Accuracy of virtual non-contrast images from dual-energy integrating detector CT and photon-counting detector CT at high iodine concentrations: a head phantom study

Objectives To evaluate the accuracy of virtual non-contrast (VNC) images at multiple radiation doses and high iodine concentrations using a head CT phantom with dual-energy integrating detector CT (EID-CT; TwinSpiral DECT) and photon-counting detector CT (PCD-CT). Materials and Methods An anthropomorphic head phantom containing brain tissue inserts and varying iodine concentrations (43.75, 175 and 350 mg/ml) was scanned three times with EID-CT and PCD-CT at 100%, 80%, 75%, 65%, 50%, and 25% radiation dose from which standard (mixed) and VNC images were obtained. Attenuations (HU) were measured in standard CT and corresponding VNC images, and both absolute and signed errors of VNC were calculated. For statistical analysis, data were reshaped from wide to long format. Two-way ANOVAs were conducted, considering signed and absolute errors with radiation dose and iodine concentration as factors. Post hoc Tukey tests were applied if p < 0.05. Normality and homoscedasticity were checked via residual diagnostics. If assumptions were violated, nonparametric methods were used. Additionally, HU of fat, bone, and white matter from EID-CT at 100% dose were compared with 16 patient scans to confirm phantom realism. Results ANOVA showed radiation dose significantly affected VNC errors in both scanners, though only 25% vs. 100% dose in PCD-CT was significant (p = 0.0383) after post-hoc Tukey; in EID-CT, no pairwise dose differences were significant (p ≥ 0.07). Iodine concentration exerted a stronger influence: in EID-CT, 350 mg/ml differed from 0, 43.75, and 175 mg/ml (p < 0.001), producing errors up to + 13.7 ± 1.1 HU. In PCD-CT, 175 mg/ml and 350 mg/ml differed from 0 mg/ml (p < 0.05) and from 43.75 mg/ml (p < 0.001), showing a negative bias up to − 10.6 ± 1.5 HU. While dose reductions had limited impact on overall VNC accuracy, higher iodine concentrations (175, 350 mg/ml) caused significant errors in both scanners, albeit with opposite signed biases. Conclusions High iodine concentrations caused significant VNC errors in both scanners—EID-CT overestimating and PCD-CT underestimating the standard baseline—yet both provided substantial visual contrast removal, with radiation dose reductions only rarely impacting accuracy.