### MATERIALS AND METHODS

### Study Population

### Multidetector CT Protocol

### Assessment of the Image Quality

^{2}circular region of interest (ROI).

^{2}sized ROI located in the left ventricle. The SNR was assessed in the sinus Valsalva with an ROI of 60 mm

^{2}in the area, and it was calculated according to the mean density divided by its standard deviation. The CNR was defined as the difference between the mean density of the contrast-filled left ventricular chamber and the mean density of the left ventricular wall with an ROI of 30 mm

^{2}in the area, and this was then divided by the image noise (4). The image-quality parameters were obtained from the 1-mm thick transverse images. All the measurements and calculations were performed by one author (with 5 years of experience with chest CT).

### Evaluation of the Effective Radiation Dose

*k*= 0.017 mSv * mGy-1 * cm -1) is averaged between male and female models.

### Statistical Analysis

*t*-test. Determining the correlation between the BMI and the objective measurement parameters was performed by using Pearson's correlation analysis. Graphs for the objective measurements versus the BMI were created using the linear regression model. For the discrete variables of the subjective analysis results, comparisons of the paired data were performed using the Wilcoxon signed rank test. Comparisons of the frequency between the two protocols, according to the overall image quality scores, were assessed by the Chi-square test. Inter-observer agreement for the interpretation of the subjective analysis results was assessed by weighted κ statistics. The κ values were interpreted as follows: 0.80-1.00, excellent agreement; 0.61-0.80, good agreement; 0.41-0.60, moderate agreement; 0.21-0.40, fair agreement; and 0.00-0.20, poor agreement.

*p*value was less than 0.05.

### RESULTS

### Characteristics of the Study Groups

### Objective Assessment of the Image Quality

*p*= 0.416).

*p*< 0.0001). On the other hand, the image noise decreased from 38.5 ± 7.5 HU for the 100-kVp protocol to 29.6 ± 4.6 HU for the 120-kVp protocol (

*p*< 0.0001). There were no significant differences in the SNR and the CNR between the groups regardless of the BMI category (Table 2).

*p*< 0.001). The Pearson correlation coefficients were -0.259 for the sinus Valsalva density, 0.610 for the image noise, -0.613 for the SNR and -0.529 for the CNR for the 100-kVp images, and these values were -0.385 for the sinus Valsalva density, 0.616 for the image noise, -0.642 for the SNR and -0.575 for the CNR for the 120-kVp images.

### Subjective Assessment of the Image Quality

*p*values < 0.0001). Images with better contrast were more frequent for the 100-kVp images: reader 1 chose 57% of the 100-kVp images, 14% of the 120-kVp images and 30% of the images were equal; for reader 2, the values were 52%, 8% and 40%, respectively (both

*p*values were < 0.0001) (Fig. 2). For the preference test, both readers showed a tendency to choose the 100-kVp images: reader 1 chose 40% of the 100-kVp images, 29% of the 120-kVp images and 31% were equal images (

*p*= 0.06); for reader 2, the values were 31%, 18% and 51%, respectively (

*p*= 0.01). There was a stronger trend toward a preference for the 100-kVp images (

*p*= 0.08 for reader 1,

*p*= 0.004 for reader 2) for the category of a BMI less than 25 than that for the category of a BMI of 25 or greater (

*p*= 0.41 for reader 1,

*p*= 0.72 for reader 2) (Fig. 3).

*p*= 0.229). In the category of a BMI less than 25, the mean scores were 4.1 and 4.0, respectively (

*p*= 0.259). For the category of a BMI 25 or greater, the mean scores were the same (3.7) for both protocols (

*p*= 0.572). Table 3 also shows that there was no difference in the frequencies according to the score between the 100-kVp and 120-kVp images (all,

*p*= 1.00).

### Reduction of the Radiation Dose

*p*= 0.685). The CTDIvol was 30.5 ± 0.3 mGy with a range of 29.7 to 31.1 mGy for the 100-kVp protocol and 38.75 ± 0.9 mGy with a range of 38.5 to 46.7 mGy for the 120-kVp protocol. The DLP based on the given CTDIvol values showed significantly lower exposure for the 100-kVp protocol (456.4 ± 25.2 mGy * cm) when compared to the 120-kVp protocol (594.3 ± 56.2 mGy * cm) (

*p*< 0.001). The mean effective dose based on the standard conversion factors was 7.8 ± 0.4 mSv for the 100-kVp protocol, resulting in an average 24% reduction of the effective dose for the 120-kVp protocol (10.1 ± 1.0 mSv) (

*p*< 0.001).