Luciano Ramello

K-edge digital subtraction imaging based on a dichromatic and compact x-ray source

This work proposes a compact dichromatic imaging system for the application of the K-edge digital subtraction technique based on a conventional x-ray tube and a monochromator system. A quasi-monochromatic x-ray beam at the energy of iodine K-edge is produced by Bragg diffraction on a mosaic crystal. Two thin adjacent beams with energies that bracket the K-edge discontinuity are obtained from the diffracted beam by means of a proper collimation system. They are then detected using an array of Si detectors. A home-made phantom is used to study the image quality as a function of iodine concentration. Signal and signal-to-noise ratio analysis has also been performed. The results are compared with theoretical expectations.

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.

Novel x-ray source for dual-energy subtraction angiography

In angiography practice an iodate contrast medium is injected in patient vessels with catheters. The absorption of x-rays raises immediately after the iodine K-edge energy. In digital subtraction angiography, two images are used, acquired before and after the injection of the contrast medium, respectively. The vessels morphology result from the difference of images so obtained. This technique involves a non-negligible risk of morbidity or mortality, due to high concentration of injected contrast agent. We are investigating a new source which produces two thin parallel quasi-monochromatic beams - having peak energies centered before and after the iodine K-edge energy, respectively - by using a conventional x-ray tube and a highly oriented pyrolytic graphite mosaic crystal. The polychromatic x-rays incident on the crystal are monochromatized by Bragg diffraction and split in two thin parallel beams, by means of a collimating system. These two beams impinge on the phantom simulating patient vessels and are detected with solid-state array detectors. The image results as difference between the remaining intensities of two beams. We report a preliminary study of the new technique performed both with theoretical stimulations and experimental measurements. Results of computer simulation give information about characteristics as size and quality of the quasi- monochromatic beams, that should be considered in detail to design a system dedicated to the clinical practice. Experimental measurements have been performed on a small- field detector in order to shows the enhancement of image contrast obtained with the application of the new technique.

A fast, high-granularity silicon multiplicity detector for the NA50 experiment at CERN

Abstract We have designed a silicon detector to measure the angular distribution and the multiplicity of charged secondaries produced in high-energy PbPb interactions. It will be used to characterize the events in the NA50 experiment. The experiment will have to function at very high rate, and the silicon detectors will have to operate in the high-radiation area close to the target. Therefore, the detector will have to be very fast (dead time below 50 ns), radiation resistant (up to the Mrad level as dose and up to more than 1013 particles/cm2 as non-ionizing damage) and of high granularity. The conditions on noise, speed and radiation hardness are comparable to the ones foreseen at the future Large Hadron Collider at CERN. We present here the detector design, discuss some of the solutions which have been investigated and report first results on the components of the system which have been designed and produced up to now.

X-ray imaging with a silicon microstrip detector coupled to the RX64 ASIC

A single photon counting X-ray imaging system, with possible applications to dual energy mammography and angiography, is presented. A silicon microstrip detector with 100 mm pitch strips is coupled to RX64 ASICs, each of them including 64 channels of preamplifier, shaper, discriminator and scaler. The system has low noise, good spatial resolution and high counting rate capability. Results on energy resolution have been obtained with a fluorescence source and quasi-monochromatic X-rays beams. Preliminary images obtained with an angiographic phantom are presented.

Results about imaging with silicon strips for Angiography and Mammography

We present results obtained with a single photon counting system consisting of 384 silicon microstrips of 100 micron pitch equipped with 6 RX64 ASICs. The ASIC includes a charge preamplifier, a shaper, a discriminator and a 20‐bit counter for each of its 64 channels. The energy resolution of the system has been measured in the range from 8 keV to 32 keV using fluorescence X‐ray lines from several targets, using either an Am‐241 source or an X‐ray tube. Then, the efficiency of the system has been determined using the specially developed quasi‐monochromatic X‐ray beams in the energy range 18–36 KeV. Good efficiency has been obtained in the edge‐on configuration, which is more suitable for the intended applications. The spatial resolution of the system has been verified using a special microfocus X‐ray tube equipped with capillaries. Finally, images of angiographic and mammographic test objects have been obtained with dual energy X‐ray beams and have then been processed with the dual energy subtraction techn...

The silicon multiplicity detector for the NA50 experiment at CERN

The design, operation and performance of the silicon strip Multiplicity Detector for the heavy-ion experiment NA50 at CERN are presented. The main features of the detector are high speed (50 MHz sampling frequency), high granularity (more than 13,000 strips), and good radiation resistance. The detector provided a measurement ofevent centrality in Pb–Pb collisions, as well as target identification and the measurement ofcharged particle pseudorapidity distributions as a function of centrality. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40

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.

Monte Carlo Simulation of a Silicon Strip Detector Response For Angiography Applications. First approach

We present First results of Monte Carlo simulation by the general purpose MCNP‐4C transport code of an experimental facility at Bologna S. Orsola hospital for studying the possible application of a X‐Ray detection system based on a silicon strip detector on a dual energy angiography. The quasi‐monochromatic X‐ray beam with the detector in the edge‐on configuration has been used to acquire images of a test object at two different energies (namely 31 and 35 keV) suitable for the K‐edge subtraction angiography application. As a test object a Plexiglas step wedge phantom with four cylindrical cavities, having 1 mm diameter was used. The cavities have been drilled and filled, with iodated contrast medium, whose concentration varied from 370 mg/ml to 92 mg/ml. Both the profiles obtained from measurements and the generated images where reproduced by computer simulation on a first approach to use this technique as an evaluation tool for future developments on the experimental setup.