Biomedical subjects

J Haueisen

Publications and source records attributed to J Haueisen.

At least 19 recordsLinked to original sources

PubMed2005

Cardio-respiratory contributions to the magnetoencephalogram.

Modern MEG technology provides whole head helmet systems which extend posterior to the base of the skull. While this provides better visualization of low temporal structures it also allows the intrusion of activity that is of cardiac origin. This consists not only of the QRS complex of the MCG but a late component (LC) during the SP interval. This tends to consist of a series of waves and has a different topographic distribution from the magnetic QRS complex. The LC is usually most prominent in the low occipital and sub-occipital sensors but can occur also in other areas. When the high pass filter is set to 0.1 Hz it can be seen that the LC rides on a slow wave of about 0.3 Hz, which is linked to respiration. Principal component analysis of cardiac cycles averaged from the ECG separates the MCG from the LC. The physiology of the LC is unknown at this time but it may be related to the ballistocardiogram. Algorhythms designed to remove the cardiac contributions to the MEG will have to take the LC and its marked variability into account.

Adult↗

PubMed2005

Methods for parameter identification in oscillatory networks and application to cortical and thalamic 600 Hz activity.

Directed information transfer in the human brain occurs presumably by oscillations. As of yet, most approaches for the analysis of these oscillations are based on time-frequency or coherence analysis. The present work concerns the modeling of cortical 600 Hz oscillations, localized within the Brodmann Areas 3b and 1 after stimulation of the nervus medianus, by means of coupled differential equations. This approach leads to the so-called parameter identification problem, where based on a given data set, a set of unknown parameters of a system of ordinary differential equations is determined by special optimization procedures. Some suitable algorithms for this task are presented in this paper. Finally an oscillatory network model is optimally fitted to the data taken from ten volunteers.

Cerebral Cortex↗

PubMed2004

Multimodal imaging of somatosensory evoked cortical activity.

Somatosensory evoked cortical activity is well investigated in both fMRI and MEG/EEG. Investigation with functional magnetic resonance spectroscopic (fMRS) imaging is relatively new and provides a means to image the metabolic activity of the brain. We for the first time combined fMRS, fMRI, MEG and EEG. This provides information about the metabolic, hemodynamic and electrical activity of the brain and also the verification of one imaging modality with the other. The dipolar source localized from the EEG/MEG data is in the vicinity of the fMRI activation site and also in the same area where lactate consumption is high as measured with fMRS imaging.

Electroencephalography↗

PubMed2004

Fetal MCG and fetal MEG measurements with a 3-channel SQUID system.

Since the high costs of common large array SQUID system may hinder widespread application of fetal magnetoencephalography (fMEG) and magnetocardiography (fMCG), we intended to investigate a small non-commercial 3-channel SQUID system. The system comprises 3 axial first order gradiometers with 7 cm base length, 2 cm diameter and 2x2 windings of niobium wire, dc-SQUIDs (UJ-111), and current locked mode SQUID electronics that form an equal length triangle (22.5 mm). The system is mounted in a Cryostat BFH-7 model 16 with 5 mm "warm"-"cold" distance. System noise is about 10 fT/Hz1/2. The fMEG and fMCG were recorded between 29 - 40 weeks of gestation after sonographic localization of the fetal head and heart using a 31-channel biomagnetometer (Philips) and the 3-channel-system, both in the same magnetically shielded room. The fMEG was recorded continuously over 500 sec (500 auditory stimuli, 100 dB SPL, 500 Hz, 50 ms, ISI 0.8-1.2/1.6-2.4 sec, trigger channel, maternal ECG lead, sampling rate 1 kHz). The fMCG was recorded over a period of 5 minutes after dewar readjustment. The detection rates of cortical auditory evoked responses (CAER) reached 100 % for both systems. Cross confirmation of the components was difficult and may have uncovered false positive component detection. The fMCG was characterized by a systematic increase in SNR under application of the smaller device. The small size array provides a profitable alternative for the fetal applications.

Cardiotocography↗

PubMed2004

Effect of model complexity on EEG source localizations.

How model complexity influences the EEG source localizations was studied with three different finite element models of the head, constructed from segmented MR images of an adult male subject. The complexity of the models varied from 9 to 11 tissue types. The lead fields due to dipolar sources in the motor cortex were computed for all three models. The inverse source localizations were performed with an exhaustive search pattern in the motor cortex area. A set of 100 trial inverse runs was made. It was found that the model with most complexity performed best in localizing the sources in the motor cortex area of the brain.

