Uta Preim

Semi-Automatic Vortex Extraction in 4D PC-MRI Cardiac Blood Flow Data using Line Predicates

Cardiovascular diseases (CVD) are the leading cause of death worldwide. Their initiation and evolution depends strongly on the blood flow characteristics. In recent years, advances in 4D PC-MRI acquisition enable reliable and time-resolved 3D flow measuring, which allows a qualitative and quantitative analysis of the patient-specific hemodynamics. Currently, medical researchers investigate the relation between characteristic flow patterns like vortices and different pathologies. The manual extraction and evaluation is tedious and requires expert knowledge. Standardized, (semi-)automatic and reliable techniques are necessary to make the analysis of 4D PC-MRI applicable for the clinical routine. In this work, we present an approach for the extraction of vortex flow in the aorta and pulmonary artery incorporating line predicates. We provide an extensive comparison of existent vortex extraction methods to determine the most suitable vortex criterion for cardiac blood flow and apply our approach to ten datasets with different pathologies like coarctations, Tetralogy of Fallot and aneurysms. For two cases we provide a detailed discussion how our results are capable to complement existent diagnosis information. To ensure real-time feedback for the domain experts we implement our method completely on the GPU.

Computer-aided diagnosis in breast DCE-MRI—Quantification of the heterogeneity of breast lesions

PURPOSE In our study we aim at the quantification of the heterogeneity for differential diagnosis of breast lesions in MRI. MATERIALS AND METHODS We tested a software tool for quantification of heterogeneity. The software tool provides a three-dimensional analysis of the whole breast lesion. The lesions were divided in regions with similar perfusion characteristics. Voxels were merged to the same region, if the perfusion parameters (wash-in, wash-out, integral, peak enhancement and time to peak) correlated to 99%. We evaluated 68 lesions from 50 patients. 31 lesions proved to be benign (45.6%) and 37 malignant (54.4%). We included small lesions which could only be detected with MRI. RESULTS The analysis of heterogeneity showed significant differences (p<0.005; AUC 0.7). Malignant lesions were more heterogeneous than benign ones. Significant differences were also found for morphologic parameters such as shape (p<0.001) and margin (p<0.007). The analysis of the enhancement dynamics did not prove successful in lesion discrimination. CONCLUSION Our study indicates that the region analysis for quantification of heterogeneity may be a helpful additional method to differentiate benign lesions from malignant ones.

Technical Section: A visual analytics approach to diagnosis of breast DCE-MRI data

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) of the breast is the most sensitive image modality for the detection of invasive breast cancer. To increase the moderate specificity of DCE-MRI, and therefore, the distinction of benign and malignant tumors, the tumors heterogeneity and the tumors enhancement kinetics have to be evaluated. In clinical practice, the tumors enhancement kinetics are analyzed via time-intensity curves after manual placement of regions of interest (ROI). A substantial limitation of the ROI analysis is the inter-observer variability as well as the potential distortion of the ROIs average curve, e.g. if the ROI covers benign and malignant tumor tissue. We present a visual analytics approach for breast tumors in DCE-MRI data that comprises a voxel-wise glyph-based overview and and a region-based analysis. The regions are extracted via region merging and each region contains voxels with similar perfusion characteristics. As a result, we avoid the inter-observer variability and reduce distortion due to averaging over differently perfused tissue. A comparative study of 20 datasets was carried out to test our approach and an adapted time-intensity curve classification method. Moreover, the influence of similarity measurements and a potential region-based exploration are discussed. In conclusion, the presented features as similarity criteria yield the best results regarding the finer classification of the early contrast agent accumulation and the regions enhancement kinetics in the intermediate and late postcontrast phase since spatial information is included and the merging of regions with different perfusion characteristics is impeded.

The LiverAnatomyExplorer: A WebGL-Based Surgical Teaching Tool

The LiverAnatomyExplorer is a real-time surgical teaching tool based on state-of-the-art Web technologies such as SVG (Scalable Vector Graphics), X3D (Extensible3D), and WebGL (Web Graphics Library). Unlike other medical e-learning systems, the LiverAnatomyExplorer combines traditional clinical 2D imagery with interactive Web-based 3D models derived from patient-specific image data. The tool is enhanced by surgical videos, a self-assessment tool, and an online authoring tool with which instructors can manage the presented case studies and create multiple-choice quizzes.

A Survey of Cardiac 4D PC-MRI Data Processing

Cardiac four‐dimensional phase‐contrast magnetic resonance imaging (4D PC‐MRI) acquisitions have gained increasing clinical interest in recent years. They allow to non‐invasively obtain extensive information about patient‐specific hemodynamics, and thus have a great potential to improve the diagnosis, prognosis and therapy planning of cardiovascular diseases. A dataset contains time‐resolved, three‐dimensional blood flow directions and strengths, making comprehensive qualitative and quantitative data analysis possible. Quantitative measures, such as stroke volumes, help to assess the cardiac function and to monitor disease progression. Qualitative analysis allows to investigate abnormal flow characteristics, such as vortices, which are correlated to different pathologies. Processing the data comprises complex image processing methods, as well as flow analysis and visualization. In this work, we mainly focus on the aorta. We provide an overview of data measurement and pre‐processing, as well as current visualization and quantification methods. This allows other researchers to quickly catch up with the topic and take on new challenges to further investigate the potential of 4D PC‐MRI data.

