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High Frequency Ultrasonic Flow Imaging
No full text在人類疾病研究、基因體研究、藥物發展等生物醫學研究上，常使用以老鼠或是其他小動物的動物模型，因此若能有一套高解析度、高靈敏度以及非侵入式小動物成像系統，可提供上述研究領域很大的幫助，並減少對實驗動物的犧牲與傷害。高頻超音波成像系統（>20MHz）由於有較高的空間解析度以及流速解析度，使我們能即時觀察小動物體內微細的組織與血流情況。在高頻超音波血流成像方面，偵測緩慢血流時會遇到一些問題。目前高頻超音波掃描的方式，是將單一固定聚焦的探頭以馬達帶動來做機械式的掃瞄，此種掃掠式掃瞄方式容易造成緩慢血流信號與組織信號發生混疊的情況，進而造成彩色都卜勒成像中血流流速估計的誤差。此外，由於微細血管內血流的超音波散射信號十分微弱，因此在血流成像上難以獲得較高的訊雜比。本研究的目標在於進一步改進小動物血流成像，期望提升系統偵測緩慢血流速度的能力，以及提高偵測微小血管的靈敏度。為了提升彩色都卜勒成像對於微細緩慢血流的偵測能力，我們針對掃描方式以及信號處理方面來做探討。掃掠式掃瞄可分為「分段掃掠式掃描」與「連續掃掠式掃描」兩種方式，為了能有效區分緩慢血流信號與組織信號，以利緩慢血流流速的估計，我們最後選擇使用低掃描速度（2mm/sec）的連續掃掠式掃描，使我們能在彩色都卜勒影像上偵測到流速5mm/sec 以下的微血管。在對比劑成像方面，使用對比劑可增加血流成像的訊雜比，對比劑非線性成像技術可進ㄧ步提升偵測血流的靈敏度。我們採用自製的微脂體來當作高頻對比劑，此對比劑可由製程控制微氣泡的尺寸大小，使微氣泡的共振頻率接近高頻超音波的頻率範圍( 20MHz~50MHz )。此外，利用微氣泡對正、負聲壓的非線性響應，我們使用脈衝反相基頻成像技術來壓制組織信號而留下微氣泡信號，以提升血流與組織在影像上的對比度以及增加偵測血流的靈敏度。體外的仿體實驗結果顯示，氣泡直徑大小1μm 的微脂體在高頻超音波(25~50MHz)下可有效增強流體信號。使用脈衝反相基頻成像技術可成功壓制組織信號，與傳統的基頻成像比較，當發射信號為頻率範圍25~50MHz 的十個週期正弦波時，脈衝反相基頻成像可提升流體與組織的對比度7~18 dB，隨著發射信號週期數的提升，其對比度提升效果越佳。在活體實驗部份，我們發現微脂體微氣泡在血液中會發生破裂的現象，無法有效增強血流散射信號，微氣泡在血液中球殼內外部的滲透壓不等可能是造成微氣泡破裂的原因之一，針對此問題我們必須改變微氣泡內部的滲透壓，期望能將對比劑成功應用在小動物血流成像上，以達到提升血流偵測靈敏度的目的。Small animal models have been used extensively in disease research, genomics research, drug development, and developmental biology. A non-invasive, small animal imaging system with high spatial resolution and high sensitivity is beneficial to the above-mentioned research. With such a system, the need to sacrifice animals can be reduced. The high frequency ultrasound imaging system (>20MHz) is ideal for such applications. However, one of the major limitations is the ability to detect slow and weak flows. A mechanical swept-scan technique is adopted in
our study, but the continuous movement of the transducer during data acquisition also potentially causes ambiguities in the Doppler spectrum. In addition, it is difficult to obtain high signal-to-noise ratio in this case
due to weak backscattering in micro circulation. Therefore, the main goal of this study is to improve the high frequency ultrasonic flow imaging on small animals in both areas. First, the scanning technique and signal
processing on color Doppler imaging for improvement of slow flow estimation is discussed. The swept-scan technique includes “block swept-scan” and “continuous swept-scan”. Continuous swept-scan with slow scanning velocity (2mm/sec) is found to be desired for slow flow
slower than 5mm/sec. On the other hand, contrast agents are used to enhance the signal-to-noise ratio and develop non-linear imaging methods. Liposome micro-bubbles are made in-house as the high frequency ultrasonic contrast agent. Based on in vitro results, it is shown that liposome bubbles can enhance the back-scattering signals in flow region at high frequencies (20~50MHz). The pulse-inversion based fundamental imaging technique is also tested to improve the contrast-to-tissue ratio. Compared to fundamental imaging, the contrast-to-tissue ratio can be
improved by 7~18dB. For the in-vivo experiments, on the other hand, the liposome bubble appears to break in the blood. So the contrast imaging of small animal is not as effective. The osmosis pressure is considered to be the major problem, and improving the effectiveness for in vivo flow imaging will be the primary future work of this research.第一章 緒論 1
1.1 高頻超音波影像系統 1
1.2 高頻超音波在小動物影像及血流量測的應用 1
1.3 高頻超音波在血流成像的限制 2
1.4 高頻對比劑 4
1.5 研究動機與目標 5
1.6 論文架構 6
第二章 傳統彩色都卜勒成像的限制 8
2.1 都卜勒效應 8
2.2 超音波血流信號取樣方式 10
2.3 都卜勒血流成像之處理流程 12
2.4 掃掠式掃瞄技術 14
2.5 組織頻寬增寬效應 18
2.6 雜波高通濾波器 22
2.7 高頻系統硬體架構 26
2.8 實驗結果 30
第三章 對比劑成像 34
3.1 超音波對比劑 34
3.1.1 對比劑的應用 34
3.1.2 微氣泡的物理特性 35
3.2 非線性成像 36
3.2.1非線性響應 36
3.2.2諧波成像 37
3.2.3 脈衝反相基頻成像 38
3.3 高頻對比劑成像 40
3.3.1對比劑應用在高頻超音波的問題 41
3.3.2高頻對比劑 41
3.3.3高頻超音波下的非線性響應 42
第四章 對比劑實驗結果 45
4.1 實驗設定 45
4.2 微脂體微氣泡的散射特性 46
4.2.1 微氣泡尺寸的影響 47
4.2.2 微氣泡濃度的影響 48
4.3脈衝反相基頻成像 50
4.3.1 對比劑仿體影像 52
4.3.2 微氣泡的頻率響應 58
4.3.3 與諧波成像的比較 60
4.3.4 組織移動的影響 61
4.4 活體實驗 64
第五章 結論與未來工作 69
5.1 結論 69
5.2 未來工作 70
5.2.1 都卜勒血流成像 71
5.2.2 對比劑成像 72
第六章 參考文獻 7
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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