A. Cabal

Contrast cancellation technique applied to digital x-ray imaging using silicon strip detectors.

Dual-energy mammographic imaging experimental tests have been performed using a compact dichromatic imaging system based on a conventional x-ray tube, a mosaic crystal, and a 384-strip silicon detector equipped with full-custom electronics with single photon counting capability. For simulating mammal tissue, a three-component phantom, made of Plexiglass, polyethylene, and water, has been used. Images have been collected with three different pairs of x-ray energies: 16-32 keV, 18-36 keV, and 20-40 keV. A Monte Carlo simulation of the experiment has also been carried out using the MCNP-4C transport code. The Alvarez-Macovski algorithm has been applied both to experimental and simulated data to remove the contrast between two of the phantom materials so as to enhance the visibility of the third one.

Improved radiographic methods for the investigation of paintings using laboratory and synchrotron X-ray sources

It is generally known that radiographic inspection of 15–17th century paintings can easily be done with a polychromatic X-ray source using a voltage between 20 kV and 40 kV in combination with classic X-ray films. Unfortunately, the spatial structure of numerous 19th and early 20th century paintings cannot be visualized with conventional radiography due to several reasons such as the use of lead white grounds or low absorbing pigments. Radiographic images are blurred or worse, they do not contain the picture of the painting. During the last decades, many technological innovations have been introduced in the field of radiography but their possibilities in cultural heritage have not been explored in full detail. In our investigation we used phosphor imaging plates, energy dispersive detectors and CCD-cameras in combination with synchrotron radiation and conventional X-ray tubes in order to improve the quality of radiographic images. Several promising techniques that could improve the quality of radiographs of paintings were identified.

Monte Carlo assisted classical method for the calculation of dpa distributions in solids materials

In the present work the extended Monte Carlo assisted Classical Method (MCCM) is presented. The method consists on a calculation procedure for the determination of the displacements per atom (dpa) distribution in solid materials, which allows studying the gamma irradiation damage in different materials. The same one is based on the electrons elastic scattering classic theories and makes use of the Monte Carlo simulation of physical processes involved in the radiation interactions with substance. Recently, the contribution from positrons to dpa distributions has been also included. This method has been applied to different materials: metals (iron), semiconductors (Si and CZT) and high temperature superconductors like YBCO. Among other things, this procedure has allowed to study the dpa cross sections and the in-depth dpa distributions in a wide range of incident gamma energies. Also in compound materials, the contribution from each atomic species is possible to be evaluated.

Feasibility of Silicon strip detectors and low noise multichannel readout system for medical digital radiography.

A x‐ray detection system based on Silicon strip detectors and low noise multichannel readout system was developed in the framework of the collaboration project. The study of the feasibility of this detector system for medical applications was done. Our system has characteristics that match the requirements of a digital image system.

Effect of x-ray energy dispersion in digital subtraction imaging at the iodine K-edge--A Monte Carlo study

The effect of the energy dispersion of a quasi-monochromatic x-ray beam on the performance of a dual-energy x-ray imaging system is studied by means of Monte Carlo simulations using MCNPX (Monte Carlo N-Particle eXtended) version 2.6.0. In particular, the case of subtraction imaging at the iodine K-edge, suitable for angiographic imaging application, is investigated. The average energies of the two beams bracketing the iodine K-edge are set to the values of 31.2 and 35.6 keV corresponding to the ones obtained with a compact source based on a conventional x-ray tube and a mosaic crystal monochromator. The energy dispersion of the two beams is varied between 0 and 10 keV of full width at half-maximum (FWHM). The signal and signal-to-noise ratio produced in the simulated images by iodine-filled cavities (simulating patient vessels) drilled in a PMMA phantom are studied as a function of the x-ray energy dispersion. The obtained results show that, for the considered energy separation of 4.4 keV, no dramatic deterioration of the image quality is observed with increasing x-ray energy dispersion up to a FWHM of about 2.35 keV. The case of different beam energies is also investigated by means of fast simulations of the phantom absorption.

Digital Radiography of Mammographic Phantoms and Biologic Samples Using a 64 Microstrips Crystalline Silicon Detector Coupled to the RX64 ASIC

The present paper synthesizes the results obtained in the evaluation of a 64 microstrips crystalline silicon detector coupled to RX64 ASIC, designed for high‐energy physics experiments, as a useful X‐ray detector in advanced medical radiography, specifically in digital mammography. Research includes the acquisition of two‐dimensional radiography of a mammography phantom using the scanning method, and the comparison of experimental profile with mathematically simulated one. The paper also shows the experimental images of three biological samples taken from breast biopsies, where it is possible to identify the presence of possible pathological tissues.

Simulation of a PET system and study of some geometry parameters

The Monte Carlo simulation of small animal conventional positron emission tomography (PET) is an important tool for geometry parameters optimization, image reconstruction algorithm tests, performance of different radioisotopic sources and some others. The present work deals with the Monte Carlo study of a small cylindrical PET system in the framework of the GEANT4 code. Two different accepted ring width values and spherical sources of 18F and 44Sc isotopes were considered. Then, the improvement of the detection efficiency and spatial resolution was analyzed in all the cases.

Multiscale modeling of radiation damage and annealing in Si samples implanted with 57-Mn radioactive ions

The radiation damage created in silicon materials by 57Mn→57Fe ion implantation has been studied and characterized by Mössbauer spectroscopy showing four main lines, assigned to: substitutional, interstitial and damaged configuration sites of the implanted ions. Nevertheless, the Mössbauer spectrum of 57Fe in this materials remains with some ambiguous identification regarding the implantation configurations before and after annealing, specially the damaged configurations and its evolution. In the present work some possible implantation configurations are suggested and evaluated using a multiscale approach by Monte Carlo ion transport and electronic structure calculations within DFT. The proposed implantation environments were evaluated in terms of stability and the 57Fe hyperfine parameters were calculated to establish the connections with the experimental observations. Good agreement was found between the experimental and the calculated hyperfine parameters for some configurations; suggesting which ones could be the implantation environments before and after sample annealing.

Comparison Between Two Monte Carlo Simulations of Angiographic Phantom Coupled to Silicon Strip Detector

Preliminary results of a dual energy angiography simulation using the Monte Carlo package GEANT 3.2113 are presented and compared to Monte Carlo MCNP‐4C results reported before. The simulation is based on an experimental set up consisting of a Plexiglas‐aluminium step wedge phantom with 4 cylindrical cavities filled with iodated contrast medium. The silicon 384 microstrip detector was set into edge‐on configuration (incoming X‐rays parallel to longitudinal axis of the strips) and the properties of the simulated detector just resemble the ones of the real detector. Monochromatic photon beams of 31.5keV and 35.5keV are used to take advantage of the discontinuous variation of the iodine photon absorption at the energy of the K‐shell, the key to dual energy subtraction imaging.