To investigate the optimal single-energy image of IQon dual-layer spectral detector CT in stent evaluation after transjugular intrahepatic portosystemic shunt (TIPS).

Imaging data of 30 patients with portal hypertension who underwent spectral CT scan of the upper abdomen in the Third Affiliated Hospital of Sun Yat-sen University from March to September 2020 were retrospectively analyzed. Among them, 18 patients were male and 12 female, aged from 38 to 72 years, with a median age of 46 years. The informed consents of all patients were obtained and the local ethical committee approval was received. The single-energy images of 40-100 keV (interval of 10 keV) and 100-200 keV (interval of 20 keV) were reconstructed at the post-processing workstation using the spectral CT data of portal venous phase. The stent curved planar reconstruction was performed with the conventional images and 12 groups of single-energy images. The CT value and noise value in the lumen and erector spinae of the same layer were measured. The contrast-to-noise ratio (CNR) of images of 13 groups was calculated. The degree of intraluminal artifacts and diagnostic confidence were scored subjectively by 2 radiologists with more than10 years' experience. The image quality evaluation indexes were compared by one-way ANOVA, LSD-t test or Friedman test. The consistency of subjective evaluation of image quality was assessed by Kappa test.

With the decrease of energy level, the intraluminal CT value of TIPS stent was gradually increased. The CT values of 80-200 keV images were significantly lower than those of conventional images (LSD-t=-2.6, -5.3, -7.1, -9.2, -10.4, -11.1, -11.6, -12.1; P<0.05). The intraluminal CT values of 40-60 keV images were significantly higher than those of conventional images (LSD-t=36.7, 18.5, 7.8; P<0.05). With the decrease of energy level, the intraluminal SD value was gradually increased. The SD values of 80-200 keVimages were significantly lower than those of conventional images (LSD-t=-4.4, -5.1, -6.0, -6.6, -6.1, -6.3, -6.3, -6.3; P<0.05). The intraluminal SD value images of 40 keV was significantly higher than those of conventional images (LSD-t=4.5, P<0.05). With the decrease of energy level, the CNR of stent was gradually increased. The stent CNR values of 90-200 keV images were significantly lower than those of conventional images (LSD-t=-2.2, -3.6, -5.4, -6.1, -6.0, -6.1, -6.2; P<0.05). The stent CNR values of 40-70 keV images were significantly higher than those of conventional images (LSD-t=22.7, 16.7, 8.4, 3.4; P<0.05). The diagnostic confidence score of each group showed that the subjective scores in 90-140 keV group were significantly higher than those in conventional image group (χ²=292.1, 302.8, 343.7, 270.8; P<0.05). The subjective score of 120 keV group was the highest. The consistency of subjective scores betweentwo radiologists was high (κ=0.81). For the subjective score of intraluminal artifacts, the subjective scores of 90-200 keV group were significantly higher than those of conventional image group (χ²=207.2, 240.1, 260.5, 281.6, 302.0, 322.4, 322.6; P<0.05). The consistency of subjective scores between two radiologists was high (κ=0.85).

Single-energy images reconstructed based on spectral CT can effectively reduce the intraluminal artifacts of stents after TIPS, and improve the diagnostic confidence and image quality. Images of 120 keV are the optimal single-energy images.