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An extension to Geant4 Monte Carlo code was developed to take into account inter-atomic (molecular) interference effects in X-ray coherent scattering. Based on our previous works, the developed code introduces a set of form factors including interference effects for a selected variety of amorphous materials useful for medical applications, namely various tissues and plastics used to build phantoms. The code is easily upgradable in order to include new materials and offers the possibility to model a generic tissue as a combination of a set of four basic components. A dedicated Geant4 application for the simulation of X-ray diffraction experiments was created to validate the proposed upgrade of Rayleigh scattering model. A preliminary validation of the code obtained through a comparison with EGS4 and an experiment is presented, showing a satisfactory agreement.

Purpose Purpose of this work is to compare image quality of Synthetic Mammography (SM) and Full Field Digital Mammography (FFDM) in four different Digital Breast Tomosynthesis (DBT) systems by using a semi-anthropomorphic phantom. Methods Four DBT systems (FujiFilm, GE, Hologic, IMS) were characterized by means of the semi-anthropomorphic CIRS-BR3D phantom. The phantom contains clusters of microcalcifications, fibers and masses embedded in a breast equivalent tissue having a heterogeneous background. For each DBT system two images (DBT and FFDM) were acquired applying clinical setup conditions. FFDM acquisitions were repeated in manual mode for each system with a fixed exposure ratio between DBT and FFDM. Comparative analyses were carried out on the contrasts and sizes of micro calcifications, on the contrasts and shapes of masses, and on the noise power spectrum of the background. The FFDM image acquired in clinical setup conditions was considered the gold standard of the metric. Results Considering the micro calcifications, contrasts were generally preserved by SM with respect to FFDM, while the sizes of the smaller details slightly increased, probably due to the blurring caused by the filtration stages of the tomographic reconstruction. Regarding the masses, no globally significant differences were noticeable in the contrasts, and the shapes were generally well preserved as well. Finally, concerning the noise power spectra, significant variations only appeared in the high frequency regime, in accordance with the above-mentioned blurring. Conclusions This preliminary analysis confirms for all systems the criticality of the synthetic image in terms of spatial resolution and noise but does not highlight significant differences in the detection capability of the details of interest. Further investigations will be made considering the DBT+SM combination compared to DBT+FFDM, as well as by extending the present analysis to other mammographic phantoms.

Purpose We propose a technique for the characterization of tissues, based on a hybrid phase contrast-attenuation imaging. The technique, first introduced in [1] , makes use of a method for material basis decomposition proposed by Alvarez and Macovski [2] . We present a semi-analytical simulation of the imaging process, as well as a preliminary implementation on a set of radiographic images of a dedicated phantom. Methods The phantom consists in a thin plastic plate composed of two “soft” materials, arranged in such a way to create a faint pattern of decreasing radiographic contrasts. The imaging was performed using synchrotron radiation (i.e. a quasi-parallel, monochromatic and coherent X-ray beam) and placing the phantom at different distances from the detector, so as to enhance the contribution of phase contrast. The images were acquired at the SYRMEP beamline of the Elettra synchrotron facility (Trieste, Italy). Results The reconstructed composition of the phantom was compared to the results of the semi-analytical simulation, showing a good agreement with the theoretical expectations. In particular, the technique proved able to enhance the visibility of faint contrasts with respect to the standard attenuation-based imaging. Moreover, it provided a precise quantitative estimate of the local composition of the imaged phantom. Conclusions The application of the basis decomposition method to the context of phase contrast imaging allows an effective rendering of a broad spectrum of radiographic patterns, from low frequency textures (which are captured by the attenuation effects) to high frequency details (highlighted by the phase shift effects). In addition, thanks to the simultaneous enforcement of two separate imaging channels, it also allows a two-component reconstruction of the imaged object.

Advanced applications of digital mammography such as dual-energy and tomosynthesis require multiple exposures and thus deliver higher dose compared to standard mammograms. A straightforward manner to reduce patient dose without affecting image quality would be removal of the anti-scatter grid, provided that the involved reconstruction algorithms are able to take the scatter figure into account [1] . Monte Carlo simulations are very well suited for the calculation of X-ray scatter distribution and can be used to integrate such information within the reconstruction software. Geant4 is an open source C++ particle tracking code widely used in several physical fields, including medical physics [2] , [3] . However, the coherent scattering cross section used by the standard Geant4 code does not take into account the influence of molecular interference. According to the independent atomic scattering approximation (the so-called free-atom model), coherent radiation is indistinguishable from primary radiation because its angular distribution is peaked in the forward direction. Since interference effects occur between x-rays scattered by neighbouring atoms in matter, it was shown experimentally that the scatter distribution is affected by the molecular structure of the target, even in amorphous materials. The most important consequence is that the coherent scatter distribution is not peaked in the forward direction, and the position of the maximum is strongly material-dependent [4] . In this contribution, we present the implementation of a method to take into account inter-atomic interference in small-angle coherent scattering in Geant4, including a dedicated data set of suitable molecular form factor values for several materials of clinical interest. Furthermore, we present scatter images of simple geometric phantoms in which the Rayleigh contribution is rigorously evaluated.

