[Impact of Contrast Enhancement and Arterial Diameter on CT Values of Virtual Non-contrast Images in Abdominal Dynamic CT Examinations with Fast kV-switching Dual-energy CT].

PURPOSE: The purpose of this study was to evaluate the impact of contrast enhancement and arterial diameter on the attenuation values of virtual non-contrast (VNC) images (HUVNC) obtained from abdominal dynamic computed tomography (CT) examinations using a rapid kilovolt-switching dual-energy CT system.

METHODS

Seventy-keV virtual monoenergetic (VME) and VNC images were reconstructed from scanned raw data of the unenhanced, arterial, portal, and delayed phases. Circular regions of interest (ROIs) were placed on four arteries of different diameters (abdominal aorta: 20 mmϕ, common iliac artery: 10 mmϕ, superior mesenteric artery: 5 mmϕ, and inferior mesenteric artery: 2.5 mmϕ) at the same anatomical level between each contrast enhancement level. The attenuation values and standard deviations of the VME images (HUVME) and HUVNC in each ROI were measured. VNCError, the differences between HUVME in the unenhanced phase and HUVNC in each contrast enhancement level, was calculated.

RESULTS

HUVME decreased as the contrast enhancement level declined, regardless of the arterial diameter. Similarly, the HUVME in the same contrast enhancement level decreased as the arterial diameter decreased. This tendency was particularly evident at high contrast enhancement levels. As arterial diameter decreased or the contrast enhancement level increased, HUVNC and VNCError increased. At HUVME of 400 Hounsfield unit (HU), the maximum VNCError was 78.47 HU at 2.5 mmϕ and 6.68 HU at 20 mmϕ. At HUVME of 130 HU, the influence on HUVNC was smaller than at other contrast enhancement levels, with VNCError of no more than 13.67 HU at 2.5 mmϕ.

CONCLUSION

This study suggests that HUVNC increases are significantly affected by both the contrast enhancement and arterial diameter, especially at high contrast enhancement levels and in narrow arteries.