Value of spectral CT imaging for improving beam-hardening artifact of myocardium / 中华放射学杂志

ABSTRACT

Objective To evaluate beam-hardening (BH) artifact reduction of myocardium in coronary computed tomography angiography(CCTA)with single-source dual-energy CT. Methods Thirty patients received CCTA on single-source dual-energy CT with findings of coronary artery stenosis reconstructed into monochromatic energy (60,70,80,90,100,110,120,130,140 keV) left vertical short-axis images via 40% ASIR and the polychromatic left vertical short-axis images were conventionally reconstructed. CT values were measured across multiple segments (basal anterior, basal lateral, basal inferior , basal septal, mid anterior, mid lateral, mid inferior , mid septal, apical anterior, apical lateral, apical inferior , apical septal and apex)of left ventricle wall at varying monochromatic energy levels and polychromatic images, and then the left ventricular myocardial average CT value and BH objective value were calculated retrospectivelyBH1=CT value of mid inferior wall-CT value of basal inferior wall ,BH2=CT value of mid septal wall-CT value of mid inferior wall. BH subjective rating were evaluated by two radiologists independently. Single sample t test was used to compare the difference of myocardial CT values among 13 segments with the left ventricular myocardial average CT value on polychromatic images ;Kruskal-Wallis test was used to compare the difference of CT values among thirteen different segments of myocardium on fixed monochromatic energy images; Wilcoxon rank test was used to compare the difference of BH objective value and subjective rating between monochromatic images with polychromatic images. Results On polychromatic images, the mean myocardial CT value was(73 ± 25)HU, the CT value of basic inferior[(58±23)HU], basic septal[(85±21)HU], mid septal[(89±24)HU], apical anterior[(64±23)HU]and apex [(61 ± 24)HU ] were different from the mean myocardial CT value(t value were -3.76,2.89,3.50,-2.30, -2.86,P all0.05). The differences of CT value of different myocardial segments had statistical significance at 60 to 80 keV images(P all0.05), suggesting that the non-uniformity of CT value among different segments was improved. On polychromatic images,BH1 M(P25,P75)was 11(6,28),BH2 M(P25,P75)was 19(1,29) HU. BH1 was improved on 90 to 140 keV images while BH2 was improved on 70 to 140 keV images, the difference had statistical significance compared with the polychromatic images(P all<0.05). BH1,BH2 decreased with the increasing of monochromatic energy level on 60 to 100 keV images, then increased a little on 110,120 keV images, and hit bottom on 130 keV images with the value of 5.20,0.34 HU ,finally exist a slight increase on 140 keV images again. On polychromatic images,BH1,BH2 subjective rating M(P25,P75)both were 1(1,2), BH1 subjective rating was improved on 70 to 140 keV images while BH2 subjective rating was improved on 90 to 140 keV , the difference had statistical significance compared with the polychromatic images(P all<0.05). Conclusion Compared with the polychromatic images,monochromatic energy images of CCTA with dual-energy CT resulted in significant BH artifact reduction and improvements in the uniformity in the myocardium, and 130 keV is the optimal Monochromatic energy.