Utilization of virtual mono-energetic images (MonoE) derived from a dual-layer spectral detector CT (SDCT) for the assessment of abdominal arteries in venous contrast phase scans

Abstract

Objectives: To investigate the utilization of virtual mono-energetic images (MonoE) at low kiloelectron volt (keV) levels derived from a dual-layer spectral detector CT (SDCT) for the assessment of abdominal arteries in venous contrast phase scans using arterial phase imaging as an internal reference standard.

Materials and methods: A total of 50 patients who received arterial and venous phase imaging of the abdomen on a SDCT system were included in this study. Absolute attenuation, noise, signal- and contrast to noise ratios (SNR; CNR) as well as arterial diameters in defined landmarks were assessed. In arterial phase, conventional reconstructions (CR_ART) as well as MonoE_ART at 40keV and in venous phase, conventional reconstructions (CR_VEN) as well as MonoE_VEN at 70 and 40keV were investigated and intra-individual comparisons were performed. If an artery stenosis (10 patients) was present, the degree of stenosis was assessed according to the system of the North American Symptomatic Carotid Endarterectomy Trial (NASCET).

Results: MonoE 40keV yielded significantly higher attenuation values (in arterial as well as in venous phase) compared to CR_ART (p<0.001) while noise levels were substantially low. This resulted in markedly superior SNR and CNR in large vessel compared to CR_ART. Luminal diameters were significantly smaller in MonoE 40keV in both contrast phases compared to CR_ART (p<0.001), whereas no significant differences were found between both MonoE reconstructions (p≥0.92). The degree of vessel stenosis was significantly higher in MonoE 40keV of both contrast phases compared to CR_ART (p≥0.02).

Conclusion: MonoE at low keV of venous contrast phase scans derived from a novel SDCT are suitable for the assessment of arteries in the abdomen and subsequent stenosis assessment. However, MonoE at 40keV constantly showed significant smaller luminal diameters than the corresponding conventional reconstructions (including the reference standard). This is possibly due to an improved differentiation of the vessel lumen from the wall and raises the question, which imaging technique should be used as an appropriate reference standard for vascular SDCT imaging studies.

Keywords: Abdominal imaging; Artery stenosis; Dual energy CT; Spectral detector CT; Venous contrast phase.