Kwong Yung

Computer-assisted trajectory planning for percutaneous needle insertions

PURPOSE Computed tomography (CT) guided minimally invasive interventions such as biopsies or ablation therapies often involve insertion of a needle-shaped instrument into the target organ (e.g., the liver). Today, these interventions still require manual planning of a suitable trajectory to the target (e.g., the tumor) based on the slice data provided by the imaging modality. However, taking into account the critical structures and other parameters crucial to the success of the intervention--such as instrument shape and penetration angle--is challenging and requires a lot of experience. METHODS To overcome these problems, we present a system for the automatic or semiautomatic planning of optimal trajectories to a target, based on 3D reconstructions of all relevant structures. The system determines possible insertion zones based on so-called hard constraints and rates the quality of these zones by so-called soft constraints. The concept of pareto optimality is utilized to allow for a weight-independent proposal of insertion trajectories. In order to demonstrate the benefits of our method, automatic trajectory planning was applied retrospectively to n = 10 data sets from interventions in which complications occurred. RESULTS The efficient (graphics processing unit-based) implementation of the constraints results in a mean overall planning time of about 9 s. The examined trajectories, originally chosen by the physician, have been rated as follows: in six cases, the insertion point was labeled invalid by the planning system. For two cases, the system would have proposed points with a better rating according to the soft constraints. For the remaining two cases the system would have indicated poor rating with respect to one of the soft constraints. The paths proposed by our system were rated feasible and qualitatively good by experienced interventional radiologists. CONCLUSIONS The proposed computer-assisted trajectory planning system is able to detect unsafe and propose safe insertion trajectories and may especially be helpful for interventional radiologist at the beginning or during their interventional training.

Towards mobile augmented reality for on-patient visualization of medical images

Despite considerable technical and algorithmic developments related to the fields of medical image acquisition and processing in the past decade, the devices used for visualization of medical images have undergone rather minor changes. As anatomical information is typically shown on monitors provided by a radiological work station, the physician has to mentally transfer internal structures shown on the screen to the patient. In this work, we present a new approach to on-patient visualization of 3D medical images, which combines the concept of augmented reality (AR) with an intuitive interaction scheme. The method requires mounting a Time-of-Flight (ToF) camera to a portable display (e.g., a tablet PC). During the visualization process, the pose of the camera and thus the viewing direction of the user is continuously determined with a surface matching algorithm. By moving the device along the body of the patient, the physician gets the impression of being able to look directly into the human body. The concept can be used for intervention planning, anatomy teaching and various other applications that require intuitive visualization of 3D data.

3D surface reconstruction for laparoscopic computer-assisted interventions: comparison of state-of-the-art methods

One of the main challenges related to computer-assisted laparoscopic surgery is the accurate registration of pre-operative planning images with patients anatomy. One popular approach for achieving this involves intraoperative 3D reconstruction of the target organs surface with methods based on multiple view geometry. The latter, however, require robust and fast algorithms for establishing correspondences between multiple images of the same scene. Recently, the first endoscope based on Time-of-Flight (ToF) camera technique was introduced. It generates dense range images with high update rates by continuously measuring the run-time of intensity modulated light. While this approach yielded promising results in initial experiments, the endoscopic ToF camera has not yet been evaluated in the context of related work. The aim of this paper was therefore to compare its performance with different state-of-the-art surface reconstruction methods on identical objects. For this purpose, surface data from a set of porcine organs as well as organ phantoms was acquired with four different cameras: a novel Time-of-Flight (ToF) endoscope, a standard ToF camera, a stereoscope, and a High Definition Television (HDTV) endoscope. The resulting reconstructed partial organ surfaces were then compared to corresponding ground truth shapes extracted from computed tomography (CT) data using a set of local and global distance metrics. The evaluation suggests that the ToF technique has high potential as means for intraoperative endoscopic surface registration.

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.

MITK-ToF—Range data within MITK

PurposeThe time-of-flight (ToF) technique is an emerging technique for rapidly acquiring distance information and is becoming increasingly popular for intra-operative surface acquisition. Using the ToF technique as an intra-operative imaging modality requires seamless integration into the clinical workflow. We thus aim to integrate ToF support in an existing framework for medical image processing.MethodsMITK-ToF was implemented as an extension of the open-source C++ Medical Imaging Interaction Toolkit (MITK) and provides the basic functionality needed for rapid prototyping and development of image-guided therapy (IGT) applications that utilize range data for intra-operative surface acquisition. This framework was designed with a module-based architecture separating the hardware-dependent image acquisition task from the processing of the range data.ResultsThe first version of MITK-ToF has been released as an open-source toolkit and supports several ToF cameras and basic processing algorithms. The toolkit, a sample application, and a tutorial are available from http://mitk.org.ConclusionsWith the increased popularity of time-of-flight cameras for intra-operative surface acquisition, integration of range data supports into medical image processing toolkits such as MITK is a necessary step. Handling acquisition of range data from different cameras and processing of the data requires the establishment and use of software design principles that emphasize flexibility, extendibility, robustness, performance, and portability. The open-source toolkit MITK-ToF satisfies these requirements for the image-guided therapy community and was already used in several research projects.

