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Aliased noise in X-ray CT images and band-limiting processing as a preventive measure

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Abstract

X-ray CT projection data often include components with frequencies that are markedly higher than the pixel Nyquist frequency f PN, which is determined by the pixel size. Noise components higher than f PN are folded back into a region lower than f PN through the backprojection process, thereby creating aliased noise. With clinical CT scanners, we evaluated the aliased noise using an aliasing prevention measure, band-limiting processing (BLP), which suppresses frequency components higher than f PN in the projection data. Indices we used to evaluate improvement by BLP were the noise power spectrum (NPS), modulation transfer function (MTF), signal-to-noise-ratio (SNR) spectrum, matched filter SNR (MF SNR), and two-alternative forced-choice (2-AFC) test. With BLP, the NPS was decreased not only beyond f PN, but also within f PN. The same level of MTF was maintained as that without BLP within f PN. No remarkable reduction in spatial resolution was observed. The SNR spectrum and the MF SNR of the BLP image nearly agreed with those of an ideal state without aliased noise. A notable improvement in the visuoperceptual image quality by BLP was recognized with a reconstruction field of view (FOV) of more than 45 cm. We then applied BLP to clinical data and confirmed that significant aliased noise of a large FOV image was removed without notable side effects. The results showed that at least some CTs suffering from aliased noise can be improved by proper band-limiting.

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Acknowledgments

This work was supported by JSPS KAKENHI Grant Number 21591591.

Conflict of interest

The authors declare that they have no conflict of interest.

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Authors and Affiliations

  1. Health Sciences, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Japan

    Kazuhiro Sato, Miho Shidahara, Mitsunori Goto, Noriyasu Homma & Issei Mori

  2. Department of Radiology, Tohoku University Hospital, 1-1 Seiryo-machi, Aoba-ku, Sendai, 980-8574, Japan

    Kazuhiro Sato & Isao Yanagawa

Authors
  1. Kazuhiro Sato
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  2. Miho Shidahara
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  3. Mitsunori Goto
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  4. Isao Yanagawa
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  5. Noriyasu Homma
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  6. Issei Mori
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Correspondence to Kazuhiro Sato.

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Sato, K., Shidahara, M., Goto, M. et al. Aliased noise in X-ray CT images and band-limiting processing as a preventive measure. Radiol Phys Technol 8, 178–192 (2015). https://doi.org/10.1007/s12194-015-0306-5

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  • DOI: https://doi.org/10.1007/s12194-015-0306-5

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