Fig. 2

a-d Estimating the shortening rate of the projection. a From a given CT scanned section, the blue line showed the actual length of TK (blue line) and the X-direction (red arrowed lines) can be determined. Note that the X-ray is not enfacing the TK with a shortened projection (red line). The blue dashed line illustrates the standard line vertical to the exam bed. The angle between the red lines and the dashed blue line equals to the projection angle (the angle β). The actual TK length in a given section (L) and the estimated projection length (P) are shown. The shortening rate can be calculated by (1-P/L) × 100%. b through d Changing the projection angle influenced the image and the projection of the TK using X-ray imaging. For each projection angle used, namely RAO30 (b), RAO45 (c) and RAOCS (d), (see text for detail), the distances (shown by the two blue lines, and labeled by the labels d1-d3) between proximal coronary sinus (CS) and ablation catheter (ABL), the degree of image shortening was determined. RVA: right ventricle apex, CS: coronary sinus, ABL: ablation catheter