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Comparison of tissue occupancy functional contrasts for 3D turbo-spin-echo acquisition
No full textIntroduction:
Functional vascular occupancy imaging has demonstrated task correlated MR signal changes using
inversion recovery (IR) prepared images, where the inversion time (TI) has been chosen to selectively
null blood (vascular space occupancy – VASO, (Lu et al., 2003)), grey matter (VASO by tissue
suppression – VAST (Wu et al., 2008)), or CSF (VASO-FLAIR (Donahue et al., 2006)). Weakness of these
approaches are that functional responses may not be due to volume changes in a single tissue
compartment, and that the underlying imaging sequence may be sensitive to other mechanisms (e.g.
BOLD) (Donahue et al., 2006). Our purpose was to compare the functional responses from different
vascular space occupancy preparations of a short TE turbo-spin echo (TSE) sequence.
Methods:
Eight healthy subjects were scanned at 3T after providing informed consent. The task consisted of
self-paced, left-hand finger tapping.
Four variants of vascular occupancy fMRI were tested: VASO (TI = 646ms), VAST (TI = 578ms),
VASO-FLAIR (TI = 781ms) and nonInVASO (no inversion pulse VASO), all based on a 3D TSE acquisition
(TE/TR 8.4ms/2.4s, 4 shots, time per volume 9.6s, 1.5x1.5x1.5mm, 8 slices, FOV 222x60x12mm, 180°
refocusing pulses, ant/post sat bands). Task blocks were 48s long, and each run consisted of 45
volumes, with the sequence order varied between subjects. These scans were centered on the focus of
BOLD response in/adjacent to the right hand knob detected with an EPI acquisition (TE/TR 30ms/3s,
3x3x3mm, 42 slices) performed during execution of the same task (30 second blocks, 70 volumes).
Whole-brain T2, 3D T1, and nonInVASO images were also obtained.
GLM analysis (1.5mm FWHM smoothing, high pass filter cut-off 100s, default gamma-variate hrf,
GRF-based voxel-wise corrected p<0.05) was per formed following motion correction and ICA denoising
(4 components) using fsl (v 5.0.1). Due to slight rotations during acquisition, only 6 slices were
retained for analysis.
Results:
Despite operator confirmation of task performance, one subject showed minimal BOLD and no significant
vascular occupancy responses, and was therefore excluded from analysis. In the other subjects, VASO,
VAST and VASO-FLAIR showed nearly identical patterns and locations of activity (Figure 1) and no
significant differences in the grey matter (GM), white matter, CSF distribution of activated voxels. The
nonInVASO scans showed smaller volumes of activity. GM was the predominant site of response for all
scans.
VAST yielded the highest % signal changes; VASO yielded the highest z-score followed closely by
VASO-FLAIR; and these all had signal changes negatively correlated with the task. The nonInVASO
responses correlated positively with the task and were the smallest % signal change and maximum
z-scores roughly one-third lower than VASO. Significant oppositely-signed responses (i.e. positive of
VASO, VAST and VASO-FLAIR, negative for nonInVASO) were not observed.Conclusions:
Our results suggest that VASO, VAST and VASO-FLAIR are sensitive to volume changes in the same
tissue compartment. VAST yielded the highest % signal changes due mainly to the smallest baseline
signal but this did not result in greater sensitivity to activation as indicated by maximum z-scores. The
negative VAST response however, suggests that the inversion was not fully optimized to grey matter but
could reflect T2 blurring of white matter signal. VASO was the most sensitive to activation followed
closely by VASO-FLAIR. Similarly located activations were seen with nonInVASO, but with smaller spatial
extents and lower sensitivity.
The implications and operative mechanism for the nonInVASO functional contrast remain to be
established. Possible mechanisms include BOLD contrast (through T2 sensitivity or blurring by the long
TSE echo train), vascular space occupancy changes coupled with inherent blood-tissue contrast,
diffusion, or changes within the tissue compartment as proposed for SEEP - signal enhancement by
extravascular protons (Stroman et al, 2003)
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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