Håkon Olav Leira

Navigated bronchoscopy: a technical review.

Background:Navigated bronchoscopy uses virtual 3-dimensional lung model visualizations created from preoperative computed tomography images often in synchronization with the video bronchoscope to guide a tool to peripheral lesions. Navigated bronchoscopy has developed fast since the introduction of virtual bronchoscopy with integrated electromagnetic sensors in the late 1990s. The purposes of the review are to give an overview and update of the technological components of navigated bronchoscopy, an assessment of its clinical usefulness, and a brief assessment of the commercial platforms for navigated bronchoscopy. Methods:We performed a literature search with relevant keywords to navigation and bronchoscopy and iterated on the reference lists of relevant papers, with emphasis on the last 5 years. Results:The paper presents an overview of the components necessary for performing navigated bronchoscopy, assessment of the diagnostic accuracy of different approaches, and an analysis of the commercial systems. We were able to identify 4 commercial platforms and 9 research and development groups with considerable activity in the field. Finally, on the basis of our findings and our own experience, we provide a discussion on navigated bronchoscopy with focus on the next steps of development. Conclusions:The literature review showed that the peripheral diagnostic accuracy has improved using navigated bronchoscopy compared with traditional bronchoscopy. We believe that there is room for improvement in the diagnostic success rate by further refinement of methods, approaches, and tools used in navigated bronchoscopy.

Bronchoscope-induced displacement of lung targets: first in vivo demonstration of effect from wedging maneuver in navigated bronchoscopy.

Background:The accuracy of navigated bronchoscopy relies on a best possible correlation between the preoperative computed tomography images used for planning and the actual tumor position during bronchoscopy. Change in lung structure during the procedure may reduce success rate. The size of the lung changes during breathing, which may be predicted and at least partly compensated by a navigation system. We have studied the effect of the bronchoscopy itself, to see if and how the procedure causes further distortions, which might be harder to predict and compensate. Methods:Using newly developed lung tracking sensors, we have measured the movement of individual lung segments during a bronchoscopy session in pigs. The bronchoscope was moved stepwise forward, ending in a wedge position, where it is often positioned when collecting peripheral biopsy specimens during conventional bronchoscopy. Results:The influence of the bronchoscope on lung segment movement was minimal while positioned in the trachea, main bronchus, or lobe bronchus. However, in the wedge position, it displaced the lung targets and reduced the natural respiratory motion. Conclusions:A bronchoscope placed in a wedge position displaces lung targets and affects their respiratory behavior. As an image navigation system guides the operator towards a position dictated by the preoperative computed tomography, the displacement found in this study may cause the operator to miss the target. This may be part of the explanation for the limited success rates reported in the literature for navigated bronchoscopy.

A novel research platform for electromagnetic navigated bronchoscopy using cone beam CT imaging and an animal model

Abstract Electromagnetic guided bronchoscopy is a new field of research, essential for the development of advanced investigation of the airways and lung tissue. Consecutive problem-based solutions and refinements are urgent requisites to achieve improvements. For that purpose, our intention is to build a complete research platform for electromagnetic guided bronchoscopy. The experimental interventional electromagnetic field tracking system in conjunction with a C-arm cone beam CT unit is presented in this paper. The animal model and the navigation platform performed well and the aims were achieved; the 3D localization of foreign bodies and their navigated and tracked removal, assessment of tracking accuracy that showed a high level of precision, and assessment of image quality. The platform may prove to be a suitable platform for further research and development and a full-fledged electromagnetic guided bronchoscopy navigation system. The inclusion of the C-arm cone beam CT unit in the experimental setup adds a number of new possibilities for diagnostic procedures and accuracy measurements. Among other future challenges that need to be solved are the interaction between the C-arm and the electromagnetic navigation field, as we demonstrate in this feasibility study.

Airway Segmentation and Centerline Extraction from Thoracic CT - Comparison of a New Method to State of the Art Commercialized Methods.

