Feasibility of replacing true non-contrast images with virtual non-contrast images in quantitative analysis of emphysema.

Objective: To evaluate the performance of virtual non-contrast (VNC) images in comparison with true non-contrast (TNC) images in dual-energy computed tomography (DECT) for the assessment of emphysema quantification.

Materials and methods: A retrospective analysis was conducted of 57 patients who underwent three-phase chest CT. The VNC images of the arterial phase (VNC(AP)) and venous phase (VNC(VP)) were generated on an AW4.7 workstation. The objective assessment of image noise in TNC and VNC images was conducted through the quantification of image quality, which was then subjected to a double-blind review by two physicians for image quality and visual classification of emphysema. Furthermore, quantified emphysema at three distinct thresholds (950 HU, 930 HU, and 910 HU) using the three sets of images was compared. Bland-Altman plots were used to compare the quantitative discrepancies at the -950HU threshold.

Results: There was no statistically significant difference in subjective image quality and emphysema visual classification between TNC and VNC images (all p > 0.05). In the quantitative measurement, no statistical difference was observed in image noise or total lung volume among the three groups. When compared with TNC, VNC(VP) images demonstrated no statistical difference in 15th percentile lung density (Perc 15), low attenuation volume (LAV), percentage of low attenuation area (LAA%), and mean lung density (MLD; all p > 0.05). The use of VNC images was found to reduce the radiation dose by 32.6%.

Conclusion: The use of VNC, particularly VNC(VP) images, in chest CT has the potential to supplant TNC for the quantitative assessment of emphysema, thereby streamlining scans and reducing radiation dose.