Dirk Selle

Analysis of vasculature for liver surgical planning

For liver surgical planning, the structure and morphology of the hepatic vessels and their relationship to tumors are of major interest. To achieve a fast and robust assistance with optimal quantitative and visual information, we present methods for a geometrical and structural analysis of vessel systems. Starting from the raw image data a sequence of image processing steps has to be carried out until a three-dimensional representation of the relevant anatomic and pathologic structures is generated. Based on computed tomography (CT) scans, the following steps are performed. 1) The volume data is preprocessed and the vessels are segmented. 2) The skeleton of the vessels is determined and transformed into a graph enabling a geometrical and structural shape analysis. Using this information the different intrahepatic vessel systems are identified automatically. 3) Based on the structural analysis of the branches of the portal vein, their vascular territories are approximated with different methods. These methods are compared and validated anatomically by means of corrosion casts of human livers. 4) Vessels are visualized with graphics primitives fitted to the skeleton to provide smooth visualizations without aliasing artifacts. The image analysis techniques have been evaluated in the clinical environment and have been used in more than 170 cases so far to plan interventions and transplantations.

Visualization and interaction techniques for the exploration of vascular structures

We describe a pipeline of image processing steps for deriving symbolic models of vascular structures from radiological data which reflect the branching pattern and diameter of vessels. For the visualization of these symbolic models, concatenated truncated cones are smoothly blended at branching points. We put emphasis on the quality of the visualizations which is achieved by anti-aliasing operations in different stages of the visualization. The methods presented are referred to as HQVV (high quality vessel visualization). Scalable techniques are provided to explore vascular structures of different orders of magnitude. The hierarchy as well as the diameter of the branches of vascular systems are used to restrict visualizations to relevant subtrees and to emphasize parts of vascular systems. Our research is inspired by clear visualizations in textbooks and is targeted toward medical education and therapy planning. We describe the application of vessel visualization techniques for liver surgery planning. For this application it is crucial to recognize the morphology and branching pattern of vascular systems as well as the basic spatial relations between vessels and other anatomic structures.

Resection proposals for oncologic liver surgery based on vascular territories

We describe the generation and visualization of resection proposals for oncologic liver surgery which are based on vascular territories of the portal and hepatic vein. Resection proposals are interactively controlled by one parameter: the desired security margin around a tumor. Resection proposals consider vascular structures inside this margin, dependent vascular structures in the periphery as well as the territories supplied by them. The methods have been applied to artificial data from corrosion casts as well as to 5 datasets obtained in the clinical routine from 3 hospitals.

Individuelle Planung leberchirurgischer Eingriffe an einem virtuellen Modell der Leber und ihrer Leitstrukturen

ZusammenfassungHintergrund: In einem interdisziplinären Ansatz wurde das speziell für die 3D-Visualisierung der Leber entwickelte Programm HepaVision (MEVIS, Bremen) für die individuelle Planung ausgedehnter Leberresektionen und von Leberlebendspenden eingesetzt und evaluiert. Erfahrungen mit dem Programm liegen bisher für >50 Volumendatensätze biphasischer Spiral-CT-Untersuchungen vor. Ergebnisse: Die räumliche Darstellung der Lagebeziehung großer Tumoren zu den kritischen Strukturen, der Nachweis und die Bewertung von Versorgungsvarianten sowie die Abschätzung des Risikos eines Leberversagens durch Volumetrie auf der Basis portalvenöser Versorgungsgebiete unterstützen die Indikationsstellung zum Eingriff. Zusätzlich wird der Sicherheitsgrad des Eingriffs durch Vorplanung und Vorbereitung etwa notwendiger Gefäßrekonstruktionen erhöht. Durch das selektive Ausblenden portalvenöser Versorgungsgebiete oder durch frei wählbare Clip-planes können sowohl Segmentresektionen als auch nicht-anatomische Resektionen simuliert und in ihren Auswirkungen analysiert werden. Der präoperativ virtuell erhobene Situs bestätigte sich intraoperativ bei allen 17 Patienten des Gesamtkollektivs, die einem Eingriff, sei es in Form einer Tumorresektion oder einer Teilorganentnahme zur Transplantation, unterzogen wurden.SummaryBackground: In an interdisciplinary approach, HepaVision (MEVIS, Bremen), a software tool specifically developed for 3D visualization of the liver, was employed for individual planning of extensive liver resections and evaluation of living-relative donations. So far there is experience with more than 50 biphasic spiral CT examinations. Results: The spatial relationship of large tumors to crucial hepatic structures, the demonstration and evaluation of anatomic variants regarding vascular supply and the risk stratification of liver failure by volumetric analysis on the basis of portal venous drainage supported precise indication for surgery. Surgical safety is increased by preoperative planning and simulation of necessary vessel reconstructions. By hiding selective areas of portal venous drainage or applying freely selectable clip planes, segmental as well as non-anatomical resections can be simulated and their effects analyzed. The virtual preoperative situs was confirmed intraoperatively in all 17 patients of our study population who underwent segmental liver resection for either a tumor or living-relative donation.

