PRINCIPAL GEODESIC ANALYSIS BOUNDARY DELINEATION WITH SUPERPIXEL-BASED CONSTRAINTS

In this paper an algorithm for accurate delineation of object boundaries is proposed. The method employs a superpixel algorithm to obtain an oversegmentation of the input image, used as a constraint in the task. A shape model is built by applying Principal Geodesic Analysis on angular representation of automatically placed uniformly distant landmark points. The shape model is used to detect the boundaries of an object on a given image by iterative elongation of a partial boundary along borders of superpixels. Contrary to many state-of-the-art methods, the proposed approach does not need an initial boundary. The algorithm was tested on two natural and two synthetic sets of images. Mean Dice coefficients between 0.91 and 0.97 were obtained. In almost all cases the object was found. In areas of relatively high gradient magnitude the borders are delineated very accurately, though further research is needed to improve the accuracy in areas of low gradient magnitude and automatically select the parameters of the proposed error function

Segmentation of bones in magnetic resonance images of the wrist

PURPOSE:   Rheumatoid arthritis (RA) is a disease characterized by progressive and irreversible destruction of bones and joints. According to current recommendations, magnetic resonance imaging (MRI) is used to asses three main signs of RA based on manual evaluation of MR images: synovitis, bone edema and bone erosions. The key feature of a future computer-assisted diagnostic system for evaluation RA lesions is accurate segmentation of 15 wrist bones. In the present paper, we focus on developing a wrist bones segmentation framework. METHOD:    The segmentation procedure consisted of three stages: segmentation of the distal parts of ulna and radius, segmentation of the proximal parts of metacarpal bones and segmentation of carpal bones. At every stage, markers of bones were determined first, using an atlas-based approach. Then, given markers of bones and a marker of background, a watershed from markers algorithm was applied to find the final segmentation. RESULTS:   The MR data for 37 cases were analyzed. The automated segmentation results were compared with gold-standard manual segmentations using a few well-established metrics: area under ROC curve AUC, mean similarity MS and mean absolute distance MAD. The mean (standard deviation) values of AUC, MS and MAD were 0.97 (0.04), 0.93 (0.09) and 1.23 (0.28), respectively. CONCLUSION:   The results of the present study demonstrate that automated segmentation of wrist bones is feasible. The proposed algorithm can be the first stage for the detection of early lesions like bone edema or synovitis

On Equivalence of Critical Collapse of Non-Abelian Fields

We continue our study of the gravitational collapse of spherically symmetric skyrmions. For certain families of initial data, we find the discretely self-similar Type II critical transition characterized by the mass scaling exponent $\gamma \approx 0.20$ and the echoing period $\Delta \approx 0.74$. We argue that the coincidence of these critical exponents with those found previously in the Einstein-Yang-Mills model is not accidental but, in fact, the two models belong to the same universality class.Comment: 7 pages, REVTex, 2 figures included, accepted for publication in Physical Review

Ocena wpływu zmiennego pola magnetycznego na wybrane parametry pracy serca - doniesienie wstępne

Wstęp: W pracy przedstawiono wyniki działania magnetoterapii na czynność serca pacjentów, u których prowadzono w warunkach klinicznych lecznicze zabiegi rehabilitacyjne po przebytych wcześniej urazach kręgosłupa lędźwiowego oraz stawów biodrowych. Materiał i metody: Stosowano przewidziane w takich przypadkach sinusoidalnie zmienne pola magnetyczne o następujących parametrach: indukcja 0,3 mT, częstotliwość 30 Hz (w rehabilitacji kręgosłupa lędźwiowego) oraz odpowiednio: 0,5 mT i 50 Hz (w rehabilitacji stawów biodrowych). Ocenę przeprowadzono na podstawie analizy nieliniowych parametrów krzywych obrazujących akcję serca: eksponent skalowania, które wyznaczono metodą DFA (detrended fluctuation analysis), diagramów Poincarego i entropii. Parametry te wyznaczono z pomiarów sygnałów fonokardiograficznych i elektrokardiograficznych, przeprowadzonych w trakcie działania pola magnetycznego oraz w 5-minutowych okresach bezpośrednio przed jego zastosowaniem i po nim. Wyniki i wnioski: W analizie otrzymanych wyników nie stwierdzono istotnych różnic pomiędzy rezultatami pomiarów na podstawie fonokardiogramu, jakie miały miejsce w trakcie działania pola magnetycznego oraz przed jego zastosowaniem i po tym okresie. Podobne wnioski dotyczą również analizy EKG zarejestrowanego przed magnetoterapią i po jej zastosowaniu. (Folia Cardiol. 2003; 10: 695–700

A new method of volume determination in three-dimensional ultrasonography

Background: The aim of this work was to develop a method of volume determination utilizing the grey scale histogram of three-dimensional (3D) ultrasonic (US) image. Volumes are calculated as the product of single voxel volume and the area of histogram peak representing investigated object. The proposed solution performance was compared with two other methods. First utilizes two-dimensional crosssection areas on subsequent image layers while the second allows the volume determination on the basis of one-dimensional measurements. Material/Methods: The 3D US phantoms images were used to test the procedure. The usefulness of the method was also demonstrated on several clinical examples. The ultrasonic 3D images were collected, their histograms calculated and fitted with model curves allowing the volume calculations. The accuracy and precision was assessed and t-test was used for evaluating performance of all considered methods. Results: The accuracy (understood as the difference between real and measured volume) achieved in the proposed solution (3.6%) was the highest comparing to alternative methods (5.2% and 8.4%). Also the p-value (two-tailed t-test) was better in the case of the presented method. The performance increase was due to the elimination of subjective delineation of measured regions of interest. Conclusions: The presented procedure can be successfully used for volume assessment concerning its simplicity, accuracy and time consumption. It should be emphasized that the new method does not require image segmentation, unlike other methods in use. The procedure was tested with 3D US imaging but can be used successfully with any 3D imaging modality

APPLICATION OF A LATTICE GAS MODEL FOR SUBPIXEL PROCESSING OF LOW-RESOLUTION IMAGES OF BINARY STRUCTURES

In the study an algorithm based on a lattice gas model is proposed as a tool for enhancing quality of lowresolution images of binary structures. Analyzed low-resolution gray-level images are replaced with binary images, in which pixel size is decreased. The intensity in the pixels of these new images is determined by corresponding gray-level intensities in the original low-resolution images. Then the white phase pixels in the binary images are assumed to be particles interacting with one another, interacting with properly defined external field and allowed to diffuse. The evolution is driven towards a state with maximal energy by Metropolis algorithm. This state is used to estimate the imaged object. The performance of the proposed algorithm and local and global thresholding methods are compared

3D GRAY-LEVEL HISTOMORPHOMETRY OF TRABECULAR BONE - A METHODOLOGICAL REVIEW

The goal of standard histomorphometry is to provide methods of qualitative description of tissue structure based on image data. Typical measurements include geometric areas, perimeters, length, angle of orientation, form factors, center of gravity coordinates etc. There are well-established procedures for deriving the aforementioned quantities from binary images. However, segmentation of in vivo images of trabecular bone poses a problem which has not been solved yet. Recent years have brought significant developments within an emerging field of “gray-level histomorphometry”. The general goal of gray-level histomorphometry is to provide procedures for measuring geometric areas, perimeters, length, angle of orientation, form factors, center of gravity coordinates etc. without the need for image segmentation. Although the field is not very mature yet, the collected results suggest that this approach opens new perspectives which should not be overlooked by the scientific community. In the present review we summarize the state-of-the-art within the 3D gray-level histomorphometry.</p