[Show abstract][Hide abstract] ABSTRACT: The combination of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has been shown to have great potential for providing a greater understanding of normal and diseased states in both human and animal studies. Simultaneous EEG-fMRI is particularly well suited for the study of epilepsy in that it may reveal the neurobiology of ictal and interictal epileptiform discharges and noninvasively localize epileptogenic foci. Spontaneous, coherent fluctuations of neuronal activity and the coupled hemodynamic responses have also been shown to provide diagnostic markers of disease, extending our understanding of intrinsically structured ongoing brain activity. Following a short summary of the hardware and software development of simultaneous EEG-fMRI, this paper reviews a unified framework of integrating neuronal and hemodynamic processes during epileptic seizures and discusses the role and impact of spontaneous activity in the mesial temporal lobe epilepsies with particular emphasis on the neural and physiological correlates of consciousness.
Epilepsy research and treatment. 01/2012; 2012:385626.
[Show abstract][Hide abstract] ABSTRACT: To demonstrate a subdermal wire electrode technique for establishing a ground (GND) and reference (REF) during long-term EEG monitoring (LTM) with intracranial electrodes. Usually, a separate GND and REF are required and this GND&REF pair can be selected contacts in the invasive electrode arrays themselves, special invasive electrodes, or standard surface disc electrodes which require frequent maintenance. We investigated the use of a pair of chronic Subdermal Wire Electrodes (SWE) for use as GND&REF.
A pair of SWEs as GND&REF was tested in nine patients undergoing invasive EEG monitoring. SWE impedances were monitored in two patients and compared to disc electrode impedances.
Without maintenance, SWE impedances remained low and stable during the entire recording period (up to 20 days), whereas disc electrodes showed rapid impedance increase after the first day. In all nine patients, the consistent and durable integrity of the GND&REF pair of SWE allowed for a good quality EEG recording. No local skin complications were observed.
A pair of SWE electrodes provides a GND&REF system that is easy to place, maintain, and provides a high quality recording with long-term stability when coupled with referential based EEG recording system from invasive electrodes.
A more efficient means of establishing a GND&REF pair during the monitoring of patients with invasive electrodes is described.
American journal of electroneurodiagnostic technology 03/2010; 50(1):50-8.
[Show abstract][Hide abstract] ABSTRACT: Continuous electroencephalogram in the intensive care unit is increasingly recognized as an important diagnostic and prognostic tool in critically ill patients. Metal disc electrodes or subdermal needle electrodes are neither computed tomography nor magnetic resonance imaging compatible. Their frequent replacement required for imaging purposes is time consuming and contributes to scalp breakdown. We have developed and report on two new types of imaging compatible electrodes. The subdermal wire electrode and the silver-epoxy-coated conductive plastic electrode are magnetic resonance imaging, computed tomography, and angiogram compatible. Moreover, the subdermal wire electrode does not require any daily maintenance. The electrodes were used on a total of 24 intensive care unit patients (subdermal wire electrode = 20, conductive plastic electrodes = 4) who required continuous electroencephalogram. During an average of 62.2 +/- 44 hours of electroencephalogram recording, 54% of the patients underwent imaging procedures (nine magnetic resonance imagings, five computed tomographic scans, and two angiograms) of good quality without the need to remove/replace the electrodes. The continuous electroencephalogram revealed epileptogenic activity that was not detected on standard 20-minute recordings in 28% of patients screened, with electrographic seizures in 11%. These two types of imaging compatible electrodes offer definite advantages in clinical practice. The combined diagnostic information of continuous electroencephalogram and easy-to-plan imaging yields important results and improves the clinical management and treatment of intensive care unit patients.
Journal of clinical neurophysiology: official publication of the American Electroencephalographic Society 09/2009; 26(4):236-43. · 1.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Continuous electroencephalogram (cEEG) recordings are being increasingly used in intensive care units (ICUs) to detect epileptic seizures and other changes. MRI scans can interrupt such recordings if the EEG electrodes need to be removed and important data can be missed.
We retrospectively examined EEG recordings from ICU patients who underwent MRI scans, comparing those from patients with the MRI-compatible EEG electrodes with those who had to have the EEG electrodes removed before scanning. We also examined technical aspects of the recording and scalp abrasions in both groups.
Fourteen of 31 (45%) EEG recordings with the MRI-compatible electrode system in patients that underwent MRI scans between 03:00 p.m. and 07:00 a.m. (when technologists were not available) captured seizures. In contrast, all of the six EEG recordings with the MRI-incompatible electrode system in patients that underwent MRI scanning during the same interval were interrupted and had no data. Recording characteristics of the EEGs were comparable between the two groups and none had scalp abrasions.
