S. N. Erné’s research while affiliated with Universitätsklinikum Jena and other places

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Publications (120)


Cardiac signal extraction in patients with Implantable Cardioverter Defibrillators
  • Article

August 2009

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42 Reads

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3 Citations

Medical Engineering & Physics

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S.N. Erne

According to the guidelines the indication for Implantable Cardioverter Defibrillator (ICD) implantation is based on the ejection fraction. However, only a fraction of patients with implanted ICD shows live threatening arrhythmic events followed by adequate shocks. For this reason, further research is needed to find a more sensitive risk stratificator for patients prone to ventricular tachycardia or fibrillation. Unfortunately, standard prospective studies are time consuming. An alternative approach is to perform retrospective studies on patients with already implanted ICDs. So far, an implanted ICD is an exclusion criterion for Magnetic Field Imaging (MFI) studies. To overcome this problem several Blind Source Separation (BSS) algorithms have been tested to find out whether it is possible to separate the disturbances from the cardiac signals, in spite of the extreme difference in amplitude. Not all the methods are able to separate cardiac signal and disturbances. Temporal Decorrelation source Separation (TDSEP) is found to be superior both from a separation and performing point of view. For the first time it is possible to extract cardiac signals from measurements disturbed by an ICD, offering the possibility for a QRS-fragmentation analysis in patients with already implanted ICDs.


Discussion of Current Distribution of Exercise 3D MCG Using an Inhomogeneous Human Volume Conductor

May 2008

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14 Reads

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1 Citation

Journal of the Magnetics Society of Japan

In this paper we present the analysis of 3D measurements of the magnetocardiogram by means of current source reconstruction. The data considered are rest and exercise stress data of test subjects. The source model used to describe the heart activation is a distributed source model, which allows to follow how the heart activation spreads over the myocardium. We developed a four compartments human torso model including the heart cavity and two lungs. Different values of the compartment conductivities are used to study the effect of the inhomogeneities on the reconstructed sources. The comparison between rest and stress data is done by means of correlations coefficients that indicate how close the reconstructed sources are in terms of dipoles moments, since in the source model considered the dipoles positions are fixed and depend on the source space model geometry. The same analyses are repeated using the 3D magnetic data and only the normal component, to investigate the additional information given by the tangential components. The results show that the torso and heart conductivities have a stronger influence than the one of the lungs, and that the 3D data are less sensitive to the changes of the compartment conductivities.



Stress testing in coronary artery disease by Magnetic Field Imaging: a 3D current distribution model
  • Article
  • Full-text available

August 2007

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72 Reads

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5 Citations

Anadolu kardiyoloji dergisi: AKD = the Anatolian journal of cardiology

Magnetic field imaging (MFI) combines depolarization and repolarization registration of the cardiac electromagnetic field with a 3D current distribution model. An interesting application for MFI is the possibility to detect myocardial ischemia under stress. Using a new reconstruction technique, it is possible to generate a pseudo-current distribution on the epicardial surface: the comparison of the time evolution of such current distributions at rest and under stress shows difference in coronary artery disease (CAD). The model works with a realistic epicardial surface generate on the basis of computerised tomography or magnetic resonance tomography data or with a standardized ellipsoidal model. To take into account the vectorial character of the epicardial current distribution, the current flow in the epicardial surface element is represented in the graphic display by a cone. Thus indicating the direction of current flow the height of the cone represents the current intensity. As an example of the method, data of pharmacological stress MFI on a CAD patient will be presented. The newly developed algorithm operates in different segments of the electromagnetic heart beat. The indicated myocardial area strongly correlated to invasive coronary angiography results. In such a situation the advantage provided by the "friendly" ellipsoidal surface on the numerical solution of the inverse problem seems to overcome the advantage of a realistic heart model. We conclude MFI is a promising procedure for a non-invasive stress testing as well as screening method as for localization of myocardial ischemia.

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RT-matcher of data with different heart beats rates

June 2007

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17 Reads

International Congress Series

The field distribution and the time evolution of the heart beat change with heart frequency. The RR interval is subject to change in patients that undergo stress exercise testing. To compare field distribution before and after stress the signals need to be reproduced on the same time scale, at least in the segment of interest. In order to achieve this aim, we apply a “matcher” operator in the time interval between R-end and T-max, obtaining rescaled signals that can be directly compared. In this study the RT-matcher was applied to magnetocardiographic (MCG) data, but it could be used in electrocardiographic (ECG) data, as well. The RT-matcher has shown to be a useful pre-processing step for the comparison of data with different ST segment lengths.


