To evaluate virtual non-contrast (VNC) accuracy at multiple radiation doses and iodine concentrations in a head CT phantom using dual-energy integrating-detector CT (EID-CT; TwinSpiral DECT) and photon-counting detector CT (PCD-CT).
Materials and Methods
A cylindrical head-sized acrylic CT phantom with brain tissue inserts and iodine (0, 43.75, 175, and 350 mg/mL; 87.5 mg/mL was excluded due to beam-hardening artifacts) was scanned three times on each system at 100%, 80%, 75%, 65%, 50%, and 25% of the standard radiation dose to generate mixed and VNC images. Attenuations (HU) were measured in standard and corresponding VNC images; signed and absolute VNC errors were analyzed with two-way ANOVA (dose, iodine) with Tukey post hoc tests (p < .05), using nonparametric alternatives when assumptions were violated. Phantom HU for fat, bone, and white matter at 100% dose on EID-CT were compared with 16 patient scans to confirm realism.
Results
Radiation dose significantly affected VNC errors in both scanners, but only 25% versus 100% dose in PCD-CT was significant after Tukey (p = .0383); no pairwise dose differences were significant in EID-CT (p ≥ .07). Iodine concentration had a stronger effect. In EID-CT, 350 mg/mL differed from 0, 43.75, and 175 mg/mL (p < .001), with errors up to +13.7 ± 1.1 HU. In PCD-CT, 175 and 350 mg/mL differed from 0 mg/mL (p < .05) and from 43.75 mg/mL (p < .001), with a negative bias up to −10.6 ± 1.5 HU.
Conclusions
Dose reduction had limited impact on VNC accuracy, whereas high iodine (175–350 mg/mL) caused significant errors with opposite signed biases (EID-CT overestimation, PCD-CT underestimation). Both scanners still achieved substantial visual contrast removal.
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