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Removal and effects of scatter-glare in cone-beam CT with an amorphous-silicon flat-panel detector.

Poludniowski, G, Evans, PM, Kavanagh, A and Webb, S (2011) Removal and effects of scatter-glare in cone-beam CT with an amorphous-silicon flat-panel detector. Phys Med Biol, 56 (6). pp. 1837-1851.

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Scatter in a detector and its housing can result in image degradation. Typically, such scatter leads to a low-spatial frequency 'glare' superimposed on the primary signal. We infer the glare-spread function (GSF) of an amorphous-silicon flat-panel detector via an edge-spread technique. We demonstrate that this spread (referred to as 'scatter-glare' herein) causes a low-spatial frequency drop in the associated modulation-transfer function. This results in a compression of the range of reconstructed CT (computed tomography) numbers and is an impediment to accurate CT-number calibration. We show that it can also lead to visual artefacts. This explains previously unresolved CT-number discrepancies in an earlier work (Poludniowski et al 2009 Phys. Med. Biol. 54 3847). We demonstrate that after deconvolving the GSF from the projection images, in conjunction with a correction for phantom-scatter, the CT-number discrepancies disappear. We show results for an in-house-built phantom with inserts of tissue-equivalent materials and for a patient scan. We conclude that where scatter-glare has not been accounted for, the calibration of cone-beam CT numbers to material density will be compromised. The scatter-glare measurement method we propose is simple and requires no special equipment. The deconvolution process is also straightforward and relatively quick (60 ms per projection on a desktop PC).

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Electronic Engineering > Centre for Vision Speech and Signal Processing
Authors :
Poludniowski, G
Evans, PM
Kavanagh, A
Webb, S
Date : 21 March 2011
DOI : 10.1088/0031-9155/56/6/019
Uncontrolled Keywords : Calibration, Cone-Beam Computed Tomography, Phantoms, Imaging, Scattering, Radiation, Silicon
Additional Information : Copyright 2011 Institute of Physics. This is the author's accepted manuscript.
Depositing User : Symplectic Elements
Date Deposited : 05 Feb 2013 11:20
Last Modified : 31 Oct 2017 14:52

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