Adult↗

PubMed2004

The dipole location shift within the auditory evoked neuromagnetic field components N100m and mismatch negativity (MMNm).

OBJECTIVE: To investigate whether within the latency range of the neuromagnetic mismatch negativity (MMNm) a similar dipole shift can be observed as found in previous studies for the auditory evoked field component N100m. METHODS: For this purpose selected neuromagnetic data of 29 subjects were analysed in a time window of 15 ms before and 15 ms beyond the peak maximum of both components. In our oddball paradigm, we applied frequency, duration and intensity deviants within one block. The time course of dipole location was analysed by means of a repeated measure analysis of variance (ANOVA). RESULTS: As expected, N100m dipoles shifted significantly from superior to inferior and from posterior to anterior within their latency range. In analogy, the MMNm dipoles of duration and intensity deviants also exhibited a significant shift from posterior to anterior within their latency range. However, the MMNm dipoles of all 3 deviants did not shift significantly from superior to inferior. Concerning this direction, the ANOVA revealed a significant TIME*COMPONENT interaction between the N100m and the MMNm of duration and intensity deviants. CONCLUSIONS: The finding of a different time course of N100m and MMNm dipoles does not support the assumption that the MMN represents an amplitude- and latency-modulated auditory N100 response.

Adult↗

PubMed2004

Role of soft bone, CSF and gray matter in EEG simulations.

Effects of soft skull bone, cerebrospinal fluid (CSF) and gray matter on scalp potentials were examined with highly heterogeneous finite element models of an adult male subject. These models were constructed from segmented T1 weighted magnetic resonance images. Models had voxel resolutions of 1x1x3.2 mm with a total of about 1.5 million voxels. The scalp potentials, due to a dipolar source in the motor cortex area, were computed with an adaptive finite element solver. It was found that the scalp potentials were significantly affected by the soft bone, CSF and gray matter tissue boundaries in the models.

Adult↗

PubMed2004

Forecasting of life threatening arrhythmias using the compression entropy of heart rate.

OBJECTIVES: Ventricular tachycardia (VT) provoking sudden cardiac death (SCD) are a major cause of mortality in the developed countries. The most efficient therapy for SCD prevention are implantable cardioverter defibrillators (ICD). In this study heart rate variability (HRV) measures were analyzed for short-term forecasting of VT in order to improve VT sensing and to enable a patient warning of forth-coming shocks. METHODS: The last 1000 normal beat-to-beat intervals before 50 VT episodes stored by the ICD were analyzed and compared to individually acquired control time series (CON). HRV analysis was performed with standard parameters of time and frequency domain as suggested by the HRV Task Force and furthermore with a newly developed and optimized nonlinear parameter that assesses the compression entropy of heart rate (Hc). RESULTS: Except of meanNN (p = 0.02) we found no significant differences in standard HRV parameters. In contrast, Hc revealed highly significant (p = 0.007) alterations in VT compared with CON suggesting a decreased complexity before the onset of VT. CONCLUSION: Compression entropy might be a suitable parameter for short-term forecasting of life-threatening tachycardia in ICD.

Arrhythmias, Cardiac↗

PubMed2003

Active magnetic shielding for biomagnetic measurement using spatial gradient fields.

Biomagnetic measurement performed outside a magnetically shielded room is subject to distortion by strong magnetic fields. Reducing such disturbances can enhance and stabilize biomagnetic measurement conditions in the absence of passive shielding. We have developed an active magnetic shielding system that produces both homogeneous and spatial gradient magnetic fields. The system is composed of anisotropic magnetoresistive sensors, a digital signal processor controller and two different coil systems. In order to improve the measurement environment for a first-order gradient coil SQUID system, the disturbing vertical magnetic fields and vertical field gradients are reduced, thus achieving a shielding factor of approximately 6 at 100 Hz. Our system provides a more flexible and less costly alternative to magnetically shielded rooms.

Artifacts↗

PubMed2002

The influence of brain tissue anisotropy on human EEG and MEG.

The influence of gray and white matter tissue anisotropy on the human electroencephalogram (EEG) and magnetoencephalogram (MEG) was examined with a high resolution finite element model of the head of an adult male subject. The conductivity tensor data for gray and white matter were estimated from magnetic resonance diffusion tensor imaging. Simulations were carried out with single dipoles or small extended sources in the cortical gray matter. The inclusion of anisotropic volume conduction in the brain was found to have a minor influence on the topology of EEG and MEG (and hence source localization). We found a major influence on the amplitude of EEG and MEG (and hence source strength estimation) due to the change in conductivity and the inclusion of anisotropy. We expect that inclusion of tissue anisotropy information will improve source estimation procedures.

