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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Impact of time-of-flight technology on PET/CT image quality and SUV quantitation

Lau, Yu-ching., 劉禹政. January 2012 (has links)
Time-of-flight technology (TOF) is at the leading edge of advancements in PET/CT imaging, and is made possible due to the availability of new scanner design, scintillating materials and fast computers. The location of annihilation is estimated according to the time difference between scintillation events produced by two 511KeV gamma photons travelling in opposite directions. The additional information is incorporated into image reconstruction to suppress noise propagation and increase signal-to-noise ratio. As shown in previous studies, these properties can be translated in to clinical usage to obtain improved image quality using the same acquisition time, while also enhancing image quality under shortened acquisition or reduce tracer dosage injected to patients. Semi-quantification units such as standardized uptake value (SUV) and standard deviation (SD) are measured on static PET images and are widely used clinically to quantify the rate of cell metabolism. Signal-to-noise ratio (SNR) and coefficient of variation (CV) can be calculated to assess image quality. However, these parameters depend on image reconstruction and are therefore expected to change with the use of TOF. Breath holding (BH) PET/CT imaging protocol has been suggested to help evaluation of lesions affected by respiratory motion. However, the PET image quality is significantly degraded since the acquisition time is shortened (e.g. 30 seconds). Noise on BH PET image may cause inaccuracy in semi-quantitation and difficulties in visual assessment. TOF can be applied to improve the image quality and enhance subtle lesions, thus helping the characterization of small lung nodules (SLN) with potential clinical impact. This thesis aims to evaluate the impact of TOF on PET image quality and the quantification of SUV in clinical practice. Firstly, the performance of a TOF PET/CT scanner is tested using a phantom mimicking human body trunk with ‘lesions’. Using the same acquisition time (2 minutes/bed), TOF images outperformed conventional images in terms of lesion detectability and background uniformity, especially for small spheres and under low lesion-to-background ratio. Moreover, TOF images acquired using a shorter scan time (1.5 minutes/bed) also maintained acceptable image quality. In the second study, the influence on SUV measurement and image quality (in terms of CV) are evaluated in twelve normal organ structures on whole-body FDG PET/CT images. TOF significantly decreased SUVmax (9/12) and SUVmean (8/12) among the twelve normal organ structures investigated. It also improved the image quality, particularly in solid organs in the abdomen. The combined utility of TOF and BH PET/CT imaging protocol for the detection of SLN is demonstrated in the third study. Lesions showing PET activity, which were misaligned with anatomical location on CT, had higher SUVmax and comparable SNR on BH images. PET/CT fusion was also markedly improved. The additional use of TOF further enhanced lesion detection and improved SNR. The results demonstrate the benefits of using TOF in clinical PET/CT, including its advantage with breath holding PET/CT imaging. This information not only offers a better understanding of this increasingly popular technology in modern PET/CT scanners, but also highlights its potential applications in clinical practice. / published_or_final_version / Diagnostic Radiology / Master / Master of Philosophy
22

Geometric object reconstruction from orthogonal ray sum data

林吉雄, Lam, Kat-hung. January 1993 (has links)
published_or_final_version / Computer Science / Master / Master of Philosophy
23

On the role of antennas in the achievable resolution and accuracy from near-field microwave tomography

Bayat, Nozhan 07 1900 (has links)
This thesis studies the role of antennas in the achievable resolution and accuracy from nearfield microwave tomography (MWT). Near-field MWT is an emerging imaging modality in which the object being imaged is successively irradiated by several antennas, located close to the object, in the microwave frequency range. The scattered fields emanating from the object are then processed to form quantitative images from the dielectric properties of the object. This thesis starts with proposing a mathematical framework to study the achievable resolution from MWT. Within this framework, the effect of the near-field distribution of the utilized antennas on the achievable image resolution will be studied. Specifically, it will be shown that the use a focused near-field distribution to irradiate the object can enhance the achievable resolution. Within the same framework, the effects of the frequency of operation, multiple frequencies of operation, signal-to-noise ratio of the measured data, and the number of antenna elements on the achievable resolution and accuracy will be studied. After establishing the importance of the antenna’s incident field distribution, this thesis continues with investigating two different methods to achieve a focused near-field distribution. The first method, which attempts to synthesize focused beams from existing omnidirectional antenna elements, will be shown to be not successful using the method employed in this thesis. The second method is based on modifying an existing antenna element so as to make its near-field distribution more focused. Through different experiments and simulations, it will be shown that the second method can make the near-field distribution of the antenna more focused while maintaining multiple frequencies of operation for the antenna, and keeping its physical size reasonably small.
24

Trends in CT abdominal doses in Malaysian practices

Ali, Mohd. Hanafi. January 2005 (has links)
Thesis (H. Sc. D.)--University of Sydney, 2005. / Title from title screen (viewed Mar. 1, 2007). Includes tables and questionnaires. Submitted in fulfilment of the requirements for the degree of Doctor of Health Sciences to the School of Medical Radiation Sciences. Includes bibliographical references. Also issued in print.
25

An investigative study of the applicability of the convolution method of geophysical tomography

Chin, Kimberley Germaine. January 1985 (has links)
Thesis (M.S.)--Ohio University, November, 1985. / Title from PDF t.p.
26

The essence of FIA : a study of the distribution of foliation intersection axes data and its significance from hand sample to regional scales /

Huddlestone-Holmes, Cameron Russell. January 2005 (has links)
Thesis (Ph.D.) - James Cook University, 2005. / Appendix A (pdf version of Chapter 1) is contained on CD-ROM. Typescript (photocopy) Includes bibliographical references.
27

Single photon emission computed tomography performance assessment, development and clinical applications /

Gillen, Gerard J. January 1990 (has links)
Thesis (Ph.D.) - University of Glasgow, 1990. / BLL. DX192708. Ph.D. thesis submitted to the Department of Clinical Physics and Bio-Engineering, University of Glasgow, 1990. Includes bibliographical references.
28

Maximum likelihood-expectation maximum reconstruction with limited dataset for emission tomography

Patel, Rahul. January 2007 (has links)
Thesis (M.S.)--University of Akron, Dept. of Biomedical Engineering, 2007. / "May, 2007." Title from electronic thesis title page (viewed 04/26/2009) Advisor, Dale Mugler; Co-Advisor, Anthony Passalaqua; Committee member, Daniel Sheffer; Department Chair, Daniel Sheffer; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
29

A comparative study of the algebraic reconstruction technique and the constrained conjugate gradient method as applied to cross borehole geophysical tomography

Masuda, Ryuichi. January 1989 (has links)
Thesis (M.S.)--Ohio University, June, 1989. / Title from PDF t.p.
30

Optical diffraction tomography an experimental method for ultrasound measurements /

Holm, Anders. January 1993 (has links)
Thesis--Lund Institute of Technology, 1993.

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