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The general-purpose EGS4 code has been used to evaluate the efficiency, the energy and the spatial resolution of a silicon crystal with double-side microstrips readout to detect X-rays in the diagnostic energy range (10–100 keV). A single crystal configuration, a sandwich arrangement with a high- Z converter foil in between two crystals and a multicrystal configuration have been investigated. The simulation with a low energy spectrum X-ray beam and a breast phantom has shown that this type of detector would be of valuable use in mammography applications: breast calcification with a diameter smaller than 500 μm can be easily identified.

This paper presents a method for identification of coronary disease using the discriminant analysis. The set of discriminant variables used is composed by the general characteristics of the patient, the lipemic values, collected by a blood analysis, and some results of a cardiac catheterism. By using all the variables a total level of classification of about 89.9% is reached, separating the healthy patients from the sick patients affected by a coronary disease. The discriminant analysis is also performed using the general characteristics of the patient and the lipemic values only (i.e. noninvasive medical examinations), and general characteristics and some results of a cardiac catheterism only. In conclusion, the diagnosis of coronary artery disease, obtained by discriminant analysis of noninvasive data, seems to be good enough to discriminate sick from healthy people and to assign patients to a further protocol.

This paper presents a set of measurements concerning the laser ability to perforate human atheromatic plaque and thrombus. Split segments of arteries were prepared under wet conditions and exposed to laser light at different power values and exposures. A multiline argon-ion laser, 5 W nominal power, coupled with a quartz fiber (600 μm diameter) was used. A dose effect correlation was found in the presence of homogeneous targets, independently of the power used. A linear fit to the data was made, which showed a very similar slope for homogeneous plaque (0.054±0.026, for a normalized χ2=0.08), as well as for organized thrombus (0.051±0.04, χ2=0.09). Such a correlation did not show up in the presence of nonhomogeneous targets.

Imaging capabilities, spatial resolution and spectroscopic analysis have been performed to compare the characteristics of imaging systems based on pixel detectors of different thickness. Each system consists of a single photon counting chip (PCC), developed in the framework of the Medipix Collaboration, bump bonded to a silicon detector. The detector is a matrix of 64times64 square pixels, with 170 mum pitch and thickness ranging from 300 to 800 mum. As expected, the intrinsic detection efficiency increases with detector thickness (for 22 keV photons the detection efficiency doubles in the examined thickness range), nevertheless the spatial resolution can be affected by a charge sharing mechanism between adjacent pixels due to charge diffusion. We have studied this effect and its dependence on the detector bias voltage and the threshold value of PCC with the aim of optimizing both the detection efficiency and the spatial resolution

To compare the characteristics of imaging systems based on pixel detectors of different thickness, we have measured the respective imaging capabilities, spatial resolution and spectroscopic characteristics. Each system consists of a single photon counting chip, developed in the framework of the Medipix Collaboration, bump bonded to a silicon detector. The detector is a matrix of 64 /spl times/ 64 square pixels, with 170 /spl mu/m pitch and thickness ranging from 300 to 800 /spl mu/m. As expected, the intrinsic detection efficiency increases with the detector thickness; nevertheless the spatial resolution can be affected by a charge sharing mechanism between adjacent pixels due to charge diffusion. The aim of the work reported in this paper is to demonstrate that, optimizing the settings of the image systems, we can increase the detection efficiency without losing in spatial resolution.

Tests on silicon pixel detector in the mammographic energy range have shown good imaging performances so, in order to improve the efficiency in this energy range, we have designed thicker detectors of the p+/n type. The detectors have been fabricated by ITC-IRST (Trento, Italy) in high resistivity silicon substrates (300 and 525 μm thick). A TCAD simulation work has been carried out to optimize the electric field distribution and to enhance the breakdown voltage. Very low leakage current and high breakdown voltage characteristics have been measured on detectors in preliminary on-wafer tests. After that, detectors have been bump-bonded to a dedicated VLSI electronic chips, realizing an assembly. Choosing the best set-up condition and using a standard mammographic tube, we have acquired a large area image (8×8 cm2) of the RMI 156 phantom, recommended for mammographic quality checks. In order to cover the whole surface, we have acquired different images translating the phantom over the assembly. We present some selected results for these assemblies both for the electrical characteristics and for the imaging performances.

Gallium Arsenide crystals are among the most efficient detectors of X-rays at room temperature. Different GaAs crystals have been irradiated with photons from radioactive sources, to compare their response in view of a possible application for Digital Radiology. The detectors have been obtained by various manufacturers and with different techniques (LEC and LPE crystals). Experimental results include I-V curves, charge collection efficiency and detection efficiency as a function of bias. A comparison is made with a simulation program.

