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CT data - A comprehensive assessment of physical image quality of five different scanners for head CT imaging as clinically used at a single hospital centre – a phantom study
No full textCT images of the Catphan 504 phantom
Tecnologie diagnostiche con raggi X: avvento, sfide attuali e nuove frontiere
Get PDFL'uso dei raggi X per acquisire immagini della struttura interna del corpo umano si è diffuso rapidamente in tutto il mondo subito dopo la prima radiografia a raggi X che fu acquisita da Wilhelm Conrad Röntgen nel 1895. Da allora nel campo delle tecnologie diagnostiche che utilizzano raggi X sono stati fatti enormi progressi sia per quanto riguarda la strumentazione di base (generatori e rivelatori di raggi X) per i sistemi di imaging bidimensionale, sia per quanto riguarda l'architettura dei sistemi di acquisizione, fino ad arrivare alla realizzazione di immagini tomografiche tridimensionali, con un un utilizzo sempre crescente anche dei sempre più sofisticati strumenti informatici e mezzi di calcolo, arrivando a coprire le più svariate esigenze cliniche
Evaluation of the Imaging Properties of a CT Scanner with the Adaptive Statistical Iterative Reconstruction Algorithm - Noise, Contrast and Spatial Resolution Properties of CT Images Reconstructed at Different Blending Levels
Get PDFX-ray Computed Tomography (CT) is an essential imaging technique for different diagnostic and therapeutic tasks. However, ionizing radiation from CT scanners represents the largest source of medical exposure for the population of industrialized countries. In order to reduce CT dose during patient examination, iterative reconstruction algorithms have been developed to help existing dose reduction methods. In this paper, we studied the image quality performance of a 64-slice CT scanner (Optima CT660, GE Healthcare, Waukesha, WI, USA) that implements both the conventional filtered back-projection (FBP) and the Adaptive Statistical Iterative Reconstruction (ASIR, GE Healthcare, Waukesha, WI, USA) algorithm. In order to compare the performance of these two reconstruction technologies, CT images of the Catphan®504 phantom were reconstructed using both conventional FBP and ASIR with different percentages of reconstruction from 20% to 100%. Noise level, noise power spectrum (NPS), contrast-to -noise ratio (CNR) and modulation transfer function (MTF) were estimated for different values of the main radiation exposure parameters (i.e. mAs, kVp, pitch and slice thickness) and contrast objects. We found that, as compared to conventional FBP, noise/CNR decreases/increases non-linearly up to 50%/100% when increasing the ASIR blending level of reconstruction. Furthermore, ASIR modifies the NPS curve shape (i.e. the noise texture). The MTF for ASIR-reconstructed images depended on both tube load and contrast level, whereas MTF of FBP-reconstructed images did not. For lower tube load and contrast level, ASIR offered lower performance as compared to conventional FBP in terms of reduced spatial resolution and MTF decreased with increasing ASIR blending level of reconstruction
Computed tomography imaging with the Adaptive Statistical Iterative Reconstruction (ASIR) algorithm: dependence of image quality on the blending level of reconstruction
No full textComputed tomography (CT) is a useful and widely employed imaging technique, which represents the largest source of population exposure to ionizing radiation in industrialized countries. Adaptive Statistical Iterative Reconstruction (ASIR) is an iterative reconstruction algorithm with the potential to allow reduction of radiation exposure while preserving diagnostic information. The aim of this phantom study was to assess the performance of ASIR, in terms of a number of image quality indices, when different reconstruction blending levels are employed. CT images of the Catphan-504 phantom were reconstructed using conventional filtered back-projection (FBP) and ASIR with reconstruction blending levels of 20, 40, 60, 80, and 100%. Noise, noise power spectrum (NPS), contrast-to-noise ratio (CNR) and modulation transfer function (MTF) were estimated for different scanning parameters and contrast objects. Noise decreased and CNR increased non-linearly up to 50 and 100%, respectively, with increasing blending level of reconstruction. Also, ASIR has proven to modify the NPS curve shape. The MTF of ASIR reconstructed images depended on tube load/contrast and decreased with increasing blending level of reconstruction. In particular, for low radiation exposure and low contrast acquisitions, ASIR showed lower performance than FBP, in terms of spatial resolution for all blending levels of reconstruction. CT image quality varies substantially with the blending level of reconstruction. ASIR has the potential to reduce noise whilst maintaining diagnostic information in low radiation exposure CT imaging. Given the opposite variation of CNR and spatial resolution with the blending level of reconstruction, it is recommended to use an optimal value of this parameter for each specific clinical application
Quantitative assessment of noise and spatial resolution properties of ASIR-reconstructed CT images at different percentages of reconstruction
No full textIntroduction
Computed tomography (CT) is the largest source of population exposure to ionizing radiation in industrialized countries. Recent advances in CT imaging include the development of iterative reconstruction algorithms in order to obtain a dose reduction without compromising the diagnostic quality of images.
