Arturo García Pérez

Localized active contour model with background intensity compensation applied on automatic MR brain tumor segmentation

Abstract This paper presents a Localized Active Contour Model (LACM) integrating an additional step of background intensity compensation. The region-based active contour models that use statistical intensity information are more sensitive to the high mean intensity distance between consecutive regions. In Magnetic Resonance Imaging (MRI) this distance is great between the foreground and the background, hence it leads to an incorrect delineation of the target. In order to resolve this problem, an automatic process is introduced in our model for balancing the mean intensity distance between an image foreground and its background. The aim is to minimize the attraction effect of the active contour model to the undesired borderlines defined by these two mentioned image regions. By using this approach not only the obtained accuracy outperforms the traditional localized mean separation active contour model, but also it reduces the computation time of the segmentation task. In addition, this method was efficiently applied on automatic brain tumor segmentation in multimodal MRI data. The Hierarchical Centroid Shape Descriptor (HCSD) was used for detecting the region of interest i.e. abnormal tissue so as to automatically initialize the active contour. The validation of experiments was carried out on synthetic images and the quantitative evaluation was performed on the BRATS2012 database. Finally, the accuracy achieved by the proposed method was compared to the localized mean separation intensity, the localized Chan-Vese, the local Gaussian distribution fitting and the local binary fitting models by using the Dice coefficient, Sensitivity, Specificity and the Hausdorff distance. The computation time of the methods was also measured for comparison purposes. The obtained results show that the proposed model outperforms the accuracy of the selected state of the art methods. Moreover, it is also faster than the comparative methods in the medical image segmentation task.

All-normal dispersion photonic crystal fiber for parabolic pulses and supercontinuum generation

We have designed an all-normal dispersion photonic crystal fiber optimized for pumping at 800 nm with initial pulses which are typical for conventional Ti:Sapphire lasers. Parabolic pulse formation and supercontinuum generation in this fiber is analyzed both in time and frequency domains.

Nonlinear pulse reshaping in passive optical fibers towards quasi-parabolic waveforms

Generation and applications of the optical pulses with a parabolic intensity profile has developed into the area of dynamic research activity over recent years. Parabolic pulses can propagate remaining their parabolic profile. Particularly these pulses resist to the deleterious effect of the optical wave breaking. They are of great interest for a number of applications including the high power pulse generation, and all optical signal processing. Alternative methods of generating parabolic pulses are of especial interest in the context of non-amplification usage, such as optical telecommunications. It is found that Gaussian waveforms provide best quasi-parabolic pulses among others and within shortest distance. There is a range of soliton numbers where the shape of quasi-parabolic pulse is closest to parabolic one.

Optical pulse transformations beyond optical wave breaking

Formation of triangular ultrashort optical pulses is demonstrated theoretically. Quality of those pulses and their properties are discussed.

Band engineering of complex asymmetric multiple quantum wells for optically pumped semiconductor disk lasers

Asymmetric multiple quantum well active regions for optically-pumped semiconductor disk lasers (OPS-DLs) are designed employing wave function engineering within GaAs/AlGaAs material system, which provide simultaneously good electronic confinement, large gain and effective carrier transport. Experimental investigation has shown that such an approach gives record values of the conversion efficiency among OPSDLs and provides high values of the output power.