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Title: Clinically practical freehand 3D ultrasound
Author: Housden, R. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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In this thesis, various alternatives to standard sensor systems are developed, with particular emphasis on improving the practicality of freehand 3D ultrasound in a clinical environment. The novel algorithms presented here are able to position a sequence of image frames qualitatively correctly even when the direction of out-of-plane motion is allowed to vary, which was not previously possible. Existing work on the subject of six-degree-of-freedom sensorless reconstruction found that it is possible to take unbiased measurements from a sensorless reconstruction, provided it is constrained to have only elevational motion and has a large proportion of fully developed speckle data. Alternatively, freehand motion and data from real tissue can be allowed at the expense of some large-scale drift in the frame positions, biasing the measurements. The approach of this thesis allows fully freehand motion and scans on any type of tissue, but consequently is found to have a drift error in the length and tilt of the sequence which can result in length measurement errors of 20% or more. A hybrid approach reintroduces position sensors, in combination with the image-based techniques. This thesis considers two sensors for use in the hybrid system. One of these is the Xsens MT9-B, which uses Micro-Electro-Mechanical Systems (MEMS) magnetometers, accelerometers and rate gyroscopes to measure orientations. This was found to be particularly unobtrusive having almost no effect on the scanning setup and protocol. A hybrid reconstruction using the MT9-B has an estimated overall length error of 5% of the sequence length and an orientation error of no more than 1°. A hybrid system using the MT9-B represents a significant step towards the goal of accurate anatomical measurements with an easy-to-use scanning system.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available