Quantitative assessment of optic nerve head pallor. - In: Physiological measurement, ISSN 1361-6579, Bd. 29 (2008), 4, S. 451-457
http://dx.doi.org/10.1088/0967-3334/29/4/003
Strahlenschutzmaßnahmen zur Verringerung der Inkorporation beim Personal während der Radiojodtherapie. - In: Strahlenschutz-Praxis, ISSN 0947-434X, Bd. 14 (2008), 2, S. 44-51
Computertomographie und Strahlenrisiko. - In: Medizintechnik, ISSN 0344-9416, Bd. 128 (2008), 2, S. 43-44
Magnetic nanoparticle imaging by means of minimum norm estimates from remanence measurements. - In: Medical & biological engineering & computing, ISSN 1741-0444, Bd. 46 (2008), 12, S. 1177-1185
http://dx.doi.org/10.1007/s11517-008-0404-1
An experimental study on the effect of the anisotropic regions in a realistically shaped torso phantom. - In: Annals of biomedical engineering, ISSN 1573-9686, Bd. 36 (2008), 11, S. 1836-1843
http://dx.doi.org/10.1007/s10439-008-9551-7
Nonlinear interactions of high-frequency oscillations in the human somatosensory system. - In: Clinical neurophysiology, ISSN 1872-8952, Bd. 119 (2008), 11, S. 2647-2657
Objective: The source of somatosensory evoked high-frequency activity at about 600 Hz is still not completely clear. Hence, we aimed to study the influence of double stimulation on the human somatosensory system by analyzing both the low-frequency activity and the high-frequency oscillations (HFOs) at about 600 Hz. Methods: We used median nerve stimulation at seven interstimuli intervals (ISIs) with a high time resolution between 2.4 and 4.8 ms to investigate the N15, N20 and superimposed HFOs. Simultaneously, the electroencephalogram and the magnetoencephalogram of 12 healthy participants were recorded. Subsequently, the source analysis of precortical and cortical dipoles was performed. Results: The difference computations of precortical dipole activation curves showed in both the low- and high-frequency range a correlation between the ISI and the latency of the second stimulus response. The cortical low-frequency response showed a similar behavior. Contrarily, in the second response of cortical HFOs this latency shift could not be confirmed. We found amplitude fluctuations that were dependent on the ISI in the low-frequency activity and the HFOs. These nonlinear interactions occurred at ISIs, which differ by one full HFO period (1.6 ms). Conclusions: Low-frequency activity and HFOs originate from different generators. Precortical and cortical HFOs are independently generated. The amplitude fluctuations dependent on ISI indicate nonlinear interference between successive stimuli. Significance: Information processing in human somatosensory system includes nonlinearity.
http://dx.doi.org/10.1016/j.clinph.2008.08.011
Influence of anisotropic compartments on magnetic field and electric potential distributions generated by artificial current dipoles inside a torso phantom. - In: Physics in medicine and biology, ISSN 1361-6560, Bd. 53 (2008), 1, S. 245-254
The purpose of this study is the analysis of the influence of anisotropic conductivity on magnetic fields and electric potentials by means of phantom measurements. An artificial rotating current dipole was placed in the middle of an anisotropic skein arrangement in a torso phantom filled with saline solution. The signal strength and the change of the shape of potential and field patterns due to anisotropic volume conduction were investigated. Different directions of the dipole were compared to corresponding orientations of measured fields and potentials (angle difference). For electric and magnetic data, the angle difference between observed signal orientations and true dipole orientations continuously increased with the angle between dipole and anisotropy (up to 80˚) and then decreased back to zero at their orthogonal orientation. Both signal strengths decreased about 10% with an increasing angle between dipole and anisotropy. While the magnetic field showed a generally stronger shape change, the changed shape of the electric potential showed similarity to an extended source. Our phantom study demonstrated that anisotropic compartments influence directions, amplitudes and shapes of potentials and fields at different degrees. We concluded that anisotropic structures should be considered in volume conductor modelling, when source orientation, extension and strength are of interest.
http://dx.doi.org/10.1088/0031-9155/53/1/017
Is the pain in chronic pancreatitis of neuropathic origin? : support from EEG studies during experimental pain. - In: World journal of gastroenterology, ISSN 2219-2840, Bd. 14 (2008), 25, S. 4020-4027
AIM: To prove the hypothesis that patients with chronic pancreatitis would show increased theta activity during painful visceral stimulation. METHODS: Eight patients and 12 healthy controls underwent an experiment where the esophagus was electrically stimulated at the pain threshold using a nasal endoscope. The electroencephalogram (EEG) was recorded from 64 surface electrodes and "topographic matching pursuit" was used to extract the EEG information in the early brain activation after stimulation. RESULTS: A major difference between controls and patients were seen in delta and theta bands, whereas there were only minor differences in other frequency bands. In the theta band, the patients showed higher activity than controls persisting throughout the 450 ms of analysis with synchronous brain activation between the channels. The main theta components oscillated with 4.4 Hz in the patients and 5.5 Hz in the controls. The energy in the delta (0.5-3.5 Hz) band was higher in the controls, whereas the patients only showed scattered activity in this band. CONCLUSION: The differences in the theta band indicate that neuropathic pain mechanisms are involved in chronic pancreatitis. This has important implications for the understanding and treatment of pain in these patients, which should be directed against drugs with effects on neuropathic pain disorders.
http://dx.doi.org/10.3748/wjg.14.4020
Boundary element computations in the forward and inverse problems of electrocardiography: comparison of collocation and Galerkin weightings. - In: IEEE transactions on biomedical engineering, ISSN 1558-2531, Bd. 55 (2008), 9, S. 2124-2133
http://dx.doi.org/10.1109/TBME.2008.923913
Tabu search optimization of magnetic sensor systems for magnetocardiography. - In: IEEE transactions on magnetics, ISSN 1941-0069, Bd. 44 (2008), 6, S. 1442-1445
http://dx.doi.org/10.1109/TMAG.2007.915911