180 research outputs found
Caratterizzazione quantitativa del materiale nella tomografia computerizzata a raggi X spettrale
No full textThis doctoral thesis embarks on a comprehensive journey of exploring the potential of spectral X-ray imaging in medicine, employing advanced techniques and cutting-edge technologies to harness the full potential of X-ray interactions with matter. The study is divided into several chapters, each contributing to our understanding of how spectral imaging, particularly through photon counting detectors and synchrotron radiation X-ray setups, can revolutionize medical diagnostics and material characterization. The research begins by delving into the intricate physics of X-ray interactions, encompassing X-ray attenuation and phase shift in matter. It lays the foundation for the subsequent exploration of X-ray detection methodologies, encompassing photon counting detectors and addressing challenges like charge sharing and pulse pile-up. A central theme of this work is quantitative imaging, focusing on material decomposition as an intermediary process for computing material characteristics - material density and effective atomic number. These quantities are derived through a mathematical framework that encapsulates the connection between decomposed material maps and the maps representing density and effective atomic numbers. Innovative material decomposition techniques such as singular value material decomposition were addressed through a comprehensive theoretical framework. Careful evaluation of the concept of effective atomic number was performed by comparing the methods published in several papers. The exploration extends to spectral data acquisition techniques, spanning dual-energy imaging systems available on earlier-generation clinical CT scanners, multi-energy photon-counting CT scanners, and pre-clinical spectral imaging using synchrotron radiation CT systems, shedding light on the advantages and disadvantages of new technology. The photon-counting detectors as a state-of-the-art technology for clinical spectral imaging were addressed in the framework of a virtual imaging platform developed at Duke University. The work consisted of modeling spatial-energetic detector response and addressing non-idealities like charge sharing and pulse pile-up. The model was validated against real measurements and special attention was focused on the influence of these non-idealities on the accuracy of spectral information, and thus the correctness of quantitative information obtained from such datasets. Besides virtual investigation, the thesis highlights the potential of the first clinical photon-counting CT scanner through the comparative assessment with dual-energy CT, demonstrating the superiority of photon-counting CT in iodine quantification at lower radiation doses. The investigation extends to synchrotron spectral CT, with a specific focus on estimating the density and effective atomic number of adipose, fibro-glandular, and cancer tissue. Synchrotron breast CT imaging was carried out at the SYRMEP beamline of Elettra, an Italian synchrotron light source in Trieste, in the framework of SYRMA-3D (SYnchrotron Radiation for MAmmography) collaboration. This endeavor illuminates the potential to differentiate various breast tissues based on their quantitative characteristics and lays the groundwork for other various spectral synchrotron-based X-ray imaging setups.This doctoral thesis embarks on a comprehensive journey of exploring the potential of spectral X-ray imaging in medicine, employing advanced techniques and cutting-edge technologies to harness the full potential of X-ray interactions with matter. The study is divided into several chapters, each contributing to our understanding of how spectral imaging, particularly through photon counting detectors and synchrotron radiation X-ray setups, can revolutionize medical diagnostics and material characterization. The research begins by delving into the intricate physics of X-ray interactions, encompassing X-ray attenuation and phase shift in matter. It lays the foundation for the subsequent exploration of X-ray detection methodologies, encompassing photon counting detectors and addressing challenges like charge sharing and pulse pile-up. A central theme of this work is quantitative imaging, focusing on material decomposition as an intermediary process for computing material characteristics - material density and effective atomic number. These quantities are derived through a mathematical framework that encapsulates the connection between decomposed material maps and the maps representing density and effective atomic numbers. Innovative material decomposition techniques such as singular value material decomposition were addressed through a comprehensive theoretical framework. Careful evaluation of the concept of effective atomic number was performed by comparing the methods published in several papers. The exploration extends to spectral data acquisition techniques, spanning dual-energy imaging systems available on earlier-generation clinical CT scanners, multi-energy photon-counting CT scanners, and pre-clinical spectral imaging using synchrotron radiation CT systems, shedding light on the advantages