Rate control in patients with chronic atrial fibrillation.
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Atrial Fibrillation↗
Biomedical subjects
Stephen E Robinson
Publications and source records attributed to Stephen E Robinson.
Improving permutation test power for group analysis of spatially filtered MEG data.
Non-parametric statistical methods, such as permutation, are flexible tools to analyze data when the population distribution is not known. With minimal assumptions and better statistical power compared to the parametric tests, permutation tests have recently been applied to the spatially filtered magnetoencephalography (MEG) data for group analysis. To perform permutation tests on neuroimaging data, an empirical maximal null distribution has to be found, which is free from any activated voxels, to determine the threshold to classify the voxels as active at a given probability level. An iterative procedure is used to determine the distribution by computing the null distribution, which is recomputed when a possible activated voxel is found within the current distributions. Besides the high computational costs associated with this approach, there is no guarantee that all activated voxels are excluded when constructing the maximal null distribution, which may reduce the statistical power. In this study, we propose a novel way to construct the maximal null distribution from the data of the resting period. The approach is tested on the MEG data from a somatosensory experiment, and demonstrated that the approach could improve the power of the permutation test while reducing the computational cost at the same time.
Adult↗
Fetal MEG redistribution by projection operators.
The fetal magnetoencephalogram (fMEG) is measured in the presence of large interference from the maternal and fetal magnetocardiograms. This interference can be efficiently attenuated by orthogonal projection of the corresponding spatial vectors. However, the projection operators redistribute the fMEG signal among sensors. Although redistribution can be readily accounted for in the forward solution, visual interpretation of the fMEG signal topography is made difficult. We have devised a general, model-independent method for correction of the redistribution effect that utilizes the assumption that we know in which channels the fMEG should be negligible (such channels are distant from the known fetal head position). In a simplified case where the fMEG can be explained by equivalent current dipoles, the correction can also be obtained from fitting the dipoles to the fMEG signal. The corrected fMEG signal topography then corresponds to the dipole forward solution, but without orthogonal projection. We illustrate the redistribution correction on an example of experimentally measured flash evoked fMEG.
Algorithms↗
Parallel distributed processing neuroimaging in the Stroop task using spatially filtered magnetoencephalography analysis.
Parallel distributed processing neuroimaging in the Stroop color word interference task in five healthy subjects was studied. The total reaction time was set at 650 ms with a time window of 200 ms in steps of 50 ms. Spatially filtered magnetoencephalography analysis, as used in synthetic aperture magnetometry, was used. Neural activation began in the left posterior parietal-occipital area (150-250 ms post-stimulus), followed by the right prefrontal polar area (250-350 ms), the left dorsolateral prefrontal cortex (250-400 ms), and the mid- to lower- primary motor area (350-400 ms). Successive and temporally overlapping activation of various cortical regions were successfully estimated within a short 200 ms time interval, contrary to previous positron emission tomography and fMRI studies.
Adult↗
Short-term serial magnetoencephalography recordings offetal auditory evoked responses.
The study objective was to determine whether short-term serial magnetoencephalographic (MEG) measurements would increase the odds in favor of obtaining fetal auditory evoked responses in normal fetuses. The recordings were performed in two phases using the newly developed 151-channel fetal MEG system, superconducting quantum interference device array for reproductive assessment. Ten pregnant subjects with gestational ages ranging from 30-35 weeks were recruited to participate. Daily recordings were performed over a minimum of 3 days during 1 week of gestation and repeated in the same subjects between 36 and 40 weeks gestation. In 80% of subjects, auditory evoked responses were detected at least once. In healthy fetuses, serial recordings over a short span of time increased the rate of detecting fetal evoked response.
Evoked Potentials, Auditory↗
Frequency-dependent spatial distribution of human somatosensory evoked neuromagnetic fields.
Using synthetic aperture magnetometry (SAM), we examined the spatial distribution of frequency changes in magnetoencephalography signal rhythms on individual magnetic resonance images following somatosensory stimulation. SAM is a novel statistical spatial filtering method that uses an adaptive beamformer. Electrical stimulation of the right median nerve demonstrated high-frequency event-related synchronization (ERS) in the 50-200-Hz range, consistently localized in the contralateral primary sensorimotor area in all subjects (n=7). Event-related desynchronization (ERD) was demonstrated in the 8-13, 13-25 and 25-50-Hz ranges bilaterally in the area surrounding the central sulcus. The differences in the spatial distribution as well as the frequency bands between ERS and ERD suggest that ERS and ERD reflect the responses of different cell assemblies rather than a frequency shift of the same cell assembly.
Adult↗
First magnetomyographic recordings of uterine activity with spatial-temporal information with a 151-channel sensor array.
OBJECTIVE: The purpose of this study was to examine the feasibility of recording the spatial-temporal magnetomyographic activity from the pregnant uterus with the use of the newly developed 151-channel noninvasive device, known as the superconducting quantum interference device array for reproductive assessment. STUDY DESIGN: Uterine magnetomyographic signals were recorded from 10 pregnant subjects with the 151-channel sensor array curved to fit the pregnant abdomen. The recording sessions were 16 minutes in length, with a sampling rate of 250 Hz. RESULTS: Uterine activity bursts were successfully recorded with the superconducting quantum interference device array for reproductive assessment system. By obtaining a contour plot of the magnetic field distribution, we were able to localize the areas of activation over the uterus during a contraction. Also, it was possible to calculate the time delay in the propagation of the activity across the uterus. CONCLUSION: Using superconducting quantum interference device array for reproductive assessment system, we have established the feasibility of recording uterine contractile activity with spatial-temporal resolution that is high enough to determine the regions of localized activation and propagation over the uterus.
Female↗