Search

Iterative CT reconstruction algorithms coupled with edge-preserving filters are attracting a growing interest in the field of biomedical X-ray imaging. In many cases the application of such algorithms results in an improved reconstruction quality when compared with filtered back-projection (FBP). Iterative algorithms commonly entail a decrease of image noise or, equivalently, an increase of contrast-to-noise ratio, while preserving image detail. Conversely, they modify the shape of noise power spectrum, producing a shift towards lower spatial frequencies with respect to FBP. This results in a "patchy" or "waxy" appearance of the reconstructed images. Changes in image texture affect radiologists’ perception of image quality, possibly influencing their willingness to use an iterative algorithm in clinical practice. In this work we present a GPU implementation of a simultaneous algebraic reconstruction technique algorithm, combined with a bilateral regularization filter, and we discuss the optimization of the algorithm’s parameters in terms of noise texture, selecting those parameters which preserve its "natural" appearance. We evaluated the performances of the algorithm, compared to FBP, both on a test phantom and on a surgical mastectomy sample by using contrast-to-noise ratio and spatial resolution metrics. Samples were imaged at the SYRMEP beamline of the Elettra synchrotron facility with a monochromatic beam (32 keV) in propagation-based phase-contrast configuration, delivering a clinically-compatible radiation dose of 5 mGy and using a large-area CdTe photon-counting detector. Results show, in the specific application on breast specimens, that the implemented algorithm can be tuned to preserve the noise texture and spatial resolution observed in FBP reconstructions, while improving contrast-to-noise ratio up to 30%.

In this work we present a novel 3D Monte Carlo photon transport program for simulation of multiple refractive scattering based on the refractive properties of X-rays in highly scattering media, like lung tissue. Multiple scattering reduces not only the quality of the image, but contains also information on the internal structure of the object. This information can be exploited utilizing image modalities such as Diffraction Enhanced Imaging (DEI). To study the effect of multiple scattering a Monte Carlo program was developed that simulates multiple refractive scattering of X-ray photons on monodisperse PMMA (poly-methyl-methacrylate) microspheres representing alveoli in lung tissue. Eventually, the results of the Monte Carlo program were compared to the measurements taken at the SYRMEP beamline at Elettra (Trieste, Italy) on special phantoms showing a good agreement between both data., 5 page, 7 figures

Diffraction Enhanced Imaging is a phase sensitive imaging modality, which recently has been demonstrated to be a powerful tool for improving the visibility of tiny low absorbing structures. Especially in medical imaging the capability to detect small details, not visible in a conventional radiograph is of relevant importance. An analyzer crystal is used as angular filter to select or reject X-rays that are deviated when traversing a sample if a gradient of the real part of the refractive index is encountered. At the medical imaging beamline of the synchrotron radiation facility Elettra (Trieste) experiments were carried out to assess the applicability of this technique to materials where a combined refraction from a large amount of small structures, not detectable separately, gives rise to an overall effect of multiple scattering. Tuning the analyzer crystal in different angular positions the variation of the contrast was studied. Strong contrast enhancement was measured in comparison to the conventional absorption image.

The SYRMEP/FRONTRAD experiment is performing a R&D program in order to assess the performances of a scanning X-ray detector operating at the ELETTRA Synchrotron light source, in an energy range optimized for mammographic imaging. The detector itself consists of a stack of silicon detectors positioned edge-on with respect to the X-ray beam direction. The data acquisition system must perform several tasks: from the control of the motors during the scanning procedure, to the collection of the data that are recorded on CAMAC modules and refer to the slots of the image while it is forming. The system has to process the data during the scan and to store them on a local disk. In addition, the environmental conditions (global dose measured by an ionization chamber, temperature, dark current of the detector and status of the electronics power supplies) have to be monitored and the proper action taken. We have implemented a multiprocessing system using TCP/IP and RPC to manage the tasks. The overall control is done by a GUI built using the Tcl/Tk package.