## 3 Results
### Confirming Brain CT Experiments  
The optimal experiment is unique and may or may not be one of the 18 original experiments that were designed according to [PERSON]'s method. However, any suggested experiment must be practically verified to confirm its suitability. A confirmatory brain CT experiment should therefore be conducted under Taguchi conditions. The highest S/N value in any individual experiment does not suffice in the real optimization design recommended by [PERSON] [14]. A confirmatory experiment was therefore carried out to validate the optimal acquisitions that were obtained from the Taguchi design. In practice, no operating parameter can be identified by the highest S/N value alone; rather, the parameter must be considered with others in determining the image quality of 128-slice CT examinations. A routine examination with A2 (5 mm thickness), B2 (350 mAs), C2 (120 kVp), D2 (standard filter), and E2 (250 mm\({}^{2}\) FOV), which is used in most hospitals, is considered for comparison [2].  
Table 5 presents the Taguchi experiment that yields the highest S/N value when the parameters are considered separately; it has A1 (2.5 mm thickness), B3 (400 mAs), C3 (140 kVp), D1 (sharp filter), and E1 (200 mm\({}^{2}\)) FOV, as mentioned in Figure 3C. Table 5 compares brain CT experiments with the routine examination, the Taguchi experiment, and the optimal experiment. Routine examination yields the average grade with an S/N value of 33.13. The Taguchi experiment yields a maximum increase of 6% because 35.03/33.13 = 106%. A significant difference in S/N (_p_ < 0.001) was observed between the routine examination, 33.13, and the Taguchi experiment, 35.03. A significant difference in S/N (_p_ < 0.001) was also observed between the routine examination, 33.13, and the optimal experiment, 34.89. In addition, Figure 5 shows the (A1) horizontal, (A2) vertical of the routine examination, (B1) horizontal, (B2) vertical of the Taguchi experiment, and (C1) horizontal, (C2) vertical of the optimal experiment in 128-slice brain CT examinations.  
The accompanying Volume Computer Tomography Dose Index (CTDIVOL) of the brain CT effective dose (H\({}_{\rm E}\)) in examinations was read directly from the CT machine [2]. During the scan, it was multiplied by the scan length (17.1 cm) to yield the dose length product (DLP) (mGy cm) [3]. H\({}_{\rm E}\) is calculated as:  
\[\rm{H_{E}}\ (mSv)=k\ \times\ DLP \tag{7}\]  
where k [mSv/(mGy cm)], the conversion factor, is 0.0019 mSv/(mGy cm) for the brain scan [3]. The H\({}_{\rm E}\) of the routine examination at LKCH was 60 mGy \(\times\) 17.5 cm \(\times\) 0.0019 mSv/ (mGy cm) = 2.01 mSv. The H\({}_{\rm E}\) values of the Taguchi experiment and the optimal experiment were evaluated as 3.34 and 2.51 mSv, respectively. The accompanying H\({}_{\rm E}\) was still under the limit of 100 mSv/year and 50 mSv/year that was recommended by the Interna  
Figure 4: Six cross-interactions between pairs of parameters in the 128-slice CT acquisition experiments. (**a**) Thickness vs. filter type (A \(\times\) D). (**b**) Thickness vs. current voltage (A \(\times\) C). (**c**) Thickness vs. FOV (A \(\times\) E). (**d**) Filter type vs. FOV (D \(\times\) E). (**e**) Current voltage vs. FOV (C \(\times\) E). (**f**) Current voltage vs. filter type (C \(\times\) D).  
tional Commission on Radiological Protection in its report no. 60 [21]. In addition, [PERSON] et al. demonstrated that the diagnosis reference level for the mean H\({}_{\text{E}}\) of head CT was 2.0 \(\pm\) 0.4 mSv in Taiwan in 2013 [22].