title: Removal and effects of scatter-glare in cone-beam CT with an amorphous-silicon flat-panel detector.
abstract: 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).
authors.affiliation: Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey SM2 5PT, UK.
authors.forename: G
authors.initials: G
authors.lastname: Poludniowski
authors.affiliation: Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey SM2 5PT, UK.
authors.forename: P M
authors.initials: PM
authors.lastname: Evans
authors.affiliation: Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey SM2 5PT, UK.
authors.forename: A
authors.initials: A
authors.lastname: Kavanagh
authors.affiliation: Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey SM2 5PT, UK.
authors.forename: S
authors.initials: S
authors.lastname: Webb
mesh_terms: D002138:Calibration; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D012542:Scattering, Radiation; D012825:Silicon / Q000737:chemistry*
chemical_list: D012825:Silicon