Peter Hassenpflug

Navigation aids and real-time deformation modeling for open liver surgery

This contribution presents a novel method for image-guided navigation in oncological liver surgery. It enables the perpetuation of the registration for deeply located intrahepatic structures during the resection. For this purpose, navigation aids localizable by an electro-magnetic tracking system are anchored within the liver. Position and orientation data gained from the navigation aids are used to parameterize a real-time deformation model. This approach enables for the first time the real-time monitoring of target structures also in the depth of the intraoperatively deformed liver. The dynamic behavior of the deformation model has been evaluated with a silicon phantom. First experiments have been carried out with pig livers ex vivo.

Medical imaging: examples of clinical applications

Clinical routine is currently producing a multitude of diagnostic digital images but only a few are used in therapy planning and treatment. Medical imaging is involved in both diagnosis and therapy. Using a computer, existing 2D images can be transformed into interactive 3D volumes and results from different modalities can be merged. Furthermore, it is possible to calculate functional areas that were not visible in the primary images. This paper presents examples of clinical applications that are integrated into clinical routine and are based on medical imaging fundamentals. In liver surgery, the importance of virtual planning is increasing because surgery is still the only possible curative procedure. Visualisation and analysis of heart defects are also gaining in significance due to improved surgery techniques. Finally, an outlook is provided on future developments in medical imaging using navigation to support the surgeons work. The paper intends to give an impression of the wide range of medical imaging that goes beyond the mere calculation of medical images.

Generation of attributed relational vessel graphs from three-dimensional freehand ultrasound for intraoperative registration in image-guided liver surgery

We propose a procedure for the intraoperative generation of attributed relational vessel graphs. It builds the prerequisite for a vessel-based registration of a virtual, patient-individual, preoperative, three-dimensional liver model with the intraopeatively deformed liver by graph matching. An image processing pipeline is proposed to extract an abstract representation of the vascular anatomy from intraoperatively acquired three-dimensional ultrasound. The procedure is transferable to other vascularized soft tissues like the brain or the kidneys. We believe that our approach is suitable for intraoperative application as basis for efficient vessel-based registration of the surgical volume of interest. By reducing the problem of intraoperative registration in visceral surgery to the mapping of corresponding attributed relational vessel graphs a fast and reliable registration seems feasible even in the depth of deformed vascularized soft tissues like in human livers.

Robuste Analyse von Gefäßstrukturen auf Basis einer 3D-Skelettierung

In dieser Arbeit wird ein Verfahren vorgestellt, welches es erlaubt, eine symbolische Beschreibung aus segmentierten Blutgefasen zu erzeugen. Im resultierenden Graphen ist der Verlauf der Gefasaste, deren Durchmesser und die Lage von Verzweigungen gespeichert. Der Algorithmus wurde auf Basis eines existierenden Ansatzes entwickelt, der in Bezug auf die Rotationsinvarianz verbessert und um ein neues Grapherzeugungsverfahren erweitert wurde. Zusatzlich werden Methoden bereitgestellt, die es erlauben, die Enstehung von fehlerhaften Asten zu vermeiden, oder sie im nachhinein ausschlieslich auf Basis der Information im Gefasgraphen zu identifizieren und zu loschen.

Superiority of autostereoscopic visualization for image-guided navigation in liver surgery

A substantial component of an image-guided surgery system (IGSS) is the kind of three-dimensional (3D) presentation to the surgeon because the visual depth perception of the complex anatomy is of significant relevance for orientation. Therefore, we examined for this contribution four different visualization techniques, which were evaluated by eight surgeons. The IGSS developed by our group supports the intraoperative orientation of the surgeon by presenting a visualization of the spatially tracked surgical instruments with respect to vitally important intrahepatic vessels, the tumor, and preoperatively calculated resection planes. In the preliminary trial presented here, we examined the human ability to perceive an intraoperative virtual scene and to solve given navigation tasks. The focus of the experiments was to measure the ability of eight surgeons to orientate themselves intrahepatically and to transfer the perceived virtual spatial relations to movements in real space. With auto-stereoscopic visualization making use of a prism-based display the navigation can be performed faster and more accurate than with the other visualization techniques.

