**5. Conclusions**

In summary, we observed the effect of filter schemes on several low-contrast materials using standard and UHR imaging protocols. Although UHR image acquisition requires a higher acquisition time and greater radiation exposure, we obtained spatial resolution up to 1.77 times higher than that of standard acquisition. In addition, the performance of UHR was affected by the FBP filter schemes, showing different *f* <sup>50</sup> values and different noise patterns for different filters. Therefore, one should consider the optimal window function that can provide the best performance when observing the fine structure of the imaging object before UHR acquisition while comparing both the MTF and NPS.

**Author Contributions:** Conceptualization, S.C.; methodology, C.-W.S.; software, S.C. and C.-W.S.; validation, S.C.; formal analysis, S.C.; investigation, S.C.; resources, B.K.C.; data curation, S.C.; writing—original draft preparation, S.C.; writing—review and editing, S.C.; visualization, S.C.; supervision, B.K.C.; project administration, B.K.C.; funding acquisition, B.K.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We would like to acknowledge the financial support from the R&D Convergence Program of NST (National Research Council of Science & Technology) of the Republic of Korea (CAP-15-04-KITECH).

**Conflicts of Interest:** The authors declare no conflict of interest.
