Diego Dreossi

Mammography with Synchrotron Radiation: First Clinical Experience with Phase-Detection Technique

PURPOSE To prospectively evaluate the diagnostic contribution of mammography with synchrotron radiation in patients with questionable or suspicious breast abnormalities identified at combined digital mammography (DM) and ultrasonography (US). MATERIALS AND METHODS The ethics committee approved this prospective study, and written informed consent was obtained from all patients. Mammography with synchrotron radiation was performed with a phase-detection technique at a synchrotron radiation laboratory. Forty-nine women who met at least one of the inclusion criteria (palpable mass, focal asymmetry, architectural distortion, or equivocal or suspicious mass at DM; none clarified at US) were enrolled. Forty-seven women (mean age, 57.8 years ± 8.8 [standard deviation]; age range, 43-78 years) completed the study protocol, which involved biopsy or follow-up for 1 year as the reference standard. Breast Imaging Reporting and Data System (BI-RADS) scores of 1-3 were considered to indicate a negative result, while scores 4-5 were considered to indicate a positive result. The visibility of breast abnormalities and the glandular parenchymal structure at DM and at mammography with synchrotron radiation was compared by using the Wilcoxon signed rank test. RESULTS In 29 of the 31 patients with a final diagnosis of benign entity, mammography with synchrotron radiation yielded BI-RADS scores of 1-3. In 13 of the remaining 16 patients with a final diagnosis of malignancy, mammography with synchrotron radiation yielded BI-RADS scores of 4-5. Therefore, a sensitivity of 81% (13 of 16 patients) and a specificity of 94% (29 of 31 patients) were achieved with use of the described BI-RADS dichotomization system. CONCLUSION These study results suggest that mammography with synchrotron radiation can be used to clarify cases of questionable or suspicious breast abnormalities identified at DM. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11100745/-/DC1.

PITRE: software for phase-sensitive X-ray image processing and tomography reconstruction

Synchrotron-radiation computed tomography has been applied in many research fields. Here, PITRE (Phase-sensitive X-ray Image processing and Tomography REconstruction) and PITRE_BM (PITRE Batch Manager) are presented. PITRE supports phase retrieval for propagation-based phase-contrast imaging/tomography (PPCI/PPCT), extracts apparent absorption, refractive and scattering information of diffraction enhanced imaging (DEI), and allows parallel-beam tomography reconstruction for conventional absorption CT data and for PPCT phase retrieved and DEI-CT extracted information. PITRE_BM is a batch processing manager for PITRE: it executes a series of tasks, created via PITRE, without manual intervention. Both PITRE and PITRE_BM are coded in Interactive Data Language (IDL), and have a user-friendly graphical user interface. They are freeware and can run on Microsoft Windows systems via IDL Virtual Machine, which can be downloaded for free and does not require a license. The data-processing principle and some examples of application will be presented.

Testing of x-ray microtomography systems using a traceable geometrical standard

X-ray computed microtomography is an interesting imaging technique for many applications, and is also very promising in the field of coordinate metrology at the micro scale. The main advantage with respect to traditional tactile-probing or optical coordinate measurement systems is that x-ray tomography can acquire dimensional and geometrical data for both inner and outer surfaces, without accessibility restrictions. However, there are no accepted test procedures available so far and measurement uncertainty is unknown in many cases, due to complex and numerous error sources. The paper presents the first results of a test procedure implemented for determining the errors of indication for length measurements of x-ray microtomography systems, using a new reference standard featuring a regular array of inner and outer cylindrical shapes. The developed test method allows the determination of specific characteristics of x-ray microtomography systems and can be used for the correction of systematic errors.

Breast tomography with synchrotron radiation: preliminary results*

A system for in vivo breast imaging with monochromatic x-rays has been designed and built at the synchrotron radiation facility Elettra in Trieste (Italy) and will be operational in 2004. The system design involves the possibility of performing both planar mammography and breast tomography. In the present work, the first results obtained with a test set-up for breast tomography are shown and discussed. Tomographic images of in vitro breasts were acquired using monochromatic x-ray beams in the energy range 20-28 keV and a linear array silicon pixel detector. Tomograms were reconstructed using standard filtered backprojection algorithms; the effect of different filters was evaluated. The attenuation coefficients of fibroglandular and adipose tissue were measured, and a quantitative comparison of images acquired at different energies was performed by calculating the differential signal-to-noise ratio of fibroglandular details in adipose tissue. All images required a dose comparable to the dose delivered in clinical, conventional mammography and showed a high resolution of the breast structures without the overlapping effects that limit the visibility of the structures in 2D mammography. A quantitative evaluation of the images proves that the image quality at a given dose increases in the considered energy range and for the considered breast sizes.

