Paolo Randaccio

EVALUATION OF ELEMENTAL AND COMPOUND SEMICONDUCTORS FOR X-RAY DIGITAL RADIOGRAPHY

Abstract We present a comparative study of the performance of elemental and compound solid state crystals of possible use in X-raY digital radiography. The general purpose EGS4 code was used to simulate photon-electron transport in the energy range 20 to 60 keV. The efficiency and the energy resolution, as a function of X-ray energy, are calculated and correlated to the different physical characteristics of the crystals considered.

Use of silicon and GaAs pixel detectors for digital autoradiography

Solid state detectors made of Si (4.8/spl times/8 mm/sup 2/) and GaAs (6.4/spl times/8 mm/sup 2/) pixel matrices bump-bonded to the Omega2 and Omega3 electronic read-out systems, developed at CERN for H.E.P. experiments, have been used to obtain autoradiographic images of clusters of human epithelial cells and DNA fragments separated via electrophoresis, both labeled with /sup 32/P. The system has shown a good minimum detectable activity per unit area of 2.10/sup -4/ cps mm/sup -2/, and has proved linear for a count rate in the range 0.2-20 cpa, typical of autoradiography. The pixel dimensions are 75/spl times/500 /spl mu/m/sup 2/ (Si-Omega2) and 50/spl times/500 /spl mu/m/sup 2/ (GaAs-Omega3), respectively. We are able to clearly localize clusters of cells which have incorporated the radioactive tracer and DNA fragments on an electrophoretic gel on paper (blots).

AUTORADIOGRAPHY WITH SILICON STRIP DETECTORS

A digital autoradiography system based on double sided silicon strip detectors (1.6 × 1.6 mm2 active surface with 100 μm pitch) has been developed and successfully tested with beta-emitting tracers. It is shown here that the system is able to perform imaging of organic material with specific sensitivity as small as 0.002 nCi/mm2, and to record activity measurements with good linearity in the range 0.002–20 nCi/mm2. Autoradiographic images of clusters of mammary cells marked with ortho-(32P)phosphate, obtained with an exposure time of about 10 min are presented.

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 design of a system for coloured digital radiology with VLSI circuits and GaAs pixel detectors

AbstractWedescribethedesignofadigitalradiologysystemwithGaAspixeldetectors,basedontheenergyselectionofthenonabsorbedX-ray spectrum.We present ageneral layout; we show that simulationand experimentaldatacorroboratetheidea for the feasibility of the system. ( 1998 Elsevier Science B.V. All rights reserved. 1. IntroductionTheuseof GaAsasahigh-eƒciencyX-rayimag-ing detector is now well known [1].An idea for a novel digital radiology device withinherent high spatial and energy resolution hasbeen proposed [2]. It is based on a GaAs pixeldetector and two custom-made VLSI electroniccircuits which process each photon pulse and clas-sify it according to its energy.The circuits store the counting and the energyinformation, allowing the acquisition of coloured X-ray images. The artiÞcial elaboration of colourcan be performedon line in a scale proportionaltotheenergyofthedetectedphoton.Thescaleresolu-tionwillbelimitedbytheelectroniccircuitsdesign.The method,generallyapplicable,has beenillus-trated before [3]. Here we describe the design fora digital imaging system with an X-ray source,a GaAs pixel detector and the VLSI circuits. Thepaperconcentratesonthegenerallayoutinarealis-tic conÞguration. We address the compromises be-tween the performances of the system, versus thefabrication technologies risks and the costs.WehaveatpresentaÞrstversionofthedetectorswith 32 pixels and the new chip with 8 energyintervals.We show data and compare with the simulationproving that the design idea is well based.2. The basic principleIn radiology, the use of the energy and count-ing information is performed simultaneously in

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. >

Medipix2 parallel readout system

A fast parallel readout system based on a PCI board has been developed in the framework of the Medipix collaboration. 1 The readout electronics consists of two boards: the motherboard directly interfacing the Medipix2 chip, and the PCI board with digital I/O ports 32 bits wide. The device driver and readout software have been developed at low level in Assembler to allow fast data transfer and image reconstruction. The parallel readout permits a transfer rate up to 64 Mbytes/s. r 2003 Elsevier Science B.V. All rights reserved. PACS: 07.05.Hd; 87.59.Hd

KeepInTouch: A telehealth system to improve the follow-up of chronic patients

With the progressive ageing of the western people, the number of chronic patients requiring a continuous follow-up by the physicians increases. Even though telehealth solution can be potentially effective in such a scenario, both the age factor and often the cost of the systems hamper the diffusion of telehealth systems. KeepInTouch is a low cost system for telehomecare conceived for the daily off-line monitoring of diabetic and cardiac patients. It exploits a mixed approach offering a simple TV-based front-end from the patient side, and a web-based one from the physician side. The web-based approach enables the authorized medical professionals to access the patient data from the web, exchanging useful information and providing textual feedback to the patient, all within the system interface. The patients front-end is based on the Digital Video Broadcasting Terrestrial (DVB-T) technology, exploiting an acquisition unit connected to the patients certified biomedical devices (sphygmomanometer, glucometer, body weight scale) and with the interactive DVB-T set-top box in order to provide a user-friendly interface on the TV for people not accustomed with computers. The system is going to be used for a first clinical trial in Italy.

Use of the EGS4 Monte Carlo code to evaluate the response of HgI2 and CdTe detectors for photons in the diagnostic energy range

Abstract We present the results of the detailed simulation of the response of a HgI 2 crystal in terms of efficiency, energy and space resolutions versus photon energy in the diagnostic energy range 20–100 keV. Some configurations of CdTe crystals for positron emission tomography are also evaluated.

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. >