| Objective: to define the low radiation dose scanning mode, optimal enhancement scanning triggering threshold(ESTT) and monochromatic-energy levels for both coronary and myocardial imaging of dual energy coronary computed tomography angiography(DE-CCTA) and explore the diagnostic performance of stasic DE-CCTA for subjective and objective diagnosing chronic myocardial infarction(CMI)) Methods:(1)100 of 135 patients who were going to receive DE-CCTA were enrolled in this study prospectively and equally assigned to five groups randomly of different ESTT as 100 HU,110 HU, 120 HU, 130 HU and 140 HU. Noise, signal-to-noise ratios(SNR),contrast-to-noise ratios(CNR) and enhancement extent(EEx) of coronary artery and myocardium, iodine concentration of myocardium and EEx of left ventricle(LV) were measured and comparied between differrent group.(2) 40 of 68 patients who were going to receive DE-CCTA were enrolled in this study prospectively and equally assigned to control group and experimental group randomly.The controlgroup(Group A, n=20) were scanned using the conventional tube output(100k V/ 140 k V, 165 m As /140 m As, full dose exposure during 30%-70% phases of cardiac cycle and 20% dose exposure during other phases of cardiac cycle) and reconstructed using filtered back projection(FBP).The experimental group(Group B, n=20) were scanned using the low radiation dose tube output(100k V/ 140 k V, 115 m As /98 m As, full dose exposure during 35%-70% phases of cardiac cycle and 4% dose exposure during other phases of cardiac cycle) and reconstructed using sinogram affirmed iterative reconstruction(SAFIRE). Noise, SNR and CNR of aortic root and myocardium, subjective scoring of left anterior descending branch(LAD) and myocardium, and radiation dose were measured and comparied between group A and B.(3) 30 of 49 patients who received DE-CCTA were enrolled in this study. SNR, CNR of myocardium and coronary artery, and myocardial BH were measured and compared across multiple segments at varying monochromatic energy levels(60-140 ke V, interval of 10 ke V, each with 40% Adaptive Statistical Iterative Reconstruction, ASi R) and the polychromatic 140 k Vp image(without ASi R);(4)DE-CCTA, late gadolinium enhancement(LGE), native and post-contrast T1 mapping images were acquired at dual soure CT(DSCT) and 1.5T MRI in 3 swine CMI models within 1 week. With LGE as gold standard, visual diagnostic performance evaluation indexs of polychromatic DE-CCTA images, 130 ke V images, optimal CNR monochromatic energy images, iodine maps, combined evaluation of 130 ke V and optimal CNR monochromatic energy images, combined evaluation of 130 ke V and iodine maps, native post-contrast T1 mapping images were calculated and compared; Iodine concentration, normalized i Iodine density(NID), native and post-contrast T1 value measuring diagnostic performance were calculated and compared basedon ROC analysis.Results:(1) Post contrast CT value of LAD, post contrast CT value and EEx of LV chamber were different with different ESTT(P all<0.05); Post contrast CT value of LAD was higher with ESTT of 100HU(404.85±48.98)HU than 130HU(355.16±59.11)HU;Post contrast CT value of LV chamber was higher with ESTT of100HU(436.96±58.56)HU than both 130HU(386.04±66.40)HU and 140HU(370.34±65.89)HU(P all<0.05); Post contrast CT value of EEx of LV chamber were higher with ESTT of 100HU(391.09±62.59)HU than 140HU(328.77±64.33)HU; Post contrast CT value and EEx of LV myocardium, noise, SNR and CNR of LAD and LV myocardium were not different between group of different ESTT(P all > 0.05);(2)Radiation dose of experimental group(4.68 ± 0.86) m Sv was lower than control group(6.69 ± 0.85)m Sv(P < 0.05); Aortic and myocardial CNR were higher in experimental group(54.79±10.35,20.58±4.04) than in control group(43.66±10.79,20.58±4.04)(P<0.05); Aortic and myocardial noise, SNR and subjective scoring