Comparison of BSS algorithms in SMCG data

June 2007

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16 Reads

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1 Citation

International Congress Series

The field distribution generated by the heart and detected by magnetocardiography (MCG) shows strong effects, comparing the field distribution at rest and under stress. To study the possible clinical application, it is convenient to avoid pharmacological stress and perform Stress MCG (SMCG) using conventional physical stress with an ergometer. Unfortunately the subject movements and the ergometer residual artefacts produce extra noise and disturbances which should be eliminated. For this purpose 4 different Blind Source Separation (BSS) algorithms were tested: fastICA, TDSEP, JADE and SHIBBS. The algorithms were applied on 12 SMCG data sets for the task to de-noise them. The correlation between odd and even beats (using the simultaneously recorded electrocardiogram (ECG)) and the known spectral content were considered for automatically detecting noise and disturbances. All the methods were able to detect the ergometer noise. The best results were achieved by TDSEP, both in computation time and in goodness of separation. This work shows that, with BSS, the extraction of heart signals from ergometer SMCG data is becoming feasible.


Noise reduction in CHD patients by means of BSS

June 2007

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6 Reads

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3 Citations

International Congress Series

In 1992, Brockmeier et al. showed the difference in magnetocardiography (MCG)-detected field distribution generated by the heart at rest and under stress. Unfortunately, routinely recorded magnetocardiograms (MCGs) are corrupted by different types of artifacts, especially during stress. This work addressed the problem of optimizing artifacts removing and improving the signal to noise ratio (SNR) in patients with coronary heart disease (CHD) under pharmacological stress MCG (PSMCG) using a technique of Blind Source Separation (BSS) called TDSEP. Techniques based on simple statistical parameters were proposed to identify the cardiac related component among the unmixed data. The presented results showed that BSS could detect and remove a variety of noise and artifact sources in PSMCG, allowing the use in clinical applications.


Epicardial current source distribution with an ellipsoid model

June 2007

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12 Reads

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1 Citation

International Congress Series

In the study of the inverse problem in magnetocardiography, distributed source models provide a general description of the current sources in the heart during activation and repolarization. To give a quick survey of the dynamics of the estimated current flow during the heart's cycle, an ellipsoidal model, which can be considered as an approximation of the heart's shape in case the individualized source space models (MRI or CT) are not available for a patient, was used. The axis of the ellipsoid has been oriented according to clinical findings. This rough definition of the source space has the advantage of a smooth surface and as a reasonable approximation of the real heart's shape.


SQUID sensor with additional compensation module for operation in an AC applied field

July 2006

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18 Reads

Journal of Physics Conference Series

A possible implementation of an in-vivo SQUID susceptometer able to estimate the liver iron concentration of humans uses a low frequency applied field together with a lock-in detection. The room-temperature magnetising coils and the detection coils are designed to minimize their mutual coupling. Nevertheless, deviation from ideal behaviour causes a residual signal in the detection coil, with an amplitude significantly larger than the patient's. In addition low frequency noise is added by any relative displacement of the magnetising and sensing coils. Thus, we designed a SQUID sensor using a compact compensating module to be used in a multichannel SQUID susceptometer. The sensor consists of two second order axial gradiometers, wounded one inside the other on the same support. The sensing channel is larger than the compensation channel which is only sensitive to the residual signal. Each gradiometer is coupled to a dc SQUID with parallel washer configuration. The output of the compensation channel is A/D converted and is processed by an adaptive algorithm running on a real time unit. The compensation signal is coupled to the sensing channel by an additional feedback loop. The performances of a prototype module will be presented.


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

July 2006

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90 Reads

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27 Citations

Medical & Biological Engineering & Computing

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.


Citations (53)


... In addition, MEG waveforms were noted to precede the corresponding EEG spike activity in most patients' recordings. Ricci et al. studied the 3 Hz spike-wave using single-channel MEG with a phantom brain model and showed cortical activity was scattered bilaterally, mainly over frontal and temporal regions, often with more involvement over one hemisphere, while bilateral synchronous activity seemed to have originated from a deeper structure (107,108). The study was the first to demonstrate evidence of primary cortical involvement in GSWDs in generalized epilepsy using neuromagnetic cortical source localization. ...

Reference:

Contributions of Magnetoencephalography to Understanding Mechanisms of Generalized Epilepsies: Blurring the Boundary Between Focal and Generalized Epilepsies?
Template Analysis on Interictal Neuromagnetic Data from Cases of Focal and Generalized Epilepsy
  • Citing Chapter
  • January 1989

... Early reports investigated inflammation of the myocardium associated with myocarditis and heart transplant rejection with MCG (47)(48)(49). In our recent work, we have shown that diseases such as inflammatory cardiomyopathy and amyloidosis can be detected with MCG (17). ...

