Initial Study Of Transluminal Attenuation Gradient And Corrected Models In Coronary CT Angiography For Determining Stenosis Severity

ObjectiveTo analysis the variation tendency of transluminal attenuation gradient(TAG),transluminal attenuation gradient with corrected contrast opacification(TAG-CCO)and transluminal attenuation gradient with excluding calcified coronary segments(TAG-ExC)derived from coronary CT angiography(CCTA)with increased stenosis severity.To compare the incremental value of TAG,TAG-CCO and TAG-ExC in determining the stenosis severity of coronary arteries using coronary angiography(CAG)as reference standard.Materials and MethodsPatients with suspected or known CAD who underwent CCTA and subsequently confirmed by CAG within 2 weeks between March 2014 and August 2015 in Shanghai Tenth People's Hospital were retrospectively enrolled for evaluation.The diameter stenosis,plaque composition,TAG and it's corrected models derived from CCTA were recorded and calculated.According to the plaque composition of the narrowest stenosis,the vessels were divided into non-calcified vessels and calcified vessels.Changes in different TAG models were compared with corresponding stenosis severities ascertained by CAG,using Kruskal-Wallis test.The correlation and consistence between TAG,TAG-CCO and TAG-ExC were then analyzed by using Pearson test and Bland-Altman test.We then analyzed and compared the diagnostic performances of TAG,TAG-CCO,TAG-ExC and the TAG/CCTA,TAG-CCO/CCTA,and TAG-ExC/CCTA combinations over that of CCTA alone in evaluating stenosis severity.Furthermore,the incremental value of the TAG and the corrected models in the reclassification of CCTA-evaluated stenosis severity were calculated with net reclassification index(NRI).Results1.A total of 115 patients,two patients(2/115;1.74%)with non-evaluable CCTA images for TAG were excluded.A total of 10 hypoplastic vessels with diameter of<1.5 mm,one left circumflex artery of anomalous origin,and 17 vessels with stents were also excluded.A total of 113 patients and 311 coronary arteries were retrospectively analyzed for final evaluation.The average age was 63.8±8.3 years old,male 75(66.45%).The results of CAG detection showed that 153(49.2%)vessels with mild stenosis,57(18.3%)with moderate stenosis,and 92(29.6%)with severe stenosis and(2.9%)with total occlusion.216(69.5%)vessels were defined as non-calcified vessels,and the other 95(30.5%)vessels were defined as calcified vessels.2.TAG decreased gradually with increased stenosis severity(P<0.001),particularly,from-8.32±5.83 HU/10 mm for the DS<50%,-14.37±11.60 HU/10mm for the DS of 50-70%to-15.77±9.91 HU/10 mm for the DS of 70%-99%(P<0.001).There were significant differences between mild stenosis with moderate stenosis and sever stenosis(P<0.05).Similar tendencies were found in TAG-CCO and TAG-ExC(P<0.001).3.TAG correlated highly with TAG-ExC(r = 0.944,P<0.001)but poorly with TAG-CCO(r = 0.404,P<0.001).The correlation between TAG-CCO and TAG-ExC were significant but low(r = 0.374,P<0.001).Bland-Altman analysis showed an excellent consistence between TAG and TAG-ExC with a bias of-0.05 and limits of agreement ranging from-6.06 to 5.96.Only 10(3.2%)TAG minus TAG-ExC values on the Bland-Altman plot were outside the 95%confidence interval.4.No statistically significant difference in value was noted between the non-calcified and calcified plaques in the different degrees of stenosis under the three TAG models as determined by CAG(P>0.05 for all comparisons).5.In total vessel evaluation,TAG and TAG-ExC improved the diagnostic performance over CCTA(AUC = 0.926 vs.0.907,P = 0.018;AUC = 0.922 vs.0.907,P = 0.030,respectively),but TAG-CCO did not(AUC:0.911±0.017 vs.0.907 ±0.017;P = 0.375).6.In calcified vessels,adding TAG to CCTA enabled a significant reclassification(n = 95;NRI = 0.1435 P = 0.038).but adding TAG-CCO(NRI = 0.073;P =0.415)or TAG-ExC to CCTA(NRI = 0.125,P = 0.061)did not.Conclusions1.TAG,TAG-CCO and TAG-ExC decreased with the increased diameter stenosis.2.TAG correlated highly with TAG-ExC,TAG-CCO correlated poorly with TAG and TAG-TxC.TAG-CCO could not diminish the impact of lack of temporal uniformity.3.The accuracy of TAG was not affected by calcified plaque.4.TAG and TAG-ExC improved the diagnostic performance over CCTA in total vessel evaluation.5.Adding TAG to CCTA significantly reclassified the stenosis severity of calcified vessels.