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The influence of scatter and beam hardening in X-ray computed tomography for dimensional metrology

The influence of scatter and beam hardening in X-ray computed tomography for dimensional metrology
The influence of scatter and beam hardening in X-ray computed tomography for dimensional metrology
This thesis is concerned with the use of X-ray computed tomography (CT) for making dimensional measurements. Scattered radiation and beam hardening are two phenomena that are well-known to severely degrade the quality of cone-beam CT data; however, the impact they have on dimensional measurements is not well understood. The aim of this work is to better understand how scatter and beam hardening influence dimensional measurements.

The influence that scattered radiation and beam hardening have on internal and external dimensional measurements is investigated for two surface determination methods: the ISO50 method and a local gradient-based method. The work includes both experiment and simulation. The influence of scatter is assessed through the use of source collimation and the beam stop array scatter correction method, whilst the influence of beam hardening is assessed using spectrum pre-filtration. The simulation makes use of empirically derived X-ray spectra and scatter signals; good agreement between measured and simulated data is seen.

The results show the presence of scatter and beam hardening decreases the measured size of internal features and increases the measured size of external features. This effect is seen for both surface determination methods, with the local method being more robust for outer features. The ISO50 surface determination method fails to give the ‘correct’ surface position for both inner and outer features in the presence of scatter and/or beam hardening. For the local surface determination method, scatter and beam hardening change the turning point of the edge gradient, this being the property by which surface points are defined for the local method; it is therefore through this change in turning point that scatter and beam hardening influence dimensional measurements.
Lifton, Joseph J.
e4b170b4-165c-4ae0-9e7d-9d53ab54247f
Lifton, Joseph J.
e4b170b4-165c-4ae0-9e7d-9d53ab54247f
Mcbride, John
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(2015) The influence of scatter and beam hardening in X-ray computed tomography for dimensional metrology. University of Southampton, Engineering and the Environment, Doctoral Thesis, 229pp.

Record type: Thesis (Doctoral)

Abstract

This thesis is concerned with the use of X-ray computed tomography (CT) for making dimensional measurements. Scattered radiation and beam hardening are two phenomena that are well-known to severely degrade the quality of cone-beam CT data; however, the impact they have on dimensional measurements is not well understood. The aim of this work is to better understand how scatter and beam hardening influence dimensional measurements.

The influence that scattered radiation and beam hardening have on internal and external dimensional measurements is investigated for two surface determination methods: the ISO50 method and a local gradient-based method. The work includes both experiment and simulation. The influence of scatter is assessed through the use of source collimation and the beam stop array scatter correction method, whilst the influence of beam hardening is assessed using spectrum pre-filtration. The simulation makes use of empirically derived X-ray spectra and scatter signals; good agreement between measured and simulated data is seen.

The results show the presence of scatter and beam hardening decreases the measured size of internal features and increases the measured size of external features. This effect is seen for both surface determination methods, with the local method being more robust for outer features. The ISO50 surface determination method fails to give the ‘correct’ surface position for both inner and outer features in the presence of scatter and/or beam hardening. For the local surface determination method, scatter and beam hardening change the turning point of the edge gradient, this being the property by which surface points are defined for the local method; it is therefore through this change in turning point that scatter and beam hardening influence dimensional measurements.

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More information

Published date: April 2015
Organisations: University of Southampton, Mechatronics

Identifiers

Local EPrints ID: 378342
URI: http://eprints.soton.ac.uk/id/eprint/378342
PURE UUID: 95e0e1db-de9c-4160-b583-93c5c5edfe36

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Date deposited: 14 Jul 2015 10:52
Last modified: 17 Jul 2017 20:53

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Contributors

Author: Joseph J. Lifton
Thesis advisor: John Mcbride

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