N. Thakor | Johns Hopkins University (original) (raw)

Papers by N. Thakor

[1991 Proceedings] Case Studies in Medical Instrument Design, 1991

ABSTRACT We have developed a portable microprocessor-bared device which samples and stores the he... more ABSTRACT We have developed a portable microprocessor-bared device which samples and stores the heart and stride rate signals. While running, the user can receive instantaneous voice feedback of his heart rate and stride rate. The device can be connected in series between a pair of stereo headphones and a porrable radio, allowing the runner to listen to music while the device is not in speech output mode.

Physics Letters A, 2003

In the present study Tsallis and Renyi entropy methods were used to study the electric activity o... more In the present study Tsallis and Renyi entropy methods were used to study the electric activity of brain following hypoxicischemic (HI) injury. We investigated the performances of these parameterized information measures in describing the electroencephalogram (EEG) signal of controlled experimental animal HI injury. The results show that (a): compared with Shannon and Renyi entropy, the parameterized Tsallis entropy acts like a spatial filter and the information rate can either tune to long range rhythms or to short abrupt changes, such as bursts or spikes during the beginning of recovery, by the entropic index q; (b): Renyi entropy is a compact and predictive indicator for monitoring the physiological changes during the recovery of brain injury. There is a reduction in the Renyi entropy after brain injury followed by a gradual recovery upon resuscitation.

Journal of Neuroscience Methods, 2001

In experiments involving small animals, the electroencephalogram (EEG) recorded during severe inj... more In experiments involving small animals, the electroencephalogram (EEG) recorded during severe injury and accompanying resuscitation exhibit the strong presence of electrocardiogram (ECG). For improved quantitative EEG (qEEG) analysis, it is therefore imperative to remove ECG interference from EEG. In this paper, we validate the use of independent component analysis (ICA) to effectively suppress the interference of ECG from EEG recordings during normal activity, asphyxia and recovery following asphyxia. Two channels of EEG from five rats were recorded continuously for 2 h. Simultaneous recording of one channel ECG was also made. Epochs of 4 s and 1 min were selected from baseline, asphyxia and recovery (every 10 min) and their independent components and power spectra were calculated. The improvement in normalized power spectrum of EEG obtained for all animals was 7.71+/-3.63 db at the 3rd minute of recovery and dropped to 1.15+/-0.60 db at 63rd minute. The application of ICA has been particularly useful when the power of EEG is low, such as that observed during early brain hypoxic-asphyxic injury. The method is also useful in situations where accurate indications of EEG signal power and frequency content are needed.

IEEE Transactions on Signal Processing, 1994

Here, we present an adaptive algorithm for estimating from noisy observations, periodic signals o... more Here, we present an adaptive algorithm for estimating from noisy observations, periodic signals of known period subject to transient disturbances. The estimator is based on the LMS algorithm and works by tracking the Fourier coefficients of the data. The estimator is analyzed for convergence, noise misadjustment and lag misadjustment for signals with both time invariant and time variant parameters. The analysis is greatly facilitated by a change of variable that results in a time invariant difference equation. At sufficiently small values of the LMS step size, the system is shown to exhibit decoupling with each Fourier component converging independently and uniformly. Detection of rapid transients in data with low signal to noise ratio can be improved by using larger step sizes for more prominent components of the estimated signal. An application of the Fourier estimator to estimation of brain evoked responses is included.

British Journal of Anaesthesia, 2012

Editor's key points † Measuring the precise point of a wakening from anaesthesia may be crucial i... more Editor's key points † Measuring the precise point of a wakening from anaesthesia may be crucial in animal studies. † The use of EEG to indicate awakening from isoflurane anaesthesia was studied in rats. † Change in gamma power parameters of EEG activity was at the moment of awakening. † Monitoring anaesthetic state of rats is possible using EEG. † This may be useful for testing new anaesthetic agents.

Applied Optics, 2007

High-resolution cerebral vasculature imaging has applications ranging from intraoperative procedu... more High-resolution cerebral vasculature imaging has applications ranging from intraoperative procedures to basic neuroscience research. Laser speckle, with spatial contrast processing, has recently been used to map cerebral blood flow. We present an application of the technique using temporal contrast processing to image cerebral vascular structures with a field of view a few millimeters across and approximately 20 m resolution through a thinned skull. We validate the images using fluorescent imaging and demonstrate a factor of 2-4 enhancement in contrast-to-noise ratios over reflectance imaging using white or spectrally filtered green light. The contrast enhancement enables the perception of approximately 10%-30% more vascular structures without the introduction of any contrast agent.

In this paper, we introduce Nonadditive Information Theory through the axiomatic formulation of T... more In this paper, we introduce Nonadditive Information Theory through the axiomatic formulation of Tsallis entropy. We show that systems with transitions from high dimensionality to few degrees of freedom are better described by nonadditive formalism. Such a biological system is the brain and brain rhythms is its macroscopic dynamic trace. We will show with simulations that Tsallis entropy is a powerful information measure, and we present results of brain dynamics analyzed using EEG recordings from a brain injury ...

Traumatic injuries, both in the central nervous system (CNS) and peripheral nervous system (PNS),... more Traumatic injuries, both in the central nervous system (CNS) and peripheral nervous system (PNS), can potentially lead to irreversible damage resulting in permanent loss of function. Investigating the complex dynamics involved in these processes may elucidate the biological mechanisms of both nerve degeneration and regeneration, and may potentially lead to the development of new therapies for recovery. A scientific overview on the biological foundations of nerve injury is presented. Differences between nerve regeneration in the central and PNS are discussed. Advances in microtechnology over the past several years have led to the development of invaluable tools that now facilitate investigation of neurobiology at the cellular scale. Microfluidic devices are explored as a means to study nerve injury at the necessary simplification of the cellular level, including those devices aimed at both chemical and physical injury, as well as those that recreate the post-injury environment.

2013 IEEE SENSORS, 2013

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