R Longo

Digital mammography with synchrotron radiation

The SYRMEP (synchrotron radiation in medical physics) Collaboration is planning to use a beam of monochromatic x‐rays provided by Elettra, the synchrotron radiation facility in operation at Trieste (Italy), in conjunction with a novel silicon pixel detector to conduct research in digital mammography. A beamline dedicated to mammography is presently under construction in Trieste; it will provide, at a distance of about 20 m from an Elettra bending magnet, a monochromatic laminar‐section (150×4 mm2) x‐ray beam. This beam will illuminate in vitro samples and will be detected by a fixed silicon microstrip device forming a matrix of pixels. Digital images of phantoms having a size common in the diagnostic practice (150×150 mm2), can then be produced by scanning the sample itself in front of the detector. A prototype detector with a sensitive area of 24×1 mm2 and pixels of 0.5×0.5 mm2 has been built and tested. We present the current status of the SYRMEP beamline and a digital image of a mammographic phantom ex...

At the frontiers of digital mammography: SYRMEP

Abstract 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 15–30xa0keV. 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 5xa0cm wide) with mammographic phantoms and human breast tissue.

Diffraction enhanced breast imaging: assessment of realistic system requirements to improve the diagnostic capabilities of mammography

A detectable difference in X-ray diffraction data of healthy and diseased breast tissues has been observed. This information can be used to generate images with a higher contrast than that of conventional transmission mammography. A diffraction enhanced breast imaging (DEBI) system that simultaneously combines transmission and diffraction breast images is currently being developed. This paper presents the imaging system requirements for a clinical DEBI system. The DEBI imaging system employs a phosphor coated L3Vision CCD camera. The DEBI principle has been assessed at the SYRMEP synchrotron beamline (Elettra, Trieste) and with a purpose built mammographic X-ray imaging unit. Diffraction enhanced images have been obtained of realistic breast tissue phantoms, consisting of 4 cm thick slabs of excised breast tissue containing embedded carcinomas. The images were obtained at pre-determined momentum transfer values, allowing some tissue characterization to be achieved during imaging, as well as optimizing image contrast This paper presents the current state of the project. The spatial resolution of the diffraction images have been studied using test phantoms and suggestions are made for the collimation systems necessary for a clinical system. A correction procedure applied to the diffraction images is also presented.

Digital mammography at the Trieste synchrotron light source

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 (<100 microns) of the system have been demonstrated by producing images of details from an Ackermann Mammographic Phantom RMI 160 illuminated by a conventional X-ray tube.

Silicon detectors for synchrotron radiation digital mammography

Abstract The knowledge of the dose and of the energy spectrum of the X-rays delivered to the patient during a radiological examination allows in principle the computation of the number of photons per unit surface useful for a good mammography. The film-screen assembly detectors used in the present standard practice require a number of photons per unit surface which, from a statistical point of view, would be unnecessarily high if single photon counting detectors with efficiency near to one were available. We discuss a possible solid state detector with these characteristics. Moreover, we propose the use of an X-ray monochromatic beam from a synchrotron radiation source in order to perform the examination at the energy where the signal to noise ratio has a maximum. Using the proposed detector in such a beam a substantial dose reduction can be foreseen.

X-ray diffraction CT of excised breast tissue sections: first results from Elettra

The scattering properties of breast tissue have been suggested as a diagnostic tool in the early detection of breast cancer. To aid in the development of a clinical imaging system based upon these properties, a series of breast tissue samples have been subjected to diffraction microCT using the SYRMEP beamline at Elettra, Italy. Using 18 keV photons, both transmission and diffraction CT data sets were collected using a specially designed microCT system. This system was based around a finely collimated, X-ray sensitive L3Vision CCD camera and a simple rotary stage controlled using Lab View software. The images were reconstructed using routines developed in IDL. This paper presents both transmission and diffraction CT images of three samples. The samples were excised breast tissue sections known to contain either tumour, normal tissue adjacent to the tumour or a mixture of each. The results demonstrate that diffraction microCT can be used to evaluate the structure of breast tissue tumours. Registration of the transmission and diffraction CT images demonstrated that both techniques showed the same principle features in the sample and allowed the main components to be identified. However, the diffraction images demonstrated an average increase in image contrast over the transmission images. Further improvements in the collimator design used in the experiments will need to be made if detailed structure is to be seen.

An "edge-on" silicon strip detector for X-ray imaging

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.

Phase Contrast Imaging in the Field of Mammography

It is very well known that imaging low contrast details in soft tissues is the main limitation of conventional X-ray radiology. Phase contrast imaging overcomes this limitation. Up to now, however, all the applications of this technique required high radiation doses, raising several questions about its utilisation in medical radiology.

Improvements in the field of radiological imaging at the SYRMEP beamline

One major goal of modern radiology is the improvement of image quality and subsequently the development of sophisticated radiographic methods which are capable of detecting low contrast and small size details in organic samples in particular in mammography where the requirements on contrast resolution and spatial resolution are extremely high. Significant improvements in image quality have been achieved by the SYRMEP (SYnchrotron Radiation for MEdical Physics) collaboration which has designed and built a beamline devoted to medical physics at the synchrotron radiation facility ELETTRA in Trieste (Italy). The detection system developed for digital mammography consists of a silicon pixel detector with a pixel size of 200 X 300 micrometers 2 used in the `edge on configuration in order to achieve a high conversion efficiency. The detector is equipped with a low noise VLSI amplifier chain; at present. Recently, a multilayer detector prototype has been implemented, consisting of a stack of three single silicon strip layers. This set-up provides a larger sensitive area and subsequently a reduction of the exposure time. Digital images of mammographic phantoms and of in vitro full breast tissue samples show a higher contrast resolution and lower absorbed dose when compared to conventional mammographic images. Besides, further promising studies have been initiated developing novel imaging methods based on the phase effects evidenced by the high degree of coherence of the SR source. At the SYRMEP beamline several experiments have been carried out in order to exploit the potentials of two different techniques, Phase Contrast and Diffraction Enhanced Imaging, respectively. Images showing better detail visibility and enhanced contrast were produced with dose lower or comparable to the conventional one.

SYRMEP front-end and read-out electronics

Abstract 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.