M. Gombia

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.

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.

A dedicated system for breast cancer study with combined SPECT–CT modalities

A prototype ofa combined CT–SPECT tomograph f or 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 ofultra f ast ceramic scintillators coupled to photodiodes whilst the SPECT system is based on two scintillator matrices coupled to position sensitive photomultipliers. CT and SPECT sinograms ofa test phantom were recorded and reconstruted with both modalities. Image f ofCT and SPECT images was then performed. The developed CT–SPECT prototype is able to detect a region of interest of 1 cm 3 ,

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...

Attenuation compensation for breast tissue in combined CT/SPECT devices dedicated to mammography

The usefulness to generate attenuation maps from computed tomography (CT) system for compensation of photon attenuation in single photon emission computed tomography (SPECT) mammographic evaluation is discussed. The present investigation is part of a general project intended to perform co-registration of functional and morphological information. The experimental apparatus consists of a quasi-monochromatic X-ray computed tomography and a high resolution compact gamma camera. The projection data are reconstructed using filtered backprojection to form the X-ray CT image, which is then properly scaled to produce an estimate of the attenuation map at the energy of the emission nuclide. The scaling is done following a two phases model of the breast tissue which takes into account the realistic average composition of the basic components. It is shown that both for simulations and measurements, the attenuation maps, generated from the CT images, estimate accurately the attenuation of breast in the reconstructed SPECT evaluations.

Dual energy imaging in mammography: Cross-talk study in a Si array detector

Abstract 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.

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.

A simulation and modeling study comparing the performance of a germanium orthogonal strip detector and an Anger camera

Progress in detector technology has led to the development of a new generation of pixel-based imaging devices as potential competitors for Anger-type scintillation cameras. We modeled a 11 mm thick orthogonal strip germanium detector (GOSD) with 2 mm pitch and compared its performance to an Anger camera with a 10 mm thick NaI(Tl) crystal. The Anger camera simulation method was validated by experimental measurements made with point and volume sources. Resolution and sensitivity were determined for air and scatter measurements. The device is intended for use in breast tumor imaging, and expected device performance was simulated in response to 5 mm spherical tumors embedded in a referenced phantom geometry previously used for the simulation of a CsI pixellated detector. The thorax, the breast and the heart background contributions are considered in this phantom. A comparison of the results obtained indicates that the GOSD provides superior contrast than the Anger camera for every tumor to collimator distance. Also signal to noise ratio, FWHM and FWTM show a better response for the Germanium pixellated detector with respect to Anger camera due to better energy and spatial resolution of the germanium-based device.

Comparative study of in-vivo image improvement and dose reduction with dual energy angiography

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.