Andrea Kovács

Harris function based active contour external force for image segmentation

Deformable active contour (snake) models are efficient tools for object boundary detection. Existing alterations of the traditional gradient vector flow (GVF) model have reduced sensitivity to noise, parameters and initial location, but high curvatures and noisy, weakly contrasted boundaries cause difficulties for them. This paper introduces two Harris based parametric snake models, Harris based gradient vector flow (HGVF) and Harris based vector field convolution (HVFC), which use the curvature-sensitive Harris matrix to achieve a balanced, twin-functionality (corner and edge) feature map. To avoid initial location sensitivity, starting contour is defined as the convex hull of the most attractive points of the map. In the experimental part we compared our methods to the traditional external energy-inspired state-of-the-art GVF and VFC; the recently published parametric decoupled active contour (DAC) and the non-parametric Chan-Vese (ACWE) techniques. Results show that our methods outperform the classical approaches, when tested on images with high curvature, noisy boundaries.

Improved Harris Feature Point Set for Orientation-Sensitive Urban-Area Detection in Aerial Images

This letter addresses the automatic detection of urban area in remotely sensed images. As manual administration is time consuming and unfeasible, researchers have to focus on automated processing techniques, which can handle various image characteristics and huge amount of data. The applied method extracts feature points in the first step, which is followed by the construction of a voting map to represent urban areas. Finally, an adaptive decision making is performed to find urban areas. This letter presents methodological contributions in two key issues to the algorithm: 1) An automatically extracted Harris-based feature point set is introduced for the first step, which is able to represent urban areas more precisely. 2) An improved orientation-sensitive voting technique is proposed, exploiting the orientation information calculated in the local neighborhood of points. Evaluation results show that the proposed contributions increase the detection accuracy of urban areas.

High Definition Feature Map for GVF Snake by Using Harris Function

In image segmentation the gradient vector flow snake model is widely used. For concave curvatures snake model has good convergence capabilities, but poor contrast or saddle corner points may result in a loss of contour. We have introduced a new external force component and an optimal initial border, approaching the final boundary as close as possible. We apply keypoints defined by corner functions and their corresponding scale to outline the envelope around the object. The Gradient Vector Flow (GVF) field is generated by the eigenvalues of Harris matrix and/or the scale of the feature point. The GVF field is featured by new functions characterizing the edginess and cornerness in one function. We have shown that the max(0,log[max(λ 1, λ 2)]) function fulfills the requirements for any active contour definitions in case of difficult shapes and background conditions. This new GVF field has several advantages: smooth transitions are robustly taken into account, while sharp corners and contour scragginess can be perfectly detected.

High on clopidogrel treatment platelet reactivity is frequent in acute and rare in elective stenting and can be functionally overcome by switch of therapy

UNLABELLED The benefit of adjusted antiplatelet therapy in patients with myocardial infarction after primary percutaneous coronary intervention is not well elucidated. We aimed to identify patients with high on treatment platelet reactivity and to gradually adjust antiplatelet therapy. MATERIALS AND METHODS We enrolled 133 acute myocardial infarction and 67 stable angina patients undergoing intracoronary stenting into our study. Maximal aggregation was determined with light transmission aggregometry. Aggregation >50% induced by 5 μM ADP was indexed with high on-clopidogrel treatment platelet reactivity. In these cases 75 mg clopidogrel was doubled and control test was performed. Patients effectively inhibited with 150 mg clopidogrel were defined as clopidogrel pseudo non-responders. Patients with high platelet reactivity even on 150 mg clopidogrel were considered as clopidogrel real non-responders and were switched to ticlopidine. RESULTS Aggregations (5ADP; p=0.046) and the ratio of real non-responders (p=0.013) were significantly higher in the myocardial infarction group. Most real non-responders were effectively treated with switch of therapy. The ratio of pseudo non-responders also tended to be higher in myocardial infarction. Platelet reactivity remained constant during follow-up; however, a new appearance of high platelet reactivity was observed at 6 and at 12 months. CONCLUSIONS Patients with acute myocardial infarction undergoing percutaneous coronary intervention may benefit from prospective platelet function testing, because of higher platelet reactivity and much higher ratio of clopidogrel real non-response. Switch of therapy may effectively overcome clopidogrel non-response. A new appearance of high platelet reactivity with unknown clinical significance is observed in both groups among the patients on clopidogrel.

Improved force field for vector field convolution method

Parametric active contours are efficient tools for boundary detection. However, existing external-energy-inspired methods have difficulties when detecting high curvature, noisy or low contrasted contours and they often suffer from initialization sensitivity. To address these issues, this paper introduces Harris-based Vector Field Convolution (HVFC), operating with the modified characteristic function of Harris corner detector used in the feature map of the external force component. Initial contour is calculated as the convex hull of the most salient points of the map. Experimental results show that HVFC outperforms other state-of-the-art methods, when tested on high curvature, noisy or low-contrasted contours.

