U. Bottigli

A completely automated CAD system for mass detection in a large mammographic database

Mass localization plays a crucial role in computer-aided detection (CAD) systems for the classification of suspicious regions in mammograms. In this article we present a completely automated classification system for the detection of masses in digitized mammographic images. The tool system we discuss consists in three processing levels: (a) Image segmentation for the localization of regions of interest (ROIs). This step relies on an iterative dynamical threshold algorithm able to select iso-intensity closed contours around gray level maxima of the mammogram. (b) ROI characterization by means of textural features computed from the gray tone spatial dependence matrix (GTSDM), containing second-order spatial statistics information on the pixel gray level intensity. As the images under study were recorded in different centers and with different machine settings, eight GTSDM features were selected so as to be invariant under monotonic transformation. In this way, the images do not need to be normalized, as the adopted features depend on the texture only, rather than on the gray tone levels, too. (c) ROI classification by means of a neural network, with supervision provided by the radiologists diagnosis. The CAD system was evaluated on a large database of 3369 mammographic images [2307 negative, 1062 pathological (or positive), containing at least one confirmed mass, as diagnosed by an expert radiologist]. To assess the performance of the system, receiver operating characteristic (ROC) and free-response ROC analysis were employed. The area under the ROC curve was found to be Az = 0.783 +/- 0.008 for the ROI-based classification. When evaluating the accuracy of the CAD against the radiologist-drawn boundaries, 4.23 false positives per image are found at 80% of mass sensitivity.

Evidence for non-exponential elastic proton-proton differential cross-section at low |t| and √ s = 8 TeV by TOTEM

Abstract The TOTEM experiment has made a precise measurement of the elastic proton–proton differential cross-section at the centre-of-mass energy s = 8 TeV based on a high-statistics data sample obtained with the β ⁎ = 90 m optics. Both the statistical and systematic uncertainties remain below 1%, except for the t-independent contribution from the overall normalisation. This unprecedented precision allows to exclude a purely exponential differential cross-section in the range of four-momentum transfer squared 0.027 | t | 0.2 GeV 2 with a significance greater than 7 σ . Two extended parametrisations, with quadratic and cubic polynomials in the exponent, are shown to be well compatible with the data. Using them for the differential cross-section extrapolation to t = 0 , and further applying the optical theorem, yields total cross-section estimates of ( 101.5 ± 2.1 ) mb and ( 101.9 ± 2.1 ) mb , respectively, in agreement with previous TOTEM measurements.

EVALUATION OF ELEMENTAL AND COMPOUND SEMICONDUCTORS FOR X-RAY DIGITAL RADIOGRAPHY

Abstract We present a comparative study of the performance of elemental and compound solid state crystals of possible use in X-raY digital radiography. The general purpose EGS4 code was used to simulate photon-electron transport in the energy range 20 to 60 keV. The efficiency and the energy resolution, as a function of X-ray energy, are calculated and correlated to the different physical characteristics of the crystals considered.

Towards breast tomography with synchrotron radiation at Elettra: First images

The aim of the SYRMA-CT collaboration is to set-up the first clinical trial of phase-contrast breast CT with synchrotron radiation (SR). In order to combine high image quality and low delivered dose a number of innovative elements are merged: a CdTe single photon counting detector, state-of-the-art CT reconstruction and phase retrieval algorithms. To facilitate an accurate exam optimization, a Monte Carlo model was developed for dose calculation using GEANT4. In this study, high isotropic spatial resolution (120 μm)(3) CT scans of objects with dimensions and attenuation similar to a human breast were acquired, delivering mean glandular doses in the range of those delivered in clinical breast CT (5-25 mGy). Due to the spatial coherence of the SR beam and the long distance between sample and detector, the images contain, not only absorption, but also phase information from the samples. The application of a phase-retrieval procedure increases the contrast-to-noise ratio of the tomographic images, while the contrast remains almost constant. After applying the simultaneous algebraic reconstruction technique to low-dose phase-retrieved data sets (about 5 mGy) with a reduced number of projections, the spatial resolution was found to be equal to filtered back projection utilizing a four fold higher dose, while the contrast-to-noise ratio was reduced by 30%. These first results indicate the feasibility of clinical breast CT with SR.

Direct analysis of molybdenum target generated x-ray spectra with a portable device

In routine applications, information about the photon flux of x-ray tubes is obtained from exposure measurements and cataloged spectra. This approach relies mainly on the assumption that the real spectrum is correctly approximated by the cataloged one, once the main characteristics of the tube such as voltage, target material, anode angle, and filters are taken account of. In practice, all this information is not always available. Moreover, x-ray tubes with the same characteristics may have different spectra. We describe an apparatus that should be useful for quality control in hospitals and for characterizing new radiographic systems. The apparatus analyzes the spectrum generated by an x-ray mammographic unit. It is based on a commercial CZT produced by AMPTEK Inc. and a set of tungsten collimator disks. The electronics of the CZT are modified so as to obtain a faster response. The signal is digitized using an analog to digital converter with a sampling frequency of up to 20 MHz. The whole signal produced by the x-ray tube is acquired and analyzed off-line in order to accurately recognize pile-up events and reconstruct the emitted spectrum. The energy resolution has been determined using a calibrated x-ray source. Spectra were validated by comparison of the HVL measured using an ionization chamber.