and disadvantages of new technology. The photon-counting detectors as a state-of-the-art technology for clinical spectral imaging were addressed in the framework of a virtual imaging platform developed at Duke University. The work consisted of modeling spatial-energetic detector response and addressing non-idealities like charge sharing and pulse pile-up. The model was validated against real measurements and special attention was focused on the influence of these non-idealities on the accuracy of spectral information, and thus the correctness of quantitative information obtained from such datasets. Besides virtual investigation, the thesis highlights the potential of the first clinical photon-counting CT scanner through the comparative assessment with dual-energy CT, demonstrating the superiority of photon-counting CT in iodine quantification at lower radiation doses. The investigation extends to synchrotron spectral CT, with a specific focus on estimating the density and effective atomic number of adipose, fibro-glandular, and cancer tissue. Synchrotron breast CT imaging was carried out at the SYRMEP beamline of Elettra, an Italian synchrotron light source in Trieste, in the framework of SYRMA-3D (SYnchrotron Radiation for MAmmography) collaboration. This endeavor illuminates the potential to differentiate various breast tissues based on their quantitative characteristics and lays the groundwork for other various spectral synchrotron-based X-ray imaging setups
Open Access to Research: Changing Researcher Behavior Through University and Funder Mandates
No full textThe primary target of the worldwide Open Access initiative is the 2.5 million articles published every year in the planet's 25,000 peer-reviewed research journals across all scholarly and scientific fields. Without exception, every one of these articles is an author give-away, written, not for royalty income, but solely to be used, applied and built upon by other researchers. The optimal and inevitable solution for this give-away research is that it should be made freely accessible to all its would-be users online and not only to those whose institutions can afford subscription access to the journal in which it happens to be published. Yet this optimal and inevitable solution, already fully within the reach of the global research community for at least two decades now, has been taking a remarkably long time to be grasped. The problem is not particularly an instance of "eDemocracy" one way or the other; it is an instance of inaction because of widespread misconceptions (reminiscent of Zeno's Paradox). The solution is for the world's research institutions and funders to (1) extend their existing "publish or perish" mandates so as to (2) require their employees and fundees to maximize the usage and impact of the research they are employed and funded to conduct and publish by (3) depositing their final drafts in their Open Access (OA) Institutional Repositories immediately upon acceptance for publication in order to (4) make their findings freely accessible to all their potential users webwide. OA metrics can then be used to measure and reward research progress and impact; and multiple layers of links, tags, commentary and discussion can be built upon and integrated with the primary research
Open Access 2012: achievements, further steps, and obstacles. An interview with Stevan Harnad
No full textOn the occasion of Open Access Week (22-28 October) I had a talk with Stevan Harnad, a pioneer and one of the world’s best-known Open Access advocates, author of the Subversive proposal (1994-1995) which triggered the whole movement. Professor Harnad highlights achievements, further steps, and obstacles ten years after the Open Access manifesto of the Budapest Open Access Initiative
From spectral decomposition through SVD to quantitative description of monochromatic CT images: a phantom study
No full textIn this work, we applied the singular value decomposition (SVD) method to a set of monochromatic images to extract the dominant physical contributions to image formation. We showed that the first two principal components can be related to an arbitrary pair of basis material in mathematically enclosed expression. The later
principal components are assumed to carry mostly sub-leading image formation effects, noise, and reconstruction artifact contribution. The proof of concept is shown on numerical (linear) images and later confirmed on
physical spectral CT phantom images obtained with monochromatic x-ray radiation at Elettra synchrotron in
Trieste, Italy. Following material decomposition, we also performed a quantitative description of tissue-equivalent
phantom materials in terms of material density and effective atomic number
Quantitative performance of photon‐counting CT at low dose: Virtual monochromatic imaging and iodine quantification
No full textBackground
Quantitative imaging techniques, such as virtual monochromatic imaging (VMI) and iodine quantification (IQ), have proven valuable diagnostic methods in several specific clinical tasks such as tumor and tissue differentiation. Recently, a new generation of computed tomography (CT) scanners equipped with photon-counting detectors (PCD) has reached clinical status.
