S N Erné

Publications of S N Erné

• Noise reduction in magnetocardiography by singular value decomposition and independent component analysis.

  Authors: D DiPietroPaolo, H P Müller, G Nolte, S N Erné

  Medical & biological engineering & computing. 07/2006; 44(6):489-99.

  In the routine recording of magnetocardiograms (MCGs), it is necessary to underline the problem of noise cancellation. Source separation has often been suggested to solve this problem. In this paper,In the routine recording of magnetocardiograms (MCGs), it is necessary to underline the problem of noise cancellation. Source separation has often been suggested to solve this problem. In this paper, blind source separation (BSS), by means of singular value decomposition (SVD) and independent component analysis (ICA), was used for noise reduction in MCG data to improve the signal to noise ratio. Special techniques, based on statistical parameters, for identifying noise and disturbances, have been introduced to automatically eliminate noise-related and disturbance-related components before reconstructing cleaned data sets. The results show that ICA and SVD can detect and remove a variety of noise and artefact sources from MCG data, as well as from stress MCG.

• A novel approach for the averaging of magnetocardiographically recorded heart beats.

  Authors: D DiPietroPaolo, H P Müller, S N Erné

  Physics in medicine and biology. 06/2005; 50(10):2415-26.

  Performing signal averaging in an efficient and correct way is indispensable since it is a prerequisite for a broad variety of magnetocardiographic (MCG) analysis methods. One of the most commonPerforming signal averaging in an efficient and correct way is indispensable since it is a prerequisite for a broad variety of magnetocardiographic (MCG) analysis methods. One of the most common procedures for performing the signal averaging to increase the signal-to-noise ratio (SNR) in magnetocardiography, as well as in electrocardiography (ECG), is done by means of spatial or temporal techniques. In this paper, an improvement of the temporal averaging method is presented. In order to obtain an accurate signal detection, temporal alignment methods and objective classification criteria are developed. The processing technique based on hierarchical clustering is introduced to take into account the non-stationarity of the noise and, to some extent, the biological variability of the signals reaching the optimum SNR. The method implemented is especially designed to run fast and does not require any interaction from the operator. The averaging procedure described in this work is applied to the averaging of MCG data as an example, but with its intrinsic properties it can also be applied to the averaging of ECG recording, averaging of body-surface-potential mapping (BSPM) and averaging of magnetoencephalographic (MEG) or electroencephalographic (EEG) signals.

• Argos 500: operation of a helmet vector-MEG.

  Authors: A Pasquarelli, R. Rossi, M De Melis, L Marzetti, A. Trebeschi, H P Müller, S N Erné

  Neurology & clinical neurophysiology : NCN. 02/2004; 2004:97.

  We here describe the MEG system recently installed at the University of Ulm; it is specifically designed for clinical application and routine use, to allow investigation of a large number of patientsWe here describe the MEG system recently installed at the University of Ulm; it is specifically designed for clinical application and routine use, to allow investigation of a large number of patients per day. To reach this goal, the system design meets the requirements of reliability, high field sensitivity, minimal set-up time before each measurement and an easy-to-handle user interface. The sensor system consists of a 163 vector-magnetometers array oriented and located in a suitable way to cover the whole head of the patient. Four additional triplets are available as references to arrange software gradiometers. The helmet shaped sensor system is positioned to accommodate the patient in a supine position. Simultaneously to the MEG, there are 64 EEG channels. Other relevant patient information can be recorded up to a total number of 660 acquisition channels. Noise level of a single magnetometer is about 5 fT/square root of Hz. Maximum sampling rate is 4200 Hz.

• Multi-channel magnetocardiography for detecting beat morphology variations in fetal arrhythmias.

  Authors: R Sturm, H P Müller, A Pasquarelli, M DeMelis, S N Erné, R Terinde, D Lang

  Prenatal diagnosis. 02/2004; 24(1):1-9.

  OBJECTIVE: Over the last few years, a number of studies have shown that fetal magnetocardiography (fMCG) is useful in describing fetal cardiac activity. A 55-channel MCG system in Ulm was used toOBJECTIVE: Over the last few years, a number of studies have shown that fetal magnetocardiography (fMCG) is useful in describing fetal cardiac activity. A 55-channel MCG system in Ulm was used to record fetal cardiac activity in 12 pregnant women (with normal fetal heart activity in echocardiography) and in 5 pregnant women in whom the echocardiography showed fetal arrhythmias. METHOD: The recorded MCG data were treated in order to eliminate the maternal signal and three MCG channels with the best signals were used to emulate a standard electrocardiogram (ECG) recording so that standard MCG analysis could be performed. RESULTS: The results in assessing fetal electrophysiology, demonstrating its potential, are presented here for two fetuses with recorded supraventricular extrasystoles (SVES) and for one with ventricular extrasystoles (VES). Concerning the SVES, the analysis software OMEGA was able to separate three different beat morphologies. The VES could be detected exactly and have been confirmed by postnatal ECG. CONCLUSION: The beat morphology and the beat-to-beat variations allow new insights into the electrophysiology of the fetal heart.

