Purpose or Case Report: We aim to assess the agreement between semi-automated segmented 3D ultrasound (US) and functional magnetic resonance urography (fMRU) for renal parenchymal volume in children with urinary tract dilation (UTD).
Methods & Materials: In this single-center prospective study, we enrolled children (<18 years) undergoing clinically indicated fMRU for UTD evaluation between January 2019 and June 2024, excluding those with acute obstruction or renal anomalies. After fMRU, 2D US was performed and UTD was scored based on the 2014 consensus classification by an experienced pediatric uroradiologist. Next, 3D renal ultrasound was performed using a Philips EPIQ Elite 7G system with an X6-1 transducer (3 cm focal zone) in both supine and prone positions. fMRU followed institutional protocol. The renal parenchyma was segmented using a validated semi-automated proprietary software for 3D US and post-processing MRI software for T2-weighted images in MRU by a single trained reader. Parenchymal kidney volume was compared between modalities using intraclass correlation coefficient (ICC) analysis, and 3D US volume was also compared with post-contrast fMRU volume.
Results: A total of 13 patients underwent fMRU and 3D ultrasound. Three kidney units were excluded, in one case, 3D images were not recorded appropriately, and in a single kidney from another case, segmentation was not possible due to severe enlargement. Thus, 23 kidneys from 12 patients (75% male, median age [IQR] 4.5 [8] years) were analyzed. Of these, 11 (47.8%) were normal, 1 (4.4%) had UTD P1, 6 (26.1%) had UTD P2, and 5 (21.7%) had UTD P3. Median (IQR) segmented parenchymal volume was 64.4 (58.8) cm3 for 3D US, 60.1 (57.7) cm3 for segmented T2 images and 56.1 (57.4) cm3 for fMRU post-contrast volume. The ICC between 3D US and T2 fMRU volumes was 0.92 (95% CI: 0.81 to 0.97), and between 3D US and post-contrast fMRU was 0.88 (95% CI: 0.71 to 0.95).
Conclusions: This study shows strong agreement in segmented renal parenchymal volumes between 3D ultrasound and (T2 and post contrast) fMRU in children with UTD, with higher agreement between 3D ultrasound and T2 images than with post-contrast fMRU. 3D ultrasound may, therefore, be a more convenient alternative for renal volume assessment in children with UTD.