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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.
1

Investigations in electrical impedance tomography

Schneider, Ingo D. January 2000 (has links)
This thesis presents an investigation of various designs and implementation aspects of multi-frequency Electrical Impedance Tomography (EIT) systems for medical applications. EIT presents a relatively new imaging modality that involves the measurement of the complex impedance of a body through voltage measurements around the body's surface, when it is subjected to electrical excitation. The primary region of interest for measurement involves excitation in the frequency range from several kHz to about a few MHz. EIT system design objectives were defined which are the starting point of a detailed error analysis of an EIT system. The analysis undertaken introduced new aspects in terms of the multiplexers' on-resistance, the CMV error analysis and the investigation of the feedthrough errors incorporating the frequency dependence of the skin-electrode interface. A specification of a novel multi-frequency EIT system has been derived through careful consideration of the design objectives based on the results of the error analysis. The merits and drawbacks of different types of stimulus signal for bio-impedance measurements are reviewed and a novel multi-frequency signal for the in vivo measurement of biological impedances has been introduced. An active electrode was built for differential voltage measurement which combines a superior CMRR performance, compared to previously reported implementations, with high input impedance. The implemented circuit has been designed to allow further miniaturisation by means of hybrid semiconductor technologies. Prototypes of several digital subsystem components of the specified EIT system were designed and validated the concept of the novel multi-frequency EIT system. For testing and calibrating the developed front-end electronics, a novel EIT phantom systems is presented, which employs active impedance elements. Utilising active impedance elements enables computer control of the actual impedance values which simplifies and automates the measurement of phantom impedances over a wide range.
2

Disease prevalence : an influential factor in radiological performance?

Barker-Mill, Susan January 2003 (has links)
No description available.
3

Copper complexes as putative imaging agents

Taylor, Michelle K. January 2005 (has links)
No description available.
4

Registration of medical images to 3D medical images

Clarkson, Matthew John January 2000 (has links)
No description available.
5

Development of techniques for site-specific labelling of peptides with fluorine-18

Namolingam, Vithiya January 2004 (has links)
No description available.
6

Comparative three-dimensional biometrics of the human head derived from CT and MRI

Saeed, Raid Saeed Ameen January 2004 (has links)
No description available.
7

Development of a high resolution gamma ray imaging module

Ryder, William John January 2006 (has links)
No description available.
8

Development and evaluation of data correction methods for the PETRRA positron camera

Divoli, Antigoni January 2004 (has links)
No description available.
9

The development and evaluation of head probes for optical imaging of the infant head

Branco, Gilberto January 2007 (has links)
The objective of this thesis was to develop and evaluate optical imaging probes for mapping oxygenation and haemodynamic changes in the newborn infant brain. Two imaging approaches are being developed at University College London (UCL): optical topography (surface mapping of the cortex) and optical tomography (volume imaging). Both have the potential to provide information about the function of the normal brain and about a variety of neurophysiologies! abnormalities. Both techniques require an array of optical fibres/fibre bundles to be held in contact with the head, for periods of time from tens of seconds to an hour or more. The design of suitable probes must ensure the comfort and safety of the subject, and provide measurements minimally sensitive to external sources of light and patient motion. A series of prototype adaptable helmets were developed for optical tomography of the premature infant brain using the UCL 32-channel time-resolved system. They were required to attach 32 optical fibre bundles over the infant scalp, and were designed to accommodate infants with a variety of head shapes and sizes, aged between 24-weeks gestational age and term. Continual improvements to the helmet design were introduced following the evaluation of each prototype on infants in the hospital. Data were acquired to generate images revealing the concentration and oxygenation of blood in the brain, and the response of the brain to sensory stimulation. This part of the project also involved designing and testing new methods of acquiring calibration data using reference phantoms. The second focus of the project was the development of probes for use with the UCL frequency-multiplexed near-infrared topography system. This is being used to image functional activation in the infant cortex. A series of probes were developed and experiments were conducted to evaluate their sensitivity to patient motion and to compression of the probe. The probes have been used for a variety of functional activation studies.
10

Building computational atlases from databases of whole-body clinical PET/CT images

Potesil, Vaclav January 2011 (has links)
Medical imaging has revolutionized cancer care and its use has grown massively over the past several decades. Images are increasingly stored in large digital image repositories such as hospital Picture Archiving and Communication System, which will hopefully provide a wealth of information on patient conditions and therapy outcomes as cancer diagnosis and therapy moves from 'one size fits all' to more personalized approaches tailored to each particular patient. However, converting the unstructured avalanche of data at thousands of different hospitals into clinically valuable biomarkers and tools requires that the images of different patients can be compared and efficiently searched. Our research aims to develop novel methods to compare whole-body scans of multiple patients; methods which incorporate 'intelligent' prior knowledge of the internal structure of the human body, as opposed to current methods of image registration which mostly rely on matching the voxel intensities and disregard their anatomical meaning. We develop computational methods for accurate and reliable automated localization of anatomical structures in whole-body images, which will help to automate key steps in cancer diagnosis and radiation treatment planning and save expensive clinicians' time while improving the reliability of their decisions. Conventional approaches to determining spatial correspondences between pairs or sets of images in medical imaging typically rely on image registration methods. There have been considerable advances in registration of multiple images of the same patient taken at different time-points, known as longitudinal studies. However, conventional methods, which rely on optimizing certain integral functions of voxel values over the entire image, are unreliable when applied to aligning whole-body images of different patients. Whole-body Computed Tomography (CT) images contain many different anatomical structures whose physical attributes and consequent appearance can be highly variable between patients. This substantial, but normal, variability is further increased by the presence of pathologies such as tumours and non-cancerous diseases, surgical interventions and degenerative changes due to aging as well as different patterns of contrast agent uptake. Conventional registration methods often get trapped in local minima that abound in such images, resulting in unreliable and inaccurate anatomical correspondences. The methods developed in this thesis tackle the problem of inter-patient registration by incorporating prior anatomical knowledge into parts-based graphical models that accurately and reliably localize arbitrary skeletal and soft-tissue anatomical landmarks in whole-body clinical oncology scans. We optimize parts-based graphical models called Pictorial Structures for accurate and reliable landmark localization in CT images and introduce novel methods that replace standard population models by models personalized to the particular patient. We also propose methods that further improve landmark localization while minimizing, as far as possible, the high costs of ground-truth annotation by expert radiologists. We do this by automatically discovering new landmark correspondences from a database of partially annotated images. The performance of the algorithms developed in my thesis is evaluated on a large database of clinical lung cancer PET/CT scans, showing superior accuracy and reliability of landmark localization compared to conventional methods.

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