1,721,003 research outputs found
Effectiveness of X-ray phase-contrast tomography: Effects of pixel size and magnification on image noise
Full text linkNoise magnitude in conventional attenuation X-ray tomography (CT) is strongly dependent on the pixel size and/or the geometrical magnification, thereby limiting the possibility of achieving high-resolution low-dose CT imaging. In this context, the use of Propagation-Based Imaging (PBI) phase-contrast technique coupled with the application of a suitable Phase-Retrieval (PhR) filter is a valuable tool to overcome such limitation. In fact, at fixed radiation dose, the noise dependence on the effective pixel size when the PhR filter is applied is much shallower with respect to conventional CT imaging. Making use of a theoretical framework developed by other authors, this work demonstrates quantitatively the dependence of CT image noise on pixel size and magnification in PBI. Calculations are compared with experimental images of a breast specimen imaged at the SYRMEP beamline at the Elettra synchrotron facility (Trieste, Italy), with a CdTe photon-counting detector in PBI configuration. The results, expressed in terms of Signal-to-Noise Ratio (SNR) gain due to the PhR application, show a good agreement between predictions and experimental data at all pixel pitches and magnifications, quantitatively demonstrating the importance of going towards detectors featuring smaller pixels (or higher spatial resolution) to fully exploit the advantages of PBI and PhR. Specifically, SNR gain up to a factor of 20 is observed at the smallest pixel pitch (60 μ m) and largest magnification (1.40). At the same time, as predicted theoretically, larger magnifications correspond to lower image noise (or higher SNR) when PhR is applied: this trend is unparalleled in attenuation-based CT imaging where larger magnifications, hence smaller effective pixel sizes, lead to a higher noise
Multi-material spectral photon-counting micro-CT with minimum residual decomposition and self-supervised deep denoising
Full text linkSpectral micro-CT imaging with direct-detection energy discriminating photon counting detectors having small pixel size (< 100×100 μm2) is mainly hampered by: i) the limited energy resolution of the imaging device due to charge sharing effects and ii) the unavoidable noise amplification in the images resulting from basis material decomposition. In this work, we present a cone-beam micro-CT setup that includes a CdTe photon counting detector implementing a charge summing hardware solution to correct for the charge-sharing issue and an innovative image processing pipeline based on accurate modeling of the spectral response of the imaging system, an improved basis material decomposition (BMD) algorithm named minimum-residual BMD (MR-BMD), and self-supervised deep convolutional denoising. Experimental tomographic projections having a pixel size of 45×45 μm2 of a plastinated mouse sample including I, Ba, and Gd small cuvettes were acquired. Results demonstrate the capability of the combined hardware and software tools to sharply discriminate even between materials having their K-Edge separated by a few keV, such as e.g., I and Ba. By evaluating the quality of the reconstructed decomposed images (water, bone, I, Ba, and Gd), the quantitative performances of the spectral system are here assessed and discusse
White Beam Differential Phase and Dark Field Imaging at High Resolution
Full text linkX-ray phase-contrast imaging (XPCI) can extend the capabilities of conventional radiography and, by
exploiting phase effects, make visible those details that lack enough absorption contrast [1]. Several
approaches have been proposed for XPCI by using synchrotron radiation, microfocal and extended
labortory sources [2]. We focus here on edge illumination [3] in view of its properties of high resolution,
sensitivity, robustness and achromaticity [4-6]. The latter is of particular interest for the study reported
here, where we used the direct beam from a bending magnet, aiming at making use of a spectral
distribution as broad as possible
Spectral micro-CT for simultaneous gold and iodine detection, and multi-material identification
Full text linkMultiple energy bin spectral micro-CT (SμCT) is an advanced imaging technique that allows multi-material decomposition according to their specific absorption patterns at a sub-100 μm scale. Typically, iodine is the preferred CT contrast agent for cardiovascular imaging, while gold nanoparticles have gained attention in recent years owing to their high absorption properties, biocompatibility and ability to target tumors. In this work, we demonstrate the potential for multi-material decomposition through SμCT imaging of a test sample at the PEPI lab of INFN Trieste. The sample, consisting of gold, iodine, calcium, and water, was imaged using a Pixirad1/PixieIII chromatic detector with multiple energy thresholds and a wide spectrum (100 kV) produced by a micro-focus X-ray tube. The results demonstrate the simultaneous detection and separation of the four materials at a spatial scale of 35 μm, suggesting the potential of this technique in improving material detectability and quantification in a range of pre-clinical applications, including cardiovascular and oncologic imaging.
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Timepix4 characterization with monochromatic X-rays at the Elettra synchrotron facility
Full text linkTimepix4 is the latest generation application-specific integrated circuit (ASIC) of the Medipix family, developed by the Medipix4 Collaboration. A characterization of a Timepix4 assembly bump-bonded to a planar 300
m thick silicon pixelated sensor has been performed by using monochromatic X-rays at the Elettra synchrotron facility (Trieste, Italy). In particular, a calibration of the ToT against the energy released in the Si detector has been performed for each pixel, to optimize energy resolution. A preliminary analysis to estimate the detector photon counting linearity and pixel readout dead time was also carried out
Optimization of a customized Simultaneous Algebraic Reconstruction Technique algorithm for breast CT
No full textIterative 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%
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Flattening filter for Gaussian-shaped monochromatic X-ray beams: An application to breast computed tomography
No full textThe vertical intensity distribution of synchrotron-based X-ray beams usually has a Gaussian profile encompassing large intensity variations. For biomedical imaging applications this may entail sub-optimal dose distributions and large fluctuations in terms of image noise. Commonly, planar metallic filters coupled with absorbing slits systems are applied to adjust the delivered flux and to limit intensity variations, respectively. The latter results in a reduction of the effective beam size. A flattening filter that counterbalances the transverse inhomogeneity, while retaining a sufficient flux, has been developed in the context of a monochromatic phase-contrast breast computed tomography application, ongoing at the Elettra synchrotron facility. The implementation of the new filtration system results in homogeneous intensity (hence dose) distribution and signal-To-noise ratio across the imaged volume. Finally, and most importantly, it allows a wider portion of the beam to be used, directly translating into a major (∼40%) reduction of the overall scan time for samples requiring a field of view larger than the beam size (i.e. multiple translation steps)
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