• Calibration of a vector-MEG helmet system.

  Authors: A Pasquarelli, M De Melis, L Marzetti, H P Müller, S N Erné

  Neurology & clinical neurophysiology : NCN. 02/2004; 2004:94.

  The MEG system Argos 500, recently installed at the University of Ulm, is designed for clinical application and routine use, to allow investigation of a large number of patients per day. To reachThe MEG system Argos 500, recently installed at the University of Ulm, is designed for clinical application and routine use, to allow investigation of a large number of patients per day. To reach this goal, the system design meets the requirements of reliability, high field sensitivity, minimal set-up overhead before each measurement and an easy-to-handle user interface.The sensor system consists of a 163 vector-magnetometer array oriented and located in a suitable way to cover the whole head of the patient. Four additional triplets are available as references to build software gradiometers. To use this system at a high performance level, it must be properly calibrated, with these goals: to determine the actual geometry of the sensors array, which can deviate from the design specifications, and to determine the actual sensitivity of each sensor. The calibrating source consists of 31 coils placed at the corners of a head-size dodecahedron. Various details of the calibration system and process are presented here.

• [Analytic methods for functional magnetic resonance data]

  Authors: S N Erné, H P Müller, H Kammrath, R Tomczak, A Wunderlich

  Biomedizinische Technik. Biomedical engineering. 02/1998; 43 Suppl:16-7.

• [Software platform for analysis of electro- and magnetocardiography databanks]

  Authors: S Link, H H Osterhues, S N Erné

  Biomedizinische Technik. Biomedical engineering. 02/1998; 43 Suppl:96-7.

• The study of steady magnetic fields associated with primary and secondary ST shift in ischaemic rabbit hearts.

  Authors: E C Monteiro, S Della Penna, L. Di Donato, S Di Luzio, A Pasquarelli, S N Erné, G L Romani

  Physiological measurement. 09/1997; 18(3):191-200.

  The study of injury potentials associated with DC currents that generate the primary or secondary ST shifts during cardiac ischaemia is possible only through the invasive technique of the DCThe study of injury potentials associated with DC currents that generate the primary or secondary ST shifts during cardiac ischaemia is possible only through the invasive technique of the DC electrogram. Clinical surface ECG recordings are AC coupled and cannot be used. This paper reports the use of non-invasive and unshielded magnetocardiographic measurements to evaluate the DC injury currents associated with ST shifts during coronary artery occlusions in the isolated rabbit heart. The effect on the magnetic ST shift is studied under different ischaemic conditions including regional ischaemia, global ischaemia, global ischaemia following long periods of regional ischaemia, regional ischaemia after repeated episodes of reversible global ischaemia, and bilateral regional ischaemia. Recording of DC magnetic fields allows the characterization of primary and secondary ST displacement for each induced ischaemic condition. Our measurements show that the ST shift starts earlier when inducing ischaemia in hearts previously subjected to ischaemic episodes than in hearts where the ischaemia was produced for the first time.

• A neuromagnetic study of movement-related somatosensory gating in the human brain.

  Authors: R Kristeva-Feige, S Rossi, V Pizzella, L Lopez, S N Erné, J Edrich, P M Rossini

  Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. 02/1996; 107(3):504-14.

  Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated under three different experimental conditions: (1) electrical stimulation of the rightNeuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated under three different experimental conditions: (1) electrical stimulation of the right index finger (task S); (2) voluntary movement of the same finger (M); (3) M+S condition, consisting of voluntary movements of the right index finger triggering the electrical stimulus at the very beginning of the electromyogram. The three conditions were administered in random order every 5-8 s. In addition, the task somatosensory evoked fields (task SEFs) gathered during condition (1) were compared with control SEFs recorded at the beginning of the experiment during rest. In all subjects the overlay of somatosensory stimulation on movement provoked a decrement in brain responsiveness (gating) as determined by the amplitude of gated SEFs. The latter was found as the difference between the neuromagnetic fields during M+S condition (overlaying of movement and sensory stimulation) minus neuromagnetic fields under M condition (M only). The gating effect was found to begin approximately 30 ms after movement onset, and to last for the whole period of the ongoing movement. The theoretical locus of gating was estimated by dipole localisation of the difference between task SEFs and gated SEFS using a moving dipole model. The site of the "early" gating effect (< 40 ms) was found to be more anteriorly located than the "later" (> 40 ms) gating effect. The task SEFs were found to be larger (significant after 30 ms) than the control SEFs elicited under the basal condition. The results are discussed with respect to timing, mechanism (centrifugal and centripetal), locus and selectivity of gating. In addition, the results are discussed with regard to clinical application (measuring attentional deficits in patients with impairments of higher mental functions and measuring gating deficits in patients with disturbed sensorimotor integration.

