The pathogenesis of ventilator-induced lung injury has predominantly been attributed to overdistension or mechanical opening and collapse of alveoli, whereas mechanical strain on the airways is rarely taken into consideration. Here, we hypothesized that mechanical ventilation may cause significant airway distension, which may contribute to the pathological features of ventilator-induced lung injury. C57BL/6J mice were anesthetized and mechanically ventilated at tidal volumes of 6, 10, or 15 ml/kg body wt. Mice were imaged by flat-panel volume computer tomography, and central airways were segmented and rendered in 3D for quantitative assessment of airway distension. Alveolar distension was imaged by intravital microscopy. Functional dead space was analyzed in vivo, and proinflammatory cytokine release was analyzed in isolated, ventilated tracheae. CT scans revealed a reversible, up to 2.5-fold increase in upper airway volume during mechanical ventilation compared with spontaneous breathing. Airway distension was most pronounced in main bronchi, which showed the largest volumes at tidal volumes of 10 ml/kg body wt. Conversely, airway distension in segmental bronchi and functional dead space increased almost linearly, and alveolar distension increased even disproportionately with higher tidal volumes. In isolated tracheae, mechanical ventilation stimulated the release of the early-response cytokines TNF-α and IL-1β. Mechanical ventilation causes a rapid, pronounced, and reversible distension of upper airways in mice that is associated with an increase in functional dead space. Upper airway distension is most pronounced at moderate tidal volumes, whereas higher tidal volumes redistribute preferentially to the alveolar compartment. Airway distension triggers proinflammatory responses and may thus contribute relevantly to ventilator-induced pathologies.

Electromagnetic tracking (EMT) systems are gaining increased attention in various fields of image-guided surgery. One of the main problems related to EMT systems is their vulnerability to distortion due to metallic objects. Several methods have been introduced to evaluate electromagnetic trackers, yet, the data acquisition has to be manually performed in a time consuming procedure, which often leads to a sparse volume coverage. The aim of this work is to present a fully automatic calibration system. It consists of a novel, parallel robotic arm and has the potential to collect a very large number of tracking data while scanning the entire tracking volume of a field generator. To prove the feasibility of our system, we evaluate two electromagnetic field generators (NDI Planar and Tabletop) in an ideal metal-free environment and in a clinical setup. Our proposed calibration robot successfully performed throughout the experiments and examined 1,000 positions in the tracking volume of each field generator (FG). According to the results both FGs are highly accurate in an ideal environment. However, in the examined clinical setup, the Planar FG is strongly distorted by metallic objects. Whereas the Tabletop FG provided very robust and accurate tracking, even if metallic objects where lying directly underneath the FG.

Navigated bronchoscopy provides benefits for endoscopists and patients, but accurate tracking information is needed. We present a novel real-time approach for bronchoscope tracking combining electromagnetic (EM) tracking, airway segmentation, and a continuous model of output. We augment a previously published approach by including segmentation information in the tracking optimization instead of image similarity. Thus, the new approach is feasible in real-time. Since the true bronchoscope trajectory is continuous, the output is modeled using splines and the control points are optimized with respect to displacement from EM tracking measurements and spatial relation to segmented airways. Accuracy of the proposed method and its components is evaluated on a ventilated porcine ex-vivo lung with respect to ground truth data acquired from a human expert. We demonstrate the robustness of the output of the proposed method against added artificial noise in the input data. Smoothness in terms of inter-frame distance is shown to remain below 2 mm, even when up to 5 mm of Gaussian noise are added to the input. The approach is shown to be easily extensible to include other measures like image similarity.

We present a novel approach to motion compensation for bronchoscope navigation where the bronchoscope trajectory is modeled using a spline curve. Initial position and orientation measurements from electromagnetic tracking are refined using the distance of the trajectory from airways segmented in preoperative CT data, and similarity between real and virtual bronchoscopic images. We present an evaluation on a dynamic motion phantom and on a moving ex-vivo porcine lung. Ground truth data is provided by human experts.

