## 3 Results and Discussion  
Low-dose CT images for each reconstruction parameter as obtained by selecting cross-sections of the aortic arch, four chambers of the heart, and the end of the heart are shown in Figure 3; Groups 1-4 images derived according to the parameter strengths and kernel combinations of each of the four ADMIRE techniques are also shown here. Group 4, which applied the NLM noise removal algorithm, showed the best visual quality among all the cross-sectional images. In particular, as compared with the resulting images of Group 3 using ADMIRE A2 and kernel B59, we confirmed that the noise level was significantly reduced in Group 4 using the NLM algorithm with ADMIRE A2 and kernel B59. Figure 2: ROI area set in each CT sample image (CNR evaluation: ROI1 and ROI2, and ERD evaluation: ROI3). Data on CNR, ERD, and BRISQUE values obtained in this study are shown in Table 3. The resulting data presented each quantitative indicator with respect to the group. The resulting graphs and values of the CNR, quantitatively analyzed in the ROI set as shown in Figure 2, are presented in Figure 4. The CNR values measured in the aortic arch were approximately 56.49 in Group 1, 64.86 in Group 2, 13.79 in Group 3, and 56.25 in Group 4. In the aortic arch, the highest value was found in Group 2; high values similar to those in Group 2 were found in Group 4. Among the four chambers, Group 4 showed the most improved value at approximately 49.33, while Group 3 showed the lowest value at approximately 8.57. At the end of the heart, as in the previous images, improved results were observed in Groups 4, 2, 1, and 3; the best value of approximately 28.94 was obtained in Group 4. The highest average value was obtained in Group 4, which  
Figure 3: Low-dose CT images according to various ADMIRE intensities and kernel combinations: (a) AD-MIRE A with kernel B40 (Group 1); (b) ADMIRE A3 with kernel B40 (Group 2); (c) ADMIRE A2 with kernel B59 (Group 3); and (d) ADMIRE A2, kernel B59, and NLM noise reduction algorithm (Group 4). applied the proposed NLM noise removal algorithm to low-dose CT images. In addition, as compared with the Group 2 images obtained based on relatively high ADMIRE intensity and low kernel, the CNR was higher in Group 4 using the NLM noise removal algorithm. The resulting graphs and figures of the ERD, quantitatively analyzed in the ROI set as shown in Figure 2, are shown in Figure 5. The ERD values measured at the aortic arch were approximately 2.77 in Group 1, 2.71 in Group 2, 2.61 in Group 3, and 2.53 in Group 4, with Group 4 showing the best value. Among the four chambers, Group 4 showed the most improved value of approximately 0.100, while Group 1 showed the lowest value of approximately 1.28. At the end of the heart, similar to the previous images, improved values were obtained in the following order: Groups 3, 4, 2, and 1. Group 4 also showed an excellent average ERD value of approximately 1.19, which was similar to that of Group 3. As a result, the best value was obtained in Group 3 based on ADMIRE A2 and kernel B59; similar results were obtained with an average of approximately 1.19 in Group 4, which applied our proposed NLM noise removal algorithm to low-dose CT images. Additionally, in Groups 1 and 3, using the same ADMIRE A2, the ERD value of Group 3 using a high kernel significantly decreased as compared to that of Group 1 (Group 1 vs. Group 3). Figure 4: Results of contrast-to-noise ratio (CNR) for reconstructed CT images of the aortic arch, 4 chamber, and end of heart areas.