New transluminal attenuation gradient derived from dynamic coronary CT angiography: diagnostic ability of ischemia detec
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ORIGINAL ARTICLE
New transluminal attenuation gradient derived from dynamic coronary CT angiography: diagnostic ability of ischemia detected by 13N‑ammonia PET Tsukasa Kojima1,2 · Michinobu Nagao3 · Hidetake Yabuuchi4 · Yuzo Yamasaki5 · Takashi Shirasaka2 · Masateru Kawakubo4 · Kenji Fukushima6 · Toyoyuki Kato2 · Atsushi Yamamoto7 · Risako Nakao7 · Akiko Sakai7 · Eri Watanabe7 · Shuji Sakai3 Received: 24 April 2020 / Accepted: 2 October 2020 © Springer Japan KK, part of Springer Nature 2020
Abstract Coronary computed tomography angiography (CCTA) has low specificity for detecting significant functional coronary stenosis. We developed a new transluminal attenuation gradient (TAG)-derived dynamic CCTA with dose modulation, and we investigated its diagnostic performance for myocardial ischemia depicted by 13N-ammonia positron emission tomography (PET). Data from 48 consecutive patients who had undergone both dynamic CCTA and 13N-ammonia PET were retrospectively analyzed. Dynamic CCTA was continuously performed in mid-diastole for five cardiac cycles with prospective electrocardiography gating after a 10-s contrast medium injection. One scan of the dynamic CCTA was performed as a boost scan for conventional CCTA at the peak phase of the ascending aorta. Absolute TAG values at five phases around the boost scan were calculated. The dynamic TAG index (DTI) was defined as the ratio of the maximum absolute TAG to the standard deviation of five TAG values. We categorized the coronary territories as non-ischemia or ischemia based on the 13 N-ammonia PET results. A receiver operating characteristic (ROC) analysis was performed to determine the optimal cutoff of the DTI for identifying ischemia. The DTI was significantly higher for ischemia compared to non-ischemia (8.8 ± 3.9 vs. 4.6 ± 2.0, p 50% does not correlate well with the functional assessment of the fractional flow reserve (FFR), which is regarded as the gold standard for determining hemodynamically significant coronary stenosis [2–4]. To overcome the weaknesses of conventional CCTA, the transluminal attenuation gradient (TAG) [5–7], myocardial perfusion CT [8–10], and noninvasive fractional flow reserve-CT (FFR-CT) [11–13] were recently introduced, and their ability to assess physiological consequences during CT examinations has been tested. There has been progress in designing functional evaluations by myocardial perfusion CT and FFR-CT, but myocardial perfusion CT requires additional radiation exposure and contrast agents to scan at the stress and rest conditions [14]. In addition, FFR-CT involves high cost and long analysis times. In contrast, TAG is calculated using a CCTA image acquired with a single contrast injection, and it is obtained without using special software. TAG is calculated by obtaining the linear regression coefficient between the luminal contrast attenuation and the distance along the vessel from the coronary ostium [5, 7, 15, 16]. The use of TAG can assist in the noninvasive assessment of hemodynamically significant coronary artery stenosis and
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