BACKGROUND:While electromagnetic tracking (EMT) holds great promise, there are substantiated concerns about interference within the clinical environment. The purpose of this study was to address accuracy and isolate pitfalls for using multiple or adjacent EMT sensors in clinical routine.METHODS:A phantom simulating an EMT-guided puncture of the kidney was used to analyse the effects of multiple sensors in the direct vicinity, common clinical environments and the influence of endo-urological instruments.RESULTS:No relevant interference due to the investigated instruments was discovered. However, there was a great decrease in accuracy in the vicinity of a C-arm's image intensifier, especially affecting the precision of two adjacent sensors.CONCLUSION:Endo-urological instruments can be safely used for multi-sensor EMT-guided procedures. When avoiding the immediate proximity of the surgical table and the image intensifier, there is a comfortable accuracy corridor. Thus, EMT-assistance is promising for a wide range of procedures if basic conditions are met.

Trackingsysteme, basierend auf elektromagnetischer Technologie (EMT), spielen eine immer wichtigere Rolle im Bereich der Image Guided Therapy. Ein Hauptproblem bezüglich EMTs ist jedoch die Anfälligkeit auf metallische Einflüsse. Es wurden bereits verschiedene Methoden vorgestellt, um EMT Systeme diesbezüglich evaluieren zu können. Allerdings sehen diese Systeme immer das manuelle Erstellen des Datensatzes vor. Dies ist im Allgemeinen eine sehr zeitaufwändige Aufgabe und kann nur durch die Verringerung des betrachteten Arbeitsraums beschleunigt werden. In dieser Arbeit wird ein vollautomatisches Kalibrierungssystem für diesen Zweck vorgestellt. Dieses System setzt eine programmierbare Positionierrobotik ein, der ein parallel-kinematisches Konzept zu Grunde liegt. Auf diese Weise wird es ermöglicht sehr viele Daten über den kompletten Arbeitsraum eines EMTs und anderer Trackingsysteme zu sammeln.

Trackingsysteme, basierend auf elektromagnetischer Technologie (EMT), spielen eine immer wichtigere Rolle im Bereich der Image Guided Therapy. Ein Hauptproblem bezüglich EMTs ist jedoch die Anfälligkeit auf metallische Einflüsse. Es wurden bereits verschiedene Methoden vorgestellt, um EMT Systeme diesbezüglich evaluieren zu können. Allerdings sehen diese Systeme immer das manuelle Erstellen des Datensatzes vor. Dies ist im Allgemeinen eine sehr zeitaufwändige Aufgabe und kann nur durch die Verringerung des betrachteten Arbeitsraums beschleunigt werden. In dieser Arbeit wird ein vollautomatisches Kalibrierungssystem für diesen Zweck vorgestellt. Dieses System setzt eine programmierbare Positionierrobotik ein, der ein parallel-kinematisches Konzept zu Grunde liegt. Auf diese Weise wird es ermöglicht sehr viele Daten über den kompletten Arbeitsraum eines EMTs und anderer Trackingsysteme zu sammeln.

Die moderne medizinische Bildgebung ermöglicht immer detailliertere Daten, deren Weiterverarbeitung sich um so zeitaufwendiger gestaltet. Von der Medizin werden jedoch immer schnellere Bildverarbeitungsalgorithmen gefordert. Um diese Forderung zu erfüllen, müssen alle zur Verfügung stehenden Ressourcen genutzt werden. Die Grafikkarte ist eine dieser verfügbaren Ressourcen und kann für die Parallelisierung von Bildverarbeitungsalgorithmen herangezogen werden. Damit die Bildverarbeitungsprozesse unkompliziert auf die Graphikkarte ausgelagert und parallel berechnet werden können, wird in diesem Beitrag eine Hardware-unabhängige Erweiterung des Medical Imaging Interaction Toolkit vorgestellt. Die Ergebnisse zeigen eine wesentliche Beschleunigung der Algorithmen auf der Grafikkarte.

