Reconstruction of quasi-radial dipolar activity using three-component magnetic field measurements.

Objective: While standard magnetoencephalographic systems record only one component of the biomagnetic field, novel vector-biomagnetometers enable measurement of all three components of the field at each sensing point. Because information content in standard one-component magnetoencephalography (MEG) is often not adequate to reconstruct quasi-radial dipolar activity, we tested the hypothesis that quasi-radial activity can be estimated using three-component MEG.

Methods: We stimulated the right median nerve in 11 healthy volunteers and recorded the somatosensory evoked fields over the contralateral hemisphere using a novel vector-biomagnetometer system comprised of SQUID-based magnetometer triplets.

In-vivo signal transmission using an intra-corporal RF transmitter.

In clinical routine, measurements of human physiological parameters are very important. In this paper, a study of RF transmission from the inside to the outside of a biological body is described. In the course of this work, an overview of the state of the art of wireless biotelemetry and the basics of biological tissue attenuation are given.

Radio Frequency Identification (RFID) in medical environment: Gaussian Derivative Frequency Modulation (GDFM) as a novel modulation technique with minimal interference properties.

Radio Frequency Identification (RFID) systems in healthcare facilitate the possibility of contact-free identification and tracking of patients, medical equipment and medication. Thereby, patient safety will be improved and costs as well as medication errors will be reduced considerably. However, the application of RFID and other wireless communication systems has the potential to cause harmful electromagnetic disturbances on sensitive medical devices.

High frequency oscillations evoked by peripheral magnetic stimulation.

The analysis of somatosensory evoked potentials (SEP) and / or fields (SEF) is a well-established and important tool for investigating the functioning of the peripheral and central human nervous system. A standard technique to evoke SEPs / SEFs is the stimulation of the median nerve by using a bipolar electrical stimulus. We aim at an alternative stimulation technique enabling stimulation of deep nerve structures while reducing patient stress and error susceptibility.

A novel marker design for magnetic marker monitoring in the human gastrointestinal tract.

Magnetic marker monitoring (MMM) is a technique to determine the motility of the gastrointestinal tract and to observe the dissolution of pharmaceutical compounds. Today's magnetic markers usually consist of magnetized magnetite. Because of their weak magnetic fields, highly sensitive sensor systems are required.

Optoelectrophysiological stimulation of the human eye using fundus-controlled silent substitution technique.

We design, characterize, and apply a novel optoelectrophysiological setup for a fundus-controlled silent substitution technique that accounts for interindividual variability in retina morphology and simultaneously monitors the stimulation site under investigation. We connect a digital color liquid crystal on silicon projector, an electron-multiplying imager, and a light-emitting diode to a fundus camera. The temporal and spatial characterization reveal a maximal contrast loss of 7% for the highest stimulation frequency (30 Hz) and maximum cutoff spatial frequencies of ∼120 cycles∕deg.

Measuring the attenuation characteristics of biological tissues enabling for low power in vivo RF transmission.

In clinical routine there is a need of periodical recording of vital parameters in high risk groups, for example the intraocular pressure. A solution for this could be an intracorporeal sensor using a wireless radio frequency (RF) transmitter. Thereby the risk of an infection is reduced, because a percutaneous connection is not necessary.

Analysis of induced components in electroencephalograms using a multiple correlation method.

Background: Evoked and induced activities are two typical components in the EEG and MEG time series after a stimulation. While evoked activity is phase-locked to the stimulus, induced activity is not. Present analysis methods are able to detect non-phase-locked parts of the signal, however, they do not improve the signal-to-noise ratio (SNR) of these signal components.

Silent substitution stimulation of S-cone pathway and L- and M-cone pathway in glaucoma.

Purpose: The study aimed for objective detection of primary open-angle glaucoma with selective color channel stimulation based on the silent substitution technique. In addition, an objective was analysis of the characteristics of individual color channels based on visual evoked potentials.

Methods: Visual evoked potentials were recorded in 141 subjects (39 patients with glaucoma, 71 healthy subjects, and 31 age-matched healthy subjects) with two scalp electrodes after cone-specific flash stimulation.

Independent component analysis: comparison of algorithms for the investigation of surface electrical brain activity.

We compared the performance of 22 algorithms for independent component analysis with the aim to find suitable algorithms for applications in the field of surface electrical brain activity analysis. The quality of the separation is assessed with four performance measures: a correlation coefficient based index, a signal-to-interference ratio, a signal-to-distortion-ratio and the computational demand. Artificial data are used consisting of typical electroencephalogram and evoked potentials signal patterns, e.

Quantification of cognitive-induced brain activity: an efficient method for online applications.

Electrical brain responses during performance of cognitive tasks contain not only evoked, but also induced activity reflecting different processes. These activities are often partially overlapped in time and frequency, so that they are even more difficult to be separated in single-trial. Therefore, online applications based on induced brain activity require specific online processing methods to separate both activities efficiently.

Magnetic nanoparticle imaging by means of minimum norm estimates from remanence measurements.