Adult↗

PubMed2002

Habituation of the auditory evoked field component N100m and its dependence on stimulus duration.

OBJECTIVES: In the current study we investigated the habituation of the neuromagnetic auditory evoked field (AEF) component N100m and its dependence on stimulus duration. METHODS: Fifteen subjects were stimulated monaurally in 3 blocks of 210 trials with 1000 Hz tones of different duration (50, 100, 200 ms) and in a single block of 70 trials with 1200 Hz tones. The order of blocks was counterbalanced within the total experiment. Tones were separated by a stimulus onset asynchrony of 2000 ms. AEF were recorded over both hemispheres by means of a 31 channel system (Philips) on two different days. The AEF were compared within and between the blocks and between the hemispheres. Additionally, the effects of block order were analyzed. RESULTS: In the course of the experiment a pronounced decrease of N100m mean global field power (MGFP) and an increase of its latency were observed. While the order of blocks clearly affected the degree of habituation, stimulus duration did not have any influence on it. Within the blocks, habituation also had an impact on dipole location in inferior-superior direction. The application of the 1200 Hz stimulus led to a slight response recovery. The change in tone pitch affected the dipole orientation, as an indicator for the tonotopic organization of the auditory cortex.

Acoustic Stimulation↗

PubMed2002

Stimulus duration influences the dipole location shift within the auditory evoked field component N100m.

The equivalent source of the neuromagnetic auditory evoked field (AEF) component N100m shifts systematically within its latency range. In the current study, possible effects of stimulus duration on this shift were analysed. 15 subjects were stimulated monaurally with tones of different duration (50, 100, 200 ms) and AEFs were recorded successively over both hemispheres. Dipoles were calculated in 5-ms-steps from 15 ms before to 15 ms after the N100m peak maximum. A dipole location shift within the N100m latency from posterior to anterior and from superior to inferior was observed. The shift in anterior-posterior direction was found to be larger in the right compared to the left hemisphere. Stimulus duration significantly affected the degree of dipole shift in this direction. It was found to be shorter the shorter the stimulus.

Acoustic Stimulation↗

PubMed2002

[Development of a nonmagnetic angle encoder for active shielding during biomagnetic measurements].

Biomagnetic fields--in particular in the low-frequency range--are subject to environmental interference, which cannot be adequately reduced by most passive shielding methods. However, the signal-to-noise ratio can be increased by active compensation. For this purpose, the interference is detected by reference sensors and fed back through integrated compensation coils. To establish deviation of normal directions between reference sensors and compensation coils, an angle encoder was developed. The rotation of the reference sensors about two axes at right angles to each other, is converted into voltage pulses by means of codewheels and photoelectric beams. The pulses are counted by incremental encoders, and represent a measure of the angles. A cardanic suspension and a plumb-line act as a reference system. The pulses counted are converted into binary angle values, which are used for coordinate transformation of the interfering fields. The angle encoder can determine the tilt of the reference sensors with an accuracy of 1 degree within a range between -45 and +45 degrees. The noise level of the system remains unaffected during a biomagnetic measurement. Magnetic signals of up to 5 pT arising during the oscillation of the plumb-line can be neglected because of the static nature of the angular measurement.

Electromagnetic Fields↗

PubMed2002

High frequency intra-QRS signals in idiopathic dilated cardiomyopathy.

We extracted and quantified high frequency intra-QRS signals in idiopathic dilated cardiomyopathy (IDC). In IDC the analysis of late potentials in the terminal QRS complex often fails in predicting clinical events because of intraventricular conduction abnormalities and the absence of a circumscribed arrhythmogenic substrate. Therefore, new approaches are required to assess the electrical state of the myocardium. We investigated 21 patients suffering from IDC with (n = 14) and without (n = 7) bundle branch block. High resolution 31 lead magnetocardiograms were filtered with a 67 point 4th order Savitzky-Golay filter. The difference of the measured and filtered signals was calculated (67-200 Hz). The spatio-temporal properties and the areas under the curves of the resulting high frequency intra-QRS signals (IQCs) were studied. We detected IQCs in all patients. The patients had individual patterns regarding the temporal and spatial properties of the IQCs during depolarisation. The IQCs predominantly appeared in the initial portion of the QRS. The ratios of the areas under the curves of the IQCs and the measured signals were linearly correlated to the left ventricular enddiastolic diameter (r = 0.71, significance 0.0012). In IDC the ventricular depolarization is accompanied by individual spatial and temporal patterns of high frequency intra-QRS signals. They can be studied non-invasively from body surface mapping data with the algorithm used in this study. This provides access to the assessment of the electrical status in patients with IDC.

