ABSTRACT The noise power spectrum (NPS) is an important quality control parameter used to characterize the noise in a digital image in the frequency domain. The NPS is divided by the square of the mean value of the pixels in the region of interest (ROI), and this ratio is referred to as the normalized noise power spectrum (NNPS) and is used for noise analysis. This study aims to determine the effect of using an anti-scatter grid on the NNPS measurement.