Showing papers by "Ivo Wolf published in 2005"

3D active shape models using gradient descent optimization of description length

Abstract: Active Shape Models are a popular method for segmenting three-dimensional medical images. To obtain the required landmark correspondences, various automatic approaches have been proposed. In this work, we present an improved version of minimizing the description length (MDL) of the model. To initialize the algorithm, we describe a method to distribute landmarks on the training shapes using a conformal parameterization function. Next, we introduce a novel procedure to modify landmark positions locally without disturbing established correspondences. We employ a gradient descent optimization to minimize the MDL cost function, speeding up automatic model building by several orders of magnitude when compared to the original MDL approach. The necessary gradient information is estimated from a singular value decomposition, a more accurate technique to calculate the PCA than the commonly used eigendecomposition of the covariance matrix. Finally, we present results for several synthetic and real-world datasets demonstrating that our procedure generates models of significantly better quality in a fraction of the time needed by previous approaches.

Intraoperative assessment of right ventricular volume and function

Abstract: Objective: Right ventricular function is an important aspect of global cardiac performance which affects patients’ outcome after cardiac surgery. Due to its geometrical complexity, the assessment of right ventricular function is still a very difficult task. Aim of this study was to investigate the value of a new technique for intraoperative assessment of right ventricle based on transesophageal 3D-echocardiography, and to compare it to volumetric thermodilution by using a new generation of fast response thermistor pulmonary artery catheters. Methods: Twentyfive patients with coronary artery disease underwent 68 intraoperative measurements by 3D-echocardiography and thermodilution simultaneously. Following parameters were analysed: right ventricular end-diastolic volume (RVEDV), end-systolic volume (RVESV) and ejection fraction (RVEF). Pulmonary, systemic and central venous pressures were simultaneously recorded. Segmentation of right ventricular volumes were obtained by the ‘Coons-Patches’ technique, which was implemented into the EchoAnalyzer w , a multitask system developed at our institution for three-dimensional functional and structural measurements. Results: Right ventricular volumes obtained by 3D-echocardiography did not show significant correlations to those obtained by thermodilution. Volumetric thermodilution systematically overestimates right ventricular volumes. Significant correlations were found between RVEF measured by 3D-echocardiography and those obtained by thermodilution (rZ0. 93; yZ0.2C0.80x; SEEZ0.03; P!0.01). Bland–Altmann analysis showed that thermodilution systematically underestimates RVEF. The bias for measuring RVEF was C15.6% with a precision of G4.3%. The patients were divided into two groups according to left ventricular function. The group of patients with impaired function showed significantly lower right ventricular ejection fraction (44.1G4.6 vs. 55.1G3.9%; P!0.01). Conclusions: Three-dimensional echocardiography provides a useful non-invasive tool for intraoperative and serial assessment of right ventricular function. This new technique, which overcomes the limitations of previous methods, may offer key insights into management and outcome of patients with severe impairment of cardiac function. q 2005 Elsevier B.V. All rights reserved.

Incremental Real-Time Recording Of Tracked Instruments In Tubular Organ Structures Inside The Human Body

Abstract: The invention relates to a method for navigation during medical interventions on tubular organ structures, characterized in that, before the intervention, static image data of the tubular organ structures are recorded and stored, the tubular organ structures are extracted from the image data and their course is converted into a geometric description used during the medical intervention for instrument/organ recording, and the instrument that is spatially localized by a tracking system is successively corrected in relation to the static data, by a transformation that is preferably defined by an optimization method, taking into account the geometric description and information on the previous distance covered by the instrument, or, conversely, the static data are successively corrected in relation to the instrument position, and thus the position of the instrument is associated with the anatomical structures in the static image data.

