Graph-based Spatial Motion Tracking Using Affine-covariant Regions

This thesis considers the task of spatial motion reconstruction from image sequences using a stereoscopic camera setup. In a variety of fields, such as flow analysis in physics or the measurement of oscillation characteristics and damping behavior in mechanical engineering, efficient and accurate methods for motion analysis are of great importance. This work discusses each algorithmic step of the motion reconstruction problem using a set of freely available image sequences. The presented concepts and evaluation results are of a generic nature and may thus be applied to a multitude of applications in various fields, where motion can be observed by two calibrated cameras. The first step in the processing chain of a motion reconstruction algorithm is concerned with the automated detection of salient locations (=features or regions) within each image of a given sequence. In this thesis, detection is directly performed on the natural texture of the observed objects instead of using artificial marker elements (as with many currently available methods). As one of the major contributions of this work, five well-known detection methods from the contemporary literature are compared to each other with regard to several performance measures, such as localization accuracy or the robustness under perspective distortions. The given results extend the available literature on the topic and facilitate the well-founded selection of appropriate detectors according to the requirements of specific target applications. In the second step, both spatial and temporal correspondences have to be established between features extracted from different images. With the former, two images taken at the same time instant but with different cameras are considered (stereo reconstruction) while with the latter, correspondences are sought between temporally adjacent images from the same camera instead (monocular feature tracking). With most classical methods, an observed object is either spatially reconstructed at a single time instant yielding a set of three-dimensional coordinates, or its motion is analyzed separately within each camera yielding a set of two-dimensional trajectories. A major contribution of this thesis is a concept for the unification of both stereo reconstruction and monocular tracking. Based on sets of two-dimensional trajectories from each camera of a stereo setup, the proposed method uses a graph-based approach to find correspondences not between single features but between entire trajectories instead. Thereby, the influence of locally ambiguous correspondences is mitigated significantly. The resulting spatial trajectories contain both the three-dimensional structure and the motion of the observed objects at the same time. To the best knowledge of the author, a similar concept does not yet exist in the literature. In a detailed evaluation, the superiority of the new method is demonstrated

Localization accuracy of region detectors

In this paper, a comparison of five state of the art region detectors is presented with regard to localization accuracy in position and region shape. Based on carefully estimated ground truth homographies, correspondences between frames are assigned using geometrical region overlap. Significant differences between detectors exist, depending on the type of images. Also, it is shown that localization accuracy linearly depends on region scale for some detectors, which may thus be used as a pre-selection criterion for the removal of error-prone regions. The presented results serve as a supplement to existing comparative studies, and can be used to facilitate the selection of an appropriate detector for a specific target application. When descriptor distance is used as assignment criterion instead of region overlap, a different set of correspondences results with lower accuracy. Set differences (and thus localization accuracy) are directly related to the density of regions in a local neighborhood. Based on the latter, a novel measure for the identification of error-prone regions- shape uniqueness- is introduced. In contrast to existing methods that are based on the descriptor distance of region correspondences, the new measure is pre-computed on each image individually. Thus, the complexity of the subsequent matching task can be significantly reduced. 1

Vehicle Data Management System for Scenario-Based Validation of Automated Driving Functions

Proving the functionality of AI-controlled automated vehicles is a challenging task due to the enormous overall complexity. Although a scenario-based validation approach is widely accepted in the literature, the identification of these scenarios is still an open issue. Real-world test drives are valuable data sources for this purpose. However, an automated system is required for data management and scenario identification to analyze the vast amount of data in a legitimate amount of time and effort. Therefore, this work proposes a modular multi-tier Vehicle Data Management System for large-scale test campaign management and analysis as the basis for scenario-based validation of automated driving functions. For system demonstration, lane-change maneuvers are identified and extracted, and an onboard DAS is evaluated with a real-world test drive sequence

Endovascular therapy with or without intravenous thrombolysis in acute stroke with tandem occlusion

