Showing papers by "Ivo Wolf published in 2009"

Comparison and Evaluation of Methods for Liver Segmentation From CT Datasets

Abstract: This paper presents a comparison study between 10 automatic and six interactive methods for liver segmentation from contrast-enhanced CT images. It is based on results from the "MICCAI 2007 Grand Challenge" workshop, where 16 teams evaluated their algorithms on a common database. A collection of 20 clinical images with reference segmentations was provided to train and tune algorithms in advance. Participants were also allowed to use additional proprietary training data for that purpose. All teams then had to apply their methods to 10 test datasets and submit the obtained results. Employed algorithms include statistical shape models, atlas registration, level-sets, graph-cuts and rule-based systems. All results were compared to reference segmentations five error measures that highlight different aspects of segmentation accuracy. All measures were combined according to a specific scoring system relating the obtained values to human expert variability. In general, interactive methods reached higher average scores than automatic approaches and featured a better consistency of segmentation quality. However, the best automatic methods (mainly based on statistical shape models with some additional free deformation) could compete well on the majority of test images. The study provides an insight in performance of different segmentation approaches under real-world conditions and highlights achievements and limitations of current image analysis techniques.

Method, system and computer program product for targeting of a target with an elongate instrument

Abstract: An embodiment is directed to a method and a system for assisting the targeting of a target with an elongate instrument, wherein the instrument is to be inserted into a living object's body part along a predetermined trajectory extending between an entry point of said instrument into said body part and a target point associated with said target. The method comprises an instrument directing assisting step for generating and displaying an image allowing a user to assess to which extend the longitudinal axis of the instrument is aligned with the vector connecting the target point and the tip portion of said instrument. Also, the method comprises an instrument guiding assisting step of generating and displaying an image allowing a user to assess to which extent the instrument motion during insertion thereof coincides with the predetermined trajectory.

Value of three-dimensional reconstructions in pancreatic carcinoma using multidetector CT: initial results.

Abstract: AIM: To evaluate the use of three-dimensional imaging of pancreatic carcinoma using multidetector computed tomography (CT) in a prospective study. METHODS: Ten patients with suspected pancreatic tumors were examined prospectively using multidetector CT (Somatom Sensation 16, Siemens, Erlangen, Germany). The images were evaluated for the presence of a pancreatic carcinoma and invasion of the peripancreatic vessels and surrounding organs. Using the isotropic CT data sets, a three-dimensional image was created with automatic vascular analysis and semi-automatic segmentation of the organs and pancreatic tumor by a radiologist. The CT examinations and the three-dimensional images were presented to the surgeon directly before and during the patient’s operation using the Medical Imaging Interaction Toolkit-based software “ReLiver”. Immediately after surgery, the value of the two images was judged by the surgeon. The operation and the histological results served as the gold standard. RESULTS: Nine patients had a pancreatic carcinoma (all pT3), and one patient had a serous cystadenoma. One tumor infiltrated the superior mesenteric vein. The infiltration was correctly evaluated. All carcinomas were resectable. In comparison to the CT image with axial and coronal reconstructions, the three-dimensional image was judged by the surgeons as better for operation planning and consistently described as useful. CONCLUSION: A 3D-image of the pancreas represents an invaluable aid to the surgeon. However, the 3D-software must be further developed in order to be integrated into daily clinical routine.

Comparing calibration approaches for 3D ultrasound probes

Abstract: Objective By adding a tracking sensor to a 3D ultrasound (US) probe and thus locating the probe in space, new applications within the fields of image guided surgery and radiation therapy are possible. To locate the US volume in space, a calibration is necessary to determine the mathematical transformation for mapping points from the tracking coordinate system to the US image coordinate system. We present a comprehensive comparison of two different approaches to perform this calibration for 3D US.

Is a circular polypropylene mesh appropriate for application at the esophageal hiatus? Results from an experimental study in a porcine model.

Abstract: Mesh reinforcement in hiatal hernia surgery is debated. Randomized controlled trials have shown that recurrences may be reduced, but there is also the fear of mesh-related complications. Experimental studies on the characteristics of specific mesh types with regard to the risk of such complications are rare. The current study aimed to investigate the properties of a circular heavy-weight polypropylene mesh in terms of stenosis, migration, erosions, and adhesions in a porcine model. A 55 × 55-mm heavy-weight polypropylene mesh with a 16.5-mm eccentric hole for the esophagus corresponding to a calculated mesh area of 2811 mm2 and a hole area of 214 mm2 were implanted in nine German Landrace pigs. Six weeks later, the meshes were explanted and investigated for size, shrinkage, migration and adhesions. The total mesh area shrank to a mean of 2,040 ± 178 mm2 (p < 0.001), and the hole for the esophagus showed a trend toward an increase to 239 ± 38 mm2 (p = 0.108). In not a single location did the mesh overhang the hiatal margin. The mean distance of retraction from the hiatal margin was 4.3 ± 2.8 mm. Therefore, no stenoses, migrations, or erosions occurred. A circular heavy-weight polypropylene mesh seems to be appropriate for the application at the esophageal hiatus in terms of safety and stability. This means that it is characterized by a position-stable centered fixation around the esophagus without a tendency toward stenosis, migration, or erosion.

