1,721,007 research outputs found
The role of radiation physics in nuclear medicine
No full textNuclear medicine is a fast-growing and dynamic specialty; in recent years with the widespread use of positron emission tomography (PET), PET combined with computed tomography (CT), single-photon emission computed tomography (SPECT)-CT, and new applications in radionuclide therapy, this discipline asks for continuous updating of nuclear medicine professionals on various aspects of the changing trends. Nuclear medicine has grown from the initial in vitro tests to advanced methods, allowing the imaging of organ function and thus becoming an important diagnostic tool. In fact, until now no other method than scintigraphy has been available to evaluate myocardial blood flow in stress and rest conditions or to evidence bone metastases
Radiation physics for nuclear medicine
No full textThe field of nuclear medicine is expanding rapidly, with the development of exciting new diagnostic methods and treatments. This growth is closely associated with significant advances in radiation physics. In this book, acknowledged experts explain the basic principles of radiation physics in relation to nuclear medicine and examine important novel approaches in the field. The first section is devoted to what might be termed the "building blocks" of nuclear medicine, including the mechanisms of interaction between radiation and matter and Monte Carlo codes. In subsequent sections, radiation sources for medical applications, radiopharmaceutical development and production, and radiation detectors are discussed in detail. New frontiers are then explored, including improved algorithms for image reconstruction, biokinetic models, and voxel phantoms for internal dosimetry. Both trainees and experienced practitioners and researchers will find this book to be an invaluable source of up-to-date information.Radiation Physics for Nuclear Medicine presents the basic principles of radiation physics in relation to nuclear medicine, while examining important novel approaches in the field. New areas, such as improved algorithms for image reconstruction, biokinetic models, and voxel phantoms, are also discussed
Radiation exposure of the embryo/foetus and the newborn child
No full textThis chapter addresses risks and radiation protection aspects in medical exposures when embryo/foetus or infants are involved, following exposures of pregnant women or breastfeeding women, including patients or workers.
The effects of radiation in prenatal exposures in the different periods of pregnancy from preimplantation to embryonic and foetal periods, taking into consideration, among others, the effects on mental development and the carcinogenic risks, are presented.
Diagnostic and therapeutic nuclear medicine procedures in relation to pregnancy are considered.
Patients administered with radiopharmaceuticals normally have family members at home, other persons taking care or giving comfort to the patient and close friends; thus, radiation protection takes into account also the protection of these individuals and in particular of children and pregnant females among them.
In nuclear medicine, the staff members should pay attention in handling radiopharmaceuticals in relation to external and internal exposures, in particular for 131I therapeutic doses. A pregnant or breastfeeding female worker should not work in areas of significant contamination risk
Scintillators and semiconductor detectors
No full textVarious processes occur during the detection of ionizing radiation within a scintillator, and proper detection designs are needed [1, 2, 3]. As a consequence of the interaction of radiation with the scintillation material, ionisation and excitation processes arise, and the energy (or part of it) of the incoming radiation is transferred to the atoms and molecules of the scintillator. Following deexcitation processes, photons originate in the ultraviolet/visible (UV/VIS) region of the electromagnetic spectrum, light that must be collected and converted in a suitable electric signal. In many cases, light collection simply may be obtained by coupling the scintillator directly with an optical detector, typically a photomultiplier tube (PMT). In other cases, depending on the particular application or measurement geometry, a light guide is required, which efficiently transmits the light emitted by the scintillator to the optical device. Finally, light photons are converted into electrons, and the resulting basic electric signal is amplified and properly processed. Let us consider in more detail the scintillation conversion mechanism in a wide band-gap material. This process may be explained by considering the energy band structure of an activated crystalline scintillator. An inorganic scintillator is indeed usually a crystalline solid containing a small amount of dopant, acting as a luminescent centre, which creates energy levels within the forbidden band between the valence band and the conduction band. Moreover, the natural impurities and defects present in the crystal are the origination of other energy levels, which may act as traps during the charge transport
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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