Figure 2:

Noise power spectra (NPS) of the original 2 mm image before denoising, the 5 mm prior image, and images after PKAID denoising using a prior image with thicknesses of 5, 8 and 10 mm. A prior image with thicker slice thickness (e.g., 10 mm) can further reduce image noise, but also shift the NPS toward the lower frequency. A prior image of 5 mm slice thickness preserves the NPS in relative to the original image while reducing image noise.