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

ABSTRACT

AIM: To compare the quality of virtual mono-energetic (VMI) and polychromatic images reconstructed with hybrid iterative (PCIHIR) or model-based reconstruction (PCIMBR) 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 PCIHIR, PCIMBR and VMI40keV, VMI70keV, and VMI100keV images. Contrast, noise, and visualization of soft-plaque, and macro-/micro-calcifications were scored in a blinded reading by two radiologists. RESULTS: VMI40keV yielded highest S-/CNR (p≤0.001). VMI70keV and PCIMBR showed comparable SNR (p≥0.999) and yielded higher SNR than PCIHIR. VMI70keV yielded higher CNR than PCIHIR (p<0.001) and PCIMBR (p<0.045). VMI100keV yielded lowest CNR (p≤0.001) and SNR (p≥0.104). In the subjective analysis, VMI40keV outperformed PCIMBR for contrast and noise, PCIMBR scored better than VMI70keV, and the latter scored better than PCIHIR for these categories (all p<0.001). PCIMBR was superior for depiction of soft-plaque and micro-calcifications (p<0.001). VMI100keV visualized micro-calcifications second best (p<0.001) and matched PCIMBR for the depiction of macro-calcifications (p>0.999), while VMI40keV scored second best for depiction of soft-plaque (p<0.020). CONCLUSIONS: VMI40keV and VMI70keV yield better S-/CNR than PCIHIR and PCIMBR; however, PCIMBR visualized arteriosclerotic plaques best, followed by VMI40keV for depiction of soft-plaque and VMI100keV for macro- and micro-calcification. Based on the present findings, PCIMBR on conventional CT and VMI40keV supplemented by VMI100keV on SDCT are recommended for the diagnostic assessment of abdominal arteries.