• Magnetic detection of a single action potential in Chara corallina internodal cells.

  Authors: Z Trontelj, R Zorec, V Jazbinsek, S N Erné

  Biophysical journal. 06/1994; 66(5):1694-6.

  The electrical activity that occurs in plants has not yet been detected magnetically. Magnetic detection of electrical activity in some animal as well as in human cells and organs, on the other hand,The electrical activity that occurs in plants has not yet been detected magnetically. Magnetic detection of electrical activity in some animal as well as in human cells and organs, on the other hand, is an established research method. Our experiments demonstrate the propagation of a single action potential in the internodal cell of the green algae Chara corallina, measured magnetically. The propagation velocity and the intracellular current were determined.

• Magnetocardiography and exercise testing.

  Authors: K Brockmeier, S Comani, S N Erné, S Di Luzio, A Pasquarelli, G L Romani

  Journal of electrocardiology. 05/1994; 27(2):137-42.

  Twenty healthy male subjects (age range, 15-25 years; median, 21 years) underwent magnetocardiography during physical exercise. Significant ST-segment displacements of the magnetic signal were foundTwenty healthy male subjects (age range, 15-25 years; median, 21 years) underwent magnetocardiography during physical exercise. Significant ST-segment displacements of the magnetic signal were found during exercise at a heart rate of 120 beats/min compared to the magnetic signal at rest (P < .001). Since no significant ST-segment changes were found in the electrocardiogram recorded simultaneously with the magnetocardiogram, it is concluded that the magnetocardiogram shows junctional ST-T segment changes earlier than the electrocardiogram.

• Multichannel magnetic recording of P300 activity.

  Authors: L Trahms, S N Erné, R Stehr, E Seibertz, A Friederici

  Physiological measurement. 12/1993; 14 Suppl 4A:A85-9.

  The magnetic correlate of the P300 wave was registered using a seven-channel detector. The spatial variation of the corresponding field suggests the contribution of outer brain layers to the neuralThe magnetic correlate of the P300 wave was registered using a seven-channel detector. The spatial variation of the corresponding field suggests the contribution of outer brain layers to the neural activity of M300.

• Nerve, plexus and spinal cord: possible targets for non-invasive neuromagnetic measurements in man.

  Authors: G Curio, L Reill, J Sandfort, S N Erné, J Scheer, R Stehr, L Trahms

  Physiological measurement. 12/1993; 14 Suppl 4A:A91-4.

  Somatosensory evoked neuromagnetic fields are recorded from peripheral nerves in the upper arm, from plexus brachialis at the ventral and dorsal thorax and from the dorsal horn of the cervical spinalSomatosensory evoked neuromagnetic fields are recorded from peripheral nerves in the upper arm, from plexus brachialis at the ventral and dorsal thorax and from the dorsal horn of the cervical spinal cord ('P13m') at the upper lateral neck. Some perspectives for clinical applications are suggested.

• Non-invasive neuromagnetic monitoring of nerve and muscle injury currents.

  Authors: G Curio, S N Erné, M Burghoff, K D Wolff, A Pilz

  Electroencephalography and clinical neurophysiology. 07/1993; 89(3):154-60.

  Structural damage inflicted on membranes of excitable cells may evoke quasi-DC injury currents driven by the transmembrane resting potential gradient. In contrast to the usually invasiveStructural damage inflicted on membranes of excitable cells may evoke quasi-DC injury currents driven by the transmembrane resting potential gradient. In contrast to the usually invasive electrophysiological approaches, superconducting quantum interference devices (SQUIDs) measure the concomitant weak biomagnetic fields non-invasively as is shown here for acutely excised rat nerves or muscles. Analysis of the field distributions showed slowly decaying equivalent current dipole moments in the nanoampmeter range as generated by microamp nerve injury currents extending intra-axonally over millimeter distances. The geometric and kinetic parameters of this experimental design may allow in vivo recordings in human patients.

• MEG: new techniques.

