Soft-tissue and half-value windows outperform bone window in ureteral stone size measurements in non-enhanced computed tomography

BackgroundInterreader variability in ureteral stone size measurements affect the predicted probability of spontaneous stone passage (SSP), especially in proximal ureteral stones. Window settings have been shown to influence interreader variability.PurposeTo investigate interreader variability of ureteral stone size measurements in four different window settings.Material and MethodsPatients with a unilateral proximal ureteral stone ≥2.0 mm detected during emergency computed tomography (CT) were included in this single-center study. Five observers measured each stone in three dimensions in a soft-tissue window, bone window, and two half-value windows (based on the mean [half-value MEAN] or maximum attenuation of the stone [half-value MAX]). Limits of agreement of the mean (LOAM) for stone size in each window setting were assessed. Logistic regression curves were created for predicted probability of SSP.ResultsIn total, 124 patients (87 men, 37 women; mean age = 52 years; age range = 22-82 years) were retrospectively evaluated. LOAM: bone window (±1.6 mm, 95% confidence interval [CI]=1.24-4.90), soft-tissue window (±0.4 mm, 95% CI=0.37-0.82), half-value MEAN window (±0.3 mm, 95% CI=0.24-0.40), half-value MAX window (±0.2 mm, 95% CI=0.14-0.30). Prediction curves aligned and shifted to the left as mean stone size decreased in the half-value window settings.ConclusionThe bone window is unsatisfactory for ureteral stone size measurements. The interreader variability in soft-tissue and half-value windows is on a sub-mm magnitude, with no expected impact on clinical decision-making. The half-value MAX window had the smallest interreader variability and should be considered for reproducible and semiautomated ureteral stone size measurements.