Robust Cardiac Function Assessment in 4D PC-MRI Data of the Aorta and Pulmonary Artery

Four‐dimensional phase‐contrast magnetic resonance imaging (4D PC‐MRI) allows the non‐invasive acquisition of time‐resolved, 3D blood flow information. Stroke volumes (SVs) and regurgitation fractions (RFs) are two of the main measures to assess the cardiac function and severity of valvular pathologies. The flow rates in forward and backward direction through a plane above the aortic or pulmonary valve are required for their quantification. Unfortunately, the calculations are highly sensitive towards the planes angulation since orthogonally passing flow is considered. This often leads to physiologically implausible results. In this work, a robust quantification method is introduced to overcome this problem. Collaborating radiologists and cardiologists were carefully observed while estimating SVs and RFs in various healthy volunteer and patient 4D PC‐MRI data sets with conventional quantification methods, that is, using a single plane above the valve that is freely movable along the centerline. By default it is aligned perpendicular to the vessels centerline, but free angulation (rotation) is possible. This facilitated the automation of their approach which, in turn, allows to derive statistical information about the plane angulation sensitivity. Moreover, the experts expect a continuous decrease of the blood flow volume along the vessel course. Conventional methods are often unable to produce this behaviour. Thus, we present a procedure to fit a monotonous function that ensures such physiologically plausible results. In addition, this technique was adapted for the usage in branching vessels such as the pulmonary artery. The performed informal evaluation shows the capability of our method to support diagnosis; a parameter evaluation confirms the robustness. Vortex flow was identified as one of the main causes for quantification uncertainties.

Bildanalyse für die präoperative Planung von Neck Dissections

Mit dem Ziel einer 3D-Visualisierung der patienten-individuellen Pathologie sollen therapeutisch relevante Strukturen des Halses praoperativ segmentiert werden. Die vorliegende Arbeit untersucht die Eignung und Automatisierbarkeit grauwertbasierter Segmentierungsverfahren (Regionenwachstum, Interaktive Wasserscheidentransformation, Live-Wire) fur diese Aufgabe. Auserdem wird die Integration der Segmentierungsverfahren in den Software-Assistenten NeckVision beschrieben.

Sketching 2D Vessels and Vascular Diseases with Integrated Blood Flow

In this paper, we present a sketch-based interface, which allows medical doctors to illustrate different vascular diseases and treatment methods as well as fluid behavior. With this sketching interface, we provide the physician with an effective tool to illustrate different medical cases, which is important in the complex field of vascular diseases with respect to patient education. We use techniques from sketch-based interfaces and GPU-based computational fluid dynamics by considering usability aspects. We provide a concept and a prototypical implementation whose usability is tested with quantitative and qualitative methods. Additionally, we interviewed a physician to assess the benefits of the tool with respect to patient education.

Delayed enhancement imaging in a contemporary patient cohort following correction of tetralogy of Fallot.

OBJECTIVE To test the hypothesis that myocardial scars after repair of tetralogy of Fallot are related to impaired cardiac function and adverse clinical outcome. METHODS A total of 53 patients were retrospectively analysed after repair of tetralogy of Fallot. The median patient age was 20 years (range 2-48). Cardiac MRI with a 1.5 T magnet included cine sequences to obtain volumes and function, phase-sensitive inversion recovery delayed enhancement imaging to detect myocardial scars, and flow measurements to determine pulmonary regurgitation fraction. In addition, clinical parameters were obtained. RESULTS An overall 83% of patients were in NYHA class I. All patients with the exception of 2 (96%) had pulmonary insufficiency. Mean ejection fraction and end-diastolic volume index were 46% and 128 ml/m2 for the right ventricle and 54% and 82 ml/m² for the left ventricle, respectively. Excluding enhancement of the septal insertion and prosthetic patches, delayed enhancement was seen in 11/53 cases (21%). Delayed enhancement of the right ventricle was detected in 6/53 patients (11%) and of the left ventricle in 5/53 patients (9%). The patient group with delayed enhancement was significantly older (p=0.003), had later repair (p=0.007), and higher left ventricular myocardial mass index (p=0.009) compared with the group without delayed enhancement. CONCLUSIONS This study reveals that scarring is common in patients after surgical repair of tetralogy of Fallot and is associated with older age and late repair. However, there was no difference in right ventricular function, NYHA class, or occurrence of clinically relevant arrhythmias between patients with and those without myocardial scars.

Ein 2-Fronten-Feder-Masse-Modell zur Segmentierung von Lymphknoten in CT-Daten des Halses

Mit dem Ziel, die praoperative Einschatzung der Operabilitat von Hals-Lymphknoten-Ausraumungen (Neck Dissections) durch eine 3D-Darstellung zu verbessern, bedarf es einer Methode, um Lymphknoten effizient zu segmentieren. Hierzu wird in dieser Arbeit ein stabiles 3D-Feder-Masse-Modell prasentiert, welches eine direkte Integration in einen Visualisierungsprozess erlaubt. Dabei werden erstmals Grauwert-, Form- und Kanteninformationen in einem Modell kombiniert. Ergebnisse einer Evaluierung werden ebenfalls diskutiert.