Adaptive bilateral filter for image denoising and its application to in-vitro Time-of-Flight data

Image-guided therapy systems generally require registration of pre-operative planning data with the patients anatomy. One common approach to achieve this is to acquire intra-operative surface data and match it to surfaces extracted from the planning image. Although increasingly popular for surface generation in general, the novel Time-of-Flight (ToF) technology has not yet been applied in this context. This may be attributed to the fact that the ToF range images are subject to considerable noise. The contribution of this study is two-fold. Firstly, we present an adaption of the well-known bilateral filter for denoising ToF range images based on the noise characteristics of the camera. Secondly, we assess the quality of organ surfaces generated from ToF range data with and without bilateral smoothing using corresponding high resolution CT data as ground truth. According to an evaluation on five porcine organs, the root mean squared (RMS) distance between the denoised ToF data points and the reference computed tomography (CT) surfaces ranged from 3.0 mm (lung) to 9.0 mm (kidney). This corresponds to an error-reduction of up to 36% compared to the error of the original ToF surfaces.

Generation of Triangle Meshes from Time-of-Flight Data for Surface Registration

One approach to intra-operative registration in computerassisted medical interventions involves matching intra-operatively acquired organ surfaces with pre-operatively generated high resolution surfaces. The matching is based on so-called curvature descriptors assigned to the vertices of the two meshes. Therefore, high compliance of the input meshes with respect to curvature properties is essential. Time-of-Flight cameras can provide the required surface data during the intervention as a point cloud. Although different methods for generation of triangle meshes from range data have been proposed in the literature, their effect on the quality of the mesh with respect to curvature properties has not yet been investigated. In this paper, we evaluate six of these methods and derive application-specific recommendations for their usage.

MITK-ToF: Time-of-Flight Kamera-Integration in das Medical Imaging Interaction Toolkit

Time-of-Flight (ToF) Kameras bieten aufgrund derMoglichkeit zur schnellen und robusten Oberflachenerfassung groses Potential fur die intra-interventionelle Akquise von Informationen uber die Patientenanatomie und Organmorphologie. Eine Nutzung der neuen Technik als medizinische Bildgebungsmodalitat erfordert eine nahtlose Integration in die verwendete Softwareinfrastruktur. Nachdem sich das Medical Imaging Interaction Toolkit (MITK) als Framework fur die medizinische Bildverarbeitung etabliert hat, stellen wir in diesem Beitrag eine Erweiterung um die Anbindung von Time-of-Flight Kamerasystemen vor (MITK-ToF). MITK-ToF unterstutzt die Ansteuerung verbreiteter ToF-Kameratypen und stellt die akquirierten Bilddaten in mehreren Dateiformaten bereit. Die durch die Integration in das MITK ermoglichte Verwendung der dort vorhandenen Komponenten zur Bildverabeitung, Visualisierung und Interaktion ermoglichen die Entwicklung komplexer ToF-basierter Anwendungen. Wir zeigen das Potential des vorgestellten Toolkits beispielhaft anhand einer Anwendung zur Darstellung, Aufnahme und Wiedergabe von ToF Daten. Zur BVM 2011 wird eine erste open-source Version des Toolkits veroffentlicht.

In-vitro Evaluation von endoskopischer Oberflächenrekonstruktion mittels Time-of-Flight-Kameratechnik

Eine der grosten Herausforderungen im Kontext von computergestutzten Systemen fur laparoskopische Eingriffe stellt die intraoperative prazise und schnelle Rekonstruktion von Organoberflachen dar. Diese ermoglicht eine Registrierung praoperativer Planungsdaten auf die Patientenanatomie zur Einblendung von Ziel- und Risikostrukturen in das Videobild. Vor diesem Hintergrund eroffnet die Time-of- Flight (ToF)-Kameratechnik aufgrund der schnellen und dichten 3D-Oberflachenvermessung neue Perspektiven fur die laparoskopische computerassistierte Chirurgie. In diesem Beitrag stellen wir die erste invitro Evaluationsstudie zum Vergleich ToF-basierter endoskopischer mit Stereoskopie-basierter Oberflachenrekonstruktion vor.

Effiziente Planung von Zugangswegen für sichere Nadelinsertionen

Automatische Systeme fur minimal-invasive perkutane Nadelinsertionen erfordern die Segmentierung von Risikostrukturen zur Bestimmung eines sicheren Zugangsweges. Mangels vollautomatischer Segmentierungsverfahren fur alle Strukturen im Abdominalraum macht dieser Segmentierungsschritt den grosten Teil der gesamten Planungsdauer aus. Um die Planung zu beschleunigen, stellen wir ein zweistufiges Konzept fur eine schnelle semiautomatische Zugangsplanung vor, bei dem (1) vollautomatisch ein Grosteil der Hautoberflache als Einstichszone ausgeschlossen wird, indem nur automatisch segmentierbare Risikostrukturen berucksichtigt werden und (2) die so erhaltene Einstichszone durch Benutzung des Prinzips der Pareto-Optimalitat weiter eingeschrankt und der finale Einstichspunkt interaktiv mit einer neuen Visualisierungtechnik unter Berucksichtigung der anderen Risikostrukturen gewahlt wird.