Volume 54, Issue 1

In the present work, a simple low noise amplifier system with relatively few components for the recording of peripheral nerve signals via electrodes, such as cuff electrodes, was developed. The amplifier system was developed with the aid of a computer-aided characterization tool, which allowed the characterization of bioelectric signal amplifiers and the identification of system parameters. Three commercially available amplifier systems were investigated with this tool regarding their technical parameters. In addition, peripheral sensory nerve mass signals were analyzed to validate the target specifications for the amplifier to be designed with regard to amplitude and frequency range. An amplifier was designed and developed according to these specifications, characterized in comparison to the commercial amplifiers, and successfully applied in pilot experiments on the sciatic nerve in a rat animal model. Zusammenfassung Innerhalb dieser Arbeit wurde ein einfaches Verstärkersystem aus wenigen Komponenten entwickelt, das sich für die Ableitung von Summensignalen peripherer Nerven eignet. Das Verstärkersystem wurde mit Hilfe eines computergestützten Werkzeuges zur Charakterisierung von Verstärkersystemen entwickelt, welches eine Charakterisierung von Verstärkern für bioelektrische Signale und die Identifikation von Systemparametern ermöglicht. Um einen Überblick über relevante Parameter kommerziell erhältlicher Verstärkersysteme zu erhalten, wurden drei kommerziell erhältliche Systeme untersucht. Zusätzlich wurden Summensignale peripherer Nerven analysiert, um die gewonnen Daten im Hinblick auf Amplitude und Frequenzgehalt in den Verstärkerentwurf einfließen zu lassen. Ein Verstärker wurde entsprechend diesen Spezifikationen entworfen, entwickelt, im Vergleich zu den untersuchten kommerziell erhältlichen Systemen verglichen und abschließend erfolgreich im Kleintiermodell am Ischiasnerv der Ratte in Verbindung mit Cuff-Elektroden eingesetzt.

This contribution introduces a computer- and robot-assisted framework for stereotactic neurosurgery on small animals. Two major elements of this framework are presented in detail: a robotic stereotactic assistant and the software framework for placement of probes into the brain. The latter integrates modules for registration, insertion control, and preoperative path planning. Two options for path planning are addressed: (a) atlas-based planning and (b) image-based planning based on computed tomography data. The framework is tested performing robot-assisted insertion of microelectrodes and acquisition of electrophysiological recordings in vivo . Concepts for data analysis pointing towards a mapping of position and neural structure to functional data are introduced. Results show that the presented framework allows precise small animal stereotaxy and therefore offers new options for brain research. Zusammenfassung Dieser Beitrag stellt eine computer- und robotergestützte Umgebung für stereotaktische Eingriffe am Kleintier vor. Zwei Bestandteile der Umgebung werden im Detail vorgestellt: ein robotischer Assistent und die Softwareumgebung, um Instrumente im Kleintierhirn einzubringen. Letztere integriert dabei Module zur Registrierung, Steuerung des stereotaktischen Assistenten und zur Planung des Eingriffs. Zwei Optionen für die Planung werden vorgestellt: (a) atlasbasierte und (b) bildbasierte Planung auf Basis von Computertomographiedaten. Die Umgebung wird anhand der Einbringung von Mikroelektroden und der Akquise von elektrophysiologischen Ableitungen in vivo getestet. Konzepte zur Evaluierung der Daten im Hinblick auf eine Zuordnung einer räumlichen Position und einer neuronalen Struktur zu funktionellen Daten werden vorgestellt. Die Ergebnisse zeigen, dass die vorgestellte Umgebung präzise stereotaktische Eingriffe am Kleintier und neue Optionen in der Hirnforschung ermöglicht.

To evaluate the possible postoperative outflow from the anterior chamber of the eye after filtration surgery, a mathematical model based on fluid mechanical principles and clinical data is proposed. Two ophthalmic surgical procedures, non-penetrating deep sclerectomy and trabeculectomy, were analyzed. Based on mathematical modeling, the amount of postoperative outflow through the fistula (after trabeculectomy) or membrane (after non-penetrating surgery) as well as the outflow through residual natural drainage pathways were calculated and compared. From our model, the following results were obtained: 1) if trabeculectomy is carried out in an eye with preoperative intraocular pressure (IOP) of 30 mm Hg and postoperative IOP=10 mm Hg, only 10% of aqueous utilizes the natural outflow pathway via the trabecular meshwork, whereas if non-penetrating surgery is carried out in the same eye with postoperative IOP=16 mm Hg, the outflow through the trabecular meshwork amounts to 35%. Thus, non-penetrating surgery provides more aqueous outflow along the natural outflow pathways than trabeculectomy. 2) Generally, the higher the postoperative IOP and/or the lower the preoperative IOP, the higher the amount of aqueous, which will utilize the natural outflow pathways postoperatively. 3) The reestablishment of aqueous production postoperatively in addition to other factors, such as wound healing, may be a reason for IOP increase during the postoperative period.

