We examined whether the superior margin of the left main bronchus is the best landmark for the starting position of computed tomography coronary angiography（CTCA）. We retrospectively evaluated 693 consecutive CTCAs. From the scout scanogram, the superior margin of the left main bronchus was noted. The relationships among and distance between the superior margin of the left main bronchus and the left coronary system were analyzed. The superior margin of the left main bronchus extended caudally to the superior margin of the left coronary system in 13 patients（1.9％）. The addition of 1cm to the superior margin of the left main bronchus kept it caudal to the superior margin of the left coronary system in only one patient（0.1％）. On the scout scanogram, 1cm above the superior margin of the left main bronchus is the most appropriate starting position for CTCA.
Alternative Starting Position for CT Coronary Angiography
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