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

Objectives: 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).
Methods: 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 (VMI ₄₀ ), 55 keV (VMI ₅₅ ), and 70 keV (VMI ₇₀ ). 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.
Results: 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 VMI ₄₀ , followed by VMI ₅₅ , VMI ₇₀ , and PCI. When VMI ₄₀ 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).
Conclusions: The lowest monoenergetic images (VMI ₄₀ ) provided the best CNR on dlDE-CTE. Furthermore, the diagnostic performance for diagnosing active CD can be significantly improved with the addition of VMI ₄₀ .
Key Points: • CNR for both normal and abnormal bowel walls is greatest on VMI ₄₀ . • Subjective image quality on VMI ₄₀ is better than those on PCI. • When VMI ₄₀ images are added to PCI, radiologists' diagnostic performance can be improved.