Intraoperative endoskopische Registrierung von engen Bohrungen im Mastoid

Eine Stichkanalbohrung durch den Mastoid gewährt einen minimalinvasiven Zugang zur Cochlea, verläuft jedoch nahe wichtiger Nervenbahnen im menschlichen Schädel. Gegenüber dem konventionellen Auffräsen von Hand geht dem Chirurgen dabei die unmittelbare Sicht auf Risikostrukturen im Operationsgebiet verloren - der Verlauf der Bohrtrajektorie ist für ihn nicht zu erkennen. Die wichtigen Geschmacks- und Gesichtsnerven werden daher einem erhöhten Verletzungsrisiko ausgesetzt und das Vertrauen von Chirurgen und Patienten in den Eingriff kann beeinträchtigt werden. Eine intraoperative Kontrolle der Bohrtrajektorie ist deshalb wichtig, um einen sicheren Eingriff zu ermöglichen und Vertrauen zu bewahren. Bekannte Methoden zur intraoperativen Lageprüfung, die auf teuren, gesundheitsschädlichen oder im Operationssaal standardmäßig nicht vorhandenen technischen Einrichtungen basieren, werden in dieser Arbeit durch einen endoskopischen Ansatz ersetzt. Die schwammartige Mastoidknochenstruktur, die ein dreidimensionales Muster bietet, wird als Feld aus Merkmalen für eine Registrierung verwendet. Dafür werden in der minimalinvasiven Bohrung intraoperativ 2D-Endoskopaufnahmen erstellt, die mit präoperativen 3D-CT-Daten verglichen werden. Konkret handelt es sich um eine 2D-3D Bild-zu-Patient-Registrierung durch 2D-2D Bild-zu-Bild-Vergleiche. Einzelne Endoskopaufnahmen werden dazu zu einem Panoramabild zusammengefügt. Vergleichbare 2D-Bilder werden aus den 3D-CT-Daten in vielen verschiedenen Bohrkanallagen extrahiert. Je nach Lage unterscheidet sich die Struktur in den CT-Bildern, sodass über den Vergleich des Musters im Endoskopbild (realer Bohrkanal) zu den CT-Bildern (simulierter Bohrkanal) die größte Übereinstimmung und damit die Lage des Bohrkanals bestimmt werden kann. Für eine Vielfalt an sichtbaren Merkmalen ist ein Großteil der Bohrkanaloberfläche aufzuzeichnen. Verschiedene Endoskoptypen führen, in Kombination mit Stitching-Techniken, zu Panoramaaufnahmen der Mastoidstruktur an der Bohrkanaloberfläche. Kommerzielle Optiken werden auf ihre Eignung hin untersucht und eine miniaturisierte Rundblickoptik entwickelt. Die Stitching-Methoden werden speziell an die endoskopischen Bilddaten der verschiedenen Optiken angepasst. Das Vorgehen zur Registrierung wird sowohl simulativ als auch in aufeinander aufbauenden Mastoidphantomen untersucht. Erreichbare Genauigkeiten werden ausgewertet, während die beteiligten Parameter Suchraumdichte, Bohrkanaldurchmesser, Größe des endoskopierten Bereichs und die Auflösung der CT-Daten variiert werden, um deren Einflüsse zu ermitteln. Endoskopische Aufnahmen in Humanpräparaten zeigen den Transfer in die Praxis und die Integration in den Verlauf einer minimalinvasiven Cochleaimplantation. Eine Registrierung ermöglicht sowohl die Kontrolle der Bohrkanallage als auch eine intraoperative Korrektur und kann so eine vom gewünschten Pfad abweichende Bohrung berichtigen.A branch canal drilling through the mastoid provides a minimally invasive access to the cochlea, but passes nearby important nerve tracts in the human skull. Compared to conventional milling by hand, the surgeon loses the immediate view of high-risk structures in the operating area - the course of the drilling trajectory is not visible to him. The important taste and facial nerves are therefore exposed to an increased risk of injury and the confidence of surgeons and patients in the surgical intervention may be impaired. Intraoperative control of the drilling trajectory is therefore important to enable a safe intervention and to maintain confidence. Known methods for intraoperative pose verification, which are based on expensive, harmful or by default non-existent technical equipment in the operating room, are replaced by an endoscopic approach in this thesis. The sponge-like mastoid bone structure, providing a three-dimensional pattern, is used as a field of features for registration. For this purpose, 2D endoscopic images are recorded intraoperatively in the minimally invasive drill hole and compared to preoperative 3D CT data. In concrete terms, this is an 2D-3D image-to-patient registration using 2D-2D image-to-image comparisons. Individual endoscopic images are combined to form a panoramic image. Comparable 2D images are extracted from the 3D CT data in many different drill hole poses. Depending on the pose, the pattern in the CT images differs, so that by comparing the pattern in the endoscope image (real drill hole) to the CT images (simulated drill hole), the best match and thus the position of the drill hole can be determined. For a variety of visible features, a large portion of the drill hole surface must be recorded. Different types of endoscopes in combination with stitching techniques lead to panoramic images of the mastoid structure at the drill hole surface. Commercial optics are investigated for their suitability and a miniaturized panoramic optics is developed. The stitching methods are specially tailored to the endoscopic image data of the different optics. The procedure for the registration is evaluated in simulations as well as in mastoid phantoms that build on one another. Achievable accuracies are evaluated while the parameters involved -- search space density, drill hole diameter, size of the area recorded via endoscope and the resolution of the CT data -- are varied to determine their influences. Endoscopic recordings in human specimens show the transfer into practice and the integration into the procedure of a minimally invasive cochlear implantation. A registration allows for both, the verification of the drill hole pose as well as an intraoperative correction, and can thus correct a drill hole that deviates from the desired pat

