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Proceedings Paper

A new image-quality evaluation method for low-contrast resolution in computed tomography
Author(s): Tsunemichi Akita; Naoyuki Yagi
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Paper Abstract

The contrast-to-noise ratio (CNR) is often used as a physical evaluation parameter for low-contrast resolution in computed tomography (CT). However, CNR is not affected by the window conditions. This study proposes a new physical evaluation method for low-contrast resolution that takes into account changes in window conditions. This new parameter is called the gray-scale contrast-to-noise ratio (GSCNR) was assessed and was compared with CNR. For each reconstruction image, the window width (WW) was varied from 100 to 400 in steps of 100 while keeping the window level (WL) fixed, and CNR and GSCNR were calculated. WL was then varied from 0 to 100 in steps of 20 while keeping WW fixed, and CNR and GSCNR were calculated again. CNR did not vary with WW, but it varied inversely with the standard deviation (SD) of the CT number (from 2.2 for an SD of 7 to 1.4 for an SD of 16). In contrast, GSCNR decreased with the increase in WW for each SD. In addition, GSCNR did not vary with WL, but it varied inversely with SD. GSCNR was found to be a useful physical evaluation parameter and was also thought to be useful for optimizing the window conditions.

Paper Details

Date Published: 8 March 2007
PDF: 8 pages
Proc. SPIE 6515, Medical Imaging 2007: Image Perception, Observer Performance, and Technology Assessment, 65151O (8 March 2007); doi: 10.1117/12.710515
Show Author Affiliations
Tsunemichi Akita, National Cancer Ctr. Hospital East (Japan)
Naoyuki Yagi, National Cancer Ctr. Hospital East (Japan)


Published in SPIE Proceedings Vol. 6515:
Medical Imaging 2007: Image Perception, Observer Performance, and Technology Assessment
Yulei Jiang; Berkman Sahiner, Editor(s)

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