**2. Pre-Processing ECG-Gated 4D CT Images**

In this study, we reconstructed CTA volumes for eight patients at 0% to 95% intervals (in 5% intervals) between the RR peaks of the heart rate. We took the volumes using a 256-slice multi-detector CT scanner (BRILLIANCE ICT 256 SLICE, Philips Healthcare) at the Cardiovascular Center of Seoul National University Bundang Hospital. This retrospective study was approved by the Institutional Review Board of Seoul National University Bundang Hospital (IRB No. B-2009-637-103).

The cross-sectional size of the image was 512 × 512 pixels, the average number of slices in the Z-axis direction was 298, and the volume voxel resolution was 0.35 × 0.35 × 0.45 mm. The left ascending and circumflex coronary arteries were segmented using the ITK-Snap software [41]. The segmented arteries were converted to mesh models using Poisson surface reconstruction, where the average number of nodes was 10,638. We selected 75% phase mesh models as templates, as the left ascending and circumflex coronary arteries are most clearly observed at 75% phase [42]. Figure 3 shows the models of the template and other phases.

**Figure 3.** Left ascending and circumflex coronary arteries of: (**a**) patient 1; (**b**) patient 2; and (**c**) patient 4. The template phase model is a white solid model, while the other phases are colored with respect to their cardiac phases.