Methods for a fusion of Optical Coherence Tomography and stereo camera image data

This work investigates combination of Optical Coherence Tomography and two cameras, observing a microscopic scene. Stereo vision provides realistic images, but is limited in terms of penetration depth. Optical Coherence Tomography (OCT) enables access to subcutaneous structures, but 3D-OCT volume data do not give the surgeon a familiar view. The extension of the stereo camera setup with OCT imaging combines the benefits of both modalities. In order to provide the surgeon with a convenient integration of OCT into the vision interface, we present an automated image processing analysis of OCT and stereo camera data as well as combined imaging as augmented reality visualization. Therefore, we care about OCT image noise, perform segmentation as well as develop proper registration objects and methods. The registration between stereo camera and OCT results in a Root Mean Square error of 284 μm as average of five measurements. The presented methods are fundamental for fusion of both imaging modalities. Augmented reality is shown as application of the results. Further developments lead to fused visualization of subcutaneous structures, as information of OCT images, into stereo vision. © 2015 SPIE

Fast and automatic depth control of iterative bone ablation based on optical coherence tomography data

Laser surgery is an established clinical procedure in dental applications, soft tissue ablation, and ophthalmology. The presented experimental set-up for closed-loop control of laser bone ablation addresses a feedback system and enables safe ablation towards anatomical structures that usually would have high risk of damage. This study is based on combined working volumes of optical coherence tomography (OCT) and Er:YAG cutting laser. High level of automation in fast image data processing and tissue treatment enables reproducible results and shortens the time in the operating room. For registration of the two coordinate systems a cross-like incision is ablated with the Er:YAG laser and segmented with OCT in three distances. The resulting Er:YAG coordinate system is reconstructed. A parameter list defines multiple sets of laser parameters including discrete and specific ablation rates as ablation model. The control algorithm uses this model to plan corrective laser paths for each set of laser parameters and dynamically adapts the distance of the laser focus. With this iterative control cycle consisting of image processing, path planning, ablation, and moistening of tissue the target geometry and desired depth are approximated until no further corrective laser paths can be set. The achieved depth stays within the tolerances of the parameter set with the smallest ablation rate. Specimen trials with fresh porcine bone have been conducted to prove the functionality of the developed concept. Flat bottom surfaces and sharp edges of the outline without visual signs of thermal damage verify the feasibility of automated, OCT controlled laser bone ablation with minimal process time. © SPIE-OSA