A significant proportion of patients undergoing MRI scans with the MRI-compatible EEG electrodes had seizures that would have been missed if the MRI-incompatible EEG electrodes had been used.
Epilepsy research 02/2009; 84(1):28-32. · 2.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied the usefulness of an MR imaging-compatible electroencephalography (EEG) electrode system for continuous EEG recordings in our epilepsy monitoring unit (EMU) by comparing 100 consecutive patients with MR imaging-compatible and MR imaging-incompatible EEG recording electrodes who underwent MR imaging between 3:00 pm and 7:00 am. The MR imaging-compatible system captured seizures in 21/50 (42%) patients and clinically valuable new electrographic data in 13/50 (26%) patients during the study interval, whereas possible seizures were lost to recording in 19/50 (38%) patients in the MR imaging-incompatible system. EEG recording was comparable by both systems, but the nurses could disconnect and reconnect the patients to their electrode cables only in the MR imaging-compatible system during the study interval while the EEG technologists were off duty. This study shows that the MR imaging-compatible system could be used routinely for long-term monitoring of the patients in EMUs.
American Journal of Neuroradiology 07/2008; 29(9):1649-51. · 3.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Specially designed optoelectronic and data postprocessing methods are described that permit electromyography (EMG) of muscle activity simultaneous with functional MRI (fMRI). Hardware characterization and validation included simultaneous EMG and event-related fMRI in 17 healthy participants during either ankle (n = 12), index finger (n = 3), or wrist (n = 2) contractions cued by visual stimuli. Principal component analysis (PCA) and independent component analysis (ICA) were evaluated for their ability to remove residual fMRI gradient-induced signal contamination in EMG data. Contractions of ankle tibialis anterior and index finger abductor were clearly distinguishable, although observing contractions from the wrist flexors proved more challenging. To demonstrate the potential utility of simultaneous EMG and fMRI, data from the ankle experiments were analyzed using two approaches: 1) assuming contractions coincided precisely with visual cues, and 2) using EMG to time the onset and offset of muscle contraction precisely for each participant. Both methods produced complementary activation maps, although the EMG-guided approach recovered more active brain voxels and revealed activity better in the basal ganglia and cerebellum. Furthermore, numerical simulations confirmed that precise knowledge of behavioral responses, such as those provided by EMG, are much more important for event-related experimental designs compared to block designs. This simultaneous EMG and fMRI methodology has important applications where the amplitude or timing of motor output is impaired, such as after stroke.
Human Brain Mapping 10/2007; 28(9):835-45. · 6.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Intracranial electroencephalogram (EEG) monitoring involves recording multi-contact electrodes. The current systems require separate wires from each recording contact to the data acquisition unit resulting in many connectors and cables. To overcome limitations of such systems such as noise, restrictions in patient mobility and compliance, we developed a miniaturized EEG monitoring system with the amplifiers and multiplexers integrated into the electrode connectors and mounted on the head.
Small, surface-mounted instrumentation amplifiers, coupled with 8:1 analog multiplexers, were assembled into 8-channel modular units to connect to 16:1 analog multiplexer manifold to create a small (55 cm(3)) head-mounted 128-channel system. A 6-conductor, 30 m long cable was used to transmit the EEG signals from the patient to the remote data acquisition system.
Miniaturized EEG amplifiers and analog multiplexers were integrated directly into the electrode connectors. Up to 128-channels of EEG were amplified and analog multiplexed directly on the patient's head. The amplified EEG data were obtained over one long wire.
A miniaturized system of invasive EEG recording has the potential to reduce artefact, simplify trouble-shooting, lower nursing care and increase patient compliance.
Miniaturization technology improves intracranial EEG monitoring and leads to >128-channel capacity.
[Show abstract][Hide abstract] ABSTRACT: To design and apply a method to quantitatively evaluate the MR compatibility of electroencephalographic (EEG) scalp electrodes based on pulse sequence-independent metrics.
Three types of electrodes (constructed primarily of brass, silver, and conductive plastic, respectively) were tested. B0 field distortions, B1 shielding, and heat induction was measured in adjacent agarose and oil phantoms at 4 T. B0 field maps were corrected for distortions caused by the measurement apparatus and passive shim heating, and projections perpendicular to the surfaces of the electrodes were fit, generating cubic coefficients representing the electrode distortion severity. Signal loss in T2-weighted images was used to determine B1 shielding by the electrodes. Temperature measurements were recorded during the application of a high-power pulse sequence.
