IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Nov 2004
Comparative StudyAdaptive denoising of event-related functional magnetic resonance imaging data using spectral subtraction.
A new adaptive signal-preserving technique for noise suppression in event-related functional magnetic resonance imaging (fMRI) data is proposed based on spectral subtraction. The proposed technique estimates a parametric model for the power spectrum of random noise from the acquired data based on the characteristics of the Rician statistical model. This model is subsequently used to estimate a noise-suppressed power spectrum for any given pixel time course by simple subtraction of power spectra. ⋯ Moreover, we demonstrate that further analysis using principal component analysis and independent component analysis shows a significant improvement in both convergence and clarity of results when the new technique is used. Given its simple form, the new method does not change the statistical characteristics of the signal or cause correlated noise to be present in the processed signal. This suggests the value of the new technique as a useful preprocessing step for fMRI data analysis.
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IEEE Trans Biomed Eng · Nov 2004
Long-term characterization of firing dynamics of spontaneous bursts in cultured neural networks.
Extracellular action potentials were recorded from developing dissociated rat neocortical networks continuously for up to 49 days in vitro using planar multielectrode arrays. Spontaneous neuronal activity emerged toward the end of the first week in vitro and from then on exhibited periods of elevated firing rates, lasting for a few days up to weeks, which were largely uncorrelated among different recording sites. On a time scale of seconds to minutes, network activity typically displayed an ongoing repetition of distinctive firing patterns, including short episodes of synchronous firing at many sites (network bursts). ⋯ This pattern persisted for the rest of the culture period. Throughout the recording period, active sites showed highly persistent temporal relationships within network bursts. These longitudinal recordings of network firing have, thus, brought to light a reproducible pattern of complex changes in spontaneous firing dynamics of bursts during the development of isolated cortical neurons into synaptically interconnected networks.
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IEEE Trans Biomed Eng · Oct 2004
Comparative StudyA new methodology for determining point-of-gaze in head-mounted eye tracking systems.
The ability to determine point-of-gaze with respect to an observed scene provides significant insight into human cognitive processes, since shifts in gaze position are generally guided by shifts in attentional focus. Using a head-mounted eye tracking system, a new methodology based on four or more point correspondences in two views was developed to reconstruct the subject's point-of-gaze. ⋯ Analysis of normalization techniques that reduce the sensitivity of the homography algorithm to input errors suggests that the point correspondences should be arranged in a radially symmetric distribution around the area to be scanned. The new methodology was used in a clinical study on visual selective attention and mood disorders; this study showed that depressed subjects spent significantly more time looking at images with dysphoric themes than normal control subjects.
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IEEE Trans Biomed Eng · Sep 2004
Comparative StudySimulation of surface EMG signals generated by muscle tissues with inhomogeneity due to fiber pinnation.
Surface electromyographic (EMG) signal modeling has important applications in the interpretation of experimental EMG data. Most models of surface EMG generation considered volume conductors homogeneous in the direction of propagation of the action potentials. However, this may not be the case in practice due to local tissue inhomogeneities or to the fact that there may be groups of muscle fibers with different orientations. ⋯ In these conditions, the potentials detected at the skin surface do not travel without shape changes. This determines numerical issues in the implementation of the model which are addressed in this work. The study provides the solution of the nonhomogenous, anisotropic problem, proposes an implementation of the results in complete surface EMG generation models (including finite-length fibers), and shows representative results of the application of the models proposed.
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IEEE Trans Biomed Eng · Sep 2004
Comparative Study Clinical TrialBlind separation of linear instantaneous mixtures of nonstationary surface myoelectric signals.
Electromyographic (EMG) recordings detected over the skin may be mixtures of signals generated by different active muscles due to the phenomena related to volume conduction. Separation of the sources is necessary when single muscle activity has to be detected. Signals generated by different muscles may be considered uncorrelated but in general overlap in time and frequency. ⋯ The ratio between root-mean-square values of the signals from the two sources detected over one of the muscles increased from (mean +/- standard deviation) 2.33 +/- 1.04 to 4.51 +/- 1.37 and from 1.55 +/- 0.46 to 2.72 +/- 0.65 for wrist flexion and rotation, respectively. This increment was statistically significant. It was concluded that the BSS approach applied is promising for the separation of surface EMG signals, with applications ranging from muscle assessment to detection of muscle activation intervals, and to the control of myoelectric prostheses.