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Equivalent Current Dipoles (equivalent + current_dipole)
Selected AbstractsNoninvasive Study of Ventricular Preexcitation Using Multichannel MagnetocardiographyPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1p2 2003RICCARDO FENICI FENICI, R., et al.: Noninvasive Study of Ventricular Preexcitation Using Multichannel Magnetocardiography. In clinical practice, noninvasive classification of ventricular preexcitation (VPX) is usually done with ECG algorithms, which provide only a qualitative localization of accessory pathways. Since 1984, single or multichannel magnetocardiograpy (MMCG) has been used for three-dimensional localization of VPX sites, but a systematic study comparing the results of ECG and MMCG methods was lacking. This study evaluated the reliability of MMCG in an unshielded electrophysiological catheterization laboratory, and compared VPX classification as achieved with the five most recent ECG algorithms with that obtained by MMCG mapping and imaging techniques. A nine-channel direct current superconducting quantum interference device (DC-SQUID) MMCG system (sensitivity is 20 fT/Hz0.5) was used for sequential MMCG from 36 points on the anterior chest wall, within an area20 × 20 cm. Twenty-eight patients with Wolff-Parkinson-White syndrome were examined at least twice, on the same day or after several months to test the reproducibility of the measurements. In eight patients, the reproducibility of MMCG was also evaluated using different MCG instrumentation during maximal VPX and/or atrioventricular reentrant tachycardia induced by transesophageal atrial pacing via a nonmagnetic catheter. The results of VPX localization with ECG algorithms and MMCG were compared. Equivalent current dipole, effective magnetic dipole, and distributed currents imaging models were used for the inverse solution. MMCG classification of VPX was found to be more accurate than ECG methods, and also provided additional information for the identification of paraseptal pathways. Furthermore, in patients with complex activation patterns during the delta wave, distributed currents imaging revealed two different activation patterns, suggesting the existence of multiple accessory pathways. (PACE 2003; 26[Pt. II]:431,435) [source] Neuromagnetic Source Localization of Epileptiform Activity in Patients with Graphogenic EpilepsyEPILEPSIA, Issue 11 2006Naoaki Tanaka Summary:,Purpose: To clarify the source localization of epileptiform activity by using magnetoencephalography (MEG) in patients with graphogenic epilepsy. Methods: MEG and simultaneous EEG were recorded with a 204-channel whole-head MEG system in two patients with graphogenic epilepsy. During the MEG recordings, the patients performed a set of tasks comprising mental arithmetic calculation, speaking, moving the right arm in a manner resembling writing, writing, and thinking of writing. Equivalent current dipoles (ECD) were calculated for epileptiform discharges on MEG by using a single-dipole model. The ECD were superimposed on the magnetic resonance images of the patients. Results: The task of writing provoked seizures, in which both patients jerked the right arms. Thinking of writing also induced these seizures. In both patients, EEG associated with the seizures showed bursts of spike-and-slow-wave complexes predominantly in the centroparietal region. MEG also showed epileptiform discharges corresponding to the EEG bursts. ECDs obtained from the discharges were clustered in the left centroparietal area. Conclusions: Thinking of writing was a trigger for the seizures, as well as the task of writing. The source of the epileptiform discharge associated with the seizures was localized in the unilateral centroparietal area. The findings suggest that the centroparietal region plays an important role in the pathophysiology underlying these two graphogenic epilepsy cases. [source] Neuromagnetic signals associated with reading a kanji character formed by combining two kanji radicalsJAPANESE PSYCHOLOGICAL RESEARCH, Issue 1 2000Toshiaki Imada To find out which brain regions are responsible for the mental construction and recognition of a kanji character initiated by visually presented kanji radicals, rather than by information retained in the memory, a left hen radical and the corresponding right tsukuri radical were simultaneously presented randomly to either the left or right visual field of seven subjects. Thirty left hen radicals and the corresponding right tsukuri radicals were prepared as stimuli; this combination formed over 500 real or pseudo kanji