Quantification of direct current in electrically active implants using MRI methods

Wojtczyk, Hanne; Graf, Hansjörg; Martirosian, Petros; Ballweg, Verena; Kraiger, Markus; Pintaske, Jörg; Schick, Fritz

doi:10.1016/j.zemedi.2010.12.001

Cited by 5 publications

(5 citation statements)

References 31 publications

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“…These studies confirm that inhomogeneous magnetic fields resulting from current flow produce “distortions” in the MRI signal that can, in turn, quantitatively predict current density in the volume (“magnetic inverse problem”). The sensitivity of phase- and magnitude-based MR current measurements to scanner intensity (1.5T or 3T) and to additional sequences (FLASH, trueFISP; MAGSUS) was explored by Wojtczyk et al (Wojtczyk et al, 2011) The present study demonstrates that imaging of low-intensity, - well tolerated -, transcranial current flow using standard fMRI sequences and protocols is possible, e.g. using gradient-echo echo-planar imaging.…”

Section: Discussionmentioning

confidence: 77%

“…Initial studies (Scott et al, 1991, Scott et al, 1992) characterized “current flow imaging” in phantoms and tissue using spin-echo or gradient-echo with EPI sequences, and using pulsed currents (synchronized to the imaging sequence) and later static (DC) currents (Bodurka et al, 1999, Wojtczyk et al, 2011). These studies confirm that inhomogeneous magnetic fields resulting from current flow produce “distortions” in the MRI signal that can, in turn, quantitatively predict current density in the volume (“magnetic inverse problem”).…”

Section: Discussionmentioning

confidence: 99%

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Imaging artifacts induced by electrical stimulation during conventional fMRI of the brain

et al. 2014

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Functional magnetic resonance imaging (fMRI) of brain activation during transcranial electrical stimulation is used to provide insight into the mechanisms of neuromodulation and targeting of particular brain structures. However, the passage of current through the body may interfere with the concurrent detection of blood oxygen level dependent (BOLD) signal, which is sensitive to local magnetic fields. To test whether these currents can affect concurrent fMRI recordings we performed conventional gradient echo-planar imaging (EPI) during transcranial direct current (tDCS) and alternating current stimulation (tACS) on two post-mortem subjects. TDCS induced signals in both superficial and deep structures. The signal was specific to the electrode montage, with the strongest signal near cerebrospinal fluid (CSF) and scalp. The direction of change relative to non-stimulation reversed with tDCS stimulation polarity. For tACS there was no net effect of the MRI signal. High-resolution individualized modeling of current flow and induced static magnetic fields suggested a strong coincidence of the change EPI signal with regions of large current density and magnetic fields. These initial results indicate that: 1) fMRI studies of tDCS must consider this potentially confounding interference from current flow and 2) conventional MRI imaging protocols can be potentially used to measure current flow during transcranial electrical stimulation. The optimization of current measurement and artifact correction techniques, including consideration of the underlying physics, remains to be addressed.

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Section: Discussionmentioning

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Imaging artifacts induced by electrical stimulation during conventional fMRI of the brain

et al. 2014

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“…Prior studies have not evaluated the simultaneous use of the optical device for FITC-sinistrin clearance and the MRI. Given that radiofrequency (RF) pulses, gradients or the magnetic field strength could cause interferences, we checked the device within the scanner for proper operation We also investigated whether the optical device created MR image artifacts [19] . The optical sensor was attached to a falcon tube (filled with water) and placed inside the receive coil and the magnet.…”

Section: Methodsmentioning

confidence: 99%

Simultaneous Measurement of Kidney Function by Dynamic Contrast Enhanced MRI and FITC-Sinistrin Clearance in Rats at 3 Tesla: Initial Results

