Diagnostic performance and dose reduction of virtual noncontrast imaging in pediatric computed tomography urography

Computed tomography urography (CTU) is critical to diagnosis in pediatric urology, but conventional four-phase protocols entail substantial cumulative radiation exposure. Minimizing radiation while preserving diagnostic efficiency is paramount in pediatric imaging. This study aimed to evaluate the diagnostic performance of dual-source dual-energy computed tomography (DECT)-derived virtual noncontrast (VNC) images as a substitute for true noncontrast (TNC) images and to assess the feasibility of omitting the unenhanced scans in pediatric CTU.

This retrospective, single-center, intraindividual paired comparative study reviewed 217 consecutive pediatric patients who underwent four-phase dual-source DECT urography between June 2022 and December 2024. The protocol included a TNC scan, dual-energy corticomedullary/arterial and nephrographic/venous phases (reconstructed from the arterial phase and venous phase, respectively), and an excretory phase. The computed tomography (CT) attenuation, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and subjective image quality scores were compared between VNC and TNC images across normal anatomical structures and various urological lesions (tumors, hydronephrosis, cysts, calculi, trauma, and malformations). Statistical analyses included paired the Student t-test, Wilcoxon signed-rank test with Bonferroni correction, the intraclass correlation coefficient (ICC), Bland-Altman analysis, and the Cohen kappa statistic. Radiation dose reduction was evaluated via the paired t-test.

VNC significantly underestimated the CT attenuation of renal calculi compared to TNC [mean difference ~330 Hounsfield units (HU)]. Subcutaneous fat attenuation was slightly higher on VNC (mean bias <2.82 HU; P<0.001). For other soft-tissue regions, VNC attenuation was slightly lower than TNC (difference <8.62 HU), showing moderate-to-excellent agreement. VNC yielded lower image noise (P<0.001) and a similar or higher CNR when compared with TNC scans. Subjective image quality scores for VNC images were ≥3 in all but one patient, satisfying diagnostic requirements. Omitting the baseline TNC phase reduced the cumulative effective radiation dose by 24.6% (from 7.98±1.71 to 6.02±1.28 mSv).

DECT-derived VNC and conventional TNC images demonstrate comparable density resolution and overall image quality, with no significant differences in SNR, CNR, or noise between the two VNC phases (P>0.017). VNC can safely replace TNC scans for routine anatomical evaluation and lesion detection in pediatric CTU, significantly reducing the radiation dose. However, a TNC scan remains necessary for the accurate quantitative assessment of renal calculi.