Fig. 2

Image registration of preoperational three-dimensional CTA (red modality, upper left) and intraoperative CBCT (green modality, bottom left). First, the LSA ostium (the ROI in this study) was marked in both CTA (yellow circle) and CBCT (purple circle) modalities. Second, automatic registration, which was based on bony landmarks by default, could be performed to ensure the two modalities are in the same field of view. Thirdly, landmarks of the LSA were aligned from coronal view and checked from other planers to complete the registration