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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.