Virtual monoenergetic dual-layer, dual-energy CT enterography: optimization of keV settings and its added value for Crohn's disease

To determine the optimal keV on dual-layer, dual-energy CT enterography (dlDE-CTE) and to investigate the added value of virtual monoenergetic images (VMIs) for the diagnosis of active Crohn's disease (CD). We collected 76 patients (including 45 CD patients) who underwent dlDE-CTE. CD was diagnosed using ileocolonoscopy. Conventional polychromatic images (PCI) were reconstructed using an iterative reconstruction algorithm at 120 kVp, and VMI at 40 keV (VMI40), 55 keV (VMI55), and 70 keV (VMI70). Contrast-to-noise ratio (CNR) was compared using Kruskal-Wallis test. Three radiologists independently reviewed PCI and subsequently combined PCI and the optimized VMI for the diagnosis of active CD using a 5-point scale. Multi-reader multi-case receiver operating characteristic analysis was performed. Mean +/- standard deviation of CNRs for both normal (13.6 +/- 6.5, 6.1 +/- 3.2, 2.0 +/- 2.1, 1.9 +/- 1.6; P < 0.001) and abnormal (9.4 +/- 7.3, 6.5 +/- 4.8, 4.9 +/- 3.1, 3.7 +/- 2.3; P < 0.001) bowels were significantly greatest on VMI40, followed by VMI55, VMI70, and PCI. When VMI40 were added to PCI, overall area-under-the-curve of the three radiologists was significantly improved from 0.891 to 0.951 for diagnosing active CD (P=0.009). The lowest monoenergetic images (VMI40) provided the best CNR on dlDE-CTE. Furthermore, the diagnostic performance for diagnosing active CD can be significantly improved with the addition of VMI40. aEuro cent CNR for both normal and abnormal bowel walls is greatest on VMI (40) . aEuro cent Subjective image quality on VMI (40) is better than those on PCI. aEuro cent When VMI (40) images are added to PCI, radiologists' diagnostic performance can be improved.