Purpose
This work aimed to investigate the performance of a new photon-counting CT (PC-CT) in low-dose quantitative imaging tasks, comparing it to an earlier generation CT scanner with an energy-integrating detector dual-energy CT (DE-CT). The accuracy and precision of the quantification across size, dose, material types (including low and high iodine concentrations), displacement from iso-center, and solvent (tissue background) composition were explored.
Methods
Quantitative analysis was performed on two clinical scanners, Siemens SOMATOM Force and NAEOTOM Alpha using a multi-energy phantom with plastic inserts mimicking different iodine concentrations and tissue types. The tube configurations in the dual-energy scanner were 80/150Sn kVp and 100/150Sn kVp, while for PC-CT both tube voltages were set to either 120 or 140 kVp with photon-counting energy thresholds set at 20/65 or 20/70 keV. The statistical significance of patient-related parameters in quantitative measurements was examined using ANOVA and pairwise comparison with the posthoc Tukey honest significance test. Scanner bias was assessed in both quantitative tasks for relevant patient-specific parameters.
Results
The accuracy of IQ and VMI in the PC-CT was comparable between standard and low radiation doses (p < 0.01). The patient size and tissue type significantly affect the accuracy of both quantitative imaging tasks in both scanners. The PC-CT scanner outperforms the DE-CT scanner in the IQ task in all cases. Iodine quantification bias in the PC-CT (−0.9 ± 0.15 mg/mL) at low doses in our study was comparable to that of DE-CT (range -2.6 to 1.5 mg/mL, published elsewhere) at a 1.7× higher dose, but the dose reduction severely biased DE-CT (4.72 ± 0.22 mg/mL). The accuracy in Hounsfield units (HU) estimation was comparable for 70 and 100 keV virtual imaging between scanners, but PC-CT was significantly underestimating virtual 40 keV HU values of dense materials in the phantom representing the extremely obese population.
Conclusions
The statistical analysis of our measurements reveals better IQ at lower radiation doses using new PC-CT. Although VMI performance was mostly comparable between the scanners, the DE-CT scanner quantitatively outperformed PC-CT when estimating HU values in the specific case of very large phantoms and dense materials, benefiting from increased X-ray tube potentials
Open Access to Peer-Reviewed Research through Author/Institution Self-Archiving: Maximizing Research Impact by Maximizing Online Access
No full textAll refereed journals will soon be available online; most of them already are. This means that anyone will be able to access them from any networked desk-top. The literature will all be interconnected by citation, author, and keyword/subject links, allowing for unheard-of power and ease of access and navigability. Successive drafts of pre-refereeing preprints will be linked to the official refereed draft, as well as to any subsequent corrections, revisions, updates, comments, responses, and underlying empirical databases, all enhancing the self-correctiveness, interactivity and productivity of scholarly and scientific research and communication in remarkable new ways. New scientometric indicators of digital impact are also emerging <http://opcit.eprints.org> to chart the online course of knowledge. But there is still one last frontier to cross before science reaches the optimal and the inevitable: Just as there is no longer any need for research or researchers to be constrained by the access-blocking restrictions of paper distribution, there is no longer any need to be constrained by the impact-blocking financial fire-walls of Subscription/Site-License/Pay-Per-View (S/L/P) tolls for this give-away literature. Its author/researchers have always donated their research reports for free (and its referee/researchers have refereed for free), with the sole goal of maximizing their impact on subsequent research (by accessing the eyes and minds of fellow-researchers, present and future) and hence on society. Generic (OAi-compliant) software is now available free so that institutions can immediately create Eprint Archives in which their authors can self-archive all their refereed papers for free for all forever <http://www.eprints.org/>. These interoperable Open Archives <http://www.openarchives.org> will then be harvested into global, jointly searchable "virtual archives" (e.g., <http://arc.cs.odu.edu/>). "Scholarly Skywriting" in this PostGutenberg Galaxy will be dramatically (and measurably) more interactive and productive, spawning its own new digital metrics of productivity and impact, allowing for an online "embryology of knowledge.
