*3.2. Reconstructed Images with Di*ff*erent Filters and Configurations*

Figure 6 shows the reconstructed images with configuration (1, 1) using the Hanning window and its cropped ROI images around the centers of five different materials. The relative contrast between each material and background with standard deviation error are plotted in Figure 6f. All five materials showed a low contrast, showing a small relative contrast below 0.15 (maximum contrast is 1). As mentioned above, the higher density material does not always represent the higher CT number when we measure the contrast between each material and the background (PMMA). M2 and M5 showed the lowest contrast among the five materials.

**Figure 6.** Reconstructed image with configuration (1, 1) using the Hanning window. (**a**–**e**) The cropped – region of interest (ROI) around the center of each material, and (**f**) relative contrast between the target and background with standard deviation error bar as a function of each material. –

The reconstructed cropped images of M1 with different configurations using the Hanning window are shown in Figure 7a. Figure 7b shows the radial profiles of each image grid in Figure 7a. The images reconstructed using standard detector resolution (configuration (1, 1) and (1, 2)) showed an unstable fluctuation in their radial profiles at the initial radial location. On the contrary, the images of configurations (2, 1) and (2, 2) showed relatively flat signals.

**Figure 7.** (**a**) Reconstructed image with different configurations using the Hanning window and (**b**) the radial profile of each configuration.

To understand the effect of filter schemes on image quality, the reconstructed images of M1 with different filters using configurations (1, 1) and (2, 2) are shown in Figure 8a. The radial profiles in Figure 8b correspond to the bottom row images in Figure 8a (configuration (2, 2)). The fluctuations of the radial profiles are gradually smoothed with an increase in the index number of filter schemes, demonstrating that the high-frequency noise was rejected by using the smoothing windows. The more oscillations in the signal, the coarser the MTF curve, as shown in Figure 9a.
