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, 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.