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Title: On ultrasound elastography : simulation, experiment, and algorithm development
Author: Al-Azawi, Aws
ISNI:       0000 0004 5921 6965
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2015
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Ultrasound elastography is investigated in this thesis based on processing backscattered raw ultrasonic data (radio frequency signals) using standard cross-correlation tool (SCC). The data are obtained using separate simulation, and experiment. In the simulation scenario, ultrasound imaging is simulated using the Field-II program, while the deformation object is simulated using finite element modelling (FEM) of ANSYS-11 program. A composition algorithm is proposed that combine Field-II and ANSYS-11 programs to produce backscattered raw data before and after compression. The experimental scenario was performed in collaboration with the Centre for Ultrasound Engineering, University of Strathclyde using DYNARY ultrasonic Phased Array Controller (Zetec, Québec, Québec, Canada) and Tissue Mimicking Material (TMM), which was manufactured in the Medical Physics Department, Edinburgh Royal Infirmary. In the experiments, uniform compression was applied over the TMM object using an adaptor that employs the 10MHz transducer and the head of an XYZ scanner, while freehand compression is applied using 5MHz transducer. A deformation estimation algorithm of displacement and a strain mapping algorithm have developed according to three levels of compression of 0.2%, 1%, and 2%-4%. The algorithm was assessed for the three stages based on the level of compression. In the first stage of 0.2% compression, backscattered raw data from a simulation model are utilized. Displacement and strain fields are estimated using the proposed deformation algorithm and then compared favourably with FEM numerical solution. In second stage of 1% compression, backscattered raw data of simulation and experiment models are utilized. Displacement and strain fields are estimated using the proposed novel deformation algorithm of refinement that includes the regularization for non-consistent measurements based on surrounding neighbours information. Results from simulation and experiment are compared, which shows a good agreement in terms of displacement field consistency and strain field contrast. In the third stage of 2%-4% compression, backscattered raw data of experiment are utilized. Displacement and strain fields are estimated using advance refinement process that involves an exclusion of estimation outliers. Displacement and strain fields are compared with two dimensional (2D) median filter operation. Results show a superiority of the proposed algorithm over 2D median operation in terms of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). In the proposed algorithm, a small correlation window length is used to ensure sufficient spatial resolution of strain estimation. Finally, the deformation estimation algorithm is validated using backscattered raw data of freehand compression. Result of freehand compression shows superiority against 2D median operation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available