Semiautomatic three-dimensional ultrasound renal volume segmentation in pediatric hydronephrosis: interrater agreement and correlation to conventional hydronephrosis grading

Abstract

Background: Two-dimensional (D) assessment of renal volume underestimates the actual value and shows high interobserver variability. Limited data exist on innovative 3-D ultrasound (US) technique for the evaluation of pediatric hydronephrosis.

Objective: To assess the interrater agreement of kidney volume segmentation by 3-D US with a matrix array transducer in children with hydronephrosis and to compare the 3-D metrics to conventional hydronephrosis grading.

Materials and methods: We prospectively acquired 48 renal volumes in 45 patients with hydronephrosis by freehand 3-D US (6-1 MHz volumetric sector array, electronic rotation; median age, 4 years; 1 month to 16 years). Semi-automated kidney segmentation was performed by two independent readers providing volumes for total kidney (renal capsule), dilated collective system, renal parenchyma (renal capsule-collective system) and hydronephrosis index (renal parenchyma/capsule). Interrater agreement was evaluated with Bland-Altman plots, intraclass correlation coefficient (ICC) and Dice similarity coefficients. The maximum calibre of renal pelvis was measured and hydronephroses were morphologically classified grade 1-4.

Results: Interrater agreement for renal capsule, collective system, hydronephrosis index, and renal parenchyma was good to excellent with ICC of 0.94, 0.87, 0.83 and 0.92 respectively (P < 0.001 each). Median Dice was 0.90 (capsule), 0.77 (collective system) and 0.88 (parenchyma). There was a positive correlation between conventional hydronephrosis grading and ultrasonic hydronephrosis index and between renal pelvis diameter and collective system volume (P < 0.001 both).

Conclusion: Semiautomatic 3-D US volumetric analysis has a high degree of interrater agreement and enables reliable assessment of renal parenchymal volume in hydronephrosis. Volumes of the collective system and hydronephrosis index correlate with the extent of hydronephrosis.

Trial registration: Trial registration number, DRKS00022772; date of registration, 07/31/2020.

Keywords: Hydronephrosis; Imaging, three-dimensional; Kidney diseases; Pediatrics; Ultrasonography.