Significantly different B0 distortions were observed in the three types of electrodes. The B1 shielding detected in all three electrodes is minimal for most human MRI, and no significant heating was detected in the electrodes or adjacent phantom.
The three types of electrodes were successfully differentiated in terms of MR compatibility based on pulse sequence-independent B0 field distortions.
Journal of Magnetic Resonance Imaging 05/2007; 25(4):872-7. · 2.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Despite its excellent temporal resolution, electroencephalogram (EEG) has poor spatial resolution to study the participation of different brain areas in epileptic discharges, and the propagation of seizures to subcortical areas is not revealed. Furthermore, EEG provides no information about metabolic changes that occur in the brain before and during the epileptic discharges. Thus, monitoring variations in blood flow and oxygenation in response to epileptic discharges can provide additional complementary information. Functional magnetic resonance imaging (fMRI) technology can be used to study the hemodynamic changes associated with interictal epileptiform discharges or epileptic seizures (i.e., before, during or after them) in experimental animal models and may noninvasively monitor these changes over time. Blood oxygenation level-dependent fMRI has superior spatial resolution compared with other functional imaging modalities and utilizes changes in local magnetic field properties to measure the amount of deoxyhemoglobin in each brain areas as an indicator of brain activity. Simultaneous recording of EEG and fMRI is required to achieve this objective. This article describes methods of acquiring and monitoring EEG during fMRI studies in experimental animals. Particular attention will be paid to methods used to eliminate artifacts induced in the acquired magnetic resonance images by EEG equipment and MR-related artifacts in EEG recordings.
[Show abstract][Hide abstract] ABSTRACT: We report on the development of an EEG recording system, comprised of electrodes and amplifiers that are compatible with TMS (single and rapid-rate) in both human and animal studies.
We assembled a versatile multi-channel EEG recording system consisting of: (1) two types of electrodes that are safe during TMS or rTMS. (2) Low slew-rate EEG amplifiers that recover within a few milliseconds after the application of TMS pulses.
The two electrode types: (a) a conductive-plastic surface electrode with a conductive-silver epoxy coat and (b) a subdermal silver wire electrode (SWE) are compatible to TMS pulses. The amplifiers recover within 30 ms, so that the EEG can be viewed online, essentially without interruption and/or blocking or excessive artifact.
Our TMS compatible electrode and EEG recording system allows safe and online viewing/recording of the subject's (human or animal) EEG/EP during experiments or studies involving TMS or rTMS applications. The TMS compatible electrode/amplifier system can be used with any EEG recording instrument.
A simple recording technique coupled with new electrodes permit safe and readable EEG records during TMS in humans and animals. Such online monitoring of the EEG would allow control of TMS/rTMS parameters based on EEG activity.
[Show abstract][Hide abstract] ABSTRACT: To compare long-term electroencephalographic (EEG) recordings of standard collodion-applied scalp disk electrodes (SDEs) with newly developed subdermal wire electrodes (SWEs) in comatose intensive care unit (ICU) patients.
Ten comatose ICU patients had simultaneous recordings from 8 active SDEs and 8 active SWE for >24 h. The timing and number of 60 Hz and other electrode artifacts were compared for each set of electrodes by an EEGer who read the recordings in a blinded manner.
Sixty Hertz artifact was seen in 16 of 80 SDE and one of 80 SWEs within the first 6 h (P=0.0002). Large, persistent artifacts occurred in 30/80 SDE and 8 of 80 SWE (P=0.0001). Motion artifact with chest physiotherapy was more common in SWEs.
SWE are less susceptible to artifacts and are more suitable for the long-term EEG monitoring in ICU.
This is the first controlled study that demonstrates the superiority of SWEs compared to SDEs in an ICU population.
[Show abstract][Hide abstract] ABSTRACT: Epileptic disorders manifest with seizures and interictal epileptic discharges (IEDs). The hemodynamic changes that accompany IEDs are poorly understood and may be critical for understanding epileptogenesis. Despite a known linear coupling of the neurovascular elements in normal brain tissues, previous simultaneous electroencephalography (EEG)-functional magnetic resonance imaging (fMRI) studies have shown variable correlations between epileptic discharges and blood oxygenation level-dependent (BOLD) response, partly because most previous studies assumed particular hemodynamic properties in normal brain tissue. The occurrence of IEDs in human subjects is unpredictable. Therefore, an animal model with reproducible stereotyped IEDs was developed by the focal injection of penicillin into the right occipital cortex of rats anesthetized with isoflurane. Simultaneous EEG-fMRI was used to study the hemodynamic changes during IEDs. A hybrid of temporal independent component analysis (ICA) of EEG and spatial ICA of fMRI data was used to correlate BOLD fMRI signals with IEDs. A linear autoregression with exogenous input (ARX) model was used to estimate the hemodynamic impulse response function (HIRF) based on the data from simultaneous EEG-fMRI measurement. Changes in the measured BOLD signal from the right primary visual cortex and bilateral visual association cortices were consistently coupled to IEDs. The linear ARX model was applied here to confirm that a linear transform can be used to study the correlation between BOLD signal and its corresponding neural activity in this animal model of occipital epilepsy.