Cast of Complex Congenital Heart Malformation in a Living Patient

Abstract: Magnetic resonance imaging data of a 20-year-old male patient was used to produce, to the best of our knowledge, the first cast model of a beating heart. Imaging was performed at the German Heart Institute Berlin, Department of Congenital Heart Disease and Pediatric Cardiology; data were transferred to the Department of Medical and Biological Informatics (German Cancer Research Center, Heidelberg). The patient had the diagnoses of dextrocardia, atrial and visceral situs inversus, L-looped ventricles, and L-malposition of the great arteries, with a large perimembranous ventricular septal defect and pulmonary atresia. A 3D whole-heart, navigator-corrected MRI data set …

Curved reformations using the medical imaging interaction toolkit (MITK)

Abstract: Modern systems for visualization, image guided procedures and display allow not only one type of visualization, but a variety of different visualization options. Only a combination of two-dimensional image display and three-dimensional rendering provides enough information for many tasks. Multiplanar orthogonal and oblique reformations of image data are standard features of medical imaging software packages today. Additionally, curved reformations are useful. For example, diagnosis of stenotic vessels can be supported by curved reformations along the centerline of the vessel, showing the complete vessel in one two-dimensional view. In this paper, we present how the open-source Medical Imaging Interaction Toolkit (MITK, www.mitk.org), which is based on the Insight Toolkit (ITK) and the Visualization Toolkit (VTK), can be used to rapidly build interactive systems that provide curved reformations. MITK supports curved reformations not only for images, but also for other data types (e.g., surfaces). Besides visualizations of curved reformations, which can be combined and are kept consistent with other two- and three-dimensional views of the data, interactions on such non-planar manifolds are supported. The developer only has to define the curved manifold, everything else is dealt with by the toolkit. We demonstrate these capabilities by means of a tool for mapping of coronary vessel trees.

Non-invasive assessment of differences between bileaflet and tilting-disc aortic valve prostheses by 3D-Doppler profiles

Abstract: The aim of this study was to analyse flow characteristics of two different prosthetic valves by means of a non-invasive 3D Doppler technique. As previously demonstrated, negative velocity peaks within a 3D-Doppler profile significantly correlate with the severity of aortic stenosis. Transesophageal echocardiography was performed in 42 patients with normal aortic valves and in 35 patients after aortic valve replacement (bileaflet n=23, tilting-disc n=12). Three-dimensional reconstruction of color Doppler data was performed by the EchoAnalyzer software developed at our institution. Cross-section velocity distribution in the ascending aorta was analysed 2 cm distal to the aortic valve in 3 different sectors (non-coronary (NC), left-coronary (LC) or right-coronary (RC)). The percentages of negative velocity values (PNVV) in native aortic valves (6.8+/-6.4%, range: 0-21.8%) were significantly lower (P<0.0001) than in prosthetic valves (bileaflet: 38.5+/-18.5%, range: 13.2-71%; tilting-disc: 47.2+/-17.6%, range: 21.7-78.1%). Significant differences between normal and prosthetic valves were found in all different sectors. Furthermore, Medtronic Hall showed significantly higher PNVV than St. Jude Medical within the LC sector (P=0.03). This method, which allows non-invasive analysis of 3D flow distributions in patients, revealed significant differences between prosthetic valves and native valves as well as among different prosthetic types.

Klinische Anwendung verschiedener Segmentierungsverfahren in der Live-3D Echokardiographie

Abstract: Die linke Herzfunktion wurde mittels handelsublicher Software zur manuellen (CardioView, Tomtec) und semi-automatischen Segmentierung (4D-LV-Analysis, Tomtec) bei 30 Patienten vor Herzoperation untersucht Analysiert wurden linksventrikulare Volumina und Ejektionsfraktionen in Live-3D Echokardiographiedaten im Vergleich zur Magnetresonanztomographie Beim Handling und der Genauigkeit schnitt die manuelle Segmentierung besser ab als die semi-automatische Der Grund hierfur lag in der Notwendigkeit des Setzens multipler Landmarken beim semi-automatischen Verfahren sowie an der rauschintensiven Ultraschall-Bildqualitat vor allem in der Diastole Nach semiautomatischer Segmentierung ware somit eine Nachkorrektur durch einen erfahrenen Untersucher notwendig Zur Okonomisierung des Prozessablaufs wird eine Umkehr der Reihenfolge von manueller und automatischer Komponente empfohlen