Este articulo describe el procedimiento seguido en la obtencion de imagenes digitales con fines medicos utilizando detectores de microcintas de silicio. Se muestra el proceso de calibracion y obtencion de los parametros de optimizacion del circuito de lectura RX64. Se describe el proceso de analisis de las imagenes obtenidas a partir de un fantoma dinamico de angiografia y su correspondiente simulacion en el codigo de transporte de particulas MCNP-4C. 0.15cm

Improvement in image contrast and dose reduction, in mammographic x-ray imaging, can be achieved using narrow energy band x-ray beams in the 16-24 keV range. As part of an Italian Government funded project, a quasi-monochromatic system for mammography applications has been developed. The system is based on a tunable narrow energy band x-ray source operating in the 16-24 keV energy range. The bremsstrahlung beam is monochromatized via Bragg diffraction by a highly oriented pyrolytic graphite mosaic crystal (HOPG). The scanning system provides a large field (18 x 24 cm2) of quasi-monochromatic x-rays with energy resolution ranging from 10% at 18 keV to 17.2% at 24 keV. The system has been characterized in terms of fluence rate and energy resolution. An x-ray tube developed ad hoc allows us to acquire images in a reasonable time to minimize the motion blur. A qualitative analysis has been performed in order to know if the prototype system performances are far from a clinical application, by evaluating the spatial resolution, the field uniformity and the image quality as a function of the quasi-monochromatic beam energy. Dose evaluation has been performed as a function of the energy and compared to a conventional system for mammography. The quasi-monochromatic prototype system can produce comparable image quality at half the dose.

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: , , and . 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.

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.

One of the research topics of the IMI project is the development of a quasi-monochromatic source for mammography applications. Quasi-monochromatic source has been produced via Bragg diffraction on mosaic crystal with a conventional X-ray tube. The system has been characterized in terms of photon flux and exposure rate, capability in low contrast detection, delivered dose and energy resolution properties. Radiographs of test phantoms have been obtained with a conventional screen-film combination. (C) 2003 Elsevier B.V. All rights reserved.

Preliminary results of a dual energy angiography simulation using the Monte Carlo package GEANT 3.2113 [1] are presented and compared to Monte Carlo MCNP-4C [2] results reported before [3]. 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.

The imaging capabilities of the dual energy angiography (DEA) based on the Bragg diffraction on a pyrolitic graphite target and CCD detectors coupled with fiber optic plate with scintillator (FOS) was evaluated using an experimental setup built for phantoms and small animals. The scanning system was built with a new X-ray source, which produces two thin parallel quasi-monochromatic beams starting from a conventional X-ray tube; these beams have peak energies centered before and after the iodine K-edge energy respectively. The polychromatic X-ray beam is monochromatized by Bragg diffraction on a pyrolitic graphite crystal and splitted in two thin parallel beams. The beams go through the phantom and are detected with a CCD coupled with FOS detector. The image results as difference between the remaining intensities of two beams. In this work, we will report results obtained in terms of sensitivity, image quality and dose reduction in comparison with standard angiographic apparatus. In particular, the capability to visualize small vessels will be discussed.

We have investigated a non-conventional angiographic imaging methodology called Dual Energy Angiography (DEA) based on a quasi-monochromatic X-rays source.An experimental DEA apparatus was developed. The Bragg monochromator, mounted on a standard W-anode X-ray tube, generates two thin parallel beams with energies peaked before (at E-L=31.1 keV) and after (at E-H= 35.3 keV) the iodine K-edge(E-K= 33.2 keV). Images result as the difference between the logarithms of the transmitted intensities of the two beams.A dedicated dynamic phantom, simulating different tissues absorption and containing calibrated vessels, was scanned under the monochromator slits by a PC-controlled scanning system.Two types of detectors were used and tested: a linear CCD coupled with FOS and a Si-strips detector with energy window discriminator.In this work resulting imaging capabilities of the DEA experimental system were compared with those of a commercial SIEMENS ANGIOSTAR digital subtraction angiographic apparatus.

