Digital imaging systems for medical applications must be based upon highly efficient detectors to ensure
low patient dose. This is considerably important, especially in mammography, because the high sensitivity
of the breast to radiation. A mammoraphy system must also provide high spatial and contrast resolution
to be able to detect important structures related to breast malignancies.
The work performed and described in this thesis is the development of a readout system for a detector
optimised for clinical mammography with synchrotron radiation. The detector called PICASSO (Phase
Imaging for Clinical Application with Silicon detector and Synchrotron radiatiOn) is developed mainly for
the mammography station of the SYRMEP beamline. The detector described in this work is based on Silicon
microstrip sensors that are illuminated edge-on. The incoming beam impinging the detector is parallel to
the strips of its sensors. This configuration permits high detection efficiency in the energy range that is of
interest for mammography. Moreover, the Silicon sensors also allow direct conversion of X-rays.
The readout electronics of the Picasso detector works on single-photon counting mode. That is, only
signals from photons that are equal or greater than a pre-set threshold are counted, and low freqency noise
are automatically rejected. The visibility of small details, normally valuable in mammograms, are maximised
because the system is quantum limited, ie, the quality of the image is limited only by the intrinsic fluctuation
of the detected photons.
Picasso has four layers, each containing three detector modules. The layers are grouped into pairs and
arranged one in front of the other along the beam of propagation. The pairs are controlled separately but are
working in parallel. The system is a modular detector that implements a read-out system with MYTHEN
II ASICs, an embedded Linux-based controller board and a Scientific Linux acquisition workstation. The
developed system architecture and its characteristics will be presented.
Preliminary imaging tests were perfomed and results with the new system will be presented. Standard
mammographic phantoms were imaged and good quality images were obtained at doses comparable with
what is delivered in conventional full field mammographic systems. The whole system was able to sustain
fast acquisition speeds up to 10ms/frame and runs stable until a breast-equivalent length acquisition is
accomplished. A delay between frame of 150μs and delay between controllers of around 750μs is achieved.
Phase-contrast imaging has revolutionized the face of mammography with synchrotron radiation in the
last ten years as the first clinical phase has been successfully implemented in our facility. This initial step
made use of commercial screen-film system producung promising results. Thanks to the coherence and
monochromaticity of light coming from synchrotron sources that edge-enhancement in the image is achieved
due to phase effects. The compatibility of the Picasso detector to phase-contrast imaging with other novel
techniques has also been evaluated in line with this project. Phase-contrast was well demonstrated with the
system, details of which will be fully described.
