RESUMO
Objective:To investigate the feasibility of using spectral CT chest enhancement venous phase images to obtain virtual non-contrast (VNC) images and virtual arterial phase images to achieve one phase scan instead of three phase scans.Methods:Imaging data of 100 patients who underwent spectral CT chest plain and dual-phase enhancement scans at the First Affiliated Hospital of Kunming Medical University from January to May 2022 were analyzed retrospectively. The venous phase images of all patients were post-processed to obtain virtual non contrast (VNC) and 40 keV virtual mono-energy images (VMI) for simulated arterial phase images (Vart). Image quality and lesion detection were compared between true non-contrast (TNC) and VNC images, and conventional arterial phase (CIart) and Vart images by paired t-test, Wilcoxon test and McNemar test. Objective evaluation indexes of image quality included thoracic aorta, all levels of pulmonary artery, T4 vertebral bone cancellous, chest wall fat CT value, background noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR); the subjective score of image quality was assessed by double-blind method on a 5-point scale; the assessment of lesion detection included the detection rate of calcified foci and pulmonary nodules size, density, volume, percentage of solid components and imaging characteristics. Results:Except for chest wall fat and T4 vertebral bone cancellous, the differences in CT values between VNC and TNC images were not statistically significant ( P>0.05); Except for right upper pulmonary artery and right lower pulmonary artery, the differences in background noise values and SNR between TNC images and VNC images were statistically significant ( P<0.05). Compared with CIart images, the CT values of chest wall fat were lower in Vart images ( P<0.05), and the CT values of the remaining sites were significantly higher ( P<0.05); the background noise values of all sites on Vart images were smaller than those on CIart images, and the SNR and CNR values were higher than those on CIart images ( P<0.05).The differences of subjective scores of images quality were not statistically significant between TNC and VNC images, between CIar and Vart images ( P>0.05). Taking TNC as the standard, the overall detection rate of VNC for calcification was 88.53% (301/340). Except for the short diameter of partially solid nodules, the differences of qualitative and quantitative assessment indexes of lung nodules between TNC and VNC images were not statistically significant ( P>0.05). Conclusions:Spectral CT chest venous phase 40 keV VMI can simulate arterial phase images in the diagnosis of vascular lesions, and venous phase VNC basically meets the standard of conventional plain scan, so it is feasible to replace plain scan, arterial phase and venous phase images in a certain range.