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-1ß. 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.

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.

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.

Multimedia article. Navigated renal access using electromagnetic tracking: an initial experience.

BACKGROUND AND AIM: 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. METHODS: For our proof-of-principle study we modified a recently established porcine ex vivo model. Via a ureteral catheter which was placed into the desired puncture site, a small sensor was introduced and located by EMT. Then, a tracked needle was navigated into the collecting system in a "rendezvous" approach. A total of 90 renal tracts were obtained in six kidneys using EMT, with a maximum of three punctures allowed per intervention. For each puncture, number of attempts to success, final distance to probe, puncture time, and localization were assessed. We compared absolute and relative frequencies using the chi-square test and applied the Mann-Whitney U-test for continuous variables. RESULTS: No major problems were encountered performing the experiment. Access to the collecting system was successfully obtained after a single puncture in 91% (82/90) and within a second attempt in the remaining 9% (8/90). Thus, a 100% success rate was reached after a maximum of two punctures. Location of the calyx did not have a significant effect on success rate (p = 0.637). After a learning phase of 30 punctures, higher success rate (96% versus 83%; p = 0.041) was accomplished within shorter puncture time (14 versus 17 s; p = 0.049) and with higher precision (1.7 versus 2.8 mm; p < 0.001). CONCLUSIONS: With respect to other established techniques, use of EMT seems to decrease the number of attempts and procedural time remarkably. This might contribute to greater safety and efficacy when applied clinically. The presented approach appears to be promising, especially in difficult settings, provided that in vivo data support these initial results.

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).