Figure 8.

(a) One projection of the Catphan phantom. A dashed line indicates the location used for noise calibration. (b) The values of ${\sigma }_X\left(u,I\right)/{\sigma }_{\widehat{N}}\left(u\right)$ as a function of u at two different mAs levels. (c) $⟨{\sigma }_X\left(u,I\right)/{\sigma }_{\widehat{N}}\left(u\right)⟩$ as a function of $1/\sqrt{\mathrm{mAs}}$ and the straight line is the linear fit.