Purpose Breast Computed Tomography (CT) is a dedicated 3D imaging modality that provides a complete volumetric reconstruction of the uncompressed organ, thus matching a high image quality with an acceptable delivered dose. The SYRMA-3D collaboration is developing the first clinical trial of phase-contrast breast CT with synchrotron radiation at the Elettra synchrotron facility in Trieste. We present a proposal for a Quality Control (QC) protocol, including a custom made QC phantom that was designed and built by the laboratories of the University of Ferrara. Methods The synchrotron beam is monochromatic in the energy range 8.5–40 keV. The images were acquired with a photon counting detector placed at about 2 m from the organ, so as to generate a phase contrast signal. The QC phantom consists of a water filled PMMA cylinder, hung from the patient support through the breast aperture. It contains several inserts that allow measurements of geometric alignment, reconstruction uniformity and linearity, low and high contrast resolution. Results CT images of the phantom were acquired at several beam energies within the range of interest, to explore the energy dependence of the results. Uniformity and linearity appeared to be preserved by the reconstruction for all energies. Conversely, low contrast details exhibited a more pronounced dependence on the energy choice. Finally, the visibility of high contrast details was always found above acceptance levels. Conclusions The main goal of the study was to verify the compatibility of the QC phantom with the experimental environment of the SYRMA-3D project, and to test the validity and feasibility of the proposed QC protocol. With minimal modifications, they proved viable instruments to perform the necessary quality assessments for the innovative diagnostic device developed by the SYRMA-3D collaboration.

An introduction to novel imaging modalities, which take advantage of energy and phase characteristics of X-ray quanta will be here provided. X-ray detection in medical imaging typically involves an integration of the spectrum of X-rays exiting a patient, weighted by the detector’s energy response. This procedure yields information related to the average energy of the spectrum exiting the patient, which for many clinical applications is sufficient. The spectral imaging methods allow instead the form, or shape, of the X-ray distribution exiting the patient to be measured [1]. In particular, energy-sensitive photon-counting detectors allow for further improvements of the diagnostic information by optimising the signal-to-noise ratio, anatomical background subtraction or quantitative analysis of object constituents [2]. Phase-contrast imaging has had an undeniable impact in the field of X-ray imaging during the last decades, and one of the main advantages lies in the fact that the phase shifting effects are related to characteristic properties of materials that are different from the ones involved in conventional X-ray imaging (i.e. the well-known absorption-contrast imaging) [3]. The mechanism that allows one to produce and to detect images according to this physical phenomenon will be here discussed, together with a review of main phase-contrast imaging techniques. Finally, the potential of both phase-contrast and spectral imaging in diagnostic radiology will be presented by means of specific applications.

Purpose We introduce a novel algorithm for dual energy (DE) subtraction proposed in [1] , [2] , based on an iterative procedure for taking into account the intrinsic polychromaticity of conventional X-ray tubes. The result is an improvement of background cancellation with respect to the currently available DE systems. The algorithm was applied to a set of DE radiographs of a dedicated anthropomorphic phantom embedding small agglomerates of contrast medium (iodine), acquired with a commercial mammography system. Methods The employed anthropomorphic phantom, specifically designed for DE applications, is a polymethyl methacrylate (PMMA) box of parallelepipedal shape. It contains a large number of PMMA spheres of different diameters, embedded in paraffin wax. Moreover, it embeds a system of cavities that can be filled with iodine solutions of various concentrations. The phantom was imaged with X-ray beams of low energy (29 ± 2 kV) and high energy (47 ± 2 kV), generated by a commercial mammography unit with a tungsten anode and additional filtrations of rhodium (low energy) and copper (high energy). Results We achieved an almost complete cancellation of the background texture, resulting in an enhanced visibility of the iodine details. Such result was achieved with lower exposures than the values typical of diagnostic practice. We noticed no significant dependence of the image quality on the particular choice of beam energies. Conclusions The implementation of the novel subtraction algorithm on a commercial unit allowed an effective background cancellation with a reduced amount of delivered dose. Such result was largely independent of the imaging parameters, which is an indication of robustness of the algorithm. In conclusion, the proposed algorithm paves the way to an improvement of the diagnostic effectiveness of DE imaging.