Extension of 2D segmentation methods into 3D by means of coons-patch interpolation

In medical imaging, segmentation is an important step for many visualization tasks and image-guided procedures. Except for very rare cases, automatic segmentation methods cannot guarantee to provide the correct segmentation. Therefore, for clinical usage, physicians insist on full control over the segmentation result, i.e., to verify and interactively correct the segmentation (if necessary). Display and interaction in 2D slices (original or multi-planar reformatted) are more precise than in 3D visualizations and therefore indispensable for segmentation, verification and correction. The usage of slices in more than one orientation (multi-planar reformatted slices) helps to avoid inconsistencies between 2D segmentation results in neighboring slices. For the verification and correction of three-dimensional segmentations as well as for generating a new 3D segmentation, it is therefore desirable to have a method that constructs a new or improved 3D segmentation from 2D segmentation results. The proposed method enables to quickly extend segmentations performed on intersecting slices of arbitrary orientation to a three-dimensional surface model by means of interpolation with specialized Coons patches. It can be used as a segmentation tool of its own as well as for making more sophisticated segmentation methods (that need an initialization close to the boundary to detect) feasible for clinical routine.

Intraoperative Navigation in der Leberchirurgie mittels Navigationshilfen und Verformungsmodellierung

In diesem Beitrag stellen wir eine neue Methode zur bildgestutzten Navigation in der onkologischen Leberchirurgie vor. Sie erlaubt die Aufrechterhaltung der Registrierung auch tiefgelegener Organstrukturen wahrend der Resektion. Dazu werden durch ein magnetisches Tracking-System erfassbare Navigationshilfen in der Leber verankert. Mit den aus den Navigationshilfen gewonnenen Positions- und Orientierungsdaten wird ein lineares Deformationsmodell parametrisiert. Dieser Ansatz ermoglicht erstmals die schritthaltende Verfolgung von Ziel Strukturen auch in der Tiefe der intraoperativ verformten Leber.

Ein radiologisches Softwaremodul für die computergestützte Operationsplanung in der onkologischen Leberchirurgie

Gerade in der Leberchirurgie ist die computergestutzte Planung chirurgischer Eingriffe von groser praktischer Bedeutung. Die hohe Rate anatomischer Abweichungen macht hier die genaue Auswertung der praoperativ gewonnenen Bilddaten zur Grundlage jeder Lebertumorresektion. Da die makroskopische Anatomie der Leber im Wesentlichen durch die Struktur der intrahepatischen Gefasbaume definiert wird, bildet die dreidimensionale Analyse der kontrastmittelverstarkten Darstellungen den zentralen Baustein einer Operationsplanungssoftware in der Leberchirurgie. Im Folgenden werden wir die verschiedenen Arbeitsschritte beschreiben, die im Rahmen einer solchen Operationsplanung durchlaufen werden mussen. Die Implementierung der Software wurde als Plugin der radiologischen Workstation CHILI vorgenommen.

Evaluation of visualization techniques for image-guided navigation in liver surgery

A substantial component of an image-guided surgery system (IGSS) is the kind of three-dimensional (3D) presentation to the surgeon because the visual depth perception of the complex anatomy is of significant relevance for orientation. Therefore, we examined in this contribution four different visualization techniques, which were evaluated by eight surgeons. The IGSS developed by our group supports the intraoperative orientation of the surgeon by depicting a visualization of the spatially tracked surgical instruments with respect to intrahepatic vessels that have to be conserved vitally, the tumor, and preoperatively calculated resection planes. In the prelimenary trial presented here we examined the human ability to percept an intraoperative virtual scene and to solve given navigation tasks. The focus of the experiments was to measure the ability of eight surgeons to orientate intrahepaticaly and to transfer the percepted spatial relation to movements in real space. An autostereoscopic visualization with a prism-based display yielded that the navigation can be performed faster and more accurately than with the other visualization techniques.

Interaktives Trennen von Gefäßbäumen am Beispiel der Leber

Der vorliegende Beitrag stellt ein interaktives Verfahren zur Trennung und Einteilung von Gefasen am Beispiel der Leberoperationsplanung vor. Die Gefase werden aus kontrastmittelverstarkten CT- oder MR-Aufnahmen extrahiert und durch einen Graphen beschrieben. Dieser Graph wird mittels Open-GL visualisiert, so dass eine direkte Manipulation der Teilsegmente des Graphen moglich wird. Auf diese Weise lassen sich Gefasstrukturen trennen bzw. klassifizieren, so dass z.B. die intrahepatischen Gerasstrukturen der Leber in Vena Porta und Vena Hepatica aufgeteilt und schlieslich die Aste der Vena Porta zu den von ihnen versorgenden Segmenten eingeteilt werden konnen.