To realize innovative instrumentation for mammography, a digital mammographic head based on several gallium arsenide detectors and on the Medipix chip (developed by the Medipix collaboration at CERN) has been designed. This device is able to perform single photon counting readout and allows a full detection efficiency at the mammographic energies. To make such detection units, industrial processes for the production of GaAs pixel detectors and for their bump-bonding to the read-out VLSI electronics have been developed by Alenia Marconi Systems (AMS S.p.A.). The detection unit is a 200 /spl mu/m thick GaAs matrix of 64/spl times/64 square pixels (170 /spl mu/m pitch), previously optimized and fully characterized, connected via bump bonding to the electronic chip. Specific studies were performed to develop a process that meets the requirements of low cost, high yield and high reliability for the bump bonding process of the GaAs detector to the silicon electronics. To ensure a high-quality electrical contact between the matrix detector and the silicon read out electronics a bump-bonding process has been set-up. It is based on a In evaporation process. In this work we present the technical characteristics of the bump bonding process and the results obtained in terms of bump-bonding yield and detection performance of the GaAs based detection units which have been realized and fully tested and are now ready to be implemented in the mammographic head.

The left ventricular reduction called Batista's procedure (BP) is a surgical technique able to improve the ventricular function in the heart disease known as Congestive Heart Failure (CHF). From a geometrical point of view the BP is a restyling of the left ventricle from a spherical configuration to an ellipsoidal one. The authors have written a program ("SoftHeart") which simulates the response of the heart after the BP. The main products of the authors' program are the new ejection fraction and the new stroke volume as a function of the equatorial surgical reduction. Using these curves it is possible to classify the patients into three categories corresponding to a Gaussian-like curve, a flat curve and a monotonic descending curve, respectively. A clinical trial performed on 165 patients allows a good correlation between the three categories built by "SoftHeart" and three different clinical situations. An explanation of the three categories produced by "SoftHeart" using the Laplace and the Frank-Starling laws is reported.

We present the imaging capabilities of a system based on a single photon counting chip, bump-bounded to a Si pixel detector. The detector is 300 µm thick a matrix of 64 x 64 square pixels with a dimension side of 170 µm. The active area is about 1.2 cm2. The photon counting chip matches the geometry of the detector so it has 4096 asynchronous read-out cells, each containing a charge preamplifier, a leading edge comparator and a pseudorandom counter. We have tested the image quality and the stability of our acquisition system imaging some phantoms used for mammografic quality checks. Our system allows to see low contrast details with a patient dose comparable with that given in mammographic examinations.

Pixel detectors for mammographic applications have been fabricated at ITC-irst on 800 μm thick silicon wafers adopting a double side n + -on-n fabrication technology. The activity aims at increasing the X-ray detection efficiency in the energy range of interest minimizing the risk of electrical discharges in hybrid systems operating at high voltages. The detectors, having a layout compatible with the Medipix2 photon counting chip, feature two different design solutions for the p-isolation between neighboring n + -pixels. We report on the characterization of the fabrication process and on preliminary results of electrical measurements on full detectors and pixel test structures. In particular, we found that the detectors can be reliably operated above the full depletion voltage regardless of the isolation design, that however, impacts the performances in terms of current–voltage characteristics, single pixel currents, inter-pixel resistances and inter-pixel capacitances.

The study that we present is part of the preparation work for the setup of the FOOT (FragmentatiOn Of Target) experiment whose main goal is the measurement of the double differential cross sections of fragments produced in nuclear interactions of particles with energies relevant for particle therapy. The present work is focused on the characterization of the gas-filled drift chamber detector composed of 36 sensitive cells, distributed over two perpendicular views. Each view consists of six consecutive and staggered layers with three cells per layer. We investigated the detector efficiency and we performed an external calibration of the space–time relations at the level of single cells. This information was then used to evaluate the drift chamber resolution. An external tracking system realized with microstrip silicon detectors was adopted to have a track measurement independent on the drift chamber. The characterization was performed with a proton beam at the energies of 228 and 80 MeV. The overall hit detection efficiency of the drift chamber has been found to be 0 . 929 ± 0 . 008 , independent on the proton beam energy. The spatial resolution in the central part of the cell is about 150 ± 10 μ m and 300 ± 10 μ m and the corresponding detector angular resolution has been measured to be 1 . 62 ± 0 . 16 mrad and 2 . 1 ± 0 . 4 mrad for the higher and lower beam energies, respectively. In addition, the best value on the intrinsic drift chamber resolution has been evaluated to be in the range 60 − 100 μ m. In the framework of the FOOT experiment, the drift chamber will be adopted in the pre-target region, and will be exploited to measure the projectile direction and position, as well as for the identification of pre-target fragmentation events.