Virtual Noncontrast Photon-counting CT Lung Attenuation Matches True Noncontrast

Virtual noncontrast photon-counting CT lung images agree with true noncontrast for lung volume and attenuation; after adjusting for inspiratory depth, 95% limits of agreement were -12.6 to 10.5 HU. Inspiratory depth, not reconstruction, drives variability.

• In 83 patients, mean lung volume did not differ between virtual and true noncontrast images (4143 vs 4111 mL, P = .41), and mean attenuation was similar (-799 vs -798 HU, P = .91).
• After inspiratory depth adjustment, attenuation differences narrowed to a mean of -1.1 HU ± 5.9, with 95% limits of agreement -12.6 to 10.5 HU, versus -0.8 HU ± 19.5 and -39.1 to 37.5 HU before adjustment.
• Density class analysis showed slight underestimation of emphysematous areas (median -0.4%, P < .001) and overestimation of normal-attenuation lung (median +0.8%, P < .001) on virtual noncontrast, with minimal voxel-wise differences within parenchyma.

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