@inproceedings{MetzlerVandenhoutenKroneetal.1998, author = {Metzler, Volker H. and Vandenhouten, Ralf and Krone, J{\"o}rg and Grebe, Reinhard}, title = {Unsupervised image segementation by stochastic reconstruction}, series = {Proceedings of SPIE}, volume = {3338}, booktitle = {Proceedings of SPIE}, issn = {1996-756X}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9329}, year = {1998}, abstract = {To segment complex and versatile image data from different modalities it is almost impossible to achieve satisfying results without the consideration of contextual information. In this approach, image segmentation is regarded as a high- dimensional optimization task, that can be solved by stochastical methods like evolutionary algorithms (EA). Initially, the iterative algorithm is provided with a set of good-quality sample segmentations. An efficient EA-based learning strategy generates a segmentation for a given target image from the provided samples. This two-level process consists of a global image-based optimization whose convergence is enhanced by locally operating pixel-based Boltzmann processes which restrict the search space to reasonable subsets. The stochastic reconstruction extracts the relevant information from the samples in order to adapt it onto the current segmentation problem, which results in a consistent labeling for the target image. The algorithm works unsupervised, because the range of possible labels and their contextual interpretation is provided implicitly by the sample segmentations. To prove the usefulness of the method experimental results based on both, reproducible phantom images and physiological NMR scans are presented. Moreover, an analysis of the basic segmentation and convergence properties is provided.}, language = {en} } @article{VandenhoutenLambertzLanghorstetal.2000, author = {Vandenhouten, Ralf and Lambertz, Manfred and Langhorst, Peter and Grebe, Reinhard}, title = {Nonstationary time-series analysis applied to investigation of brainstem system dynamics}, series = {IEEE Transactions on Biomedical Engineering (T-BME)}, volume = {47}, journal = {IEEE Transactions on Biomedical Engineering (T-BME)}, number = {6}, issn = {1558-2531}, doi = {10.1109/10.844220}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9337}, pages = {729 -- 737}, year = {2000}, abstract = {Previous investigations of the dynamic organization of the lower brainstem and its relation to peripheral and other central nervous systems were predominantly performed by linear methods. These are based on time-averaging algorithms, which merely can be applied to stationary signal intervals. Thus, the current concept of the common brainstem system (CBS) in the reticular formation (RF) of the lower brainstem and basic types of its functional organization have been developed. Here, the authors present experiments where neuronal activities of the RF and the nucleus tractus solitarii (NTS, first relay station of baroreceptor afferents) were recorded together with related parameters of electroencephalogram (EEG), respiration, and cardiovascular system. The RF neurons are part of the CBS, which participates in regulation and coordination of cardiovascular, respiratory, and motor systems, and vigilance. The physiological time series, thus acquired, yield information about the internal dynamic coordination of the participating regulation processes. The major problem in evaluating these data is the nonlinearity and nonstationarity of the signals. The authors used a set of especially designed time resolving methods to evaluate nonlinear dynamic couplings in the interaction between CBS neurons and cardiovascular signals, respiration and the EEG, and between NTS neurons (influenced by baroreceptor afferents) and CBS neurons.}, language = {en} } @article{PerlitzLambertzCotuketal.2004, author = {Perlitz, Volker and Lambertz, Manfred and Cotuk, Birol and Grebe, Reinhard and Vandenhouten, Ralf and Flatten, Guido and Petzold, Ernst Richard and Schmid-Sch{\"o}nbein, Holger and Langhorst, Peter}, title = {Cardiovascular rhythms in the 0.15-Hz band: common origin of identical phenomena in man and dog in the reticular formation of the brain stem?}, series = {Pfl{\"u}gers Archiv: European Journal of Physiology}, volume = {448}, journal = {Pfl{\"u}gers Archiv: European Journal of Physiology}, number = {6}, issn = {1432-2013}, doi = {10.1007/s00424-004-1291-4}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9348}, year = {2004}, abstract = {Selected examples from experiments in humans and dogs with time series of reticular neurons, respiration, arterial blood pressure and cutaneous forehead blood content fluctuations were analysed using multiscaled time-frequency distribution, post-event-scan and pointwise transinformation. We found in both experiments a "0.15-Hz rhythm" exhibiting periods of spindle waves (increasing and decreasing amplitudes), phase synchronized with respiration at 1:2 and 1:1 integer number ratios. At times of wave-epochs and n:m phase synchronization, the 0.15-Hz rhythm appeared in heart rate and arterial blood pressure. As phase synchronization of the 0.15-Hz rhythm with respiration was established at a 1:1 integer number ratio, all cardiovascular-respiratory oscillations were synchronized at 0.15 Hz. Analysis of a canine experiment supplied evidence that the emergence of the 0.15-Hz rhythm and n:m phase synchronization appears to result from a decline in the level of the general activity of the organism associated with a decline in the level of activity of reticular neurons in the lower brainstem network. These findings corroborate the notion of the 0.15-Hz rhythm as a marker of the "trophotropic mode of operation" first introduced by W.R. Hess.}, language = {en} }