Elevated C1rC1sC1inh levels independently predict atherosclerotic coronary heart disease

UNLABELLED Clinical studies as well as animal models emphasized the importance of the complement system in the pathogenesis of coronary atherosclerosis and cardiovascular diseases. Our aim was to examine the extent and clinical implication of complement system activation in patients with stable atherosclerotic coronary heart disease (ACHD). Seventy-six patients with stable angina pectoris (SAP) scheduled for elective coronary angiography were enrolled into the study. Percutaneous coronary intervention (PCI) was performed in 24 patients, in 27 patients (NOPCI group) the coronary angiography showed significant stenosis and bypass surgery (CABG) or optimal medical therapy (OMT) were advised, whereas in 25 patients the coronary angiography was negative (NC group). 115 volunteers served as healthy controls (HC). In all individuals, the plasma level of several complement activation products - C1rC1sC1inh, C3bBbP and SC5b-9 - were determined on admission, strictly before the coronary angiography. In patients with angiographically proven ACHD (PCI and NOPCI groups), the baseline C1rC1sC1inh levels were significantly higher compared to NC group and HC (p<0.0001, for both comparisons). According to the multiple logistic regression analysis, high C1rC1sC1inh level proved to be an independent biomarker of coronary heart disease (p<0.026, OR: 65.3, CI: 1.628-2616.284). CONCLUSION Activation of the classical complement pathway can be observed in angiographically proven coronary atherosclerosis. Elevated C1rC1sC1inh levels might represent an useful biomarker for coronary artery disease.

New Saliency Point Detection and Evaluation Methods for Finding Structural Differences in Remote Sensing Images of Long Time-Span Samples

The paper introduces a novel methodology to find changes in remote sensing image series. Some remotely sensed areas are scanned frequently to spot relevant changes, and several repositories contain multi-temporal image samples for the same area. The proposed method finds changes in images scanned by a long time-interval difference in very different lighting and surface conditions. The presented method is basically an exploitation of Harris saliency function and its derivatives for finding featuring points among image samples. To fit together the definition of keypoints and their active contour around them, we have introduced the Harris corner detection as an outline detector instead of the simple edge functions. We also demonstrate a new local descriptor by generating local active contours. Saliency points support the boundary hull definition of objects, constructing by graph based connectivity detection and neighborhood description. This graph based shape descriptor works on the saliency points of the difference and in-layer features. We prove the method in finding structural changes on remote sensing images.

Local contour descriptors around scale-invariant keypoints

Describing local patches to register image keypoints is an important task for building a huge database from video frames. When searching for an efficient descriptor, task is twofold: features must describe the featuring patches at a high efficiency, while the dimensionality should be kept at a manageable low value. The main assumption in finding local descriptors is the defect of continuity in the discrete neighborhood or the imperfectness of local shape formats. Curve fitting methods for noisy shapes are called: active contours are generated around keypoints. Local contours are characterized by a small number of Fourier descriptors, resulting a new feature set of low dimensionality. Similarity among different images are searched through these descriptors. The method was tested on 22 real-life video frames made by an outdoor surveillance camera of a city police central.

Alternative complement pathway activation during invasive coronary procedures in acute myocardial infarction and stable angina pectoris

The effect of invasive percutaneous coronary procedures on complement activation has not been elucidated. We enrolled stable angina patients with elective percutaneous coronary intervention (SA-PCI, n=24), diagnostic coronary angiography (CA, n=52) and 23 patients with ST segment elevation myocardial infarction and primary PCI (STEMI-PCI). Complement activation products (C1rC1sC1inh, C3bBbP and SC5b-9) were measured on admission, 6 and 24h after coronary procedures. The alternative pathway product, C3bBbP significantly and reversibly increased 6h after elective PCI (baseline: 7.81AU/ml, 6h: 16.09AU/ml, 24h: 4.27AU/ml, p<0.01, n=23) and diagnostic angiography (baseline: 6.13AU/ml, 6h: 12.08AU/ml, 24h: 5.4AU/ml, p<0.01, n=52). Six hour C3bBbP values correlated with post-procedural CK, creatinine level and the applied contrast material volume (r=0.41, r=0.4, r=0.3, p<0.05, respectively). In STEMI-PCI, baseline C3bBbP level was higher, compared to SA-PCI or CA patients (11.33AU/ml vs. 7.81AU/ml or 6.13AU/ml, p<0.001). Similarly, the terminal complex (SC5b-9) level was already elevated at baseline compared to SA-PCI group (3.49AU/ml vs. 1.87AU/ml, p=0.011). Complement pathway products did not increase further after primary PCI. Elective coronary procedures induced transient alternative complement pathway activation, influenced by the applied contrast volume. In STEMI, the alternative complement pathway is promptly activated during the atherothrombotic event and PCI itself had no further detectable effect.

Flying target detection and recognition by feature fusion

Abstract. We present a near-real-time visual-processing approach for automatic airborne target detection and classification. Detection is based on fast and robust background modeling and shape extraction, while recognition of target classes is based on shape and texture-fused querying on a-priori built real datasets. The presented approach can be used in defense and surveillance scenarios where passive detection capabilities are preferred (or required) over a secured area or protected zone.