Maximizing Research Impact Through Institutional and National Open-Access Self-Archiving Mandates
No full textNo research institution can afford all the journals its researchers may need, so all articles are losing research impact (usage and citations). Articles made “Open Access,” (OA) by self-archiving them on the web are cited twice as much, but only 15% of articles are being spontaneously self-archived. The only institutions approaching 100% self-archiving are those that mandate it. Surveys show that 95% of authors will comply with a self-archiving mandate; the actual expe-rience of institutions with mandates has confirmed this. What institutions and funders need to mandate is that (1) immediately upon acceptance for publication, (2) the author’s final draft must be (3) deposited into the Institutional Repository. Only the depositing needs to be mandated; set-ting access privileges to the full-text as either OA or Restricted Access (RA) can be left up to the author. For articles published in the 93% of journals that have already endorsed self-archiving, access can be set as OA immediately; for the remaining 7%, authors can email the eprint in re-sponse to individual email requests automatically forwarded by the Repository
Evaluating Citebase, an open access Web-based citation-ranked search and impact discovery service
No full textCitebase is a new citation-ranked search and impact discovery service that measures citations of scholarly research papers which are openly accessible on the Web, i.e. papers that are assessable continuously online. Other services, such as ResearchIndex, have emerged in recent years to offer citation indexing of Web research papers. In the first detailed user evaluation of an open access Web citation indexing service, Citebase has been evaluated by nearly 200 users from different backgrounds. The paper details the procedures used in the evaluation, and analyses the results of this study, which took place between June and October 2002. It was found that within the scope of its primary components, the search interface and services available from its rich bibliographic records, Citebase can be used simply and reliably for the purpose intended, and that it compares favourably with other bibliographic services. It is shown tasks can be accomplished efficiently with Citebase regardless of the background of the user. More data need to be collected and the process refined before it is as reliable for measuring citation impact of indexed papers. Better explanations and guidance are required for first-time users. Coverage is seen as a limiting factor, even though Citebase indexes over 200,000 papers from arXiv. Non-physicists were frustrated at the lack of papers from other sciences. The principle of citation searching of open access archives has thus been demonstrated and need not be restricted to current users. Since the evaluation, Citebase has become a featured service of the ArXiv physics eprint archives
No-Fault Peer Review Charges: The Price of Selectivity Need Not Be Access Denied or Delayed
No full textPlans by universities and research funders to pay the costs of Open Access Publishing ("Gold OA") are premature. Funds are short; 80% of journals (including virtually all the top journals) are still subscription-based, tying up the potential funds to pay for Gold OA; the asking price for Gold OA is still high; and there is concern that paying to publish may inflate acceptance rates and lower quality standards. What is needed now is for universities and funders to mandate OA self-archiving (of authors' final peer-reviewed drafts, immediately upon acceptance for publication) ("Green OA"). That will provide immediate OA; and if and when universal Green OA should go on to make subscriptions unsustainable (because users are satisfied with just the Green OA versions) that will in turn induce journals to cut costs (print edition, online edition, access-provision, archiving), downsize to just providing the service of peer review, and convert to the Gold OA cost-recovery model; meanwhile, the subscription cancellations will have released the funds to pay these residual service costs. The natural way to charge for the service of peer review then will be on a "no-fault basis," with the author's institution or funder paying for each round of refereeing, regardless of outcome (acceptance, revision/re-refereeing, or rejection). This will minimize cost while protecting against inflated acceptance rates and decline in quality standards
Open Access 2012: achievements, further steps, and obstacles. An interview with Stevan Harnad
No full textn the occasion of Open Access Week (22-28 October) I had a talk with Stevan Harnad, a pioneer and one of the world’s best-known Open Access advocates, author of the Subversive proposal (1994-1995) which triggered the whole movement. Professor Harnad highlights achievements, further steps, and obstacles ten years after the Open Access manifesto of the Budapest Open Access Initiative
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