Introduction Our motivation is increased bronchoscopic diagnostic yield and optimized preparation, for navigated bronchoscopy. In navigated bronchoscopy, virtual 3D airway visualization is often used to guide a bronchoscopic tool to peripheral lesions, synchronized with the real time video bronchoscopy. Visualization during navigated bronchoscopy, the segmentation time and methods, differs. Time consumption and logistics are two essential aspects that need to be optimized when integrating such technologies in the interventional room. We compared three different approaches to obtain airway centerlines and surface. Method CT lung dataset of 17 patients were processed in Mimics (Materialize, Leuven, Belgium), which provides a Basic module and a Pulmonology module (beta version) (MPM), OsiriX (Pixmeo, Geneva, Switzerland) and our Tube Segmentation Framework (TSF) method. Both MPM and TSF were evaluated with reference segmentation. Automatic and manual settings allowed us to segment the airways and obtain 3D models as well as the centrelines in all datasets. We compared the different procedures by user interactions such as number of clicks needed to process the data and quantitative measures concerning the quality of the segmentation and centrelines such as total length of the branches, number of branches, number of generations, and volume of the 3D model. Results The TSF method was the most automatic, while the Mimics Pulmonology Module (MPM) and the Mimics Basic Module (MBM) resulted in the highest number of branches. MPM is the software which demands the least number of clicks to process the data. We found that the freely available OsiriX was less accurate compared to the other methods regarding segmentation results. However, the TSF method provided results fastest regarding number of clicks. The MPM was able to find the highest number of branches and generations. On the other hand, the TSF is fully automatic and it provides the user with both segmentation of the airways and the centerlines. Reference segmentation comparison averages and standard deviations for MPM and TSF correspond to literature. Conclusion The TSF is able to segment the airways and extract the centerlines in one single step. The number of branches found is lower for the TSF method than in Mimics. OsiriX demands the highest number of clicks to process the data, the segmentation is often sparse and extracting the centerline requires the use of another software system. Two of the software systems performed satisfactory with respect to be used in preprocessing CT images for navigated bronchoscopy, i.e. the TSF method and the MPM. According to reference segmentation both TSF and MPM are comparable with other segmentation methods. The level of automaticity and the resulting high number of branches plus the fact that both centerline and the surface of the airways were extracted, are requirements we considered particularly important. The in house method has the advantage of being an integrated part of a navigation platform for bronchoscopy, whilst the other methods can be considered preprocessing tools to a navigation system.

Learning endobronchial ultrasound transbronchial needle aspiration – a 6-year experience at a single institution

Endobronchial ultrasound with transbronchial needle aspiration (EBUS‐TBNA) has become an important diagnostic tool for the pulmonologist. Learning this procedure and maintaining technical skills requires continuous practice and evaluation.

Intraoperative localized constrained registration in navigated bronchoscopy

Purpose: One of the major challenges in electromagnetic navigated bronchoscopy is the navigation accuracy. An initial rigid image‐to‐patient registration may not be optimal for the entire lung volume, as the lung tissue anatomy is likely to have shifted since the time of computer tomography (CT) acquisition. The accuracy of the initial rigid registration will also be affected throughout the procedure by breathing, coughing, patient movement and tissue displacements due to pressure from bronchoscopy tools. A method to minimize the negative impact from these factors by updating the registration locally during the procedure is needed and suggested in this paper. Methods: The intraoperative local registration method updates the initial registration by optimization in an area of special interest, for example, close to a biopsy position. The local registration was developed through an adaptation of a previously published registration method used for the initial registration of CT to the patient anatomy. The method was tested in an experimental breathing phantom setup, where respiratory movements were induced by a robotic arm. Deformations were also applied to the phantom to see if the local registration could compensate for these. Results: The local registration was successfully applied in all 15 repetitions, five in each of the three parts of the airway phantom. The mean registration accuracy was improved from 11.8–19.4 mm to 4.0–6.7 mm, varying to some degree in the different segments of the airway model. Conclusions: A local registration method, to update and improve the initial image‐to patient registration during navigated bronchoscopy, was developed. The method was successfully tested in a breathing phantom setup. Further development is needed to make the method more automatic. It must also be verified in human studies.

