Stochastic model for quantum noise analysis in flat-panel detectors for medical imaging applications.

A one-dimensional stochastic model is proposed to analyze the characteristics of quantum noise in flat-panel detectors (FPD) for medical imaging applications. The number of x-ray photons is modeled as a Poisson process, and explicit expressions for the autocorrelation function and noise power spectrum density (NPSD) are obtained in terms of the exposure dose, blur shape in the capture element, and pixel size. The results from the proposed model are validated with numerical simulations, and it is shown that this model can be used for the analysis of the noise properties of the FPD. The influence of these three parameters on the NPSD is then investigated.

Cartoon-texture image decomposition using blockwise low-rank texture characterization.

Using a novel characterization of texture, we propose an image decomposition technique that can effectively decomposes an image into its cartoon and texture components. The characterization rests on our observation that the texture component enjoys a blockwise low-rank nature with possible overlap and shear, because texture, in general, is globally dissimilar but locally well patterned. More specifically, one can observe that any local block of the texture component consists of only a few individual patterns. Based on this premise, we first introduce a new convex prior, named the block nuclear norm (BNN), leading to a suitable characterization of the texture component. We then formulate a cartoon-texture decomposition model as a convex optimization problem, where the simultaneous estimation of the cartoon and texture components from a given image or degraded observation is executed by minimizing the total variation and BNN. In addition, patterns of texture extending in different directions are extracted separately, which is a special feature of the proposed model and of benefit to texture analysis and other applications. Furthermore, the model can handle various types of degradation occurring in image processing, including blur+missing pixels with several types of noise. By rewriting the problem via variable splitting, the so-called alternating direction method of multipliers becomes applicable, resulting in an efficient algorithmic solution to the problem. Numerical examples illustrate that the proposed model is very selective to patterns of texture, which makes it produce better results than state-of-the-art decomposition models.

A reduced rank approach for covariance matrix estimation in EEG signal classification.

Common Spatial Pattern (CSP) methods are widely used to extract the brain activity for brain machine interfacing (BMI) based on electroencephalogram (EEG). For each mental task, CSP methods estimate a covariance matrix of EEG signals and adopt the uniform average of the sample covariance matrices over trials. However, the uniform average is sensitive to outliers caused by e.g. unrelated brain activity. In this paper, we propose an improvement of the estimated covariance matrix utilized in CSP methods by reducing the influence of the outliers as well as guaranteeing positive definiteness. More precisely, our estimation is the projection of the uniform average onto the intersection of two convex sets: the first set is a special reduced dimensional subspace which alleviates the influence of the outliers; the second is the positive definite cone. A numerical experiment supports the effectiveness of the proposed technique.

Enhanced surface sensitivity in secondary ion mass spectrometric analysis of organic thin films using size-selected Ar gas-cluster ion projectiles.

A size-selected argon (Ar) gas-cluster ion beam (GCIB) was applied to the secondary ion mass spectrometry (SIMS) of a 1,4-didodecylbenzene (DDB) thin film. The samples were also analyzed by SIMS using an atomic Ar(+) ion projectile and X-ray photoelectron spectroscopy (XPS). Compared with those in the atomic-Ar(+) SIMS spectrum, the fragment species, including siloxane contaminants present on the sample surface, were enhanced several hundred times in the Ar gas-cluster SIMS spectrum. XPS spectra during beam irradiation indicate that the Ar GCIB sputters contaminants on the surface more effectively than the atomic Ar(+) ion beam. These results indicate that a large gas-cluster projectile can sputter a much shallower volume of organic material than small projectiles, resulting in an extremely surface-sensitive analysis of organic thin films.

Immunohistological findings of suppurative granulomas of Yersinia enterocolitica appendicitis: a report of two cases.

We report on the histopathologic and immunohistologic findings of two cases of suppurative granulomatous appendicitis of Yersinia enterocolitica (Y. ent.). Using formalin-fixed, paraffin-embedded materials, polymerase chain reaction revealed Y. ent. in both cases. Histologically, the epithelioid cell granulomas (EPGs) were transmural in both cases. The EPGs were predominantly nonsuppurative, and were surrounded by a lymphoid cuff composed of small lymphocytes. A portion of EPGs contained suppuration of the centers of the granulomas (central microabscesses). The EPGs were composed of numerous histiocytes with or without epithelioid cell features, along with scattered small T-lymphocytes and plasmacytoid monocytes. None of the EPGs contained monocytoid B-cells. Immunohistochemical study demonstrated that EPGs were usually surrounded by surface IgM/D+ small mantle zone lymphocytes. Moreover, CNA.42 immunostaining occasionally demonstrated residual follicular dendritic cells in the center of the EPGs. The overall histomorphologic and immunohistochemical findings demonstrated that the EPGs with Y. ent. are of the B-cell negative hypersensitivity type and occur in reactive germinal centers. In one case, regional lymph nodes contained EPGs showing the same histologic and immunohistologic findings as those of the appendix. The present study indicates that among abscesses forming epithelioid granulomatous lesions, EPGs with Y. ent. were B-cell negative granulomas, and it demonstrates histopathologic and immunohistochemical findings different from those of cat scratch disease and lymphogranuloma venerum, which contain numerous monocytoid B-cells.