To investigate the effect of different monochromatic image on the image quality of renal artery with dual-layer detector spectral CT, defining the optimal monochromatic image.

The imaging data of 40 patients with renal artery computerized tomography angiography by dual-layer spectral CT were retrospectively analyzed. The CT values and noise (SD) values of renal artery trunk and the same layer psoas major muscle were measured on conventional arterial phase images and 40, 50, 60, 70 keV monochromatic images, and the SNR and CNR of the images were calculated. Besides, two radiologists with more than 8 years of diagnosis experiences made subjective scoring on the images. One-way ANOVA was used to compare the CT values and SD values, the SNR and CNR between conventional images and four groups of monochromatic images, evaluating the optimal monochromatic images for renal artery display.

The CT value, SNR and CNR of renal artery trunk in 40, 50 and 60 keV groups were significantly higher than those in the conventional group, with statistical significance (P<0.05); The SD value of renal artery trunk and CT value of psoas major muscle in 40 and 50 keV group were higher than those in the conventional group, with statistical significance (P<0.05), and the CT value, SNR and CNR were the highest in 40 keV group. Subjective score results showed that 40 keV had the highest, the sharpest vascular edge and the most branching vessels.

40 keV is the optimal monochromatic image on the image quality of renal artery with dual-layer detector spectral CT.