title: Image quality in CT: From physical measurements to model observers.
abstract: Evaluation of image quality (IQ) in Computed Tomography (CT) is important to ensure that diagnostic questions are correctly answered, whilst keeping radiation dose to the patient as low as is reasonably possible. The assessment of individual aspects of IQ is already a key component of routine quality control of medical x-ray devices. These values together with standard dose indicators can be used to give rise to 'figures of merit' (FOM) to characterise the dose efficiency of the CT scanners operating in certain modes. The demand for clinically relevant IQ characterisation has naturally increased with the development of CT technology (detectors efficiency, image reconstruction and processing), resulting in the adaptation and evolution of assessment methods. The purpose of this review is to present the spectrum of various methods that have been used to characterise image quality in CT: from objective measurements of physical parameters to clinically task-based approaches (i.e. model observer (MO) approach) including pure human observer approach. When combined together with a dose indicator, a generalised dose efficiency index can be explored in a framework of system and patient dose optimisation. We will focus on the IQ methodologies that are required for dealing with standard reconstruction, but also for iterative reconstruction algorithms. With this concept the previously used FOM will be presented with a proposal to update them in order to make them relevant and up to date with technological progress. The MO that objectively assesses IQ for clinically relevant tasks represents the most promising method in terms of radiologist sensitivity performance and therefore of most relevance in the clinical environment.
authors.affiliation: Institute of Radiation Physics, Lausanne University Hospital, 1 Rue du Grand-Pré, 1007 Lausanne, Switzerland. Electronic address: Francis.Verdun@chuv.ch.
authors.forename: F R
authors.initials: FR
authors.lastname: Verdun
authors.affiliation: Institute of Radiation Physics, Lausanne University Hospital, 1 Rue du Grand-Pré, 1007 Lausanne, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: Racine
authors.affiliation: Institute of Radiation Physics, Lausanne University Hospital, 1 Rue du Grand-Pré, 1007 Lausanne, Switzerland.
authors.forename: J G
authors.initials: JG
authors.lastname: Ott
authors.affiliation: STUK-Radiation and Nuclear Safety Authority, PO Box 14, FIN-00881 Helsinki, Finland.
authors.forename: M J
authors.initials: MJ
authors.lastname: Tapiovaara
authors.affiliation: STUK-Radiation and Nuclear Safety Authority, PO Box 14, FIN-00881 Helsinki, Finland.
authors.forename: P
authors.initials: P
authors.lastname: Toroi
authors.affiliation: Institute of Radiation Physics, Lausanne University Hospital, 1 Rue du Grand-Pré, 1007 Lausanne, Switzerland.
authors.forename: F O
authors.initials: FO
authors.lastname: Bochud
authors.affiliation: Department of Radiology, Leiden University Medical Center, C2-S, PO Box 9600, 2300RC Leiden, The Netherlands; Dutch reference Centre for Screening (LRCB), Radboud University Medical Centre, PO Box 6873, 6503 GJ Nijmegen, The Netherlands.
authors.forename: W J H
authors.initials: WJH
authors.lastname: Veldkamp
authors.affiliation: Department for Radiation Protection and Health External and Internal Dosimetry, Biokinetics, Ingolstädter Landstr, 1, 85764 Neuherberg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Schegerer
authors.affiliation: Dutch reference Centre for Screening (LRCB), Radboud University Medical Centre, PO Box 6873, 6503 GJ Nijmegen, The Netherlands.
authors.forename: R W
authors.initials: RW
authors.lastname: Bouwman
authors.affiliation: Department of Radiology, Leiden University Medical Center, C2-S, PO Box 9600, 2300RC Leiden, The Netherlands.
authors.forename: I Hernandez
authors.initials: IH
authors.lastname: Giron
authors.affiliation: Katholieke Universiteit Leuven, Oude Markt 13, 3000 Leuven, Belgium.
authors.forename: N W
authors.initials: NW
authors.lastname: Marshall
authors.affiliation: Medical Dosimetry Group, Centre for Radiation Chemicals and Environmental Hazards, Public Health England, Didcot, UK.
authors.forename: S
authors.initials: S
authors.lastname: Edyvean
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D015588:Observer Variation; D011785:Quality Assurance, Health Care / Q000379:methods*; D014057:Tomography, X-Ray Computed
keywords: Computed tomography; Image quality; Model observer; Patient dose optimisation