characters. Instead of their usual left and right positions, the left hen radical was always presented above the right tsukuri radical. As quickly and correctly as possible, the subjects released a key when two kanji radicals constituted a single real kanji character and released another key otherwise. We recorded neuromagnetic responses as well as accuracy and reaction time. Left visual field superiority was observed as regards accuracy. This is in good agreement with previous neuropsychological results. Equivalent current dipoles were localized mainly in the left and/or right occipitotemporal regions (ventral visual pathways), the bilateral occipitoparietal regions (dorsal visual pathways) including the supramarginal region, and the areas surrounding the left superior temporal cortex. We suggest that these regions are related to reading and the mental construction of a kanji character from its radicals. [source] A Magnetoencephalographic Study of Patients with Panayiotopoulos SyndromeEPILEPSIA, Issue 7 2005Osamu Kanazawa Summary:,Purpose: Panayiotopoulos syndrome (PS) is a newly identified type of benign childhood epilepsy characterized by ictal vomiting and eye deviation. It is usually accompanied by occipital spike discharges; however, its classification as an early-onset benign childhood occipital epilepsy is controversial. To characterize this condition further, we examined the localization of equivalent current dipoles (ECDs) of spike discharges by magnetoencephalography (MEG) in patients with PS. Methods: We studied 13 patients with a mean age at time of examination of 5 years (range, 3,14 years). MEG was measured by using a whole-head 204-channel neuromagnetometer with simultaneous EEG recordings. The estimated locations of ECDs of each peak of the spike discharges were overlaid on magnetic resonance images of the brain. Results: Eleven (84.6%) patients showed clustered ECDs in the areas alongside the parietooccipital sulcus (eight of 13; 61.5%) and/or the calcarine sulcus (four of 13; 30.8%). Despite Fp-O synchronization of the spike discharges in the scalp EEG of five patients, no frontal locations of ECDs were found. All five (38.5%) boys with sylvian seizures, who also showed clustered ECDs in rolandic areas, had an earlier age at onset and higher seizure frequency than did other patients. ECD orientations were regular in all but one patient, who showed irregular and dispersed ECDs alongside bilateral calcarine sulci. Conclusions: Our results demonstrate localized cortical hyperexcitability in the areas alongside major cortical sulci in PS and indicate that PS is closely related to benign childhood epilepsy with centrotemporal spikes. [source] Dipole Tracing Examination for the Electric Source of Photoparoxysmal Response Provoked by Half-Field StimulationEPILEPSIA, Issue 2000Kazuhiko Kobayashi Purpose: Dipole tracing (DT) is a computer-aidcd noninvasive method used to estimate the location of epileptic discharges from the scalp EEG. In DT equivalent current dipoles (ECDs), which rcflcct the electric source in the brain, are rcsponsible for the potential distribution on the scalp EEC. Thercfore, the DT method is useful to estimatc the focal paroxysmal discharges. In this study we examined the location of the clectric source of photoparoxysmal response (PPR) using scalpskull-brain dipolc tracing (SSB-DT) after hal[-field stimulation, which produced focal PPR on the scalp EEG. Methods: We studied 4 cases of photoscnsitive epilepsy. Wc performed 20 Hz red flicker and flickcring dot pattern half-ficld stimulation to provoke PPR. In this method, the loci of gcnerators corresponding to the paroxysmal discharges were estimated as ECDs by I - and 2-dipole analyses. Each location of the ECDs was estimated by iterative calculation. Algorithms minimizing the squarcd difference betwccn the electrical potentials recorded from the scalp EEG and those calculated theoretically from the voluntary dipoles were uscd. In the SSB model, the scalp shell was reconstructed from the helmet mcasurements, and the shapc of the skull and brain was 3-dimcnsionally reconstructed from CT images. A dipolarity larger than 98% w the accuracy of the estimation. We recorded thcir 2 I channel monopolar scalp EEG. Each spike was sampled analyzed at 10 points around the peaks of at least 10 spikes in each patient using the SSB-DT method. The ECDs were then supcrimposed on thc MRI of each palient to idcntify the more cxact anatomical region. Results: This study showed the location of cach focus and a dipolarity of greater than 98% in all cases, although the results from the 2-dipole