5.1. DT overview

The DT system (SonialVision Safire II; Shimadzu Co., Kyoto, Japan) comprised an X-ray tube [anode: tungsten with rhenium and molybdenum; real filter: inherent; aluminum (1.1 mm), additional; aluminum (0.9 mm), and copper (0.1 mm)] with a 0.4 mm focal spot and 362.88 � 362.88 mm amorphous selenium digital flat-panel detector (detector element, 150 � <sup>150</sup> <sup>μ</sup>m2 ). The source-to-isocenter and isocenter-to-detector distances were 924 and 1100 mm, respectively (antiscatter grid, focused type; grid ratio, 12:1).

### 5.2. DE-DT acquisition

Collimator motion was synchronized by measuring the misalignment of the low-voltage (60 kV) and high-voltage (120 kV) images at a constant tube motion. A large energy gap between low and high tube potential kVp imaging yields better material decomposition [28–33]. We selected the abovementioned kV values because this study aimed to improve contrast and artifact reduction during DT acquisition while maintaining an imaging performance similar to that of conventional DT.

Pulsed X-ray exposures and rapid switching between low and high tube potential kVp values were used for DE-DT imaging. Linear system movement and a swing angle of 40� were used when performing tomography, and 37 low- and high-voltage projection images were sampled during a single tomographic pass. We used a low voltage, and each projection image was acquired at 416 mA. A 9.4 ms exposure time was used for low-voltage (60 kV) X-rays at 416 mA, and a 2.5 ms exposure time was used for high-voltage (120 kV) X-rays. To generate reconstructed tomograms of the desired height, we used a 768 � 7684 matrix with 32 bits (single-precision floating number) per image (pixel size, 0.252 mm/pixel; reconstruction interval, 1 mm).
