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The SYRMEP Collaboration (SYnchrotron Radiation for MEdical Physics) is conducting a research project in digital mammography and plans to use a monochromatic X-ray beam provided by Elettra, the synchrotron radiation facility in operation in Trieste (Italy), in conjunction with a novel silicon pixel detector. A set of silicon strip detectors was arranged to form a vector of pixels. This prototype with a sensitive area of 24 mm2 (i.e. 2 × 48 pixels of 0.5 × 0.5 mm2) has been used to produce images with X-rays both from a 109Cd source and a standard radiological tube.

The SYRMEP (SYnchrotron Radiation for MEdical Physics) collaboration is presently taking data at a beamline at the synchrotron ELETTRA in Trieste to study the performances of a digital silicon pixel imaging system for mammography. Images are obtained with a scanning technique in the energy range 15–30 keV. The readout electronics operates in a single photon counting mode with a photon rate of about 10 6 /( mm 2 s ) , which is still 4 times lower than the maximum rate reachable with the present beamline configuration. Two different detector layouts have been designed, the first one consisting of a single-layer silicon microstrip detector positioned edge-on with respect to the beam, and the second innovative one represented by a matrix of these detectors stacked to cover the full beam dimension (100×4 mm 2 ) . We present here the results obtained with a single-layer detector and a double-layer detector (both 5 cm wide) with mammographic phantoms and human breast tissue.

The SYRMEP approach to digital mammography implies the use of a monochromatic X-ray beam from a synchrotron source and a slot of superimposed silicon microstrip detectors as a scanning image receptor. The microstrips are read by 32-channel chips mounted on 7-layer hybrid circuits which receive control signals and operating voltages from a MASTER-SLAVE configuration of cards. The MASTER card is driven by the CIRM, a dedicated CAMAC module whose timing function can be easily excluded to obtain data-storage-only units connected to different MASTERs: this second-level modular expansion capability fully achieves the tasks of an electronics system able to follow the SYRMEP detector growth till the final size of seven thousands of channels.

A silicon strip detector for the SYRMEP (SYncrotron Radiation for MEdical Physics) experiment has been designed and realised. The main features of this detector are AC-coupling through integrated coupling capacitors, DC biasing by means of a gated punch-through structure, bulk contact on the junction side through a forward-biased p/sup +/ implant and integrated fan-in on active silicon. Results of laboratory tests of the detector parameters, allowing a thorough evaluation of the technological solutions employed, are presented. The functionality of the detectors and the charge collection linearity have been tested with different /spl gamma/ sources, using a hybrid, low-noise front-end electronics.

We present a VLSI CMOS-mixed analog-digital circuit for high-rate pixel X-ray imaging applications. It consists of 32 channels at 80 μm pitch. The total die size is 3.7×14 mm 2 . Each channel features: a low-noise charge preamplifier, a CR-RC shaper, a buffer, a threshold discriminator and a 16-bit binary counter. The readout is done serially on a tri-state buffer. The main parameters of the analog part are: shaping time of 850 ns at 5 pF input capacitance, gain of 180 mV/fC, ENC( e − rms) = 60 + 17 C d (pF) and a power consumption of 3.8 mW/channel. The counting rate is limited by the analog part to around 100 kHz/channel for 1 fC charge pulses. Due to the parallelism of the circuit, photon rate in the order of 1 GHz/cm 2 can be measured for a pixel size of the order of 200 × 200 μ m 2 . The parameters of the circuit were optimised for the Syrmep experiment, an R&D project in digital mammography. The circuit was produced in 1.2 μm CMOS technology by AMS (Austria). Characterisation of the circuit, as well as first-imaging results of the circuit connected to microstrips or pixel detectors are presented. They show the circuit works according to specification and can be used for imaging applications.

We present images of a mammographic test object obtained using a linear array silicon pixel detector capable of single-photon counting. The detector pixel size was 200 x 300 microns2 and images were acquired by scanning the test object between the laminar detector and the x-ray source with a scanning step of 100 microns. A molybdenum anode tube was used with two different filtrations: 2 mm aluminium and 25 microns molybdenum. Conventional film-screen images were also obtained in order to compare spatial and contrast resolution. In our digital images it is possible to recognize low-contrast details having dimensions smaller than or equal to the dimensions of details visible by means of a clinical mammographic unit. The detection of microcalcifications smaller than 150 microns was possible only when using the Mo filtration. However a copper wire of 50 microns diameter was detectable when embedded in a simulated tissue. We discuss in detail the mean glandular doses (MGDs) delivered during the image acquisition. The MGDs necessary to obtain good-quality images are always smaller than at a conventional mammographic unit. Since MGDs depend on the x-ray spectrum, the dose reduction becomes larger when the applied spectrum is harder than in film-screen acquisition (Al filtration and 35 kVp).

The SYRMEP project (SYnchrotron Radiation for MEdical Physics) intends to improve mammography performances using two non-traditional means: synchrotron radiation and silicon detectors. A silicon crystal (the monochromator) allows to choose the optimal beam energy that leads to the maximum signal to noise ratio, while the detectors are arranged to form a matrix of pixels and coupled to low noise high-gain VLSI integrated circuits making the single photon counting technique possible. We present the data acquisition system implemented to read out the VLSI circuit with particular emphasis on two dedicated CAMAC modules that generate the control signals and store the chip digital output on memories that can be accessed via the CAMAC bus. It has been useful in testing the chip performances and can be considered a prototype of the final SYRMEP data acquisition system.