International audienceBackground Endovascular therapy (EVT) is effective and safe in patients with tandem occlusion. The benefit of intravenous thrombolysis (IVT) prior to EVT in acute tandem occlusion is debatable. Objective To compare EVT alone with EVT plus IVT in patients with acute ischemic stroke due to anterior circulation tandem occlusions. Methods This is an individual patient pooled analysis of the Thrombectomy In TANdem lesions (TITAN) and Endovascular Treatment in Ischemic Stroke (ETIS) Registries. Patients were divided into two groups based on prior IVT treatment: (1) IVT+ group, which included patients who received IVT prior to EVT, (2) IVT− group, which included patients who did not receive IVT prior to EVT. Propensity score (inverse probability of treatment weighting (IPTW)) was used to reduce baseline between-group differences. The primary outcome was favorable outcome—that is, modified Rankin Scale (mRS) score 0 to 2 at 90 days. Results Overall, 602 consecutive patients with an acute stroke with tandem occlusion were included (380 and 222 in the bridging therapy and EVT alone groups, respectively). Onset to imaging time was shorter in the IVT+ group (median 103 vs 140 min). In contrast, imaging to puncture time was longer in the IVT+ group (median 107 vs 91 min). In IPTW analysis, the IVT+ group had higher odds of favorable outcome, excellent outcome (90-day mRS score 0–1), and successful reperfusion (modified Thrombolysis in Cerebral Infarction score 2b/3 at the end of EVT). There was no difference in the risk of significant hemorrhagic complications between groups. In secondary analysis of patients treated with acute cervical internal carotid artery stenting, bridging therapy was associated with higher odds of favorable outcome and lower odds of mortality at 90 days. Conclusions Our results suggest that bridging therapy in patients with acute ischemic stroke due to anterior tandem occlusion is safe and may improve functional outcome, even in the setting of acute cervical internal carotid artery stenting during EVT

Safety and Outcome of Carotid Dissection Stenting During the Treatment of Tandem Occlusions: A Pooled Analysis of TITAN and ETIS

International audienceBackground and Purpose: The efficacy of endovascular therapy in patients with acute ischemic stroke due to tandem occlusion is comparable to that for isolated intracranial occlusion in the anterior circulation. However, the optimal management of acute cervical internal carotid artery lesions is unknown, especially in the setting of carotid dissection, but emergency carotid artery stenting (CAS) is frequently considered. We investigated the safety and efficacy of emergency CAS for carotid dissection in patients with acute stroke with tandem occlusion in current clinical practice. Methods: We retrospectively analyzed a prospectively maintained database composed of 2 merged multicenter international observational real-world registries (Endovascular Treatment in Ischemic Stroke and Thrombectomy in Tandem Lesion). Data from endovascular therapy performed in the treatment of tandem occlusions related to acute cervical carotid dissection between January 2012 and January 2019 at 24 comprehensive stroke centers were analyzed. Results: The study assessed 136 patients with tandem occlusion due to dissection, including 65 (47.8%) treated with emergency CAS and 71 (52.2%) without. The overall rates of favorable outcome (90-day modified Rankin Scale score, 0–2) and successful reperfusion (modified Thrombolysis in Cerebral Infarction, 2b–3) were 58.0% (n=76 [95% CI, 49.6%–66.5%]) and 77.9% (n=106 [95% CI, 71.0%–85.0%]), respectively. In subgroup analyses, the rate of successful reperfusion (89.2% versus 67.6%; adjusted odds ratio, 2.24 [95% CI, 1.33–3.77]) was higher after CAS, whereas the 90-day favorable outcome (54.3% versus 61.4%; adjusted odds ratio, 0.84 [95% CI, 0.58–1.22]), symptomatic intracerebral hemorrhage (sICH; 10.8% versus 5.6%; adjusted odds ratio, 1.59 [95% CI, 0.79–3.17]), and 90-day mortality (8.0% versus 5.8%; adjusted odds ratio, 1.00 [95% CI, 0.48–2.09]) did not differ. In sensitivity analyses of patients with successful intracranial reperfusion, CAS was not associated with an improved clinical outcome. Conclusions: Emergency stenting of the dissected cervical carotid artery during endovascular therapy for tandem occlusions seems safe, whatever the quality of the intracranial reperfusion