Characteristics of liver virtual non-contrast images from three-phase dynamic CT obtained with second-generation dual-layer spectral CT

Objective To clarify the characteristics of virtual non-contrast (VNC) images generated from each phase of triphasic dynamic liver computed tomography (CT) using second-generation dual-layer spectral CT (DLCT). Methods A second-generation DLCT system, the Spectral CT 7500, was used for the three-phase dynamic liver CT examination of 31 patients from August 2024 to February 2025. VNC images were generated from the arterial phase (AP), portal venous phase (PVP), and equilibrium phase (EP). For a quantitative evaluation, the agreement between liver parenchymal CT values from the VNC images created from the three phases and the true non-contrast (TNC) images was assessed by a Bland-Altman analysis (pre-set clinical limit: ±10 HU). In the qualitative evaluation, five parameters (vascular remnants, visibility of the portal and hepatic veins, image noise, image distortion, and overall image quality) were assessed using a four-point rating scale. Results In the quantitative analysis, the mean difference (bias) between the VNC and TNC images was −2.19 for AP, −0.14 for PVP, and −2.11 HU for EP, and the 95% limits of agreement were within the pre-set clinical limit for all phases. In the qualitative analysis, vascular remnants were significantly more pronounced in the AP and PVP compared to the EP. Consequently, vessel visibility and overall image quality were significantly higher in the VNC images derived from the EP. Conclusion Although incomplete removal of vascular contrast enhancement was noted (arterial in the AP and venous in the PVP/EP), VNC images from DLCT are quantitatively interchangeable with TNC images.