Ingmar Wegner

The Medical Imaging Interaction Toolkit

Thoroughly designed, open-source toolkits emerge to boost progress in medical imaging. The Insight Toolkit (ITK) provides this for the algorithmic scope of medical imaging, especially for segmentation and registration. But medical imaging algorithms have to be clinically applied to be useful, which additionally requires visualization and interaction. The Visualization Toolkit (VTK) has powerful visualization capabilities, but only low-level support for interaction. In this paper, we present the Medical Imaging Interaction Toolkit (MITK). The goal of MITK is to significantly reduce the effort required to construct specifically tailored, interactive applications for medical image analysis. MITK allows an easy combination of algorithms developed by ITK with visualizations created by VTK and extends these two toolkits with those features, which are outside the scope of both. MITK adds support for complex interactions with multiple states as well as undo-capabilities, a very important prerequisite for convenient user interfaces. Furthermore, MITK facilitates the realization of multiple, different views of the same data (as a multiplanar reconstruction and a 3D rendering) and supports the visualization of 3D+t data, whereas VTK is only designed to create one kind of view of 2D or 3D data. MITK reuses virtually everything from ITK and VTK. Thus, it is not at all a competitor to ITK or VTK, but an extension, which eases the combination of both and adds the features required for interactive, convenient to use medical imaging software. MITK is an open-source project (www.mitk.org).

The Medical Imaging Interaction Toolkit (MITK) - a toolkit facilitating the creation of interactive software by extending VTK and ITK

The aim of the Medical Imaging Interaction Toolkit (MITK) is to facilitate the creation of clinically usable image-based software. Clinically usable software for image-guided procedures and image analysis require a high degree of interaction to verify and, if necessary, correct results from (semi-)automatic algorithms. MITK is a class library basing on and extending the Insight Toolkit (ITK) and the Visualization Toolkit (VTK). ITK provides leading-edge registration and segmentation algorithms and forms the algorithmic basis. VTK has powerful visualization capabilities, but only low-level support for interaction (like picking methods, rotation, movement and scaling of objects). MITK adds support for high level interactions with data like, for example, the interactive construction and modification of data objects. This includes concepts for interactions with multiple states as well as undo-capabilities. Furthermore, VTK is designed to create one kind of view on the data (either one 2D visualization or a 3D visualization). MITK facilitates the realization of multiple, different views on the same data (like multiple, multiplanar reconstructions and a 3D rendering). Hierarchically structured combinations of any number and type of data objects (image, surface, vessels, etc.) are possible. MITK can handle 3D+t data, which are required for several important medical applications, whereas VTK alone supports only 2D and 3D data. The benefit of MITK is that it supplements those features to ITK and VTK that are required for convenient to use, interactive and by that clinically usable image-based software, and that are outside the scope of both. MITK will be made open-source (http://www.mitk.org).

Standardized assessment of new electromagnetic field generators in an interventional radiology setting.

PURPOSE Two of the main challenges associated with electromagnetic (EM) tracking in computer-assisted interventions (CAIs) are (1) the compensation of systematic distance errors arising from the influence of metal near the field generator (FG) or the tracked sensor and (2) the optimized setup of the FG to maximize tracking accuracy in the area of interest. Recently, two new FGs addressing these issues were proposed for the well-established Aurora(®) tracking system [Northern Digital, Inc. (NDI), Waterloo, Canada]: the Tabletop 50-70 FG, a planar transmitter with a built-in shield that compensates for metal distortions emanating from treatment tables, and the prototypical Compact FG 7-10, a mobile generator designed to be attached to mobile imaging devices. The purpose of this paper was to assess the accuracy and precision of these new FGs in an interventional radiology setting. METHODS A standardized assessment protocol, which uses a precisely machined base plate to measure relative error in position and orientation, was applied to the two new FGs as well as to the well-established standard Aurora(®) Planar FG. The experiments were performed in two different settings: a reference laboratory environment and a computed tomography (CT) scanning room. In each setting, the protocol was applied to three different poses of the measurement plate within the tracking volume of the three FGs. RESULTS The two new FGs provided higher precision and accuracy within their respective measurement volumes as well as higher robustness with respect to the CT scanner compared to the established FG. Considering all possible 5 cm distances on the grid, the error of the Planar FG was increased by a factor of 5.94 in the clinical environment (4.4 mm) in comparison to the error in the laboratory environment (0.8 mm). In contrast, the mean values for the two new FGs were all below 1 mm with an increase in the error by factors of only 2.94 (Reference: 0.3 mm; CT: 0.9 mm) and 1.04 (both: 0.5 mm) in the case of the Tabletop FG and the Compact FG, respectively. CONCLUSIONS Due to their high accuracy and robustness, the Tabletop FG and the Compact FG could eliminate the need for compensation of EM field distortions in certain CT-guided interventions.