An accurate segmentation of vascular systems is fundamental for many medical applications. Stability against different contrast levels and noise are very important. In this paper we propose an approach for the segmentation of the vascular system of the liver. It is based on the gradient vector flow (GVF) and Frangis vesselness measure. This method avoids multi-scale analysis and related scale space problems. It was evaluated on ten CT data-sets.

Ziel dieser Arbeit ist es eine neuartige Aspirationsnadel mit integriertem elektromagnetischen Sensor vorzustellen und bezüglich ihrer Zuverlässigkeit und Genauigkeit zu evaluieren. Hierfür wurde ein Navigationssystem bestehend aus virtueller Bronchoskopie und Echtzeit Positionsangabe der Nadel entwickelt und in einer beatmeten Schweinelunge untersucht. Es wurden sieben Punktionsversuche während normaler Atembewegung durchgeführt und die Genauigkeit des Navigationssystems für jeden Versuch evaluiert. Den Ergebnissen zufolge ist das vorgestellte Navigationssystem performant und stellt einen vielversprechenden Ansatz dar um die Trefferrate von transbronchialen Biopsien zu erhöhen.

Navigation systems are promising tools for improving efficacy and safety in surgical endoscopy and other minimally invasive techniques. The aim of the current study is to investigate electromagnetic tracking (EMT) for navigated renal access in a porcine model.

Transbronchial needle aspiration (TBNA) is a common procedure to collect tissue samples from the inside of the lung for diagnostic use. However, the main drawback of the procedure is that it has to be blindly performed because the biopsy target region is behind the bronchial wall and hence not within the field of view of the bronchoscope. Thus, the diagnostic yield rate is low. To increase success rate of TBNA biopsy an electromagnetic trackable TBNA needle has been introduced. Nevertheless, the introduced prototype TBNA instrument was evaluated in a rigid rubber phantom without taking respiratory motion into account. The purpose of this study is to present a new TBNA needle where the electromagnetic sensor is directly integrated into a TBNA needle and to access its performance in a regularly ventilated lung. Using our previously presented navigation system, seven TBNA interventions were performed in a porcine lung during regular respiration lung movement; respectively a control computer tomography scan was acquired. We evaluated tracking accuracy of the electromagnetically tracked needle during the entire respiratory cycle for each intervention. The newly developed TBNA needle successfully operated throughout all seven interventions. According to the results, our electromagnetic TBNA tracking system is a promising approach to increase the TBNA biopsy success rate.

Das Verfolgen von tubulären Strukturen aus 3D medizinischen Bilddaten ist essentiell für viele computergestützte medizinische Anwendungen. In diesem Beitrag wird ein Algorithmus zur automatischen Detektion der Verzweigungen für das statistische Tracking der Koronararterien vorgestellt. Basierend auf einem zylindrischen Modell wird ein Maß für die Erkennung der Verzweigungen entwickelt. Dieser Ansatz vermeidet aufwendiges Suchen der Bifurkationen in jedem Iterationsschritt und ist somit effizient. Für die Detektion der Verzweigungen wird das gleiche geometrische Modell wie für das Tracking der Gefäße verwendet. Die erste Evaluation auf 8 CTA-Datensätzen von Koronararterien zeigt, dass 91.7