The aim of this study was to analyze and evaluate the oral mucosa and the surface constitution of dental materials to display the characteristics and the behaviour of dental composites concerning the margin fit. Therefore, the gingiva and composite restorations of 45 patients aged 17–69 years were examined with a new digital confocal laser scanning microscope developed in Rostock. The device works in contact with the surface of the examination region using a water immersion objective and a diode laser with a wavelength of 670 nm. As a result of a PMMA-Cap with a thickness of 0.5 mm, we can create images with exact depth information and of very good quality. The epithelium of the gingiva with its cellular and subcellular structures could be observed up to a depth of 200 μm. Also, papillary crests, blood vessels and even the blood flow were visible. An inflammation of the gingiva could be verified because of the existence of inflammatory cells. The enamel and dental restorations could be observed up to a depth of 80 μm and allowed the evaluation of the margin fit. Confocal laser scanning microscopy seems to be suitable for the non-invasive examination of oral mucosa and dental materials in vivo .

Fetal magnetocardiography (fMCG) has been shown to augment fetal ultrasound evaluation for high-risk conditions, but the clinical utility of fMCG depends on the reliability of the cardiac traces reconstructed. We performed a methodological study to examine the influence of gestational age on the properties of the fetal magnetocardiograms extracted with two methods of signal reconstruction: the template matching technique (TMT), which extracts the maternal components from the signal using only temporal information, and independent component analysis (ICA), which separates the fetal signals by using information on the spatial distribution of the mixed source signals in addition to higher order temporal statistics. Efficiency and accuracy were evaluated in terms of fetal beat detection, signal characteristics, and duration of cardiac time intervals (CTIs) on the averaged traces. ICA outperformed TMT with regard to beat detection and signal-to-noise ratio. The timing of the heartbeats and the duration of the CTIs were essentially the same, whereas some alterations in signal morphology were observed in the ICA traces. We conclude that ICA may be useful in early gestation when the signals are noisy, while TMT may be preferred when accurate beat morphology is required for diagnostic purposes.

Background : Fluid dynamics play an important role in arterial diseases. PC-velocimetry as a magnetic resonance (MR) method is a useful tool for the examination of blood vessels, in particular in haemodynamics and morphology. Due to signal loss caused by turbulent flow, classification of stenoses remains difficult. In the presence of metallic stents, susceptibility effects and RF-artefacts further deteriorate image quality. Materials and methods : Regarding fluid dynamics, stenosis, stent and restenosis (i.e., re-closing of the vessel in areas with stents) have similar properties: the flow close to an obstacle is accelerated and after a specific length, the so-called reattachment length, it redevelops into its original flow profile. Depending on the shape of the obstacle and its reattachment length, a method is developed to classify stenosis using MR-imaging. Enlarged, simplified stenosis models (phantoms) were examined and were also modelled using computational fluid dynamics (CFD). Results : MR- and CFD-measurements show influences of the stenosis shape, especially the diameter. In graphical analysis (streamline and vector plots), a reattachment length of 6.7×step size could be determined under laminar conditions and nonpulsatile flow. Discussion : Stenosis and other narrowing of vessels are classifiable more exactly using PC-velocimetry. From the flow behaviour in the area around the narrowing of the vessel wall, the character of the stenosis can be derived. But more parameters, as bended vessel shapes, pulsated flow, non-Newtonian flow behaviour as well as elastic properties of the vessels need to be incorporated.

During the last two decades micro-computed tomography has become the method of choice for the non-destructive assessment and quantitative morphometry of hard tissues in three dimensions. With the advent of third-generation synchrotron radiation sources, micro-computed tomography in the micrometer range has become feasible and has been employed to analyze local bone tissue properties. However, owing to limitations regarding the tradeoff between object size and spatial resolution, non-destructive conventional global computed tomography of hard tissues, such as bone, remains unachievable in the submicrometer domain so far. Here, we report on a post-processing technique for the assessment of hard tissues using local synchrotron radiation-based computed tomography, which overcomes this experimental limitation. Zusammenfassung Hinsichtlich einer zerstörungsfreien Erfassung und quantitativen Morphometrie harten Gewebes in drei Dimensionen hat sich die Mikro-Computertomographie im Verlaufe der letzten zwei Jahrzehnte zur Methode der Wahl entwickelt. Mit dem Aufkommen von Synchrotronstrahlungsquellen der dritten Generation wurde Mikro-Computertomographie im Mikrometerbereich möglich und angewandt, um lokale Knocheneigenschaften zu untersuchen. Jedoch bleibt – infolge von Beschränkungen hinsichtlich des Kompromisses zwischen Objektgröße und Ortsauflösung – zerstörungsfreie herkömmliche globale Computertomographie für hartes Gewebe wie Knochen im Submikrometerbereich bis heute unerreichbar. An dieser Stelle berichten wir über eine Nachbearbeitungstechnik für die Erfassung harten Gewebes im Submikrometerbereich mittels synchrotronstrahlungsbasierter lokaler Computertomographie, die diese experimentelle Beschränkung überwindet.