U. Bottigli

First X-ray images with a double-sided microstrips silicon crystal. A novel detector for digital radiography?

In the framework of an experimental program to study the possibility of using a silicon crystal for X-ray detection in the diagnostic energy range (10-100 keV), the authors present the first experimental results obtained with a silicon detector (300 mu m thick, 1.4*1.4 cm2 surface) with microstrips deposited on each side: 25 mu m spacing on the junction side and 50 mu m spacing on the ohmic side: 25 mu m spacing on the junction side and 50 mu m spacing on the ohmic side; the read-out pitch is 100 mu m for both sides. Energy and spatial resolutions have been measured by means of collimated radioactive sources: 241Am (E gamma =60 keV) and 109Cd (E gamma =24 and 88 keV). A very good linearity in the response to the photon energy has been measured. Tantalum wires, i.e. high contrast objects, have been used as phantoms when exposing the detector to the 60 keV photons; the authors present the images thus obtained.

The MAGIC-5 Project: medical applications on a GRID infrastructure connection

The MAGIC-5 Project aims at developing computer aided detection (CAD) software for medical applications on distributed databases by means of a GRID infrastructure connection. The use of automatic systems for analyzing medical images is of paramount importance in the screening programs, due to the huge amount of data to check. Examples are: mammographies for breast cancer detection, computed-tomography (CT) images for lung cancer analysis, and the positron emission tomography (PET) imaging for the early diagnosis of the Alzheimer disease. The need for acquiring and analyzing data stored in different locations requires a GRID approach of distributed computing system and associated data management. The GRID technologies allow remote image analysis and interactive online diagnosis, with a relevant reduction of the delays actually associated to the screening programs. From this point of view, the MAGIC-5 Collaboration can be seen as a group of distributed users sharing their resources for implementing different virtual organizations (VO), each one aiming at developing screening programs, tele-training, tele-diagnosis and epidemiologic studies for a particular pathology.

GPCALMA: an italian mammographic database of digitized images for research

In this work the implementation of a database of digitized mammograms is described. The digitized images were collected since 1999 by a community of physicists in collaboration with radiologists in several Italian hospitals, as a first step in order to develop and implement a Computer Aided Detection (CAD) system. 3369 mammograms were collected from 967 patients; they were classified according to the type and the morphology of the lesions, the type of the breast tissue and the type of pathologies. A dedicated Graphical User Interface was developed for mammography visualization and processing, in order to support the medical diagnosis directly on a high-resolution screen. The database has been the starting point for the development of other medical imaging applications such as a breast CAD, currently being upgraded and optimized for the use in conjunction of the GRID technology in the framework of the INFN-funded MAGIC-5 project.

Digital imaging in radiology: preliminary results obtained with a high spatial resolution 2D silicon detector

Double-sided microstrip silicon crystals are being tested as detectors for X-rays in the diagnostic energy range (10-100 keV) for digital radiology. An analog-to-digital-converter and CAMAC based acquisition system has been developed to study the imaging capabilities of a silicon microstrip detector with 100 and 200 mu m read-out pitch. The authors present the first images of submillimeter high-contrast phantoms obtained with an X-ray mammography tube operating at high flux density. A preliminary contrast transfer function study was performed; a low frequency contrast of about 0.97 for a high-contrast phantom and a decrease of contrast at a frequency of 5 1p/mm corresponding to the detector intrinsic spatial resolution (100 mu m) were measured. >

GaAs detector optimization for different medical imaging applications

Abstract We have investigated the detection performance of GaAs detectors made with different thickness and contact geometries. A comparison is made between these detection capabilities and the imaging requirements for the following medical applications: digital mammography, digital chest radiography and nuclear medicine. Experimental results and preliminary images are presented and discussed.

X-RAY-IMAGING USING A PIXEL GAAS DETECTOR

The electrical characteristics, charge collection efficiency and energy resolution of a GaAs detector made out of LEC material have been studied. A matrix of 36 square pixels was deposited on a 70 μm thick crystal; each pixel had an area of 200 × 200 μm2 with 20 μm spacing between adjacent pixels. This detector showed a charge collection efficiency uniformity among the pixels better than 88% when exposed to 60 keV photons, which ensures that a comfortable common threshold setting can be adopted without affecting the uniformity of the measurement. It was successful in recording (60 keV photon energy) the image of a wolframium slab, 100 μm thick.

Characterization of the response of a double side mu -strip silicon detector to X-rays in the diagnostic energy range

The use of a double sided mu -strip silicon crystal for X-ray detection is being investigated. The detector is 300 mu m thick and the read-out pitch is 100 mu m for both sides. It operates in capacitance charge division mode by means of floating strips between read-out strips. The detector has been irradiated by /sup 241/Am and /sup 109/Cd sources. Different zones within the 100- mu m read-out pitch have been individually exposed. The following characteristics have been studied as a function of the impact point of the photon: (a) the charge collection mechanism; (b) the relative detection efficiency; (c) the energy resolution; and (d) the spatial resolution. The absolute efficiency of the detector has been measured at three energy values. >

Imaging spectroscopic performances for a Si based detection system

We present the imaging and spectroscopic capabilities of a system based on a single photon counting chip (PCC) bump-bonded on a Si pixel detector. The system measures the energy spectrum and the flux, produced by a standard mammographic tube. We have also made some images of low contrast details, achieving good results.

Electrical characterization and detection performances of various semi-insulating GaAs crystals for low energy gamma-rays

In order to investigate the correlation between the electrical characteristics of the semi-insulating GaAs and its properties as a possible detector for low energy gamma-rays, we have measured, for various materials, the forward and the reverse I-V characteristic, the capacitance as a function of the frequency at various bias voltages and the capacitance as a function of the bias voltage at various frequencies. To measure the charge collection efficiency, the energy resolution and the detection efficiency as a function of the bias voltage the crystals have been irradiated with 22, 60, 88 and 122 keV photons. The results are discussed and a comparison between materials from various factories, of different thickness and equipped with different contacts is also presented. >

X-ray imaging test of a /spl mu/-strip silicon detector with a transputer DAQ

The authors have developed a TDC+Transputer-based acquisition system to study the X-ray imaging capabilities of a silicon /spl mu/-strip detector with 100 and 200 /spl mu/m read-out pitch. This system allows real-time image acquisition and display. The authors present images obtained with an X-ray mammography tube using sub-millimeter high contrast test objects on a 16*16 channels prototype. >