How to measure CT image quality: Variations in CT-numbers,uniformity and low contrast resolution for a CT quality assurance phantom |
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| Affiliation: | 1. The Intervention Centre, Oslo University Hospital, Rikshospitalet, Oslo, Norway;2. Faculty of Health Sciences, Oslo and Akershus University College of Applied Sciences, Oslo, Norway;3. Department of Physics, University of Oslo, Oslo, Norway;1. Department of Medical Physics, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto 862-0976, Japan;2. The Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, USA;3. Department of Diagnostic Radiology, Faculty of Life Sciences, Kumamoto University, Japan;4. Department of Diagnostic Radiology, Kumamoto Chuo Hospital, Japan;5. CT Clinical Science, Philips Electronics Japan, Japan;1. Department of Computer Science and Engineering, UIT, Uttaranchal University, Dehradun, India;2. Department of Computer Science, Babasaheb Bhimrao Ambedkar University, Lucknow, India;1. Inselspital – Bern University Hospital, University Institute of Diagnostic, Interventional, and Pediatric Radiology, Freiburgstrasse 10, 3010 Bern, Switzerland;2. Roentgeninstitut Duesseldorf, Kaiserswerterstrasse 89, 40476 Duesseldorf, Germany;3. University Medical Center Hamburg Eppendorf, Department of Diagnostic and Interventional Radiology, Martinistrasse 52, 20246 Hamburg, Germany;4. University of Würzburg, Insitute of Diagnostic and Interventional Radiology, Oberdürrbacher Str. 6, 97080 Würzburg, Germany;1. Unitat de Física Mèdica, Universitat Rovira i Virgili (URV), Spain;2. Radiology Department, Leiden University Medical Center (LUMC), The Netherlands;3. Departamento de Radiología, Universidad Complutense de Madrid (UCM), Spain |
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| Abstract: | PurposeQuality assurance (QA) phantoms for testing different image quality parameters in computed tomography (CT) are commercially available. Such phantoms are also used as reference for acceptance in the specifications of CT-scanners. The aim of this study was to analyze the characteristics of the most commonly used QA phantom in CT: Catphan 500/504/600.MethodsNine different phantoms were scanned on the same day, on one CT-scanner with the same parameter settings. Interphantom variations in CT-number values, image uniformity and low contrast resolution were evaluated for the phantoms. Comparisons between manual image analysis and results obtained from the automatic evaluation software QAlite were performed.ResultsSome interphantom variations were observed in the low contrast resolution and the CT-number modules of the phantoms. Depending on the chosen regulatory framework, the variations in CT-numbers can be interpreted as substantial. The homogenous modules were found more invariable. However, the automatic image analysis software QAlite measures image uniformity differently than recommended in international standards, and will not necessarily give results in agreement with these standards.ConclusionsIt is important to consider the interphantom variations in relation to ones framework, and to be aware of which phantom is used to study CT-numbers and low contrast resolution for a specific scanner. Comparisons with predicted values from manual and acceptance values should be performed with care and consideration. If automatic software-based evaluations are to be used, users should be aware that large differences can exist for the image uniformity testing. |
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| Keywords: | Quality assurance CT Catphan |
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