Towards a mixed reality environment for preoperative planning of cardiac surgery

Abstract: We present a novel approach to studying physical heart models by coupling them with virtual 3D representations in a mixed reality environment. The limitations of standalone physical models (non-interactive, static) are overcome by the corresponding virtual models, which in turn become more natural to interact with. The potential of this approach is exemplified by a setup which enables cardiac surgeons to interactively trace the mitral annulus, a part of the cardiac skeleton playing a vital role in mitral valve surgery. We present results of a pilot study and discuss ways of improving and extending the system. The described mixed reality environment could easily be adapted to other fields and thus has the potential to become a new tool for investigating 3D medical data.

A quality-refinement process for medical imaging applications

Abstract: Objectives: To introduce and evaluate a process for refinement of software quality that is suitable to research groups. In order to avoid constraining researchers too much, the quality improvement process has to be designed carefully. The scope of this paper is to present and evaluate a process to advance quality aspects of existing research prototypes in order to make them ready for initial clinical studies. The proposed process is tailored for research environments and therefore more lightweight than traditional quality management processes. Methods: Focus on quality criteria that are important at the given stage of the software life cycle. Usage of tools that automate aspects of the process is emphasized. To evaluate the additional effort that comes along with the process, it was exemplarily applied for eight prototypical software modules for medical image processing. Results: The introduced process has been applied to improve the quality of all prototypes so that they could be successfully used in clinical studies. The quality refinement yielded an average of 13 person days of additional effort per project. Overall, 107 bugs were found and resolved by applying the process. Conclusions: Careful selection of quality criteria and the usage of automated process tools lead to a lightweight quality refinement process suitable for scientific research groups that can be applied to ensure a successful transfer of technical software prototypes into clinical research workflows.

Computer-Assisted Needle Insertion for Abdominal Interventions

Abstract: Clinical practice is increasingly replacing traditional open surgical procedures with minimally invasive techniques for cancer diagnosis and therapy. These procedures typically require placement of a surgical instrument into the organ of interest with a high degree of accuracy. In general, the success of a treatment or of a diagnosis is highly dependent on the accuracy of instrument insertion and thus depends crucially on the skills and experience of the physician. While intra-operative navigation has been proven to be highly effective in interventions on bony or sufficiently rigid structures, such as the spine and the brain, computer aided soft tissue procedures are still limited to non-invasive diagnostics and surgical planning. This can primarily be attributed to the lack of robust methods for compensation of intra-interventional organ motion caused by respiration, heartbeat, patient movement and manipulation by surgical instruments. To address these issues, we developed and evaluated a clinically applicable concept for computer-assisted percutaneous needle insertion into soft tissue featuring high accuracy and an efficient guidance concept. This paper summarizes our research activities related to the project.

RepliExplore: coupling physical and virtual anatomy models.

Abstract: We present a system which co-registers physical anatomy models with virtual three-dimensional (3D) representations. Interactions performed on the physical model by means of a 3D pointing device are directly reflected on its virtual counterpart. Complex anatomical information integrated into the virtual model thus becomes accessible through the physical interface in a simple and intuitive manner. Using an optical tracking system, we implemented and tested a reference application that includes several tools for the exploration and quantification of anatomical models. We theoretically evaluated the accuracy of the landmark-based registration for different landmark configurations. Physicians and computer scientists found the system simple to learn and intuitive to use. By optimizing landmark configurations, the accuracy could be significantly increased, particularly for scenarios in which only selected regions required higher accuracy. Physical anatomical models can benefit from the combination with a virtual counterpart in several ways. Applications include anatomical education and the study of patient-individual organ models. Optimizing the registration landmark configuration for specific applications can lower the accuracy requirements for the tracking system.

MITK-IGT: Eine Navigationskomponente für das Medical Imaging Interaction Toolkit

Abstract: MITK-IGT ist eine Erweiterung des Medical Imaging Interaction Toolkits, die es ermoglicht Softwareprogramme im Bereich bildgestutzte Therapie zu erstellen. Dieser Beitrag stellt die Architektur und Designprinzipien von MITK-IGT vor und vergleicht sie mit anderen Open Source Losungen. Neben der Ansteuerung von Trackingsystemen und Visualisierungsmodulen liegt der Fokus von MITK-IGT auf einer Filterarchitektur, die das schrittweise Verarbeiten von Trackingdaten erlaubt. Zur BVM 2009 wird die erste Version von MITK-IGT als Open Source veroffentlicht.

