Marta Peracaula

Breast segmentation with pectoral muscle suppression on digital mammograms

Previous works on breast tissue identification and abnormalities detection notice that the feature extraction process is affected if the region processed is not well focused. Thereby, it is important to split the mammogram into interesting regions to achieve optimal breast parenchyma measurements, breast registration or to put into focus a technique when we search for abnormalities. In this paper, we review most of the relevant work that has been presented from 80s to nowadays. Secondly, an automated technique for segmenting a digital mammogram into breast region and background, with pectoral muscle suppression is presented.

Hints for a fast precessing relativistic radio jet in LS I +61 ◦ 303

Here we discuss two consecutive MERLIN observations of the X-ray binary LS I +61 ◦ 303. The first observation shows a double-sided jet extending up to about 200 AU on both sides of a central source. The jet shows a bent S-shaped structure similar to the one displayed by the well-known precessing jet of SS 433. The precession suggested in the first MERLIN image becomes evident in the second one, showing a one-sided bent jet significantly rotated with respect to the jet of the day bef ore. We conclude that the derived precession of the relativistic (β=0.6) jet explains puzzling previous VLBI results. Moreover, the fact that the precession is fast could be the explanation of t he never understood short term (days) variability of the associated gamma-ray source 2CG 135+01/3EG J0241+6103.

Development of a two-sided relativistic jet in Cygnus X-3

We present multi-epoch radio maps of the microquasar Cygnus X-3 obtained with the Very Large Array (VLA). The observations were carried out as a Target-of-Opportunity (ToO) project triggered by a series of strong (>5 Jy) radio outbursts in September 2000. We nd that Cygnus X-3 was well resolved and clearly elongated in the North-South direction at the VLA resolution in the weeks after the triggering events. In particular, the VLA map from our nal epoch of observation perfectly shows the development of a two-sided radio jet extending over 0.05 pc scales. We interpret both the proper motion and the brightness asymmetry between the jet components in the framework of special relativity eects. Assuming a distance of 10 kpc, the true jet velocity that we derive is close to 0:5c with a large angle with the line of sight. The possible connection between the VLA bipolar jets and the elongated one-sided structures observed at milli-arcsecond angular scales is also discussed.

The Cygnus X-3 Radio Jets at Arcsecond Scales

A deep Very Large Array map of the X-ray binary Cygnus X-3 is presented. The compact and highly variable core of the system has been carefully removed through a special subtraction process. This procedure allows us to reveal weak extended structures very close to it that otherwise would be masked by variability artifacts. In this way, we have been able to detect a symmetric pair of plasma condensations at arcsecond distances from the core. These features are very likely to be the remnants of a strong radio flare that occurred three months before our observing run. Accepting this association, the ejection velocity derived for both condensations is highly relativistic and amounts to 0.6c[D/10 kpc]. On the other hand, we also tentatively suggest that the Cygnus X-3 radio jets may be related to other larger scale symmetric radio lobes.

Radio continuum and near-infrared study of the MGRO J2019+37 region

Context. MGRO J2019+37 is an unidentified extended source of very high energy gamm a-rays originally reported by the Milagro Collaboration as the brightest TeV source in the Cygnus region. Its extended emission could be powered by either a single or several sources. The GeV pulsar AGL J2020.5+3653, discovered by AGILE and associated with PSR J2021+3651, could contribute to the emission from MGRO J2019+37. Aims. Our aim is to identify radio and near-infrared sources in the field of the extended TeV source MGRO J2019+37, and study potential counterparts to explain its emission. Methods. We surveyed a region of about 6 square degrees with the Giant Metrewave Radio Telescope (GMRT) at the frequency 610 MHz. We also observed the central square degree of this survey in the near-infrared Ks-band using the 3.5 m telescope in Calar Alto. Archival X-ray observations of some specific fiel ds are included. VLBI observations of an interesting radio source were performed. We explored possible scenarios to produce the multi-TeV emission from MGRO J2019+37 and studied which of the sources could be the main particle accelerator. Results. We present a catalogue of 362 radio sources detected with the GMRT in the field of MGRO J2019+37, and the results of a cross-correlation of this catalog with one obtained at n ear-infrared wavelengths, which contains∼ 3× 10 5 sources, as well as with available X-ray observations of the region. Some peculiar sources inside the∼1 ◦ uncertainty region of the TeV emission from MGRO J2019+37 are discussed in detail, including the pulsar PSR J2021+3651 and its pulsar wind nebula PWN G75.2+0.1, two new radio-jet sources, the Hii region Sh 2-104 containing two star clusters, and the radio source NVSS J202032+363158. We also find that the hadronic scenario is the most likely in case of a s ingle accelerator, and discuss the possible contribution f rom the sources mentioned above. Conclusions. Although the radio and GeV pulsar PSR J2021+3651 / AGL J2020.5+3653 and its associated pulsar wind nebula PWN G75.2+0.1 can contribute to the emission from MGRO J2019+37, extrapolation of the GeV spectrum does not explain the detected multi-TeV flux. Other sources discussed here could contribute to the emission of the Milagro source.

