RESUMEN
Objective:To investigate the optimal monochromatic level for evaluation of in-stent lumen after transjugular intrahepatic portosystemic shunt (TIPS) by dual-layer detector CT.Methods:Twenty-nine patients after TIPS were retrospectively enrolled who underwent abdomen enhanced examinations with portal venous phases by a dual-layer detector CT between December 2019 and July 2021. The mixed iterative image (conventional group) and monochromatic images (40 keV group, 50 keV group, 60 keV group and 70 keV group) were obtained by reconstruction. Circular regions of interest were placed in the in-stent of the cross-sectional reconstructed image and in the vertical spinal muscle on the same plane to obtain the corresponding average CT value and noise. The contrast to noise ratio (CNR) and signal to noise ratio (SNR) were calculated. Then 4-point scale was performed to evaluate image quality subjectively by 2 physicians blindly and separately. One-way ANOVA or Kruskal Wallis H rank-sum test was used for the overall analysis between groups, and LSD test or Dunn′s Bonforoni test was used for pairwise comparison within groups. Results:There was no significant difference in noise values among the 5 groups ( P>0.05). The difference of CNR and SNR between the 5 groups was statistically significant ( F=72.28, 56.45, P<0.001). The CNR and SNR in the 40 keV group were the highest, which were 50.4±15.7 and 59.3±18.4 respectively, and the difference was statistically significant ( P<0.001). Subjective scores showed statistically significant differences among the 5 groups (χ2=101.61, P<0.001). The score of the 40 keV group was higher than that of the 60 keV group, 70 keV group, and conventional group ( P<0.001), and there was no significant difference when compared with the subjective score of the 50 keV group ( P>0.05). Conclusions:The 40 keV monochromatic image of dual detector spectral CT is the best image to observe the lumen of the stent after TIPS.