Defining window settings for abdominopelvic photon-counting CT virtual monoenergetic imaging: quantitative and qualitative evaluation.

BACKGROUND

Virtual monoenergetic images (VMIs) at 60 keV are recommended for contrast-enhanced soft tissue imaging with decreased radiation dose on clinical photon-counting CT (PCCT). However, 60 keV VMIs appear brighter with default windowing compared to standard 120-kV CT, necessitating manual window adjustments.

OBJECTIVE

To determine optimal soft tissue and liver window settings for PCCT abdominopelvic imaging at 60 and 70 keV, and to quantitatively and qualitatively evaluate default versus optimal windowing.

METHODS

With IRB approval, retrospective analysis was performed on dual-phase abdominopelvic PCCT 60 and 70 keV VMIs from 39 patients. Three radiologists manually adjusted center/width (C/W) settings for optimal soft tissue and liver visualization. Contrast-to-noise ratio (CNR) was quantified for each phase and keV level, and display-CNR (dCNR) was quantified across multiple windows: PACS default and optimal windows for soft tissue and liver, and vendor-recommended soft tissue windowing. Readers ranked datasets viewed in different windows from most to least preferred and assigned an overall impression (optimal, acceptable, or poor). Expected ranking and impression scores were analyzed, with p-values < 0.05 indicating statistical significance.

RESULTS

Mean CNR increased by 24-27 % (p < 0.001) on 60 keV compared to 70 keV images. With default soft tissue windowing, dCNR at 60 keV decreased by 7 % (arterial) and increased by 19 % (venous) compared to 70 keV but increased by 51 % (arterial) and 27 % (venous) with optimal windowing. Liver dCNR decreased by 10-14 % at 60 keV using default windowing but increased by 75-92 % with optimal windowing on both phases. 60 keV images viewed at optimal windowing scored significantly better in terms of both ranking and impression compared to the default windowing for both soft tissue and liver evaluation on both phases (p < 0.001).

CONCLUSION

Optimized window settings significantly enhance soft tissue and liver visualization on PCCT VMIs, particularly at 60 keV.