PURPOSE:Bronchoscopic interventions, such as transbronchial needle aspiration (TBNA), are commonly performed procedures to diagnose and stage lung cancer. However, due to the complex structure of the lung, one of the main challenges is to find the exact position to perform a biopsy and to actually hit the biopsy target (e.g., a lesion). Today, most interventions are accompanied by fluoroscopy to verify the position of the biopsy instrument, which means additional radiation exposure for the patient and the medical staff. Furthermore, the diagnostic yield of TBNA is particularly low for peripheral lesions.METHODS:To overcome these problems the authors developed an image-guided, electromagnetic navigation system for transbronchial interventions. The system provides real time positioning information for the bronchoscope and a transbronchial biopsy instrument with only one preoperatively acquired computed tomography image. A twofold respiratory motion compensation method based on a particle filtering approach allows for guidance through the entire respiratory cycle. In order to evaluate our system, 18 transbronchial interventions were performed in seven ventilated swine lungs using a thorax phantom.RESULTS:All tracked bronchoscope positions were corrected to the inside of the tracheobronchial tree and 80.2% matched the correct bronchus. During regular respiratory motion, the mean overall targeting error for bronchoscope tracking and TBNA needle tracking was with compensation on 10.4 ± 1.7 and 10.8 ± 3.0 mm, compared to 14.4 ± 1.9 and 13.3 ± 2.7 mm with compensation off. The mean fiducial registration error (FRE) was 4.2 ± 1.1 mm.CONCLUSIONS:The navigation system with the proposed respiratory motion compensation method allows for real time guidance during bronchoscopic interventions, and thus could increase the diagnostic yield of transbronchial biopsy.

Vessel tree tracking is an important and challenging task for many medical applications. This paper presents a novel bifurcation detection algorithm for Bayesian tracking of vessel trees. Based on a cylindrical model, we introduce a bifurcation metric that yields minimal values at potential branching points. This approach avoids searching for bifurcations in every iteration of the tracking process (as proposed by prior works) and is therefore computationally more efficient. We use the same geometric model for the bifurcation metric as for the tracking; no specific bifurcation model is needed. In a preliminary evaluation of our method on 8 CTA datasets of coronary arteries, all side branches and 95.8% of the main branches were detected correctly.

Although the field of a navigated bronchoscopy gains increasing attention in the literature, robust guidance in the presence of respiratory motion and electromagnetic noise remains challenging. The robustness of a previously introduced motion compensation approach was increased by taking into account the already traveled trajectory of the instrument within the lung. To evaluate the performance of the method a virtual environment, which accounts for respiratory motion and electromagnetic noise was used. The simulation is based on a deformation field computed from human computed tomography data. According to the results, the proposed method outperforms the original method and is suitable for lung motion compensation during electromagnetically guided interventions.

Kurzfassung. Obwohl viele Forschungsgruppen auf dem Bereich der navigierten Bronchoskopie arbeiten, ist das Problem der stabilen Positionsbestimmung noch nicht gelöst, da es sich als schwierig erweist die Veränderung der Lunge durch die Atembewegung mit zu berücksichtigen. Ein in der Literatur beschriebener Ansatz basiert auf Partikelfilterung. Die Evaluation erfolgte jedoch ohne Berücksichtigung der Atembewegung. Ziel dieser Arbeit ist es, Partikelfilterung ausführlich unter Atembewegung zu evaluieren. Des Weiteren soll untersucht werden inwieweit eine Parametrisierung des Partikelfilters in Abhängigkeit des Bronchusdurchmessers sinnvoll ist. Hierfür wurde eine Simulationsumgebung basierend auf einem aus Human CT-Datensätzen berechneten Deformationsfeld verwendet. Den Ergebnissen zufolge schneidet die Partikelfilterung besser als vorherige Verfahren ab und ist zur Kompensation der Lungenbewegung während einer navigierten Bronchoskopie geeignet.

To analyse the flow in natural geometries of central airways an interdisciplinary project by medical and engineering partners has been created. The work presented summarises necessary developments, preliminary investigations and new insights into the unsteady flow with a focus on numerical fluid mechanics. The objective of the investigations is the analysis and physical understanding of the dynamic flow in central airways, which should later allow to improve artificial ventilation towards a more lung protective approach than actual strategies.

We have developed an image quality theory for reconstruction that we apply to filtered back-projection (FBP) and statistical reconstruction (OSEM) for Single Photon Emission Computed Tomography (SPECT). Quantitative measures of reconstruction performance are given in terms of signal and noise power spectra, SPS and NPS, that we derive from phantom images. This allows evaluating the properties of statistical reconstruction, especially signal recovery, noise, impact of phantom size, and detector resolution. Our analysis shows how noise in reconstructed images is reduced by iterative resolution recovery.