Towards breast tomography with synchrotron radiation at Elettra: First images

The aim of the SYRMA-CT collaboration is to set-up the first clinical trial of phase-contrast breast CT with synchrotron radiation (SR). In order to combine high image quality and low delivered dose a number of innovative elements are merged: a CdTe single photon counting detector, state-of-the-art CT reconstruction and phase retrieval algorithms. To facilitate an accurate exam optimization, a Monte Carlo model was developed for dose calculation using GEANT4. In this study, high isotropic spatial resolution (120 μm)(3) CT scans of objects with dimensions and attenuation similar to a human breast were acquired, delivering mean glandular doses in the range of those delivered in clinical breast CT (5-25 mGy). Due to the spatial coherence of the SR beam and the long distance between sample and detector, the images contain, not only absorption, but also phase information from the samples. The application of a phase-retrieval procedure increases the contrast-to-noise ratio of the tomographic images, while the contrast remains almost constant. After applying the simultaneous algebraic reconstruction technique to low-dose phase-retrieved data sets (about 5 mGy) with a reduced number of projections, the spatial resolution was found to be equal to filtered back projection utilizing a four fold higher dose, while the contrast-to-noise ratio was reduced by 30%. These first results indicate the feasibility of clinical breast CT with SR.

The effects of the imaging system on the validity limits of the ray-optical approach to phase contrast imaging.

A theoretical analysis of the x-ray phase contrast imaging and its validation via synchrotron radiation imaging is here presented. Two different mathematical models have been followed: the simpler ray-optical approach and the more rigorous Fresnel-Kirchoff diffraction theory. Subsequently, the conditions upon which the x-ray optical approximation can be used to describe the image formation mechanism have been analyzed, taking into account also the effects due to the finite source size and detector resolution. It is possible to demonstrate that the ray-optics results can also be obtained by opportunely developing the diffraction formalism only with some restrictions on the spatial frequencies present in the final image, without any limitation on the maximum phase shift. The conditions allowing the use of the simplified ray-optical approach to describe the phase contrast images have been here defined and their validation has been proved by means of computer simulations and phantom experiments.

A quantitative, non-interferometric X-ray phase contrast imaging technique

We present a quantitative, non-interferometric, X-ray differential phase contrast imaging technique based on the edge illumination principle. We derive a novel phase retrieval algorithm which requires only two images to be acquired and verify the technique experimentally using synchrotron radiation. The technique is useful for planar imaging but is expected to be important for quantitative phase tomography also. The properties and limitations of the technique are studied in detail.

Beeswax as dental filling on a Neolithic human tooth

Evidence of prehistoric dentistry has been limited to a few cases, the most ancient dating back to the Neolithic. Here we report a 6500-year-old human mandible from Slovenia whose left canine crown bears the traces of a filling with beeswax. The use of different analytical techniques, including synchrotron radiation computed micro-tomography (micro-CT), Accelerator Mass Spectrometry (AMS) radiocarbon dating, Infrared (IR) Spectroscopy and Scanning Electron Microscopy (SEM), has shown that the exposed area of dentine resulting from occlusal wear and the upper part of a vertical crack affecting enamel and dentin tissues were filled with beeswax shortly before or after the individual’s death. If the filling was done when the person was still alive, the intervention was likely aimed to relieve tooth sensitivity derived from either exposed dentine and/or the pain resulting from chewing on a cracked tooth: this would provide the earliest known direct evidence of therapeutic-palliative dental filling.

Enhanced and Flexible Software Tools for X-ray Computed Tomography at the Italian Synchrotron Radiation Facility Elettra

X-ray computed tomography (CT) experiments performed at synchrotron radiation fa- cilities require adequate computing and storage resources due to the large amount of acquired and reconstructed data produced. To satisfy the heterogeneous needs of beamline users, flexible solu- tions are also required. Moreover, the growing demand of quantitative image analysis impose an easy integration between the CT reconstruction process and the subsequent feature extraction step. This paper presents some of the software solutions adopted by the SYRMEP beamline of the Italian synchrotron radiation facility Elettra. By using the enhanced version of the reconstruction software here presented as well as data reduction and data analysis tools, beamline users can easily imple- ment an integrated and comprehensive approach to the digital image processing and image analysis required by a tomography-oriented scientific workflow.

Theory and preliminary experimental verification of quantitative edge illumination x-ray phase contrast tomography

X-ray phase contrast imaging (XPCi) methods are sensitive to phase in addition to attenuation effects and, therefore, can achieve improved image contrast for weakly attenuating materials, such as often encountered in biomedical applications. Several XPCi methods exist, most of which have already been implemented in computed tomographic (CT) modality, thus allowing volumetric imaging. The Edge Illumination (EI) XPCi method had, until now, not been implemented as a CT modality. This article provides indications that quantitative 3D maps of an objects phase and attenuation can be reconstructed from EI XPCi measurements. Moreover, a theory for the reconstruction of combined phase and attenuation maps is presented. Both reconstruction strategies find applications in tissue characterisation and the identification of faint, weakly attenuating details. Experimental results for wires of known materials and for a biological object validate the theory and confirm the superiority of the phase over conventional, attenuation-based image contrast.