method showed scattered location. We considered that the analyzed signals were generated from single source. PPR was elicitcd cross-lateral to the field stimulated. By red flicker half-field stimulation, EEG revealed eithcr focal spikes and waves in the contralatcral occipital, temporo-occipitel region, or diffuse spikes and wave complex bursts, sccn dominantly at the contralateral hcmisphere. The supcrimposed ESDs on MRI were located at the occipital or inferior temporal lobe. PPR, provoked by flickering dot pattern half-field stimulation, werc focal spikes and waves, mainly in the occipital, parieto-occipital region, or diffuse spikes and wave complcx bursts, seen dominantly at thc contralateral hcmiaphere. The ECDs of their PPRs were located in the occipital, inferior temporal, or inferior pirietal lobules on MRI. Conclusion: Our findings suggest that the inferior temporal and inferior parictal lobules which are important for the processing sequence of the visual system in addition to the occipital lobc, might he responsible for thc mechanism of PPR by half-ficld stimulation, espccially for electric source expansion. [source] Comparing MEG and fMRI views to naming actions and objectsHUMAN BRAIN MAPPING, Issue 6 2009Mia Liljeström Abstract Most neuroimaging studies are performed using one imaging method only, either functional magnetic resonance imaging (fMRI), electroencephalography (EEG), or magnetoencephalography (MEG). Information on both location and timing has been sought by recording fMRI and EEG, simultaneously, or MEG and fMRI in separate sessions. Such approaches assume similar active areas whether detected via hemodynamic or electrophysiological signatures. Direct comparisons, after independent analysis of data from each imaging modality, have been conducted primarily on low-level sensory processing. Here, we report MEG (timing and location) and fMRI (location) results in 11 subjects when they named pictures that depicted an action or an object. The experimental design was exactly the same for the two imaging modalities. The MEG data were analyzed with two standard approaches: a set of equivalent current dipoles and a distributed minimum norm estimate. The fMRI blood-oxygen-level dependent (BOLD) data were subjected to the usual random-effect contrast analysis. At the group level, MEG and fMRI data showed fairly good convergence, with both overall activation patterns and task effects localizing to comparable cortical regions. There were some systematic discrepancies, however, and the correspondence was less compelling in the individual subjects. The present analysis should be helpful in reconciling results of fMRI and MEG studies on high-level cognitive functions. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] Difference in somatosensory evoked fields elicited by mechanical and electrical stimulations: Elucidation of the human homunculus by a noninvasive methodHUMAN BRAIN MAPPING, Issue 4 2005Ken Inoue Abstract We recently recorded somatosensory evoked fields (SEFs) elicited by compressing the glabrous skin of the finger and decompressing it by using a photosensor trigger. In that study, the equivalent current dipoles (ECDs) for these evoked fields appeared to be physiologically similar to the ECDs of P30m in median nerve stimulation. We sought to determine the relations of evoked fields elicited by mechanically stimulating the glabrous skin of the great toe and those of electrically produced P40m. We studied SEFs elicited by mechanical and electrical stimulations from the median and tibial nerves. The orientations of dipoles from the mechanical stimulations were from anterior-to-posterior, similar to the orientations of dipoles for P30m. The direction of the dipole around the peak of N20m from median nerve electrical stimulation was opposite to these directions. The orientations of dipoles around the peak of P40m by tibial nerve stimulation were transverse, whereas those by the compression and decompression stimulation of the toe were directed from anterior-to-posterior. The concordance of the orientations in ECDs for evoked fields elicited by mechanical and electrical stimulations suggests that the ECDs of P40m are physiologically similar to those of P30m but not to those of N20m. The discrepancy in orientations in ECDs for evoked field elicited by these stimulations in the lower extremity suggests that electrical and compression stimulations elicit evoked fields responding to fast surface rubbing stimuli and/or stimuli to the muscle and joint. Hum. Brain Mapping 24:274,283, 2005. © 2005 Wiley-Liss, Inc. [source] | ||||||||||