Assessment of the Image Quality of Virtual Non-Contrast Dual-Energy CT Liver Scans Using Both PSNR and SSIM Methods

The purpose of this study was to investigate the feasibility of replacing true non-contrast (TNC) dual-energy computed tomography (DECT) images with virtual non-contrast (VNC) DECT images by comparing their quality on the basis of both the peak signal-to-noise ratio (PSNR) and structural similarity index (SSIM). Methods: A prospective analysis was conducted on TNC and enhanced three-phase DECT images of the livers of 33 patients. Post-processing was used to obtain the arterial-phase (VNCa), venous-phase VNC (VNCv), and delayed-phase VNC (VNCd) images. Both the PSNR and SSIM methods were used to compare the overall and local TNC and three-phase VNC images. The CT numbers and noise values (standard deviation) of the liver and erector spinae muscle were measured, and the SNR and contrast-to-noise ratio (CNR) were calculated. The dose length product values of the TNC and enhanced three-phase VNC scans were recorded, and the objective evaluation indicators and radiation doses of the three-phase VNC and TNC images were compared. Bland-Altman scatter plots were drawn to analyze the consistency of the liver CT numbers, SNRs, and CNRs. Results: The overall comparison of the three-phase VNC and TNC images showed PSNR values of (18.01±1.06), (18.33±0.99), and (18.20±1.04) and SSIM values of (0.76±0.04), (0.77±0.03), and (0.78±0.04), with the differences being not statistically significant. The local comparison of these images showed PSNR values of (29.90±2.50), (30.97±2.34), and (30.61±2.76) and SSIM values of (0.75±0.04), (0.77±0.03), and (0.77±0.04), and the differences were also not statistically significant. The CT number of the liver in the three-phase VNC image was higher than that in the TNC image. The CNR of the three-phase VNC image and the SNR of the VNCv image were not statistically different from those of the TNC image (P>0.05), and the liver CT numbers, SNRs, and CNRs in the three-phase VNC and TNC images were highly consistent. Using the VNC+three-phase enhancement scheme can reduce the radiation dose by approximately 29.63% by removing the TNC part. Conclusion: The VNC DECT image of the liver is of good quality and can accurately reproduce the TNC image, meeting clinical diagnostic needs.