Comparison of two portable solid state detectors with an improved collimation and alignment device for mammographic x-ray spectroscopy

We describe a portable system for mammographic x-ray spectroscopy, based on a 2 X 2 X 1 mm3 cadmium telluride (CdTe) solid state detector, that is greatly improved over a similar system based on a 3 X 3 X 2 mm3 cadmium zinc telluride (CZT) solid state detector evaluated in an earlier work. The CdTe system utilized new pinhole collimators and an alignment device that facilitated measurement of mammographic x-ray spectra. Mammographic x-ray spectra acquired by each system were comparable. Half value layer measurements obtained using an ion chamber agreed closely with those derived from the x-ray spectra measured by either detector. The faster electronics and other features of the CdTe detector allowed its use with a larger pinhole collimator than could be used with the CZT detector. Additionally, the improved pinhole collimator and alignment features of the apparatus permitted much more rapid setup for acquisition of x-ray spectra than was possible on the system described in the earlier work. These improvements in detector technology, collimation and ease of alignment, as well as low cost, make this apparatus attractive as a tool for both laboratory research and advanced mammography quality control.

Performance of a limited streamer tube hadron calorimeter

The energy response and the resolution of a hadron calorimeter test module prepared by the ALEPH collaboration at LEP have been studied between 5 and 50 GeV. The energy resolution for pions follows a 0.78√E law for orthogonally incident particles. Effects of different incident polar angles (θ = 90°, 60°, 50°) are studied. The wire readout and the trigger capability are also discussed.

Low contrast imaging with a GaAs pixel digital detector

A digital mammography system based on a GaAs pixel detector has been developed by the INFN (Istituto Nazionale di Fisica Nucleare) collaboration MED46. The high atomic number makes the GaAs a very efficient material for low energy X-ray detection (10-30 keV is the typical energy range used in mammography). Low contrast details can be detected with a significant dose reduction to the patient. The system presented in this paper consists of a 4096 pixel matrix built on a 200 /spl mu/m thick semi-insulating GaAs substrate. The pixel size is 170/spl times/170 /spl mu/m/sup 2/ for a total active area of 1.18 cm/sup 2/. The detector is bump-bonded to a VLSI front-end chip which implements a single-photon counting architecture. This feature allows to enhance the radiographic contrast detection with respect to charge integrating devices. The system has been tested by using a standard mammographic tube. Images of mammographic phantoms will be presented and compared with radiographs obtained with traditional film/screen systems. Monte Carlo simulations have been also performed to evaluate the imaging capability of the system. Comparison with simulations and experimental results will be shown.

Use of silicon and GaAs pixel detectors for digital autoradiography

Solid state detectors made of Si (4.8/spl times/8 mm/sup 2/) and GaAs (6.4/spl times/8 mm/sup 2/) pixel matrices bump-bonded to the Omega2 and Omega3 electronic read-out systems, developed at CERN for H.E.P. experiments, have been used to obtain autoradiographic images of clusters of human epithelial cells and DNA fragments separated via electrophoresis, both labeled with /sup 32/P. The system has shown a good minimum detectable activity per unit area of 2.10/sup -4/ cps mm/sup -2/, and has proved linear for a count rate in the range 0.2-20 cpa, typical of autoradiography. The pixel dimensions are 75/spl times/500 /spl mu/m/sup 2/ (Si-Omega2) and 50/spl times/500 /spl mu/m/sup 2/ (GaAs-Omega3), respectively. We are able to clearly localize clusters of cells which have incorporated the radioactive tracer and DNA fragments on an electrophoretic gel on paper (blots).

GaAs pixel radiation detector as an autoradiography tool for genetic studies

Abstract We present an autoradiography tool to be used mainly for genetic studies. It performs a quantitative analysis of radioactivity and can follow a dynamic process. We designed several applications, in particular one aimed at detecting hybridization of radio-labeled DNA fragments with known DNA-probes deposited on a micro-array. The technique is based on GaAs pixel array detector and low threshold, large dynamic range and good sensitivity integrated electronics developed for medical applications, suitable to detect markers (gamma or beta) such as 14C, 35S, 33P, 32P, 125I, even at very low activities. A Monte Carlo simulation of β− detection in GaAs is presented here in order to study the spatial resolution characteristics of such a system. For several biological applications, the electronics is required to perform at high temperatures (from 37° to 68°): we present here studies of noise and minimum threshold as a function of the temperature.