[Show abstract][Hide abstract] ABSTRACT: Purpose: The occurrence of hypoxemia in adults with partial seizures has not been systematically explored. Our aim was to study in detail the temporal dynamics of this specific type of ictal-associated hypoxemia.Methods: During long-term video/EEG monitoring (LTM), patients underwent monitoring of oxygen saturation using a digital Spo2 (pulse oximeter) transducer. Six patients (nine seizures) were identified with oxygen desaturations after the onset of partial seizure activity.Results: Complex partial seizures originated from both left and right temporal lobes. Mean seizure duration (±SD) was 73 ± 18 s. Mean Spo2 desaturation duration was 76 ± 19 s. The onset of oxygen desaturation followed seizure onset with a mean delay of 43 ± 16 s. Mean (±SD) Spo2 nadir was 83 ± 5% (range, 77–91%), occurring an average of 35 ± 12 s after the onset of the desaturation. One seizure was associated with prolonged and recurrent Spo2 desaturations.Conclusions: Partial seizures may be associated with prominent oxygen desaturations. The comparable duration of each seizure and its subsequent desaturation suggests a close mechanistic (possibly causal) relation. Spo2 monitoring provides an added means for seizure detection that may increase LTM yield. These observations also raise the possibility that ictal ventilatory dysfunction could play a role in certain cases of sudden unexpected death in epilepsy in adults with partial seizures.
[Show abstract][Hide abstract] ABSTRACT: Maintaining a stable physiologic state is essential when studying animal models of epilepsy with simultaneous electroencephalograph (EEG) and functional magnetic resonance imaging (fMRI) or EEG and magnetic resonance spectroscopy (MRS). To achieve and maintain such stability in rats in the MRI environment, a minimally invasive but comprehensive system was developed to monitor body temperature, heart rate, blood pressure, blood oxygen saturation and end-tidal CO2 (ETCO2) of expired gas. All physiologic parameters were successfully monitored in Sprague-Dawley rats without interfering with EEG recordings during simultaneous fMRI and MRS studies. Body temperature, heart rate, blood pressure, blood oxygen saturation, and ETCO2, were maintained between 36.5 and 37.5 degrees C, 250-450 beats/min, 136+/-17 mmHg, >90%, and 20-35 mmHg, respectively for 6-8 h under inhalational anesthesia. This set-up could be extended to study in vivo applications in other laboratory animals with only minor modifications.
Journal of Neuroscience Methods 06/2005; 144(2):207-13. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The main limiting factor of EEG monitoring in the critical/intensive care environments is, and always has been, the recording electrode. The electrode and its application to the scalp has changed very little since EEG was first discovered and developed as a clinical tool. However, the evolution of amplifiers and data acquisition systems have made tremendous strides. Modern-day EEG recording systems now have the capability to record for days and weeks with little intervention, whereas the EEG electrode requires constant attention and skilled adjustment every 10 to 24 hours. If one surveys the vast array of electrodes used now and in the past, the only electrode that, once placed, never needed any further adjustment for days and weeks on end, was the chronic silver-silver/chloride (Ag-Ag/Cl) sphenoidal (Sp) electrode. This Sp electrode has now been modified to permit it to be placed subdermally, similar to that of a subdermal needle electrode, but now the needle is removed to leave in place a fine, flexible, durable, chronic Ag-Ag/Cl electrode. Once placed, this subdermal wire electrode (SWE, patent pending) starts to record immediately with a low impedance of 3 to 4 Komega. This electrode can record any biopotential, in humans and in animals, and in most recording environments; it never needs adjustment, and records high-quality biopotential signals for as long as it is left in place. The SWE is also MRI and computed-tomography compatible. It takes less than half the time to place the SWE, and placement can now be performed by any medically trained personnel to obtain a low-maintenance, high-quality EEG recording.