Particle filtering for respiratory motion compensation during navigated bronchoscopy

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.

Evaluation and extension of a navigation system for bronchoscopy inside human lungs

For exact orientation inside the tracheobronchial tree, clinicians are in urgent need of a navigation system for bronchoscopy. Such an image guided system has the ability to show the current position of a bronchoscope (instrument to inspect the inside of the lung) within the tracheobronchial tree. Thus orientation inside the complex tree structure is improved. Our approach of navigated bronchoscopy considers the problem of using a static image to navigate inside a constantly moving soft tissue. It offers a direct guidance to a preinterventionally defined target inside the bronchial tree to save intervention time spent on searching the right path and to minimize the duration of anesthesia. It is designed to adapt to the breathing cycle of the patient, so no further intervention to minimize the movement of the lung has to stress the patient. We present a newly developed navigation sensor with allows to display a virtual bronchoscopy in real time and we demonstrate an evaluation on the accuracy within a non moving ex vivo lung phantom.

An electromagnetic navigation system for transbronchial interventions with a novel approach to respiratory motion compensation

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.

Mechanical ventilation causes airway distension with proinflammatory sequelae in mice

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.

Pitfalls of electromagnetic tracking in clinical routine using multiple or adjacent sensors

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.

Simplified development of image-guided therapy software with MITK-IGT

Due to rapid developments in the research areas of medical imaging, medical image processing and robotics, computer assistance is no longer restricted to diagnostics and surgical planning but has been expanded to surgical and radiological interventions. From a software engineering point of view, the systems for image-guided therapy (IGT) are highly complex. To address this issue, we presented an open source extension to the well-known Medical Imaging Interaction Toolkit (MITK) for developing IGT systems, called MITK-IGT. The contribution of this paper is two-fold: Firstly, we extended MITK-IGT such that it (1) facilitates the handling of navigation tools, (2) provides reusable graphical user interface (UI) components, and (3) features standardized exception handling. Secondly, we developed a software prototype for computer-assisted needle insertions, using the new features, and tested it with a new Tabletop field generator (FG) for the electromagnetic tracking system NDI Aurora ®. To our knowledge, we are the first to have integrated this new FG into a complete navigation system and have conducted tests under clinical conditions. In conclusion, we enabled simplified development of imageguided therapy software and demonstrated the utilizability of applications developed with MITK-IGT in the clinical workflow.

Tracking und Segmentierung baumförmiger, tubulärer Strukturen mit einem hybriden Verfahren

Bereichswachstumsverfahren weisen bei der Segmentierung von tubularen Strukturen geringe Laufzeiten auf, bergen aber die Gefahr von Ubersegmentierungen in Form von Auslaufen in benachbarte Strukturen in sich. Modellbasierte Verfahren liefern hier robustere Ergebnisse, sind jedoch deutlich rechenintensiver. Dieser Beitrag beschreibt die Entwicklung eines Verfahrens, welches die Zentralgeometrie eines Gefasbaumes per erweitertem Bereichswachstum segmentiert und ein modellbasiertes Verfahren fur die Peripherie anschliest. Die Ergebnisse zeigen eine Verbesserung der Resultate bei akzeptabler Laufzeiterhohung gegenuber Bereichswachstumsverfahren.