Impact of operator experience on the variability of fetal lung volume estimation by 3D-ultrasound (VOCAL) and magnetic resonance imaging in fetuses with congenital diaphragmatic hernia

OBJECTIVE: To evaluate the impact of operator experience in volumetric measurements on intra- and inter-observer variability of lung volume estimation by 3-dimensional (3D) ultrasound and magnetic resonance imaging (MRI) in fetuses with congenital diaphragmatic hernia (CDH). METHODS: We conducted a retrospective single-center study. Total fetal lung volume (TFLV) was measured twice using 52 stored 3D-ultrasound volumes and 52 corresponding MRI exams by a fetal medicine specialist with no experience in volumetric measurements and two operators experienced in the respective techniques. Bland-Altman analysis was performed to evaluate intra- and inter-observer variability. RESULTS: Measurements of TFLV by 3D-ultrasound showed higher intra-observer variability compared with MRI irrespective of operator experience, with narrower 95% limits of agreement on MRI as compared with ultrasound measurements. Similarly, 3D-ultrasound showed higher inter-observer variability as compared with MRI. Finally the 95% limits of agreement at ultrasound were quite comparable for intra-observer variability between the experienced and the inexperienced operator. CONCLUSION: Our study shows that operator experience has an impact on the variability of TFLV and, in the absence of experience in volumetric measurements, estimation of TFLV in fetuses with CDH by 3D-ultrasound shows higher variability than MRI measurements, but even in experienced hands variability is greater for 3D-ultrasound.