  Authors: V Pizzella, G L Romani, S N Erné, P M Rossini

  Brain topography. 02/1993; 5(4):351-4.

• Exploratory mapping of evoked neuromagnetic activity from human peripheral nerve, brachial plexus and spinal cord.

  Authors: G Curio, S N Erné, J Sandfort, J Scheer, R Stehr, L Trahms

  Electroencephalography and clinical neurophysiology. 01/1992; 81(6):450-3.

  Upon conventional median nerve stimulation at the wrist early magnetic fields were recorded using a SQUID magnetometer. At the upper arm, mono- and biphasic compound nerve action fields wereUpon conventional median nerve stimulation at the wrist early magnetic fields were recorded using a SQUID magnetometer. At the upper arm, mono- and biphasic compound nerve action fields were detected, depending on the subject's distribution of single fiber conduction velocities. At the upper thorax, brachial plexus fields reversed polarity at the level of Erb's point; their distribution was asymmetric, probably due to volume currents. At the upper lateral neck, fields from proximal plexus, spinal cord (P13m) and the primary somatosensory cortex contralateral to the sensor position were detected. The observed P13m field distribution agrees with the electrophysiological concept of a sagittal segmental dorsal horn generator.

• A 37-channel DC SQUID magnetometer system.

  Authors: D Drung, R Zimmermann, R. Cantor, S N Erné, H Koch, K P Matthies, M. Peters, H J Scheer, D Stollfuss

  Clinical physics and physiological measurement : an official journal of the Hospital Physicists' Association, Deutsche Gesellschaft für Medizinische Physik and the European Federation of Organisations for Medical Physics. 02/1991; 12 Suppl B:21-9.

  A 37-channel DC SQUID magnetometer system has been built for biomagnetic studies. The SQUID loop of each magnetometer serves as the active sensing element, thereby eliminating the need for fluxA 37-channel DC SQUID magnetometer system has been built for biomagnetic studies. The SQUID loop of each magnetometer serves as the active sensing element, thereby eliminating the need for flux coupling circuits. The magnetometers are located approximately 3 cm above the outer dewar bottom. The SQUIDs are directly coupled to highly simplified read-out electronics using only five wires per channel; no helium temperature impedance matching circuits are required. Each channel can be independently inserted into or removed from the dewar. Using a novel electronic noise reduction technique the system white and 1 Hz flux density noise values are typically 5 and 10 fT Hz-1/2, respectively, including the noise contribution of the in-house fabricated dewar and the magnetically shielded room. The two parts of the data-processing system allow independent handling of the acquisition and analysing task. Two example measurements demonstrate the advantage of the electronic noise reduction method.

• Multipole expansions in the representation of current sources.

  Authors: Z Trontelj, V Jazbinsek, S N Erné, L Trahms

  Acta oto-laryngologica. Supplementum. 02/1991; 491:88-92; discussion 93.

  After obtaining the measured magnetic field or its components in the form of an isofield map one has to decide which approximation to use in solving the inverse problem. A single current dipole as anAfter obtaining the measured magnetic field or its components in the form of an isofield map one has to decide which approximation to use in solving the inverse problem. A single current dipole as an equivalent current source is often used. It will be shown when this approximation fails and one possible way to improve the equivalent source description. The expansion of current multipoles is discussed up to the second order. The localization of an equivalent current source in this case is considered. The application of this type of expansion is analysed and discussed.

• Neuromagnetic topography of photoconvulsive response in man.

  Authors: G B Ricci, R M Chapman, S N Erné, L Narici, M Peresson, V Pizzella, G L Romani, G. Torrioli, M Cilli

  Electroencephalography and clinical neurophysiology. 03/1990; 75(2):1-12.

  The neuromagnetic method was applied to the study of photoconvulsive responses. The identification of specific magnetic field distributions over the scalp was achieved by; (a) a stimulation paradigmThe neuromagnetic method was applied to the study of photoconvulsive responses. The identification of specific magnetic field distributions over the scalp was achieved by; (a) a stimulation paradigm consisting of series of trains of flicker stimuli randomly presented to the epileptic patient, after eye closure, to get epileptic responses while avoiding seizures; (b) a novel procedure for data analysis, to select consistent responses. These patterns, when sufficiently stable in time and dipolar in shape, were used for source localization in the usual biomagnetic framework of the equivalent current dipole source representation. The results of this approach suggest that different specific cortical areas are repeatedly and randomly activated, involving mainly the frontal, occipital and temporal areas, often with a hemispheric prevalence.

• Short-latency evoked magnetic fields from the human auditory brainstem.

  Authors: S N Erné, M Hoke

  Advances in neurology. 02/1990; 54:167-76.