Detection of superimposed periodic signals using wavelets

In this paper we present a wavelet-based algorithm that is able to detect superimposed periodic signals in data with low signal-to-noise ratio. In this context, the results given by classical period determination methods depend strongly on the intrinsic characteristics of each periodic signal, like amplitude or profile. It is then difficult to detect the different periods present in the data set. The results given by the wavelet-based method for period determination we present here are independent of the characteristics of the signals.

Multi-Scale Image Analysis Applied to Radioastronomical Interferometric Data

Multi-Scale image analysis is specially suited to detect objects in deep wide field radio astronomical images obtained through interferometric aperture synthesis techniques. These images are usually complex and show a diversity of objects that can be characterized at different scales. In this context wavelet decomposition can be a tool to detect and separate the components of the image. However, the presence of very bright sources produce polluting artifacts in the planes of the wavelet decomposition that difficult the analysis. To overcome this problem we propose a hybrid method where in a first stage bright sources are detected through thresholding techniques and a image that does not contain them is created. In a second stage wavelet decomposition is applied to this residual image in order to detect fainter sources. We show the validity of the method using a previously catalogued image.

Segmenting extended structures in radio astronomical images by filtering bright compact sources and using wavelets decomposition

The automatic segmentation of extended real structures (such as SNRs, HII regions, bow shocks, etc) in large surveys is a difficult task due to their morphological complexity and their wide variety in scale and surface brightness. With the aim of dealing with these issues we propose in this paper an automatic segmentation method based on applying wavelet decomposition in the residual thresholded images. The use of this strategy, instead of a wavelet decomposition on the original image, allows to avoid the artifacts produced by strong sources. Experimental results with radio images demonstrate that the proposed method successfully segments extended structures at different scales and therefore is suitable for further morphological analysis and object recognition processes.

A boosting based approach for automatic micro-calcification detection

In this paper we present a boosting based approach for automatic detection of micro-calcifications in mammographic images Our proposal is based on using local features extracted from a bank of filters for obtaining a description of the different micro-calcifications morphology The approach performs an initial training step in order to automatically learn and select the most salient features, which are subsequently used in a boosting classifier to perform the detection The validity of our method is demonstrated using 112 mammograms of the well-known digitised MIAS database and 280 mammograms of a full-field digital database The experimental evaluation is performed in terms of ROC analysis, obtaining Az=0.88 and Az=0.90 respectively, and FROC analysis The obtained results show the feasibility of our approach for detecting micro-calcifications in both digitised and digital technologies.

Detecting Faint Compact Sources Using Local Features and a Boosting Approach

Several techniques have been proposed so far in order to perform faint compact source detection in wide field interferometric radio images. However, all these methods can easily miss some detections or obtain a high number of false positive detections due to the low intensity of the sources, the noise ratio, and the interferometric patterns present in the images. In this paper we present a novel strategy to tackle this problem. Our approach is based on using local features extracted from a bank of filters in order to provide a description of different types of faint source structures. We then perform a training step in order to automatically learn and select the most salient features, which are used in a Boosting classifier to perform the detection. The validity of our method is demonstrated using 19 real images that compose a radio mosaic. The comparison with two well-known state of the art methods shows that our approach is able to obtain more source detections, reducing also the number of false positives.