The purpose of this study was to quantitatively assess noise reduction and spatial resolution in CT imaging with the ASIR (Adaptive Statistical Iterative Reconstruction, GE Healthcare) reconstruction algorithm at different percentages of reconstruction as well as different kVp, mAs and contrasts. Acquisitions of the Catphan-504 phantom were performed on a PET/CT scanner (Discovery-710, GE Healthcare). CT images were reconstructed using both filtered back projection (FBP) and ASIR with different percentages of reconstruction (20%, 40%, 60%, 80%, 100%). The image noise was estimated for different values of scanning parameters (i.e. mAs, kVp, pitch, slice thickness). Then, 3D/2D/1D noise power spectrum was estimated. Also, spatial resolution was assessed by obtaining the modulation transfer function (MTF) for a wide range of scanning parameters values and different contrast objects by the circular Edge Spread Function method and the Point Spread Function method. Image noise decreased (up to 50% as compared to FBP) when increasing the percentage of ASIR reconstruction (behaviour more relevant for higher spatial frequencies). Only for low tube load (<56 mAs) and lower contrast objects (with respect to phantom background - i.e. PMP, Delrin, LDPE and Polystyrene) acquisitions, MTF analysis showed that, increasing the ASIR percentage, the reconstructed images were characterized by an appreciable reduction in spatial resolution, when compared to FBP-reconstructed images. When compared to FBP, ASIR allows a relevant noise reduction without appreciably affecting image quality, except for very low dose and contrast acquisitions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Evaluation of the Adaptive Statistical Iterative Reconstruction Algorithm in Chest CT (Computed Tomography) - A Preliminary Study toward Its Employment in Low Dose Applications, Also in Conjunction with CAD (Computer Aided Detection)
No full textLung cancer is one of the leading cause of cancer death worldwide. Computed Tomography (CT) is the best imaging modality for the detection of small pulmonary nodules and for this reason its employment as a screening tool has been widely studied. However, radiation dose delivered in a chest CT examination must be considered, especially when potentially healthy people are examined in screening programs. In this context, iterative reconstruction (IR) algorithms have shown the potential to reduce image noise and radiation dose and computer aided detection (CAD) systems can be employed for supporting radiologists. Thus, the combined use of IR algorithms and CAD systems can be of practical interest. In this preliminary work we studied the potential improvements in the quality of phantom and clinical chest images reconstructed trough the Adaptive Statistical Iterative Reconstruction (ASIR, GE Healthcare, Waukesha, WI, USA) algorithm, in order to evaluate a possible employment of this algori thm in low dose chest CT imaging with CAD analysis. We analysed both clinical and phantom CT images. Noise, noise power spectrum (NPS) and modulation transfer function (MTF) were estimated for different inserts in the phantom images. Image contrast and contrast-to-noise ratio (CNR) of different nodules contained in clinical chest images were evaluated. Noise decreases non-linearly when increasing the ASIR blending level of reconstruction. ASIR modified the NPS. The MTF for ASIR-reconstructed images depended on tube load, contrast and blending level. Both image contrast and CNR increased with the ASIR blending level
Variations on the Author
Get PDF“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
Get PDFWe 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
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