R. Beccherle

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.

Microstrip silicon detectors for digital radiography

Abstract We present the first results obtained using a digital imaging system, operating at room temperature, developed for medical applications working with a standard mammogrphic beam.

A high-rate X-Y coincidence VLSI system for 2-D imaging detectors

Abstract We describe a VLSI-based processing system performing X - Y coincidence at a very high rate in the synchronous mode. The processor has been designed for applications in digital mammography with two-sided μ-strip silicon detectors but can be used to provide the computational section of any imaging system that needs fast coincidence. The VLSI chip has been successfully tested on a 32 + 32 channels DAQ chain.

Two VLSI CMOS ICs for digital X-ray 2-D imaging system: low noise front-end amplifier and 80 MHz digital encoder interface

We describe a VLSI-based data acquisition to perform X-Y coincidences with a two side microstrip digital detector, optimized for applications in digital mammography. A two components chip set is described in detail: a low noise Front-End analog amplifier and an 80 MHz synchronous digital encoder. These two components can be used to solve the problems arising with the use of a large number of channels and low signal amplitude as in our application.

A VLSI front-end circuit for microstrip silicon detectors for medical imaging applications

Abstract An analog CMOS-Integrated Circuit has been developed as Front-End for a double-sided microstrip silicon detector. The IC processes and discriminates signals in the 5–30 keV energy range. Main features are low noise and precise timing information. Low noise is achieved by optimizing the cascoded integrator with the 8 pF detector capacitance and by using an inherently low noise 1.2 μ m CMOS technology. Timing information is provided by a double discriminator architecture. The output of the circuit is a digital pulse. The leading edge is determined by a fixed threshold discriminator, while the trailing edge is provided by a zero crossing discriminator. In this paper we first describe the architecture of the Front-End chip. We then present the performance of the chip prototype in terms of noise, minimum discrimination threshold and time resolution.

PD/sup 3/, a low-noise precise timing analog front-end integrated circuit

An analog CMOS integrated circuit (IC) for low-noise, precise timing (peak detector double discriminator) has been developed. The IC processes signals detected by a double sided microstrip detector used in the 9-18 keV energy range. The timing information is provided by a novel architecture based on a double discriminator. The leading edge of the output pulse is determined by a fixed threshold discriminator while timing information is provided by a zero crossing discriminator able to detect the maximum of the shaped signal that corresponds to the trailing edge. The PD/sup 3/ is a 64 channel front-end IC designed to be part of the MEDIM experiment, whose aim is to build a system suitable for digital mammography based on a silicon microstrip detector. Low-noise was achieved by using HP 1.2 /spl mu/m technology and optimizing the cascaded integrator with the 3.4 pF detector capacitance. In this paper we will describe the overall topology of the PD/sup 3/ and analyze the main goals of the IC which are low-noise and good timing information. In the third section circuit performance is presented, including noise and time walk measurements. The last section will present some concluding remarks on timings achievable with low-noise front-end circuits.

Photons counting of a 2D silicon /spl mu/-strip detector in high X-rays flux environment: double coincidences recovery

The double coincidence probability is a well known limitation to the rate capability of a 2-D detector with independent X- and Y-readout. The authors have implemented a parametric Monte Carlo simulation which could help in optimizing the double coincidence recovery. They have applied the parametric simulation to a specific 2-D solid state detector, they are developing for application in digital mammography.