IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Dec 2009
Sleep apnea screening by autoregressive models from a single ECG lead.
This paper presents a method for obstructive sleep apnea (OSA) screening based on the electrocardiogram (ECG) recording during sleep. OSA is a common sleep disorder produced by repetitive occlusions in the upper airways and this phenomenon can usually be observed also in other peripheral systems such as the cardiovascular system. Then the extraction of ECG characteristics, such as the RR intervals and the area of the QRS complex, is useful to evaluate the sleep apnea in noninvasive way. ⋯ In addition to the minute-by-minute classification, the results showed that the two classifiers are able to separate entirely (100%) the normal recordings from the apneic recordings. Finally, an additional database with eight recordings annotated as normal or apneic was used to test again the classifiers. Also in this new dataset, the results showed a complete separation between apneic and normal recordings.
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IEEE Trans Biomed Eng · Dec 2009
Influence of system integration and packaging on its inductive power link for an integrated wireless neural interface.
In an integrated wireless neural interface based on the Utah electrode array, the implanted electronics are supplied with power through inductive coupling between two coils. This inductive link is affected by conductive and dielectric materials and media surrounding the implant coil. In this study, the influences of the integration of an implant coil on a silicon-based IC and electrode array, thin-film Parylene-C encapsulation, and physiological medium surrounding the coil were investigated systematically and quantitatively by empirical measurements. ⋯ The parasitic influences affecting the inductive link were empirically investigated by measuring the electrical properties of coils in different configurations and in different media. The distance of power transmission between the transmit and receive coils was measured when the receive coil was in air and immersed in phosphate buffered saline solution to simulate an implanted physiological environment. The results from this study quantitatively address the influences of factors such as device integration, encapsulation, and implantation on its inductive power link, and suggest how to maximize the efficiency in power transmission for such neural interface devices powered inductively.
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IEEE Trans Biomed Eng · Dec 2009
Wavelet-domain medical image denoising using bivariate laplacian mixture model.
In this paper, we proposed novel noise reduction algorithms that can be used to enhance image quality in various medical imaging modalities such as magnetic resonance and multidetector computed tomography. The noisy captured 3-D data are first transformed by discrete complex wavelet transform. Using a nonlinear function, we model the data as the sum of the clean data plus additive Gaussian or Rayleigh noise. ⋯ Our experiments on CT images show that among our derived shrinkage functions usually BiLapGausMAP produces images with higher peak SNR. However, BiLapGausMMSE is preferred especially for CT images, which have high SNRs. Furthermore, BiLapRayMAP yields better noise reduction performance for low SNR MR datasets such as high-resolution whole heart imaging while BiLapGauMAP results in better performance in MR data with higher intrinsic SNR such as functional cine data.
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IEEE Trans Biomed Eng · Dec 2009
Spontaneous calcium transients in cultured cortical networks during development.
Spontaneous neuronal activity plays an important role in the development of the brain. Developmental changes in the spontaneous activity pattern of neuronal networks in vitro have been extensively studied by using the microelectrode array (MEA) recording system. However, little is known about the transition of spontaneous intracellular calcium dynamics, and the relationship between calcium transients and electrical activity during development. ⋯ Between these two states, in two-week cultures, slow, radial propagation of calcium waves independent of electrical activity is observed. Pharmacological treatments with the purinergic receptor antagonist suramin and gap junction blocker 18- beta glycyrrhetinic acid reveal that the spontaneous radial calcium waves are mediated by the astrocytic network, and suggest that the astrocytic calcium waves can influence the electrical firing patterns of networks by locally affecting neuronal signaling. These results indicate that the various dynamics of intracellular calcium transients regulate the network maturation processes.
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IEEE Trans Biomed Eng · Nov 2009
A Bayesian clustering method for tracking neural signals over successive intervals.
This paper introduces a new, unsupervised method for sorting and tracking the action potentials of individual neurons in multiunit extracellular recordings. Presuming the data are divided into short, sequential recording intervals, the core of our strategy relies upon an extension of a traditional mixture model approach that incorporates clustering results from the preceding interval in a Bayesian manner, while still allowing for signal nonstationarity and changing numbers of recorded neurons. As a natural byproduct of the sorting method, current and prior signal clusters can be matched over time in order to track persisting neurons. ⋯ We present results in a principal components space; however, the algorithm may be applied in any feature space where the distribution of a neuron's spikes may be modeled as Gaussian. Applications of this signal classification method to recordings from macaque parietal cortex show that it provides significantly more consistent clustering and tracking results than traditional methods based on expectation-maximization optimization of mixture models. This consistent tracking ability is crucial for intended applications of the method.