Virtual mono-energetic images and iterative image reconstruction: abdominal vessel imaging in the era of spectral detector CT.

Aim: To compare the quality of virtual mono-energetic (VMI) and polychromatic images reconstructed with hybrid iterative (PCI _HIR ) or model-based reconstruction (PCI _MBR ) derived from dual-layer spectral detector computed tomography (SDCT) in arterial phase images to visualise the aorta and abdominal main branches.
Material and Methods: A retrospective review of 50 patients with abdominal arterial phase scans was undertaken. Attenuation, intraluminal noise, and signal-/contrast-to-noise ratio (S-/CNR) were assessed in the PCI _HIR , PCI _MBR and VMI _40keV , VMI _70keV , and VMI _100keV images. Contrast, noise, and visualization of soft-plaque, and macro-/micro-calcifications were scored in a blinded reading by two radiologists.
Results: VMI _40keV yielded highest S-/CNR (p≤0.001). VMI _70keV and PCI _MBR showed comparable SNR (p≥0.999) and yielded higher SNR than PCI _HIR . VMI _70keV yielded higher CNR than PCI _HIR (p<0.001) and PCI _MBR (p<0.045). VMI _100keV yielded lowest CNR (p≤0.001) and SNR (p≥0.104). In the subjective analysis, VMI _40keV outperformed PCI _MBR for contrast and noise, PCI _MBR scored better than VMI _70keV, and the latter scored better than PCI _HIR for these categories (all p<0.001). PCI _MBR was superior for depiction of soft-plaque and micro-calcifications (p<0.001). VMI _100keV visualized micro-calcifications second best (p<0.001) and matched PCI _MBR for the depiction of macro-calcifications (p>0.999), while VMI _40keV scored second best for depiction of soft-plaque (p<0.020).
Conclusions: VMI _40keV and VMI _70keV yield better S-/CNR than PCI _HIR and PCI _MBR ; however, PCI _MBR visualized arteriosclerotic plaques best, followed by VMI _40keV for depiction of soft-plaque and VMI _100keV for macro- and micro-calcification. Based on the present findings, PCI _MBR on conventional CT and VMI _40keV supplemented by VMI _100keV on SDCT are recommended for the diagnostic assessment of abdominal arteries.
(Copyright © 2020 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.)