Author + information
- Eun-Ah Park, MD, PhD and
- Whal Lee, MD, PhD∗ ()
- ↵∗Department of Radiology, Seoul National University Hospital, 28 Yongon-Dong, Chongno-Gu, Seoul 110-744, Republic of Korea
We thank Dr. Choi and colleagues for their interest in our work (1). The responses to their questions are as follows. First, the possible explanation as to why only transluminal diameter gradient (TDG) shows significant differences between stenotic and nonstenotic segments in our clinical study, despite a correlation between TDG and transluminal attenuation gradient (TAG) (1), is that the decreased flow due to significant stenosis eventually results in a reduction in the caliber of the downstream artery. TDG is free from confounding factors, such as vessel length, which cause inaccurate results in TAG, and therefore, TDG may reflect the coronary volume flow more directly than TAG. Second, we intentionally compared the TAG values of short left anterior descending artery with those of long left circumflex (LCx) to emphasize the fact that TAG is largely affected by the length of the vessel. Although the vessel-specific TAG values would be more appropriate to minimize this bias, we should keep in mind that analyzing vessel-specific TAG should not be the solution to eliminate the effect of the vessel length, because the length of the coronary artery depends on the coronary circulation dominance. Third, in animal models, the dynamic volume computed tomography scanning was performed every heartbeat for 40 s, and TAG values were measured and compared at each time point covering sufficiently both earlier and later periods to peak aortic enhancement (Figure 2 of our paper ). Figure 3 of our paper (1) is just 1 example of the multiple time-point scans showing significantly different TAG values among animal models. The reason why we selected the fifth scans after peak aortic enhancement as the representative figures was that the reverse TAG in an occluded artery is well visualized in the delayed scan. However, the trend of the difference in the TAG values between stenotic and nonstenotic LCx is the same over time after peak aortic enhancement (Figure 2 of our paper ). Fourth, the reverse attenuation gradient sign, defined as a reverse intraluminal opacification gradient of the distal segment to occlusion (2), contributed to the reverse TAG, which was clearly exhibited in the delayed scans in our animal study (Figure 2 in our paper ). Fifth, we agree that the number of animals we studied is too small for an adequate statistical workup. However, our objective of whether the diameter change affects TAG significantly was successfully carried out. Figure 2 in our paper (1) showed that the TAG values of the stenotic LCx tended to be lower than those of the nonstenotic LCx, as Choi and colleagues correctly pointed out; however, at the same time, we also found that the diameter of the stenotic LCx is smaller than that of the nonstenotic LCx (Table 1 in our paper ). Finally, our phantom and clinical results are perfectly reproduced in our animal study. In brief, the distal segments having smaller caliber did not reach peak attenuation of the larger proximal segments, and it is clearly shown that the relative peak enhancement of each segment depends on its diameter (Table 1 in our paper ).
Please note: The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- American College of Cardiology Foundation