Magnetocardiographic diagnosis of graft rejection after heart transplantation

... As shown in Fig. 9, the reconstructed current source around C5 ran in the dorsal to ventral direction and its waveform was very similar to the SEPs recorded with a C5S-AC montage. This result is consistent with the results of a previous study on magnetic recording using a single-channel SQUID system by Curio et al. (1989). ...

Short-Latency Somatosensory Evoked Magnetic Fields Recorded over the Brachial Plexus and Cervical Spine in Man
  • Citing Chapter
  • January 1989

... In clinical applications, magnetocardiography has been mainly used for localization of cardiac arrhythmias [23][24][25][26][27] and for early diagnosis of myocardial ischemia. 28,29 Furthermore, early reports in literature have described its potential in detecting heart transplant rejection, suggesting a potential role in detecting myocardial inflammation. ...

Magnetocardiography in Patients with Cardiomyopathy and Operated Congenital Heart Disease

... During the last years several algorithms and analysis procedures were developed for the evaluation of biomagnetic and bioelectric data. To obtain clinical validation, an Magnetocardiography (MCG) system especially designed for clinical studies on large patient number has been installed in Ulm (Figs. 1-3) [1]. Fig. 1: Global view of the facility. ...

Magnetocardiographic Technology: State of the Art
  • Citing Chapter
  • January 2000

... Magnetocardiography (MCG) is a noninvasive technique that monitors the spontaneous activity of the heart by measuring the weak magnetic field variations associated with the primary ionic currents flowing through the myocardium during the cardiac cycle (Siltanen 1989). Since superconducting multi-channel systems have become available, the cardiac magnetic field can be recorded with great sensitivity simultaneously from a number of positions over the chest (Pasquarelli andDi Luzio1993, Tavarozzi et al 2002a), hence allowing accurate field mapping during the cardiac cycle, useful for several clinical applications, particularly for arrhythmias (Weismuller et al 1992, Brockmeier et al 1997, Muller et al 1999, Hren et al 1999, Kandori et al 2001, Comani et al 2001, 2004a, Tavarozzi et al 2002b. ...

Magnetic map analysis during ventricular repolarization to differentiate between normal subjects and patients affected by cardiac hypertrophy
  • Citing Article
  • January 2001

Physica Medica

... where G mult is built by concatenating G dip and G quad into a p  12 multipole gain matrix and m mult is the 12  1 multipole moment vector obtained by concatenating the elements of q and Q ˜ into a single column vector. Note that the general multipole model presented here differs from the multipole solutions derived for the inverse problem in magnetocardiography (e.g. Ernè et al., 1988; Karp et al., 1980; Katila, 1983; Nenonen et al., 1991) in that the latter are based on expansions of the normal (or radial) component of the magnetic field only and hence the volume currents do not need to be taken into account. In contrast, if the multipolar approach is to be used on neural data recorded by a realistic whole-head MEG sensor configuration, an expansion of the full magnetic vector field in terms of the primary current sources is needed (see Jerbi et al., 2002a,b for details). ...

Current multipoles as sources of biomagnetic fields
  • Citing Article
  • January 1988

... When the isofield maps during the T wave were analyzed with eigenvectors for data reduction, the symptomatic patients displayed more disparity in their maps, suggesting more heterogeneous repolarization. The relative smoothness score has also shown lower values in this patient group (Brockmeier et al. 1989). ...

Magnetocardiography in Patients with the Long QT-Syndrome

... We used Fig. 6 in their publication to estimate the actual strength of the B field in each preparation. Jazbinšek et al. (1989) carried out a similar calculation for higher poles. ...

Influence of the Finite Pickup Coil Size on the Localization of Current Sources with Quadrupolar Components
  • Citing Chapter
  • January 1989

... In addition, the stability of EGG recordings is affected by a variety of artefacts, such as the overlap of the electrical activities of the colon and stomach in cutaneous EGG recordings (Amaris et al 2002). In response to many of these concerns, two techniques dubbed magnetogastrography (MGG) and magnetoenterography (MENG) were pioneered in the late 1980s and early 1990s as non-invasive alternatives to EGG, the first one by Comani et al in 1989 (DiLuzio et al 1989, Comani et al 1996) and the second one by Staton, Richards and Bradshaw in 1993 (Staton et al 1993, Golzarian et al 1994, Bradshaw 1995). In 1997, Bradshaw et al showed that a high degree of correlation exists between the ECA frequency values determined using EGG and MGG (Bradshaw et al 1997). ...

Non-invasive detection of gastric myoelectrical activity: Comparison between results of magnetogastrography and electrogastrography in normal subjects
  • Citing Article
  • January 1996

Physica Medica