Adult↗

PubMed2002

DTI measurements of isotropic and anisotropic media.

The ability to measure different rates of diffusion along different directions is one of the features that distinguish DTI from other imaging methods. It allows to extract and visualize information on tissue microstructure and microdynamics. However, to correctly determine the full diffusion tensor, the so-called b-matrix has to be calculated by taking into account the non-negligible influences of image gradients and cross-terms between imaging and diffusion gradients. In this work validation of this b-matrix correction was investigated by determining self-diffusion coefficients of several isotropic media on a 1.5 T clinical whole-body scanner. To investigate these influences on the measurements of anisotropic media the same experiments were performed with a carrot.

1-Propanol↗

PubMed2001

Involuntary motor activity in pianists evoked by music perception.

Pianists often report that pure listening to a well-trained piece of music can involuntarily trigger the respective finger movements. We designed a magnetoencephalography (MEG) experiment to compare the motor activation in pianists and nonpianists while listening to piano pieces. For pianists, we found a statistically significant increase of activity above the region of the contralateral motor cortex. Brain surface current density (BSCD) reconstructions revealed a spatial dissociation of this activity between notes preferably played by the thumb and the little finger according to the motor homunculus. Hence, we could demonstrate that pianists, when listening to well-trained piano music, exhibit involuntary motor activity involving the contralateral primary motor cortex (M1).

Acoustic Stimulation↗

PubMed2001

Passive finger movement evoked fields in magnetoencephalography.

We studied neuromagnetic fields during passive finger movements in 11 normal subjects. Activation started 27 ms after the onset of movement and remained for about 100 ms. Four activation maxima occurred within this time range, PM1 at 27 ms, PM2 at 46 ms, PM3 at 85 ms, and PM4 at 125 ms. Not all components were distinguishable in every subject partly due to overlapping effects, but PM3 was present in all subjects. Magnetic source imaging (MSI) revealed dipolar sources within 1 cm of the central sulcus for all four components. The results suggest that studying the integrity of the sensorimotor system in patients regardless of their degree of motor impairment is feasible.

Adult↗

PubMed2001

Reproducibility of HTS-SQUID magnetocardiography in an unshielded clinical environment.

A new technology has been developed which measures the magnetic field of the human heart (magnetocardiogram, MCG) by using high temperature superconducting (HTS) sensors. These sensors can be operated at the temperature of liquid nitrogen without electromagnetic shielding. We tested the reproducibility of HTS-MCG measurements in healthy volunteers. Unshielded HTS-MCG measurements were performed in 18 healthy volunteers in left precordial position in two separate sessions in a clinical environment. The heart cycles of 10 min were averaged, smoothed, the baselines were adjusted, and the data were standardized to the respective areas under the curves (AUC) of the absolute values of the QRST amplitudes. The QRS complexes and the ST-T intervals were used to assess the reproducibility of the two measurements. Ratios (R(QRS), R(STT)) were calculated by dividing the AUC of the first measurement by the ones of the second measurement. The linear correlation coefficients (CORR(QRS), CORR(STT)) of the time intervals of the two measurements were calculated, too. The HTS-MCG signal was completely concealed by the high noise level in the raw data. The averaging and smoothing algorithms unmasked the QRS complex and the ST segment. A high reproducibility was found for the QRS complex (R(QRS)=1.2+/-0.3, CORR(QRS)=0.96+/-0.06). Similarly to the shape of the ECG it was characterized by three bends, the Q, R, and S waves. In the ST-T interval, the reproducibility was considerably lower (R(STT)=0.9+/-0.2, CORR(STT)=0.66+/-0.28). In contrast to the shape of the ECG, a baseline deflection after the T wave which may belong to U wave activity was found in a number of volunteers. HTS-MCG devices can be operated in a clinical environment without shielding. Whereas the reproducibility was found to be high for the depolarization interval, it was considerably lower for the ST segment and for the T wave. Therefore, before clinically applying HTS-MCG systems to the detection of repolarization abnormalities in acute coronary syndromes, further technical development of the systems is necessary to improve the signal-to-noise ratio.

Adult↗