Journal of Clinical Neurophysiology 05/2005; 22(2):119-23. · 1.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Simultaneous recording of electroencephalogram (EEG) and functional MRI (fMRI) or MR spectroscopy (MRS) can provide further insight into our understanding of the underlying mechanisms of neurologic disorders. Current technology for simultaneous EEG and MRI recording is limited by extensive postacquisition processing of the data. Real-time display of artifact-free EEG recording during fMRI/MRS studies is essential in studies that involve epilepsy to ensure that they address specific EEG features such as epileptic spikes or seizures. By optimizing the EEG recording equipment to maximize the common mode rejection ratio of its amplifiers, a unique EEG system was designed and tested that allowed real-time display of the artifact-free EEG during fMRI/MRS in an animal model of epilepsy. Spike recordings were optimized by suppression of the background EEG activity using fast-acting and easily controlled inhalational anesthesia. Artifact suppression efficiency of 70-100% was achieved following direct subtraction of referentially recorded filtered EEG tracings from active electrodes, which were located in close proximity to each other (over homologous occipital cortices) and a reference electrode. Two independent postacquisition processing tools, independent component analysis and direct subtraction of unfiltered digital EEG data in MATLAB, were used to verify the accuracy of real-time EEG display.
Magnetic Resonance in Medicine 03/2005; 53(2):456-64. · 3.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe an electroencephalographic (EEG) device and protocol that allows recording of electrophysiological signals generated by the human brain during transcranial magnetic stimulation (TMS) despite the TMS-induced high-voltage artifacts. The key hardware components include slew-rate limited preamplifiers to prevent saturation of the EEG system due to TMS. The protocol involves artifact subtraction to isolate the electrophysiological signals from residual TMS-induced contaminations. The TMS compatibility of the protocol is illustrated with examples of two data sets demonstrating the feasibility of the approach in the single-pulse TMS design, as well as during repetitive TMS. Our data show that both high-amplitude potentials evoked by visual checkerboard stimulation and low-amplitude steady-state oscillations induced by auditory click-trains can be retrieved with the present protocol. The signals recorded during TMS perfectly matched control EEG responses to the same visual and auditory stimuli. The main field of application of the present protocol is in cognitive neuroscience complementing behavioral studies that use TMS to induce transient, 'virtual lesions'. Combined EEG-TMS techniques provide neuroscientists with a unique method to test hypothesis on functional connectivity, as well as on mechanisms of functional orchestration, reorganization, and plasticity.
Journal of Neuroscience Methods 03/2005; 141(2):207-17. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on the development of an electroencephalographic (EEG) recording system that is Magnetic Resonance Imaging (MRI) compatible and can safely be left on the scalp during anatomical imaging or used to obtain simultaneous EEG and metabolic or hemodynamic data using functional imaging techniques such as functional MRI or MR spectroscopy.
We assembled a versatile EEG recording set-up with medically acceptable materials that contained no ferromagnetic components. It was tested for absence of excess heating and distortion of the image quality in a spherical phantom similar in size to average adult human head in a clinical 1.5 T GE scanner. After testing its safety in four volunteers, 100 consecutive patients from our epilepsy long-term monitoring unit were studied.
There was no change in the temperature of the EEG electrode discs during the various anatomical MRI sequences used in our routine clinical studies (maximum temperature change was -0.45 degrees C with average head SAR<==1.6 W/Kg in the selected subjects) nor were there any reported complications in the others. The brain images were not distorted by the susceptibility artifact of the EEG electrodes.
Our MRI compatible EEG set-up allows safe and artifact free brain imaging in 1.5T MR scanner with average SAR<==1.6 W/Kg. This EEG system can be used for EEG recording during anatomical MRI studies as well as functional imaging studies in patients requiring continuous EEG recordings.
[Show abstract][Hide abstract] ABSTRACT: Transcranial magnetic stimulation (TMS) is a non-invasive technique that uses the principle of electromagnetic induction to generate currents in the brain via pulsed magnetic fields. The magnitude of such induced currents is unknown. In this study we measured the TMS induced current densities in a patient with implanted depth electrodes for epilepsy monitoring. A maximum current density of 12 microA/cm2 was recorded at a depth of 1 cm from scalp surface with the optimum stimulation orientation used in the experiment and an intensity of 7% of the maximal stimulator output. During TMS we recorded relative current variations under different stimulating coil orientations and at different points in the subject's brain. The results were in accordance with current theoretical models. The induced currents decayed with distance form the coil and varied with alterations in coil orientations. These results provide novel insight into the physical and neurophysiological processes of TMS.