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Title: Pseudo inverse filter design for improving the axial resolution of ultrasound images
Author: Young, Warren Frazer
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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This thesis is concerned with improving the quality of images from medical ultrasound examinations which often suffer from poor picture quality. In addition, the resolution of ultrasound images is poor compared to other medical imaging techniques. Ultrasound images have comparatively poor resolution (axial, lateral and contrast), and poor dynamic range. The axial resolution, and contrast resolution of medical ultrasound images can be improved by appropriate filtering of the RF ultrasound signal, prior to signal demodulation. In this thesis I present a pseudo inverse filter, suitable for improving the axial and contrast resolution of medical ultrasound images. This filter is based on a sigmoid function, and it approximates an inverse filter - but is less sensitive to noise than an inverse filter. I present results from applying the proposed filter, with a variety of parameter settings, to ultrasound images of three target objects: a near perfect plane reflector, a tissue mimicking phantom, and intravascular ultrasound (IVUS) images from the aorta of a rabbit. These three targets provide good test cases for the filter; the near perfect plane reflector is a good test of the filter under (near) ideal circumstances; the IVUS images are a realistic test of a medical situation in that they are virtually identical to human IVUS images; and the phantom provides a good midpoint between the first two cases. This midpoint is useful since it allows me to analyse a realistic image, while knowing exactly what the structure and shape of the target object is - this knowledge is not available for the IVUS images. Lastly, I present extensive comparisons with other filters that have been proposed for the filtering of ultrasound. These comparisons are both subjective and - more importantly - objective. In particular I make comparisons with the following filters: matched, inverse, phase correction, square root based, fourth root based, and Wiener filters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available