Several techniques have been introduced in the last year to reduce the dose to the patient by minimizing the risk of tumour induced by radiation. In this work the radiological potential of dose reduction in quasi-monochromatic spectra produced via mosaic crystal Bragg diffraction has been evaluated, and a comparison with conventional spectra has been performed for four standard examinations: head, chest, abdomen and lumbar sacral spine. We have simulated quasi-monochromatic x-rays with the Shadow code, and conventional spectra with the Spectrum Processor. By means of the PCXMC software, we have simulated four examinations according to parameters established by the European Guidelines, and calculated absorbed dose for principal organs and the effective dose. Simulations of quasi-monochromatic laminar beams have been performed without anti-scatter grid, because of their inherent scatter geometry, and compared with simulations with conventional beams with anti-scatter grids. Results have shown that the dose reduction due to the introduction of quasi-monochromatic x-rays depends on different parameters related to the quality of the beam, the organ composition and the anti-scatter grid. With parameters chosen in this study a significant dose reduction can be achieved for two out of four kinds of examination.

We present results obtained with a single photon counting system of 384 silicon microstrips (100 micron pitch) equipped with six RX64DTH ASICs including charge preamplifier, shaper, two discriminators and two 20-bit counters for each channel. The energy resolution of the system was determined to be of 0.72 keV (rms) with a spread of threshold setting of 0.32 keV for the whole 384-channel module (at energies of 29-33 keV), indicating its excellent potential for dual-energy imaging. Images of a mammographic test object made of PMMA, polyethylene and water were taken in scanning mode (strips parallel to incoming X-rays) under the dual energy X-ray beams. Images were subsequently processed with the dual energy subtraction technique (Alvarez and Macovski, 1976). Experimental results agree well with MCNP simulations of the mammographic phantom and demonstrate the capability of our system to obtain contrast cancellation between two kinds of materials, thereby enhancing the visibility of small features in the third material.

A prototype of a combined CT-SPECT tomograph for breast cancer study has been developed and evaluated. It allows to perform scintimammography and X-ray CT in the same geometrical conditions. The CT system is based on a quasi-monochromatic beam tuned at 28 keV and an array of ultra fast ceramic scintillators coupled to photodiodes whilst the SPECT system is based on two scintillator matrices coupled to position sensitive photomultipliers. CT and SPECT sinograms of a test phantom were recorded and reconstruted with both modalities. Image fusion of CT and SPECT images was then performed. The developed CT-SPECT prototype is able to detect a region of interest of 1 cm(3), with a 10:1 tumour/background concentration ratio, within an object having a diameter of 8 cm. (C) 2002 Elsevier Science B.V. All rights reserved.

An angiographic practice an iodate contrast medium is injected in patient vessels with catheters. The absorption of X-rays rises immediately above the Iodine K-edge energy (33.17 keV), permitting to distinguish human soft tissues characterized by similar absorption's coefficients. Conventional image subtraction technique uses two images, acquired before and after the injection of the contrast medium, respectively. The vessels' morphology results from the difference of images so obtained. A different approach is presented: two quasimonochromatic peaks, having mean energies lower and higher than the Iodine K-edge, are produced with a pyrolytic graphite crystal monochromator and split in two thin parallel beams, respectively. These two beams impinge on phantoms simulating patient vessels and are detected with solid-state array detectors. The image results as the difference between the intensities of the two beams emerging from patient tissues and Iodine. In this work, we show results and first image of a phantom, characterized by calibrated vessels inside, obtained with an experimental apparatus to perform a double energy scanning in a 120 mm /spl times/ 120 mm field of view.

