance tomography (MREIT) still requires significant sensitivity improvements. Here, the measurement of the current-induced magnetic field (ΔBz,c) is improved using systematic efficiency analyses and optimization of multi-echo spin echo (MESE) and steady-state free precession free induction decay (SSFP-FID) sequences. Theory and Methods Considering T1, T2, and math formula relaxation in the signal-to-noise ratios (SNRs) of the MR magnitude images, the efficiency of MESE and SSFP-FID MREIT experiments, and its dependence on the sequence parameters, are analytically analyzed and simulated. The theoretical results are experimentally validated in a saline-filled homogenous spherical phantom with relaxation parameters similar to brain tissue. Measurement of ΔBz,c is also performed in a cylindrical phantom with saline and chicken meat. Results The efficiency simulations and experimental results are in good agreement. When using optimal parameters, ΔBz,c can be reliably measured in the phantom even at injected current strengths of 1 mA or lower for both sequence types. The importance of using proper crusher gradient selection on the phase evolution in a MESE experiment is also demonstrated. Conclusion The efficiencies observed with the optimized sequence parameters will likely render in-vivo human brain MREIT feasible. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler http://onlinelibrary.wiley.com/doi/10.1002/mrm.26727/epdf 10.1002/mrm.26727 cgoksuCGöksu schefflerKScheffler ehsesPEhses LGHanson thielscherAThielscher poster GoksuHSEST2018 2018 6 21 5607 MRCDI is a novel technique, utilizing different phase-sensitive MR methods for non-invasive measurements of weak currents in the human body, which is important in several neuroscience applications. Here, we compare the in-vivo performance of two different MR methods, multi-echo spin echo (MESE) and steady-state free precession free induction decay (SSFP-FID), with single- vs. multi-gradient-echo readouts. We demonstrate that multi-gradient-echo readouts improve both methods. We validate the linear dependence of the measured current-induced magnetic field on the injected current strength for both methods, and propose the more efficient SSFP-FID method as being well suited for highly sensitive single-slice human in-vivo MRCDI. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler https://www.ismrm.org/18/program_files/EP24.htm https://www.ismrm.org/18/Electronic_Posters.pdf Paris, France Joint Annual Meeting ISMRM-ESMRMB 2018 cgoksuCGöksu AHanson HSiebner pehsesPEhses schefflerKScheffler thielscherAThielscher poster GoksuGEST2017 2017 4 25 4039 MRCDI aims at imaging an externally injected current flow in the human body, and might be useful for many biomedical applications. However, the method requires very sensitive measurement of the current-induced magnetic field component ?Bz,c parallel to main field. We systematically optimized MESE to determine its most efficient parameters. In one of the first human in-vivo applications of MRCDI, the optimized sequence was successfully used to image the ?Bz,c distribution in the brain caused by a two-electrode montage, as confirmed by finite-element calculations of ?Bz,c. Further improvements will be performed to increase its robustness to field drifts. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler http://www.ismrm.org/17/program_files/EP07.htm Honolulu, HI, USA 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017) cgoksuCGöksu LGanson ehsesPEhses schefflerKScheffler thielscherAThielscher conference GoksuHSEST2018_3 Physica Medica 2018 8 52 Supplement 1 8 Purpose Information on the electrical tissue conductivity might be useful for the diagnosis and characterization of pathologies such as tumors [1]. MRCDI and MREIT are two emerging non-invasive techniques for imaging of weak currents and ohmic conductivities. In this study, we demonstrated human in vivo brain MRCDI to pave the way for its clinical use [2], [3]. Methods In short, weak alternating currents up to 1–2 mA are injected into human head in synchrony with tailored phase-sensitive MRI. The currents create a magnetic field , which shifts the precession frequency of the magnetization and modulates the acquired MR images. The acquired images are used to measure and reconstruct the current flow and conductivity distributions. We employed a steady-state free precession free-induction-decay (SSFP-FID) sequence in five subjects, and injected currents of 1 mA by an MR-conditional current source via electrodes attached to the scalp (two current profiles: Right-left (RL), electrodes placed near the temporoparietal junctions; anterior-posterior (AP), one attached to the forehead and one above the inion). Additionally, an ultra-short-echo-time sequence was performed to track the feeding cables for correcting the stray magnetic fields induced by cable currents. Corrected measurements were used to calculate current flow distributions and compared with Finite-Element simulations of the current flow based on individualized head models [4]. Results The current-induced magnetic field with was reliably measured and the reconstructed current flows showed good agreement with the simulations (average coefficient of determination R2= 71%). The injected current flow differed substantially among individuals according to the electrode placements and anatomical differences. The calculated currents are stronger in CSF-filled highly conductive regions, e.g. the longitudinal fissure. Conclusions The strong correlation between the simulations and measurements validates the accuracy of the method and demonstrates the potential of the method for determining accurate brain tissue conductivities. These initial current flow recordings pave the way for human brain MREIT that might complement standard MR methods for tumor characterization. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler Abstract Talk https://www.sciencedirect.com/science/article/pii/S1120179718305738 Copenhagen, Denmark 2nd European Congress of Medical Physics (ECMP 2018) 10.1016/j.ejmp.2018.06.091 cgoksuCGöksu LGHanson HRSiebner ehsesPEhses schefflerKScheffler thielscherAThielscher conference GoksuHSEST2018_2 2018 6 19 0542 MRCDI is a novel technique for non-invasive measurement of weak currents in the human head, which is important in several neuroscience applications. Here, we present reliable in-vivo MRCDI measurements in the human brain based on SSFP-FID, yielding an unprecedented accuracy. We demonstrate the destructive influences of stray magnetic fields caused by the current passing through feeding cables, and propose a correction method. Also, we show inter-individual differences in MRCDI measurements for two different current profiles, and compare the measurements with simulations based on individualized head models. The simulations of the current-induced magnetic fields show good agreement with in-vivo brain measurements. http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de http://www.kyb.tuebingen.mpg.de Department Scheffler Abstract Talk https://www.ismrm.org/18m/ https://www.ismrm.org/18/ToC.pdf Paris, France Joint Annual Meeting ISMRM-ESMRMB 2018 cgoksuCGöksu LGHanson HRSiebner ehsesPEhses schefflerKScheffler thielscherAThielscher