Mathematical Methods in Medical Imaging: Analysis of Vascular Structures for Liver Surgery Planning

Mathematics and medicine do not have a long history of close and fruitful cooperation. The application of mathematical methods in medical applications has become viable due to the increasing performance of computers and since more and more digital image data is acquired. While in former times conventional X-ray images — recorded at an analog film — have been used for diagnosis and treatment planning, more and more (digital) 3D datasets, such as Computed Tomography (CT-images) and Magnetic Resonance Imaging (MRI) are acquired for patients with severe diseases. With mathematical methods these 3D datasets may be quantitatively analyzed and visualized such that medical diagnosis and the assessment of therapeutic strategies becomes more reliable and reproducible.

Interaction Techniques and Vessel Analysis for Preoperative Planning in Liver Surgery

We present visualization and interaction techniques for preoperative planning in oncologic liver surgery. After several image processing steps a 3d visualization of all relevant anatomic and pathologic structures is created. In this 3d visualization a surgeon can flexibly specify resection regions with resection tools which can be applied selectively to different structures. The combination of several views which can be synchronized makes it easy to compare different views on the resection plan.

Precise determination of aortic length in patients with aortic stent grafts: in vivo evaluation of a thinning algorithm applied to CT angiography data

Abstract The aim of this study was to develop a technique for precise determination of the aortic length using volumetric CT data for potential use prior to endovascular stent-graft placement. The study population consisted of 20 patients (38 measurements) with already performed endoluminal grafting. This allowed for in vivo evaluation of our technique. Its length according to the graft specifications served as a gold standard for our own measurements. The implemented graft length varied between 120 and 195 mm. Computed tomography angiography was performed with 3-mm slice collimation, 5-mm table feed and a reconstruction interval of 2 mm. Following semi-automatic segmentation of the aorta and its large side branches, the median centerline (skeleton) of the vessels was determined employing a modified three-dimensional thinning algorithm. The algorithm was validated by comparing the calculated length of the resulting skeleton with the specifications of the grafts. The calculated length was sufficiently precise despite the limiting reconstruction interval of 2 mm of our CT data which only permitted an assessment of stent length in 2-mm steps. The differences in the measured length and graft length were in the range between 0 and 8 mm ( < 5 %) with a mean fractional error of 2.46 ± 2.37 mm. The use of an intelligent region growing algorithm capable of coping with variable arterial enhancement significantly reduced operator post-processing time. The average time necessary for segmentation was 7 min (range 3–10 min). Our algorithm provides a non-invasive method for objective and precise measurement of aortic length apparently even in tortuous vessels. It has the potential to replace angiography for aortic and iliac length measurements with calibrated catheters prior to endovascular intervention.

Analysis of the morphology and structure of vessel systems using skeletonization

In the field of liver surgery 3D, visualizations of the intrahepatic vessel systems and their relationship to tumors are of major interest for the preoperative planning. To achieve a fast and robust computer assistance with optimal quantitative and visual information, we present methods for a geometrical and structural analysis of vessel systems. Based on CT and MR scans the following steps are performed: (1) The volume data is preprocessed and the vessels are segmented. (2) The skeleton of the vessels is determined. (3) The skeleton is transformed into a graph enabling a geometrical (radii, length of branches) and structural (ramifications, hierarchy) shape analysis. Using this information the different intrahepatic vessel systems are identified automatically. Interactive measuring of length, volume and diameter of vessels is supported. Also the devascularized territories of the liver due to tumor resections can be estimated. The methods have been evaluated in the clinical environment in more than 120 cases so far.

Segmentbestimmung im Computertomogramm der Lunge In-vitro Validierung

Fur die radiologische Diagnostik ist die Kenntnis der Lungenlappensegmente zur segmentgenauen Berechnung von CT-Funktionsparametern und zur Tumorlokalisation ein Gewinn. Nach Vorverarbeitung der computertomographischen Bilddaten der Lunge wird der Bronchialbaum mit einem speziellen Bereichswachstumsverfahren segmentiert und automatisch in seine Unterbaume zerlegt. Ein auf Wachstumsmodellen basierender Algorithmus approximiert daraus die Grenzen der Lungenlappensegmente. Die Validierung mit zwei in-vitro Praparaten der Lunge ergab fur klinische HRCT-Daten eine Genauigkeit der Segmentapproximation von ca. 70%.

ILabMed-Workstation — Eine Entwicklungsumgebung für radiologische Anwendungen

Die ILabMed-Workstation ist eine Entwicklungsumgebung fur die medizinische Bildverarbeitung. Basierend auf einer grosen Anzahl an Bildverarbeitungsalgorithmen konnen verschiedenste radiologische Probleme gelost werden. Das System kann in einfacher Weise um neue Algorithmen erweitert und die individuellen Problemlosungen konnen mit einer Bedienoberflache versehen werden. Dies wird in der neu entwickelt en Programmiersprache APrIL durchgefuhrt, die durch eine interpretierte Ausfuhrung kurze Entwicklungszyklen ermoglicht. Die ILabMed-Workstation wird am Centrum fur Medizinische Diagnosesysteme und Visualisierung zur Entwicklung von radiologischen Anwendungsprojekten u.a. im Bereich der praoperativen Planung der Leberchirurgie eingesetzt.