Reevaluating diagnostic confidence: the impact of delayed excretory phase imaging in CT urography on detecting renal and urinary tract abnormalities.

Objective: To assess the diagnostic value of the delayed excretory phase in computed tomography urography (CTU) for detecting renal and urinary tract abnormalities and its impact on readers' confidence in patients with hematuria, given concerns about radiation exposure, cost, and limited added benefit.

Methods: This IRB-approved, HIPAA-compliant retrospective cross-sectional study included 489 CTU exams performed at a quaternary center between 2012 and 2023. Each scan included non-contrast, nephrographic, and delayed phases. Six radiologists with varying experience independently reviewed exams in two sessions: Session 1 (without delayed phase) and Session 2 (with delayed phase), separated by a minimum three-week washout period. Abnormalities were assessed using standardized criteria; diagnostic confidence was rated (0-100%). Analyses included McNemar's test, mixed-effects logistic regressions, and Wilcoxon signed-rank tests; p < 0.05 was statistically significant.

Results: No significant differences were found in detecting most abnormalities between sessions. Cystic renal masses were more often detected in Session 1 (p = 0.05, OR = 1.40, 95% CI: 0.99-1.98). Detection increased in Session 2 for renal (p = 0.002, OR = 0.35) and ureteral congenital anomalies (p = 0.004, OR = 0.30). Intermediate-experience readers had lower odds of detecting renal (OR = 0.09) and cystic masses (OR = 0.08); experienced readers missed more ureteral anomalies (OR = 0.21). Delayed imaging did not improve overall detection or reader performance. Diagnostic confidence was lower in Session 2 (p < 0.001), particularly among less experienced readers.

Conclusion: The delayed excretory phase in CTU modestly improved detection of congenital anomalies but did not enhance identification of ureteral or bladder lesions or diagnostic confidence. Selective use may reduce radiation exposure without compromising diagnostic performance.