In magnetic nanoparticle imaging, magnetic nanoparticles are coated and functionalized to bind to specific targets. After measuring their magnetic relaxation or remanence, their distribution can be determined by means of inverse methods. The reconstruction algorithm presented in this paper includes first a dipole fit using a Levenberg-Marquardt optimizer to determine the reconstruction plane.

Reconstruction of multiple neuromagnetic sources using augmented evolution strategies-- a comparative study.

The localization of dipolar sources in the brain based on electroencephalography (EEG) or magnetoencephalography (MEG) data is a frequent problem in the neurosciences. Deterministic standard approaches such as the Levenberg-Marquardt (LM) method often have problems in finding the global optimum of the associated nonlinear optimization function, when two or more dipoles are to be reconstructed. In such cases, probabilistic approaches turned out to be superior, but their applicability in neuromagnetic source localizations is not yet satisfactory.

Decomposition of biomedical signals in spatial and time-frequency modes.

Objectives: The purpose of this paper is to introduce a new method for spatial-time-frequency analysis of multichannel biomedical data. We exemplify the method for data recorded with a 31-channel Philips biomagnetometer.

Methods: The method creates approximations and decompositions of spatiotemporal signal distributions using elements (atoms) chosen from a very large and redundant set (dictionary).

Circular correlation methods for the analysis of oscillations in dependent time series.

Phases of signals can be regarded as circular data. Time series of phases statistically depend in time. There are also dependencies between diverse circular time series.

Identifying mutual information transfer in the brain with differential-algebraic modeling: Evidence for fast oscillatory coupling between cortical somatosensory areas 3b and 1.

Understanding information transfer in the brain is a major challenge in today's neurosciences. Commonly, information transfer between brain areas is analyzed with the help of correlation measures for electrophysiological data. However, such approaches cannot distinguish between mutual coupling and other mechanisms of creating correlations between responses, such as common input from other sources.

Comparison of time-variant coherence algorithms in single-trial: a dynamic analysis.

Synchronization in the electroencephalogram, which can be quantified by time-variant coherence measures, reveals a communication between brain regions reflecting different functions (e.g. learning or memory).

Threshold adaptation for mean value based operant conditioning.

Biofeedback and a variety of brain-computer-interface methods imply as very first stages the obtainment of control of selected signals e.g. the related generating psycho-physiological processes.

Analysis of time-variant quadratic phase couplings in the tracé alternant EEG by recursive estimation of 3rd-order time-frequency distributions.

The quantification of transient quadratic phase couplings (QPC) by means of time-variant bispectral analysis is a useful approach to explain several interrelations between signal components. A generalized recursive estimation approach for 3rd-order time-frequency distributions (3rd-order TFD) is introduced. Based on 3rd-order TFD, time-variant estimations of biamplitude (BA), bicoherence (BC) and phase bicoherence (PBC) can be derived.

A database for therapy evaluation in neurological disorders: application in epilepsy.

Due to the high diversity of cases and the variety of treatment modalities, the information to be managed and processed in therapy evaluation is excessive in many neurological diseases. Additionally, in order to gain more insight into, not only the disorders, but also the applied therapies, more objectivity is requested in clinical practice. Therefore, in this study, a database system is designed for assisting therapy evaluation in neurological diseases.

Phase coupling between different motor areas during tongue-movement imagery.

Motor imagery can be accompanied by an enhancement of brain oscillations (event-related synchronization, ERS) within specific frequency bands. To characterize the neuronal couplings involved during these prominent power changes, we have chosen a certain coupling measure that bears directly on the issue of transient cortical connections. Specifically, we applied for the first time the phase-locking value to investigate the phase coupling of sensorimotor rhythms in different motor areas during tongue-movement imagery.

Spectral characteristics of light sources for S-cone stimulation.

Purpose: Electrophysiological investigations of the short-wavelength sensitive pathway of the human eye require the use of a suitable light source as a S-cone stimulator. Different light sources with their spectral distribution properties were investigated and compared with the ideal S-cone stimulator.

Methods: First, the theoretical background of the calculation of relative cone energy absorption from the spectral distribution function of the light source is summarized.

A finite difference model of load-induced fluid displacements within bone under mechanical loading.

Load-induced fluid flow in the lacunocanalicular network, induced by the mechanical loading of bone, is believed to play an important role in bone modelling, remodelling and adaptation processes. There are strong indications that this fluid flow is responsible for the mechanotransduction from external mechanical loads to the cells responsible for bone apposition or removal. Since direct flow measurements (especially in compact bone, in vivo and in situ) are not yet possible, theoretical modelling offers an alternative approach to determine the fluid flow velocities, displacements and effects of interstitial fluid flow.

The implementation of a quality-net as a part of the European project DIABCARE Q-Net.

DIABCARE Q-Net is a European project with a consortium of partners in healthcare, industry, and research, which has the overall target of improvement in diabetes care by aggregation, evaluation, and feedback of anonymized patient data with the tools of modern telematics, resulting from the initiative of the St. Vincent-Declaration, St. Vincent, Italy.