EUNIS Habitat Classification: Expert system, characteristic species combinations and distribution maps of European habitats

Aim: The EUNIS Habitat Classification is a widely used reference framework for European habitat types (habitats), but it lacks formal definitions of individual habitats that would enable their unequivocal identification. Our goal was to develop a tool for assigning vegetation‐plot records to the habitats of the EUNIS system, use it to classify a European vegetation‐plot database, and compile statistically‐derived characteristic species combinations and distribution maps for these habitats. Location: Europe. Methods: We developed the classification expert system EUNIS‐ESy, which contains definitions of individual EUNIS habitats based on their species composition and geographic location. Each habitat was formally defined as a formula in a computer language combining algebraic and set‐theoretic concepts with formal logical operators. We applied this expert system to classify 1,261,373 vegetation plots from the European Vegetation Archive (EVA) and other databases. Then we determined diagnostic, constant and dominant species for each habitat by calculating species‐to‐habitat fidelity and constancy (occurrence frequency) in the classified data set. Finally, we mapped the plot locations for each habitat. Results: Formal definitions were developed for 199 habitats at Level 3 of the EUNIS hierarchy, including 25 coastal, 18 wetland, 55 grassland, 43 shrubland, 46 forest and 12 man‐made habitats. The expert system classified 1,125,121 vegetation plots to these habitat groups and 73,188 to other habitats, while 63,064 plots remained unclassified or were classified to more than one habitat. Data on each habitat were summarized in factsheets containing habitat description, distribution map, corresponding syntaxa and characteristic species combination. Conclusions: EUNIS habitats were characterized for the first time in terms of their species composition and distribution, based on a classification of a European database of vegetation plots using the newly developed electronic expert system EUNIS‐ESy. The data provided and the expert system have considerable potential for future use in European nature conservation planning, monitoring and assessment

Traits of dominant plant species drive normalized difference vegetation index in grasslands globally

Theoretical, experimental and observational studies have shown that biodiversity–ecosystem functioning (BEF) relationships are influenced by functional community structure through two mutually non-exclusive mechanisms: (1) the dominance effect (which relates to the traits of the dominant species); and (2) the niche partitioning effect [which relates to functional diversity (FD)]. Although both mechanisms have been studied in plant communities and experiments at small spatial extents, it remains unclear whether evidence from small-extent case studies translates into a generalizable macroecological pattern. Here, we evaluate dominance and niche partitioning effects simultaneously in grassland systems world-wide. Location: Two thousand nine hundred and forty-one grassland plots globally. Time period: 2000–2014. Major taxa studied: Vascular plants. Methods: We obtained plot-based data on functional community structure from the global vegetation plot database “sPlot”, which combines species composition with plant trait data from the “TRY” database. We used data on the community-weighted mean (CWM) and FD for 18 ecologically relevant plant traits. As an indicator of primary productivity, we extracted the satellite-derived normalized difference vegetation index (NDVI) from MODIS. Using generalized additive models and deviation partitioning, we estimated the contributions of trait CWM and FD to the variation in annual maximum NDVI, while controlling for climatic variables and spatial structure. Results: Grassland communities dominated by relatively tall species with acquisitive traits had higher NDVI values, suggesting the prevalence of dominance effects for BEF relationships. We found no support for niche partitioning for the functional traits analysed, because NDVI remained unaffected by FD. Most of the predictive power of traits was shared by climatic predictors and spatial coordinates. This highlights the importance of community assembly processes for BEF relationships in natural communities. Main conclusions: Our analysis provides empirical evidence that plant functional community structure and global patterns in primary productivity are linked through the resource economics and size traits of the dominant species. This is an important test of the hypotheses underlying BEF relationships at the global scale