Arterial Phase CTA Replacement by a Virtual Arterial Phase Reconstruction from a Venous Phase CTA: Preliminary Results Using Detector-Based Spectral CT

Objective: To assess the feasibility of creating virtual monoenergetic arterial images from venous phase CTA obtained on a detector-based spectral CT scanner and quantitatively compare the signal-to-noise (SNR) and contrast-to-noise (CNR) ratios of the major arteries to those on polyenergetic true arterial phase images. Methods: In this retrospective study, 23 patients (15 men and 8 women, median age 68 years) who underwent triple-phase CTA on a spectral CT scanner for aortic endograft surveillance were included. The venous phase CTA of each study was reconstructed to generate virtual monoenergetic images at various keV, which were compared to true arterial phase CTA images. SNR and CNR of the aortoiliac arteries were evaluated by testing the differences in means and non-inferiority of virtual arterial images to true arterial images. Effective radiation dose was calculated for standard triple-phase studies in comparison with dual-phase and single-phase spectral CT examinations. Results: Virtual monoenergetic images demonstrated non-inferior (P < 0.05) arterial SNR and CNR compared to true arterial images at 40 keV for all arteries, at 45–50 keV for the thoracic and suprarenal aorta, and at 45–55 keV for the infrarenal aorta and iliac arteries. Significantly higher (P < 0.05) arterial attenuation was obtained at 40 keV for the aortoiliac arteries. Mean effective dose for conventional triple-phase studies was 32.5 mSv in comparison with 21.3 mSv for dual-phase non-contrast/venous scans and 11.3 mSv for single-phase venous scans. Conclusions: Detector-based spectral CT enables creation of virtual monoenergetic arterial images from venous phase CTA with equivalent and in some cases significantly higher SNR/CNR of major arteries compared to images from true arterial phase polyenergetic CTA.