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How Different Iterative and Filtered Back Projection Kernels Affect Computed Tomography Numbers and Low Contrast Detectability

Völgyes, David MSc; Pedersen, Marius PhD; Stray-Pedersen, Arne PhD, MD; Waaler, Dag PhD; Martinsen, Anne Catrine Trægde PhD

Journal of Computer Assisted Tomography: January 2017 - Volume 41 - Issue 1 - p 75–81
doi: 10.1097/RCT.0000000000000491
Physics and Image Processing

Objective: The aim of this study was to evaluate how different iterative and filtered back projection kernels affect the computed tomography (CT) numbers and low contrast detectability.

Methods: Five different scans were performed at 6 different tube potentials on the same Catphan 600 phantom using approximately the same dose level and otherwise identical settings. The scans were reconstructed using all available filtered back projection body kernels and with iterative reconstruction techniques.

Results: The CT numbers and the contrast-to-noise ratios were reported and how they are affected by the kernel choice and strength of iterative reconstruction.

Conclusions: Iterative reconstruction improved contrast-to-noise ratio in most cases, but in certain situations, it decreased it. Variations in CT numbers can be large between kernels with similar sharpness for certain densities.

From the *Faculty of Computer Science and Media Technology, Gjøvik University College, Gjøvik; †Department of Research and Development in Forensic Pathology, The Norwegian Institute of Public Health; ‡Department of Forensic Medicine, University of Oslo, Oslo; §Faculty of Health, Care and Nursing, Gjøvik University College, Gjøvik; ∥The Intervention Centre, Oslo University Hospital Rikshospitalet; and ¶Department of Physics, University of Oslo, Oslo, Norway.

Received for publication December 22, 2015; accepted May 23, 2016.

Correspondence to: David Völgyes, MSc, Ragnhild Schibbyes vei 16, 0968, Oslo, Norway (e-mail:

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This research has been funded by the Research Council of Norway through project no. 221073 “HyPerCept—Colour and quality in higher dimensions.”

The authors declare no conflict of interest.

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