Search

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 authors evaluated the effect on mammographic examinations of the use of synchrotron radiation to detect phase-perturbation effects, which are higher than absorption effects for soft tissue in the energy range of 15-25 keV. Detection of phase-perturbation effects was possible because of the high degree of coherence of synchrotron radiation sources. Synchrotron radiation images were obtained of a mammographic phantom and in vitro breast tissue specimens and compared with conventional mammographic studies. On the basis of grades assigned by three reviewers, image quality of the former was considerably higher, and the delivered dose was fully compatible.

Phase contrast x-ray imaging is a powerful technique for the detection of low-contrast details in weakly absorbing objects. This method is of possible relevance in the field of diagnostic radiology. In fact, imaging low-contrast details within soft tissue does not give satisfactory results in conventional x-ray absorption radiology, mammography being a typical example. Nevertheless, up to now all applications of the phase contrast technique, carried out on thin samples, have required radiation doses substantially higher than those delivered in conventional radiological examinations. To demonstrate the applicability of the method to mammography we produced phase contrast images of objects a few centimetres thick while delivering radiation doses lower than or comparable to doses needed in standard mammographic examinations (typically approximately 1 mGy mean glandular dose (MGD)). We show images of a custom mammographic phantom and of two specimens of human breast tissue obtained at the SYRMEP bending magnet beamline at Elettra, the Trieste synchrotron radiation facility. The introduction of an intensifier screen enabled us to obtain phase contrast images of these thick samples with radiation doses comparable to those used in mammography. Low absorbing details such as 50 microm thick nylon wires or thin calcium deposits (approximately 50 microm) within breast tissue, invisible with conventional techniques, are detected by means of the proposed method. We also find that the use of a bending magnet radiation source relaxes the previously reported requirements on source size for phase contrast imaging. Finally, the consistency of the results has been checked by theoretical simulations carried out for the purposes of this experiment.

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.

A synchrotron radiation beamline devoted to medical imaging has been built by the SYRMEP collaboration at Elettra in Trieste, Italy, and is now in operation. The SYRMEP imaging system is based on the combination of a monochromatic, laminar X-ray beam, with a laminar, high-efficiency pixel silicon detector. To image soft tissue, including small, low-contrast details, as in mammography, beam energies should be chosen in the range from 15 keV to 30 keV and the detector should be capable of single-photon counting. The SYRMEP beamline originates from a bending magnet light port and consists basically of a Be window, a slit system and a Si(1,1,1) crystal monochromator. The experimental area is equipped with a radiation flux monitor, a sample movement stage, and a positioning system holding the silicon detector. Images are obtained by keeping the detector stationary with respect to the beam and by scanning the sample through the beam itself. The current detector is a linear array of 200/spl times/300 /spl mu/m/sup 2/ pixels, each coupled to its electronic counting chain on a custom VLSI read-out chip. We present a summary of beam studies, and digital images of standard RMI 160 and RMI 180 Ackermann Mammographic phantoms. Results show the high contrast resolution, the good spatial resolution and the large dynamic range which constitute the defining characteristics of the SYRMEP imaging system.

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 (

A 3-layer edge-on silicon microstrip detector for the SYRMEP/FRONTRAD project has been designed and realised. The image matrix is made by 764 pixels with dimensions 300 (thickness of the single detectors) × 200 (strip pitch) μm2. The system has a sensitive area of 50 × 1 mm2, an inter-layer distance of ≈ 100 μm and an efficiency of ≈ 80% for 20 keV photons. The image is acquired by scanning the object across the beam cross-section and the overall statistics on the single pixel is obtained by summing up the information of corresponding pixels in the three layers, thereby reducing the effect of possible noisy or not functioning pixels. Experimental results obtained at the SYRMEP/FRONTRAD beam line of the ELETTRA synchrotron radiation machine with this innovative detector are presented.

The SYRMEP (SYnchrotron Radiation for MEdical Physics) imaging system is based on the combination of a monochromatic laminar X-ray beam, with a laminar high-efficiency pixel silicon detector. The use of synchrotron radiation X-rays has the advantage of minimising the radiation dose delivered to the sample because it is possible to choose the best energy for the considered radiological examination. The high efficiency of the detector (about 90% in 18-28 keV energy range) also lowers this dose figure. Since the detector is capable of single-photon counting, the information contained in the beam is fully exploited, leading to high contrast resolution. The present phase of the SYRMEP project involves a systematic study of in vitro breast tissue samples. The same samples are then imaged by means of a conventional mammographic Mo anode tube used in the common diagnostic practice and recorded on film/screen system. The comparison of the two imaging modalities shows the advantages, with special regard to contrast resolution, of the SYRMEP imaging system compared with conventional film-screen devices.