One of the main limitation to the extensive use of breast-cancer screening as a prevention method is the relatively high X-ray dose released to the patient. A new approach is under study in which two quasi-monochromatic beams with mean energies of 18.0 and 36.0 keV - are produced simultaneously, starting from an X-ray tube, by means of a monochromator based on a pyrolytic graphite crystal. The two beams are superimposed in space. The removal of the energy components with low content of diagnostic information from the spectrum, leads to a reduction of the dose released to patients maintaining (or improving) the image quality. The two quasi-monochromatic beams impinge on the patient and then are detected with a solid-state array detector; the image results as the difference between the transmitted intensities of the two detected beams.In this work, the performances of two different electronic readouts and three pixel widths of a silicon position sensitive array detector are simulated and described in order to minimize cross-talk effects between adjacent pixels. The use of a detector with spectrometric capabilities is necessary to separate, by means of thresholds, the high energy photons from the low energy ones. (C) 2003 Elsevier B.V. All rights reserved.

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 9 keV to 32 keV using fluorescence Xray 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 technique. In particular, the contrast for the angiographic test object has been evaluated for different concentrations of an iodate solution injected into 1 mm and 2 mm diameter vessels. Further developments, including a double threshold version of the ASIC, are also discussed.

A simple prototype system for static two-dimensional soft X-ray imaging using silicon microstrip detectors irradiated at normal incidence is presented. Radiation sensors consist of single-sided silicon detectors made from 300 mum thick wafers, read by RX64 ASICs. Data acquisition and control is performed by a Windows PC workstation running dedicated LabVIEW routines, connected to the sensors through a PCI-DIO-96 interface.Two-dimensional images are obtained by scanning a lead collimator with a thin slit perpendicular to the strip axis, along the whole detector size; the several strip profiles (slices) taken at each position are then put together to form a planar image.Preliminary results are presented, illustrating the high-resolution imaging capabilities of the system with soft X-rays. (C) 2003 Elsevier B.V. All rights reserved.

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.

First results from a silicon microstrip detector with 100μm pitch coupled to the RX64 ASIC are presented. The system is capable of single photon counting in digital X-ray imaging, with possible applications to dual energy mammography and angiography. The main features of the detecting system are low noise, good spatial resolution and high counting rate capability. The energy resolution and the conversion efficiency of the system are discussed, based on results obtained with fluorescence X-ray sources and quasi-monochromatic X-ray beams in the 8–36keV energy range, with strips being either orthogonal or parallel to the incoming X-rays. We present also preliminary imaging results obtained with a plexiglass phantom with tiny cylindrical cavities filled with iodate solution, simulating patient vessels; in this case the X-ray beam has two components, respectively below and above the iodine K-edge at 33.17keV.

A single photon counting X-ray imaging system, with possible applications to dual energy mammography and angiography, is presented. A silicon microstrip detector with 100μm 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.

Monochromatic x-ray beams are desirable in various fields of diagnostic radiology; in fact a reduction of the dose and an enhancement of the contrast could be achieved. In this work two different methods to monochromatize x-ray beams produced by conventional tubes have been compared. In the first one the beam is obtained via Bragg diffraction on mosaic crystal and in the second one by attenuating the polychromatic beam with aluminium filters. We have simulated quasi-monochromatic x-ray spectra by setting suitable values of Bragg's angle to obtain beams tuned to 20, 30, 40 and 50 keV with the SHADOW code, an x-ray tracing program designed to study the propagation and the interaction of a photon beam through an optical system. We have validated such a program by comparing some calculated data with measurements carried out on an experimental apparatus. Attenuated polychromatic x-ray spectra have been simulated by setting appropriate values of aluminium filters and potential with the SPECTRUM PROCESSOR, the software version of the Catalogue of Spectral Data for Diagnostic X-Rays, which provides radiographic x-ray spectra that can be attenuated with several material filters. The relation between the energy resolution and the flux as a function of the mean energy has been investigated and results have been compared. Results show that quasi-monochromatic x-ray beams produced via Bragg diffraction exhibit, for a given mean energy and energy resolution, a higher total flux compared to attenuated spectra.