Optimal geometry toward uniform current density electrodes

Song, Yizhuang; Lee, Eun Jung; Woo, Eung Je; Seo, Jin Keun

doi:10.1088/0266-5611/27/7/075004

Cited by 8 publications

(8 citation statements)

References 25 publications

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“…This, however, could mean imposing many more constraints and higher computational burden. A simpler yet more effective solution may be to design electrodes that distribute the current across electrode-scalp interface more uniformly by, for example, varying the sponge depth through the electrode [49]. …”

Section: Discussionmentioning

confidence: 99%

Optimization of focality and direction in dense electrode array transcranial direct current stimulation (tDCS)

et al. 2016

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Objective Transcranial direct current stimulation (tDCS) aims to alter brain function noninvasively via electrodes placed on the scalp. Conventional tDCS uses two relatively large patch electrodes to deliver electrical currents to the brain region of interest (ROI). Recent studies have shown that using dense arrays containing up to 512 smaller electrodes may increase the precision of targeting ROIs. However, this creates a need for methods to determine effective and safe stimulus patterns as the degrees of freedom is much higher with such arrays. Several approaches to this problem have appeared in the literature. In this paper, we describe a new method for calculating optimal electrode stimulus pattern for targeted and directional modulation in dense array tDCS which differs in some important aspects with methods reported to date. Approach We optimize stimulus pattern of dense arrays with fixed electrode placement to maximize the current density in a particular direction in the ROI. We impose a flexible set of safety constraints on the current power in the brain, individual electrode currents, and total injected current, to protect subject safety. The proposed optimization problem is convex and thus efficiently solved using existing optimization software to find unique and globally optimal electrode stimulus patterns. Main results Solutions for four anatomical ROIs based on a realistic head model are shown as exemplary results. To illustrate the differences between our approach and previously introduced methods, we compare our method with two of the other leading methods in the literature. We also report on extensive simulations that show the effect of the values chosen for each proposed safety constraint bound on the optimized stimulus patterns. Significance The proposed optimization approach employs volume based ROIs, easily adapts to different sets of safety constraints, and takes negligible time to compute. In-depth comparison study gives insight into the relationship between different objective criteria and optimized stimulus patterns. In addition, the analysis of the interaction between optimized stimulus patterns and safety constraint bounds suggests that more precise current localization in the ROI, with supposably improved safety criterion, may be achieved by careful selection of the constraint bounds.

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Section: Discussionmentioning

confidence: 99%

Optimization of focality and direction in dense electrode array transcranial direct current stimulation (tDCS)

et al. 2016

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“…It can be seen that the highest current density magnitudes seem to be located on the electrode sponge-scalp interface (e.g., Song et al, 2011). Further, the impact of high conducting CSF can be clearly seen with higher current density magnitudes values close to the injecting electrodes.…”

Section: Resultsmentioning

confidence: 99%

Visualizing simulated electrical fields from electroencephalography and transcranial electric brain stimulation: A comparative evaluation

et al. 2014

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Electrical activity of neuronal populations is a crucial aspect of brain activity. This activity is not measured directly but recorded as electrical potential changes using head surface electrodes (electroencephalogram - EEG). Head surface electrodes can also be deployed to inject electrical currents in order to modulate brain activity (transcranial electric stimulation techniques) for therapeutic and neuroscientific purposes. In electroencephalography and noninvasive electric brain stimulation, electrical fields mediate between electrical signal sources and regions of interest (ROI). These fields can be very complicated in structure, and are influenced in a complex way by the conductivity profile of the human head. Visualization techniques play a central role to grasp the nature of those fields because such techniques allow for an effective conveyance of complex data and enable quick qualitative and quantitative assessments. The examination of volume conduction effects of particular head model parameterizations (e.g., skull thickness and layering), of brain anomalies (e.g., holes in the skull, tumors), location and extent of active brain areas (e.g., high concentrations of current densities) and around current injecting electrodes can be investigated using visualization. Here, we evaluate a number of widely used visualization techniques, based on either the potential distribution or on the current-flow. In particular, we focus on the extractability of quantitative and qualitative information from the obtained images, their effective integration of anatomical context information, and their interaction. We present illustrative examples from clinically and neuroscientifically relevant cases and discuss the pros and cons of the various visualization techniques.

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“…The current density of 2 A/m 2 adopted in the present study is at the lower end of both safety ranges reported above. It is worth noting that the copper electrode used in this study usually has strong edge singularity (Song et al 2011) as can be seen from figure 2. Carbon-Hydrogel electrodes or optimal geometry recessed electrodes (Song et al 2011) which are supposed to produce more uniform current density distributions should be investigated in future studies.…”

Section: Conclusion and Discussionmentioning

confidence: 97%

A feasibility study of magnetic resonance electrical impedance tomography for prostate cancer detection

Liu

Zhang

2014

Physiol. Meas.

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Magnetic resonance electrical impedance tomography (MREIT) is an imaging technique that reconstructs the conductivity distribution inside the subject using magnetic flux density or current density measurements acquired by a magnetic resonance imaging (MRI) system. Since the primary prostate cancer diagnostic method, prostate biopsy, has limited accuracy in cancer diagnosis and malignant tissues have shown significantly different electrical properties from normal or benign tissues, MREIT has potential application in prostate cancer detection. The feasibility of utilizing MREIT in detecting prostate cancer was evaluated via a series of well-designed computer simulations in the present study. MREIT techniques with three different electrode configurations (external, trans-rectal, and trans-urethral electrode arrays) and two different reconstruction algorithms (J-substitution algorithm and harmonic Bz algorithm) were successfully developed. The performance of different MREIT techniques were evaluated and compared based on the imaging accuracy of the reconstructed conductivity distribution in the prostate. Without the presence of noise, the external MREIT achieves a better imaging accuracy than the two endo-MREIT (trans-rectal and trans-urethral) techniques, while the trans-urethral MREIT achieves the best imaging accuracy in noisy environments. We also found that the J-substitution reconstruction algorithm consistently offered better imaging accuracy than the harmonic Bz algorithm. When Gaussian distributed random noise with a standard deviation of 0.25 nT was added, the relative errors (RE) between the reconstructed and target conductivity distributions inside the prostate were observed to be 14.18% and 17.35% by the trans-urethral MREIT with the J-substitution and harmonic Bz algorithms respectively. The lower REs of 9.64% and 11.17% were achieved respectively when the standard deviation of noise was reduced to 0.05 nT. The simulation results demonstrate the feasibility of applying MREIT for prostate cancer detection.

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Optimal geometry toward uniform current density electrodes

Cited by 8 publications

References 25 publications

Optimization of focality and direction in dense electrode array transcranial direct current stimulation (tDCS)

Optimization of focality and direction in dense electrode array transcranial direct current stimulation (tDCS)

Visualizing simulated electrical fields from electroencephalography and transcranial electric brain stimulation: A comparative evaluation

A feasibility study of magnetic resonance electrical impedance tomography for prostate cancer detection

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