et al. 2013

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Glomerular filtration rate (GFR) is an essential parameter of kidney function which can be measured by dynamic contrast enhanced magnetic resonance imaging (MRI-GFR) and transcutaneous approaches based on fluorescent tracer molecules (optical-GFR). In an initial study comparing both techniques in separate measurements on the same animal, the correlation of the obtained GFR was poor. The goal of this study was to investigate if a simultaneous measurement was feasible and if thereby, the discrepancies in MRI-GFR and optical-GFR could be reduced. For the experiments healthy and unilateral nephrectomised (UNX) Sprague Dawley (SD) rats were used. The miniaturized fluorescent sensor was fixed on the depilated back of an anesthetized rat. A bolus of 5 mg/100 g b.w. of FITC-sinistrin was intravenously injected. For dynamic contrast enhanced perfusion imaging (DCE-MRI) a 3D time-resolved angiography with stochastic trajectories (TWIST) sequence was used. By means of a one compartment model the excretion half-life (t1/2) of FITC-sinistrin was calculated and converted into GFR. GFR from DCE-MRI was calculated by fitting pixel-wise a two compartment renal filtration model. Mean cortical GFR and GFR by FITC-sinistrin were compared by Bland-Altman plots and pair-wise t-test. Results show that a simultaneous GFR measurement using both techniques is feasible. Mean optical-GFR was 4.34±2.22 ml/min (healthy SD rats) and 2.34±0.90 ml/min (UNX rats) whereas MRI-GFR was 2.10±0.64 ml/min (SD rats) and 1.17±0.38 ml/min (UNX rats). Differences between healthy and UNX rats were significant (p<0.05) and almost equal percentage difference (46.1% and 44.3%) in mean GFR were assessed with both techniques. Overall mean optical-GFR values were approximately twice as high compared to MRI-GFR values. However, compared to a previous study, our results showed a higher agreement. In conclusion, the possibility to use the transcutaneous method in MRI may have a huge impact in improving and validating MRI methods for GFR assessment in animal models.

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“…Активный протез / имплантат, по определению, не только «не мешает жить организму», но и имитирует «жизнь» утраченной им электрофизиологически активной области. В связи с этим, логичной представляется разработка функционально активных протезов посредством молекулярной инженерии биомиметических полимерных материалов с реактивностью (соответствующих дефиниции сенсоров и актуаторов) и способностью вырабатывать или конвертировать энергию [75,103,172,176] [54]. Такие системы могут быть имплементированы как в форме объёмных изделий, так и в форме покрытий обычных имплантатов, обеспечивающих их биосовместимость.…”

Section: от электрохимических критериев биосовместимости к активным и...unclassified

Biocompatible Biomimetic Polymer Structures With an Active Response for Implantology and Regenerative Medicine Part I: Basic Principles of the Active Implant’s Biocompatibility

Градов

Gradova

Kochervinskiĭ

2023

SJLSA

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Physical and chemical criteria of biocompatibility of the active polymer implants and stimuli-responsive scaffolds are considered. From the standpoint of the surface physics and controlled wetting, the possibilities of dynamic control of biocompatibility and adaptive changes in the implant properties in response to the signal from the surrounding tissues are considered. The basic properties of the active biocompatible and biomimetic implantable materials, which distinguish them from the passive implants, are summarized. The latter include: electrophysical and electrophysiological membrane biocompatibility (up to the analogy with biomembranes – the so-called Fendler’s “membrane mimetics”); excitability, that is, the ability to qualitatively change their state in response to the external stimulus; compatibility of the matching parameters and impedances of biomembranes and active implantable materials; the presence of the main types of the energy conversion characteristic of biomembranes (chemiosmotic, electrochemical, electromechanical, etc.); the ability to transport and release pharmaceuticals consistent with the parameters of the cellular microenvironment and regulated by its state. Due to the qualitative change in the biomedical aim of such implants (from replacing the natural function to its regeneration and maintenance), there is a possibility of implementing various new biologically relevant functions using these materials, such as the ability to sensing and actuation, based on their reactivity and signal / energy conversion capacity. Of particular interest is the adaptive realization of the above functions in a growing and developing organism during its ontogenesis.

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Quantification of direct current in electrically active implants using MRI methods

Cited by 5 publications

References 31 publications

Imaging artifacts induced by electrical stimulation during conventional fMRI of the brain

Imaging artifacts induced by electrical stimulation during conventional fMRI of the brain

Simultaneous Measurement of Kidney Function by Dynamic Contrast Enhanced MRI and FITC-Sinistrin Clearance in Rats at 3 Tesla: Initial Results

Biocompatible Biomimetic Polymer Structures With an Active Response for Implantology and Regenerative Medicine Part I: Basic Principles of the Active Implant’s Biocompatibility

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