Noninvasive Imaging of Head-Brain Conductivity Profiles

Zhang, Xiaolin; Yan, Dawei; Zhu, Shanan; He, Bin

doi:10.1109/memb.2008.923953

Cited by 10 publications

(3 citation statements)

References 20 publications

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“…Because only a minority of the blood vessels included in our model was within the white matter compartment, we expect no major insights for the questions addressed in the present study from modeling white matter anisotropy. Recent advances in electrical impedance tomography (EIT) and more specifically in magnetic resonance EIT (Zhang et al, 2008; Woo and Seo, 2008; Meng et al, 2013; Degirmenci and Eyuboglu, 2013; Kim et al, 2008) suggest that using individualized anisotropic and inhomogeneous conductivities for head modeling may be possible in the future, opening up exciting new possibilities in volume conductor head modeling.…”

Section: Discussionmentioning

confidence: 99%

The role of blood vessels in high-resolution volume conductor head modeling of EEG

et al. 2016

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Reconstruction of the electrical sources of human EEG activity at high spatiotemporal accuracy is an important aim in neuroscience and neurological diagnostics. Over the last decades, numerous studies have demonstrated that realistic modeling of head anatomy improves the accuracy of source reconstruction of EEG signals. For example, including a cerebrospinal fluid compartment and the anisotropy of white matter electrical conductivity were both shown to significantly reduce modeling errors. Here, we for the first time quantify the role of detailed reconstructions of the cerebral blood vessels in volume conductor head modeling for EEG. To study the role of the highly arborized cerebral blood vessels, we created a submillimeter head model based on ultra-high-field-strength (7 T) structural MRI datasets. Blood vessels (arteries and emissary/intraosseous veins) were segmented using Frangi multi-scale vesselness filtering. The final head model consisted of a geometry-adapted cubic mesh with over 17 × 106 nodes. We solved the forward model using a finite-element-method (FEM) transfer matrix approach, which allowed reducing computation times substantially and quantified the importance of the blood vessel compartment by computing forward and inverse errors resulting from ignoring the blood vessels. Our results show that ignoring emissary veins piercing the skull leads to focal localization errors of approx. 5 to 15 mm. Large errors (>2 cm) were observed due to the carotid arteries and the dense arterial vasculature in areas such as in the insula or in the medial temporal lobe. Thus, in such predisposed areas, errors caused by neglecting blood vessels can reach similar magnitudes as those previously reported for neglecting white matter anisotropy, the CSF or the dura — structures which are generally considered important components of realistic EEG head models. Our findings thus imply that including a realistic blood vessel compartment in EEG head models will be helpful to improve the accuracy of EEG source analyses particularly when high accuracies in brain areas with dense vasculature are required.

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Section: Discussionmentioning

confidence: 99%

The role of blood vessels in high-resolution volume conductor head modeling of EEG

et al. 2016

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“…In reality, each configuration was a combination of anodal and cathodal stimulation points which likely resulted in complex local current flows and contributed to the wide range of subject-specific changes seen in response to the tDCS. Future studies of tDCS-EEG will need to integrate computational modeling, anatomical MRI scans and stereoscopic targeting to optimize tDCS treatment protocols for individual subjects, similar to recent TMS, deep brain stimulation and transcranial ultrasound stimulation studies [63]–[68]. …”

Section: Discussionmentioning

confidence: 99%

High-Definition Transcranial Direct Current Stimulation Induces Both Acute and Persistent Changes in Broadband Cortical Synchronization: A Simultaneous tDCS–EEG Study

Roy

Baxter

2014

IEEE Trans. Biomed. Eng.

100

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The goal of this study was to develop methods for simultaneously acquiring electrophysiological data during high definition transcranial direct current stimulation (tDCS) using high resolution electroencephalography (EEG). Previous studies have pointed to the after effects of tDCS on both motor and cognitive performance, and there appears to be potential for using tDCS in a variety of clinical applications. However, little is known about the real-time effects of tDCS on rhythmic cortical activity in humans due to the technical challenges of simultaneously obtaining electrophysiological data during ongoing stimulation. Furthermore, the mechanisms of action of tDCS in humans are not well understood. We have conducted a simultaneous tDCS-EEG study in a group of healthy human subjects. Significant acute and persistent changes in spontaneous neural activity and event related synchronization (ERS) were observed during and after the application of high definition tDCS over the left sensorimotor cortex. Both anodal and cathodal stimulation resulted in acute global changes in broadband cortical activity which were significantly different than the changes observed in response to sham stimulation. For the group of 8 subjects studied, broadband individual changes in spontaneous activity during stimulation were apparent both locally and globally. In addition, we found that high definition tDCS of the left sensorimotor cortex can induce significant ipsilateral and contralateral changes in event related desynchronization (ERD) and ERS during motor imagination following the end of the stimulation period. Overall, our results demonstrate the feasibility of acquiring high resolution EEG during high definition tDCS and provide evidence that tDCS in humans directly modulates rhythmic cortical synchronization during and after its administration.

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“…Both EIT and MIT are cost-effective and can provide dynamic information in regard to tissue EPs, but they are limited by low spatial resolution due to the surface measurements and the need to solve an ill-posed inverse problem. A technique called “Magnetic Resonance Electrical Impedance Tomography (MREIT)”, which is based on the Magnetic Resonance Current Density Imaging (MRCDI) technique [12] and measures current injection inducted MR phase shifts, has been pursued [13-16]. While MREIT eliminates the need to solve the ill-posed inverse problem and provides high spatial resolution in imaging electrical conductivity in vivo , it requires current injection into the body within an MRI scanner, which limits its applicability in medical applications.…”

Section: Introductionmentioning

confidence: 99%

Imaging Electric Properties of Biological Tissues by RF Field Mapping in MRI

Zhang

Zhu²,

2010

IEEE Trans. Med. Imaging

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The electric properties (EPs) of biological tissue, i.e., the electric conductivity and permittivity, can provide important information in the diagnosis of various diseases. The EPs also play an important role in specific absorption rate (SAR) calculation, a major concern in high-field Magnetic Resonance Imaging (MRI), as well as in non-medical areas such as wireless-telecommunications. The high-field MRI system is accompanied by significant wave propagation effects, and the radio frequency (RF) radiation is dependent on the EPs of biological tissue. Based on the measurement of the active transverse magnetic component of the applied RF field (known as B1-mapping technique), we propose a dual-excitation algorithm, which uses two sets of measured B1 data to noninvasively reconstruct the electric properties of biological tissues. The Finite Element Method (FEM) was utilized in three-dimensional (3D) modeling and B1 field calculation. A series of computer simulations were conducted to evaluate the feasibility and performance of the proposed method on a 3D head model within a transverse electromagnetic (TEM) coil and a birdcage (BC) coil. Using a TEM coil, when noise free, the reconstructed EP distribution of tissues in the brain has relative errors of 12% ∼ 28% and correlated coefficients of greater than 0.91. Compared with other B1-mapping based reconstruction algorithms, our approach provides superior performance without the need for iterative computations. The present simulation results suggest that good reconstruction of electric properties from B1 mapping can be achieved.

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Noninvasive Imaging of Head-Brain Conductivity Profiles

Cited by 10 publications

References 20 publications

The role of blood vessels in high-resolution volume conductor head modeling of EEG

The role of blood vessels in high-resolution volume conductor head modeling of EEG

High-Definition Transcranial Direct Current Stimulation Induces Both Acute and Persistent Changes in Broadband Cortical Synchronization: A Simultaneous tDCS–EEG Study

Imaging Electric Properties of Biological Tissues by RF Field Mapping in MRI

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