Research papersImage quality evaluation of dual-layer spectral detector CT of the chest and comparison with conventional CT imaging

- Mono-energetic reconstructions in dual-layer spectral detector CT improve image quality compared to poly-energetic images.
- Noise levels and CNR were better for mono-energetic reconstructions compared to conventional images in contrast-enhanced chest CT.
- Whether mono-energetic images have added diagnostic value compared to conventional images, is still unknown.

ObjectivesTo evaluate image quality parameters of virtual mono-energetic (MonoE) and conventional (CR) imaging derived from a dual-layer spectral detector CT (DLCT) in oncological follow-up venous phase imaging of the chest and comparison with conventional multi-detector CT (CRMDCT) imaging.Materials and methodsA total of 55 patients who had oncologic staging with conventional CT and DLCT of the chest in venous phase were included in this study. Established image quality parameters were derived from all datasets in defined thoracic landmarks. Attenuation, image noise, and signal-/contrast- to noise ratios (SNR, CNR) were compared between CRDLCT and MonoE as well as CRMDCT imaging. Two readers performed subjective image analysis.ResultsCRMDCT showed significant lower attenuation values compared to CRDLCT and MonoE at 40-70 keV (p ≤ 0.05). Moreover, MonoE at 40-70 keV revealed significantly higher attenuations values compared to CRDLCT (p < 0.001). Noise was statistically lower in CRMDCT compared with CRDLCT and MonoE at 40 keV (11.4 ± 2.3 HU vs. 12.0 ± 3.1 HU vs. 11.7 ± 5.2 HU; p < 0.001). In contrast, all MonoE levels showed significantly lower noise levels compared to CRDLCT (p < 0.001). SNR was not significantly different between CRMDCT and CRDLCT (13.5 ± 3.7 vs. 14.4 ± 5.3; p > 0.99). SNR values were significantly increased for MonoE at 40-80 keV compared to CRMDCT and CRDLCT (p < 0.001). CRDLCT and MonoE (40-70 keV) from DLCT revealed significantly higher CNR values than CRMDCT (p < 0.001). In subjective analysis, MonoE at 40 keV surpassed all other image reconstructions except for noise in MonoE at 70 keV.ConclusionIn dual-layer spectral detector CT, MonoE at low keV showed superior image quality compared to conventional images derived from the same system and may therefore be added to clinical routine imaging protocols. Whether MonoE reconstructions yield additional diagnostic information is still unknown.