A silicon strip detector for the SYRMEP (SYnchrotron Radiation for MEdical Physics) experiment has been designed and realised. The main features of this detector are AC-coupling through integrated coupling capacitors, DC bias of the strips by means of a gated punch-through structure, bulk contact on the junction side through a forward-biased p + implant, thinned entrance window for the incoming radiation (in an “edge-on” geometry) and integrated fan-in on active silicon. Results of laboratory tests of the detector parameters, allowing a thorough evaluation of the technological solutions employed, are presented.

In the last few years the interest for application of silicon radiation detectors to the detection of X-rays in the 15–30 keV region has been growing. One of the main reasons of such an interest is the development of devices for medical and biological applications, in particular for the diagnostic radiology of soft tissues. For these applications, to ensure a high detection efficiency is of crucial importance. This leads to the use of “on purpose” geometrical arrangements and technological solutions for the detector, as well as the use of specifically designed read-out electronics. In this paper we present results and images obtained with silicon microstrip detectors in a “pixel-like” geometry, with the X-ray beam impinging parallel to the strips. An efficiency close to 80% has been obtained for photons of energies around 20 keV. The ongoing developments, concerning the realisation of a dedicated silicon detector for digital radiology at the SYRMEP (SYnchrotron Radiation for MEdical Physics) beam line of the ELETTRA synchrotron radiation facility, are described.

The SYRMEP collaboration is developing a digital mammography project using a synchrotron radiation monochromatic X-ray beam and a silicon pixel detector. The combination of a monochromatic laminar beam with a high efficiency laminar detector, capable of single-photon counting, allows one to minimize the radiation dose delivered to the sample, while maximizing contrast resolution and dynamic range. The SYRMEP detector is a silicon microstrip device used in an innovative configuration in which radiation impinges on the side rather than on the surface of the chip and is therefore totally absorbed within the detector active volume. The high contrast resolution and spatial resolution (

The SYRMEP (SYnchrotron Radiation for MEdical Physics) collaboration is now developing a microstrip silicon detector with high granularity and high efficiency for research in digital mammography. The project is planning to use a monochromatic X-ray beam, from a bending magnet, of ELETTRA, the synchrotron facility installed in Trieste. The detector is a matrix of pixels, formed by the slacking of different layers of strip silicon pads, with pixel dimensions determined by the pitch and the thickness of the pads themselves. The final detector, an AC-coupled FOXFET-type high resistivity silicon pad, will cover the whole beam region of 4 x 150 mm(2). Different pixel sizes have been tested (from 0.5 x 0.5 mm(2) to 0.3 x 0.2 mm(2)). The dead volume in the front of the detector has been reduced in order to reach 80% efficiency in the photon collection. The stacking of the layers has been obtained by means of screen printing deposits of non-conductive glue whose height has been chosen in order to minimize the inter-layer dead region and the cross talk of superimposed pixels, We present here the results of our studies in terms of imaging and the status of the final detector.

The SYRMEP / FRONTRAD (SYnchrotron Radiation for MEdical Physics / FRONTier RADiology) collaboration has developed a digital X-Ray imager for the mammography beamline at ELETTRA, the synchrotron radiation facility in operation in Trieste, Italy. This imaging device is composed of three stacked layers of FOXFET-biased silicon microstrip detectors, positioned with the strips along the beam direction. In this way a very high absorption efficiency is guaranteed, since the strip length (1 cm) absorbs nearly all the incoming photons in the energy range of interest (15-30 keV). Furthermore, the active surface is by construction subdivided into pixels, the dimensions of which are determined by the strip pitch (200 μm) in one direction and by the thickness of the single layer (300 μm) in the other. Each layer has 256 implanted strips, and therefore the whole device has an active surface of ∼50x1 mm2 subdivided into 764 pixels (the inter-layer distance is nearly equal to 100 μm). The electronic chain reading out the detector signal operates in "single photon counting" mode: this gives the possibility of extracting the maximum information from the radiation beam, since the only limitation to the signal-to-noise ratio in the images is the quantum noise. Two-dimensional images are obtained by scanning the samples through the synchrotron laminar beam, while the detector is kept stationary with respect to the beam itself. The desired statistics is obtained by combining the information from the three layers, thus reducing the overall acquisition time by a factor of three. Results from extensive tests carried out on this imaging device by means of a synchrotron radiation beam are reported on this paper.

The Mammography Project at ELETTRA whose acronym is SYRMEP (SYnchrotron Radiation for Medical Physics), developed along two lines: the design, construction and test of the synchrotron radiation beam line and the design, manufacturing and test of the imaging device; both are now in the commissioning phase. The X ray beam originates from an ELETTRA bending magnet, it is laminar, with maximum cross section 150 x 4 mm2, further adjustable through a vertical and horizontal slit system so as to match the cross section of the imaging device; it is monochromatized by a Si(1,1,1) channel cut monochromator that delivers photons in the range 8 to 32 keV, the intensities ranging from 4 x 108 to 1 x 107 sec-1 mm-2 according to energy. The detecting system consists of a single stage flux monitor followed downstream by a Si strip detector on which the photons impinge sideways; in this, way each strip behaves as a pixel detector with a cross section determined by the detector thickness and strip pitch (0.2 x 0.3 mm2), while the crystal breadth (10 mm) guarantees the proper absorption depth in the range of energies of interest; the read-out electronics is such to perform single photon counting.