Accuracy of non-rigid registration for local analysis of elasticity restrictions of the lungs

Abstract: Diseases of the lung often begin with regionally limited changes altering the tissue elasticity. Therefore, quantification of regional lung tissue motion would be desirable for early diagnosis, treatment monitoring, and follow-up. Dynamic MRI can capture such changes, but quantification requires non-rigid registration. However, analysis of dynamic MRI data of the lung is challenging due to inherently low image signal and contrast. Towards a computer-assisted quantification for regional lung diseases, we have evaluated two Demons-based registration methods for their accuracy in quantifying local lung motion on dynamic MRI data. The registration methods were applied on masked image data, which were pre-segmented with a graph-cut algorithm. Evaluation was performed on five datasets from healthy humans with nine time frames each. As gold standard, manually defined points (between 8 and 24) on prominent landmarks (essentially vessel structures) were used. The distance between these points and the predicted landmark location as well as the overlap (Dice coefficient) of the segmentations transformed with the deformation field were calculated. We found that the Demons algorithm performed better than the Symmetric Forces Demons algorithm with respect to average landmark distance (6.5 mm ± 4.1 mm vs. 8.6 mm ± 6.1 mm), but comparable regarding the Dice coefficient (0.946 ± 0.018 vs. 0.961 ± 0.018). Additionally, the Demons algorithm computes the deformation in only 10 seconds, whereas the Symmetric Forces Demons algorithm takes about 12 times longer.

Reduktion der Invasivität bei nadelbasierter Bewegungskompensation für navigierte Eingriffe im Abdomen

Abstract: Diese Arbeit stellt eine in-vivo Genauigkeitsstudie uber das Kombinieren interner und externer Marker fur die Bewegungskompensation bei Leberinterventionen vor. Abhangig von der Anzahl und Anordnung der verwendeten Marker sowie der angewandten Echtzeittransformation wurde bei kontinuierlicher Atmung eine Schatzgenauigkeit der Zielposition zwischen 1 und 5 mm erreicht. Das Hinzufugen einer einzigen Hilfsnadel zu einer Menge von Hautmarkern fuhrte zu einer Fehlerreduktion von uber 50%. Die Ergebnisse dieser Studie konnen in der Praxis verwendet werden, um basierend auf dem Tradeoff zwischen geringer Invasivitat und hoher Genauigkeit eine geeignete Kombination von internen und externen Markern fur eine gegebene Fragestellung zu wahlen.

4D MRT Lungen-Volumetrie und funktionale Analyse mittels deformierbarer Formmodelle

Abstract: Segmentierung mit Hilfe von deformierbaren modellbasierten Ansatzen hat sich zu einer gangigen Praxis in der medizinischen Bildanalyse entwickelt, da sie eine schnelle und robust Methode zur semioder vollautomatischen Detektion von Strukturen darstellt, also z.B. Organen. In diesem Paper wird die Anwendung eines deformierbaren Formmodells zur funktionalen Analyse der Atmung aus MR-Bildem vorgestellt. Die Segmentierungsergebnisse stimmen sehr gut mit gleichzeitig aufgenommenen Spirometriedaten uberein, bei einem mittleren Fehler des Gesamtvolumens von etwa 70ml. Zusatzlich erlaubt der Formmodell-Ansatz jedoch eine unabhangige Analyse beider Lungenflugel und ermoglicht damit eine Detektion von lokalen Bewegungseinschrankungen. Weiterhin zeigen wir, dass die Kalibrierung der Segmentierungsergebnisse auf das Respirationsvolumen weitestgehend durch Subtraktion eines konstanten Faktors moglich ist.

Computer-aided patch planning for treatment of complex coarctation of the aorta

Abstract: Between five and eight percent of all children born with congenitally malformed hearts suffer from coarctations of the aorta. Some severe coarctations can only be treated by surgical repair. Untreated, this defect can cause serious damage to organ development or even lead to death. Patch repair requires open surgery. It can affect patients of any age: newborns with severe coarctation and/or hypoplastic aortic arch as well as older patients with late diagnosis of coarctation of the aorta. Another patient group are patients of varying age with re-coarctation of the aorta or hypoplastic aortic arch after surgical and/or interventional repair. If anatomy is complex and interventional treatment by catheterization, balloon angioplasty or stent placement is not possible, surgery is indicated. The choice of type of surgery depends not only on the given anatomy but also on the experience the surgical team has with each method. One surgical approach is patch repair. A patch of a suitable shape and size is sewed into the aorta to expand the aortic lumen at the site of coarctation. At present, the shape and size of the patch are estimated intra-operatively by the surgeon. We have developed a software application that allows planning of the patch pre-operatively on the basis of magnetic resonance angiographic data. The application determines the diameter of the coarctation and/or hypoplastic segment and constructs a patch proposal by calculating the difference to the normal vessel diameter pre-operatively. Evaluation of MR angiographic datasets from 12 test patients with different kinds of aortic arch stenosis shows a divergence of only (1.5±1.2) mm in coarctation diameters between manual segmentations and our approach, with comparable time expenditure. Following this proposal the patch can be prepared and adapted to the patient's anatomy pre-operatively. Ideally, this leads to shorter operation times and a better long-term outcome with a reduced rate of residual stenosis and re-stenosis and aneurysm formation.