Learning EBUS‐TBNA – a 6‐year experience at a single institution

Endobronchial ultrasound with transbronchial needle aspiration (EBUS‐TBNA) has become an important diagnostic tool for the pulmonologist. Learning this procedure and maintaining technical skills requires continuous practice and evaluation.

Navigated bronchoscopy with electromagnetic tracking-cone beam computed tomography influence on tracking and registration accuracy.

Current image guidance systems for bronchoscopy are limited to the diagnosis of small tumors and placing fiducials for radiation therapy and surgery. Ideally, a navigation system should be useable for the range of bronchoscopic procedures, including therapy with concurrent radiology imaging for control. As most guidance systems rely on electromagnetic (EM) fields, it is advised to leave the C-arm mounted fluoroscopy unit outside the operating field during navigation. We have assessed the accuracy of our research navigation platform, containing an EM field generator and a C-arm fluoroscopy unit. We have simulated a regular bronchoscopy session with an initial image-to-patient registration procedure, and a subsequent bronchoscopy with the C-arm inside the EM field. The registration accuracy was significantly influenced, introducing an error that may be carried through to the bronchoscopy procedure. During the bronchoscopy session, the C-arm caused a wave drift in the tracking positions and distorted the EM field, causing a translation error up to 22 mm. Even by averaging out the drift, there was a systematic shift in the x, y, and z positions. The errors were more evident in some C-arm positions and seem to be linked more to the electrical current in the fluoroscopy unit than the metallic C-arm itself. A fluoroscopy unit may be used during a navigation procedure, but care must be taken. To enable real-time navigation, the C-arm could be removed sufficiently from the EM tracking field or correction schemes must be implemented to compensate for the distortions.

A new visualization method for navigated bronchoscopy

Abstract Objective: In flexible endoscopy techniques, such as bronchoscopy, there is often a challenge visualizing the path from start to target based on preoperative data and accessing these during the procedure. An example of this is visualizing only the inside of central airways in bronchoscopy. Virtual bronchoscopy (VB) does not meet the pulmonologist’s need to detect, define and sample the frequent targets outside the bronchial wall. Our aim was to develop and study a new visualization technique for navigated bronchoscopy. Material and methods: We extracted the shortest possible path from the top of the trachea to the target along the airway centerline and a corresponding auxiliary route in the opposite lung. A surface structure between the centerlines was developed and displayed. The new technique was tested on non-selective CT data from eight patients using artificial lung targets. Results: The new display technique anchored to centerline curved surface (ACCuSurf) made it easy to detect and interpret anatomical features, targets and neighboring anatomy outside the airways, in all eight patients. Conclusions: ACCuSurf can simplify planning and performing navigated bronchoscopy, meets the challenge of improving orientation and register the direction of the moving endoscope, thus creating an optimal visualization for navigated bronchoscopy.

Pulmonologist evaluation on new CT visualization for guidance to lung lesions during bronchoscopy

Abstract Objective: Endoluminal visualization in virtual and video bronchoscopy lacks information about the surrounding structures, and the traditional 2 D axial, coronal and sagittal CT views can be difficult to interpret. To address this challenge, we previously introduced a novel visualization technique, Anchored to Centerline Curved Surface, for navigated bronchoscopy. The current study compares the ACCuSurf to the standard ACS CT views as planning and guiding tools in a phantom study. Material and methods: Bronchoscope operators navigated in physical phantom guided by virtual realistic image data constructed by fusion of CT dataset of phantom and anonymized patient CT data. We marked four different target positions within the virtual image data and gave 12 pulmonologists the task to navigate, with either ACCuSurf or ACS as guidance, to the corresponding targets in the physical phantom. Results: Using ACCuSurf reduced the planning time and increased the grade of successful navigation significantly compared to ACS. Conclusion: The phantom setup with virtual patient image data proved realistic according to the pulmonologists. ACCuSurf proved superior to ACS regarding planning time and navigation success grading. Improvements on visualisation or display techniques may consequently improve both planning and navigated bronchoscopy and thus contribute to more precise lung diagnostics.