Local Phase Symmetry Research Articles

Simetria, Transi¸c˜ao de Fase e Viola¸c˜ao Espontˆanea de Simetria

Simetrias e leis de conserva¸c˜ao s˜ao excelentes guias na formula¸c˜ao de modelos f´ısicos em diversas escalas de energia. A viola¸c˜ao de simetrias por transi¸c˜ao de fase ( viola¸c˜ao espontˆanea de simetria ) consegue descrever sistemas que v˜ao desde a Mat´eria Condensada at´e a F´ısica de Altas Energias. Neste ensaio irei apresentar um desenvolvimento conceitual de simetrias e suas viola¸c˜oes usando inicialmente como exemplo a simetria global de rota¸c˜ao e sua viola¸c˜aoespontˆanea, por um fluido escalar real, gerando o ferromagnetismo. O potencial usado por Landau-Ginzburg para explicar a supercondutividade por um fluido escalar complexo ´e muito similar ao ferromagnetismo. Atrav´es deste modelo podemos compreender a simetria de fase local ( simetria de calibre ) que este modelo apresenta gra¸cas ao acoplamento m´ınimo do campo eletromagn´etico com o fluido supercondutor. A partir da viola¸c˜ao espontˆanea desta simetria localdiscutimos como ocorre a gera¸c˜ao de massa do f´oton em ambiente supercondutor ( expuls˜ao do campo eletromagn´etico). Este processo ficou conhecido como o Mecanismo de Anderson-Higgs. Este mesmo mecanismo que ocorre em supercondutividade ´e utilizado para unificar o Eletromagnetismo e a intera¸c˜ao Fraca no Modelo Padr˜ao. Finalizamos este ensaio contextualizando o que veio a ser conhecido como campo de Higgs, cuja a excita¸c˜ao ( b´oson de Higgs ) acaba de ser verificada no LHC.

Bone enhancement in ultrasound using local spectrum variations for guiding percutaneous scaphoid fracture fixation procedures.

The scaphoid bone is the most frequently fractured bone in the wrist. When fracture fixation is indicated, a screw is inserted into the bone either in an open surgical procedure or percutaneously under fluoroscopic guidance. Due to the complex geometry of the wrist, fracture fixation is a challenging task. Fluoroscopic guidance exposes both the patient and the physician to ionizing radiation. Ultrasound-based guidance has been suggested as a real-time, radiation-free alternative. The main challenge of using ultrasound is the difficulty in interpreting the images due to the low contrast and noisy nature of the data. We propose a bone enhancement method that exploits local spectrum features of the ultrasound image. These features are utilized to design a set of quadrature band-pass filters and subsequently estimate the local phase symmetry, where high symmetry is expected at the bone locations. We incorporate the shadow information below the bone surfaces to further enhance the bone responses. The extracted bone surfaces are then used to register a statistical wrist model to ultrasound volumes, allowing the localization and interpretation of the scaphoid bone in the volumes. Feasibility experiments were performed using phantom and in vivo data. For phantoms, we obtain a surface distance error 1.08 mm and an angular deviation from the main axis of the scaphoid bone smaller than 5°, which are better compared to previously presented approaches. The results are promising for further development of a surgical guidance system to enable accurate anatomy localization for guiding percutaneous scaphoid fracture fixations.

Localisation of luminal epithelium edge in digital histopathology images of IHC stained slides of endometrial biopsies

Diagnosis of recurrent miscarriage due to abnormally high number of uterine natural killer (uNK) cells has recently been made possible by a protocol devised by Quenby et al. Hum Reprod 2009;24(1):45–54. The diagnosis involves detection and counting of stromal and uNK cell nuclei in endometrial biopsy slides immunohistochemically stained with haematoxylin for staining cell nuclei and CD56 as a marker for the uNK cells. However, manual diagnosis is a laborious process, fraught with subjective errors. In this paper, we present a novel method for detection of uterine natural killer (uNK) cells in the human female uterus lining and localisation of the luminal epithelium edge in endometrial biopsies. Specifically, we employ a local phase symmetry based method to detect stromal cell nuclei and propose an adaptive background removal method that significantly eases the segmentation of uNK cell nuclei regions. We also propose a novel method using alpha shapes for the identification of epithelial cell nuclei and B-Spline curve fitting on identified cell nuclei to localise the luminal epithelium edge. The objective of edge localisation is to avoid cell nuclei near the luminal epithelium edge being counted in the diagnosis process due to their non-relevance to the calculation of stromal to uNK cell ratio that determines the diagnosis of recurrent miscarriages in the end. The resulting algorithm offers a promising potential for computer-assisted diagnosis of recurrent miscarriage due to its high accuracy.

Automatic Adaptive Parameterization in Local Phase Feature-Based Bone Segmentation in Ultrasound

Intensity-invariant local phase features based on Log-Gabor filters have been recently shown to produce highly accurate localizations of bone surfaces from three-dimensional (3-D) ultrasound. A key challenge, however, remains in the proper selection of filter parameters, whose values have so far been chosen empirically and kept fixed for a given image. Since Log-Gabor filter responses widely change when varying the filter parameters, actual parameter selection can significantly affect the quality of extracted features. This article presents a novel method for contextual parameter selection that autonomously adapts to image content. Our technique automatically selects the scale, bandwidth and orientation parameters of Log-Gabor filters for optimizing local phase symmetry. The proposed approach incorporates principle curvature computed from the Hessian matrix and directional filter banks in a phase scale-space framework. Evaluations performed on carefully designed in vitro experiments demonstrate 35% improvement in accuracy of bone surface localization compared with empirically-set parameterization results. Results from a pilot in vivo study on human subjects, scanned in the operating room, show similar improvements.

Gauge theories and Galilean symmetry

Relations between a nonrelativistic local phase symmetry and the Galilean structure of the operator algebra are studied. The latter is derived from a few simple assumptions. For interacting systems, the assumption of phase independent localization leads to a unique Hamiltonian. Superselection rules for mass, time, and charge appear in intimate interrelationships.