were not different between experiment and control group(P all > 0.05);(3) CT value and iodine concentration of various myocardial segments were different(P all < 0.05) and myocardial BH exist in polychromatic images.CT value and iodine concentration were lower in apical anterior[(63.86±22.84)HU,(1.46±0.53)mg/ml], apex[(60.95±23.88)HU,(1.53±0.38)mg/ml)] and basal inferior wall[(57.98±22.52)HU,(1.55±0.46)mg/ml] than mean value[(73.43±24.52)HU,(1.87±0.57)mg/ml], and higher in mid septal wall[(88.71±23.92)HU,(2.31±0.44)mg/ml] than mean value(P all <0.05); Compared with the polychromatic images, myocardial BHs were all improved at(90-140) ke V+40%ASi R images and images at 130 ke V+40% ASi R showed the optimal improvement for myocardial BHs(BH1:3.77 HU vs 11.04HU; BH2:2.76 HU vs 19.49HU); Myocardial and coronary noise were all improved at(90-140) ke V+40% ASi R images; Myocardial and coronary SNR, CNR were all improved at 70 ke V + 40% ASi R images, and images at 70 ke V+ 40% ASi R showed the optimal improvement for both myocardial and coronary SNR, CNR(SNR of mid-inferior wall:6.19±2.13 vs 3.98±1.38;CNR of mid-inferior wall:13.32±3.85 vs 10.54±3.06; SNR of LAD: 15.92±7.50 vs 12.93±5.88; CNR of LAD:27.33±6.47 vs 16.79±5.36)(P all<0.05);(4) With LGE as gold standard: optimal CNR monochromatic energy images showed higher sensitivity(Se)(71.74%), specificity(Sp)(87.5%) and the highest diagnostic coincidence rate(DCR)(80.39%), youden index(YI)(0.59) and Kappa value(0.6) in different reconstructed images of DE-CCTA while130 ke V images showed(96.43%) and iodine image show the hightest Se(82.61%); As positive in both optimal CNR monochromatic energy and 130 ke V images was positive certainly, specificity and positive predictive value(PPV) are all 100%; As negative in both iodine map and 130 ke V images was negative certainly, Se(84.78%) was higher than iodine map; Iodine concentration, normalized iodine density(NID), pre-and post-contrast T1 value of infarcted and and remote myocardium were different(P all<0.05); ROC analysis showed: with 2.45mg/ml as cutoff value, Sp, Se and area under the curve(AUC) of iodine concentration for diagnosing CMI were 96.3%, 97% and 0.99(95%CI: 0.98-1); With 0.16 as cutoff value, Sp, Se and AUC of NID for diagnosing CMI were96.3%, 97% and 0.99(95%CI: 0.96-1); With 1143.55 ms as cutoff value, Sp, Se and AUC of native T1 value for diagnosing CMI were 100%, 87.5 % and 0.98(95%CI:0.95-1); With 503.4ms as cutoff value, Sp, Se and AUC of post-contrast T1 value for diagnosing CMI were 95.2%, 83.3% and 0.92(95%CI: 0.84-1); Conclution:(1) ESTT could influence image quality of myocardium and coronary artery.130 HU and 140 HU is optimal ESTT of DE-CCTA for showing myocardium and coronary artery simultaneously as monitoring position at aortic root;(2) By combined using of low tube current, automatic current adjustment, minidose and iterative reconstruction(IR)technique, DE-CCTA could reduce radiation dose effectively with precondition of ensuring image quality, therefore patients with slow heart rate could receive DE-CCTA with low radiation doses for obtaining more diagnostic information for clinical physicians;(3) BH exist in polychromatic images and iodine map of DE-CCTA.Monochromatic images with IR could offer significant improvement for SNR, CNR of both myocardium and coronary artery(optimal at 70 ke V+40%ASi R), and myocardial BH(optimal at 130 ke V+40%ASi R);(4) Stactic DE-CCTA could offer various combined evaluation for CMI.Combined evaluation of monochromatic images and iodine map could improve visual diagnostic performance of DE-CCTA for CMI effectively;Iodine concentration and NID of stastic DE-CCTA could offer reliably quantitative diagnosing for CMI, stastic DE-CCTA is a feasible way for “one-stop” diagnosing CMI and has great clinical application potential. |
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