Offline ultrasound-MRI fusion imaging for assessment of normal fetal brain development

Offline fusion imaging refers to a posteriori merging of two datasets, from the same or from different imaging modalities. The objectives were to assess the feasibility of a standardized manual method for the offline fusion of three-dimensional (3D) ultrasound (US) and magnetic resonance imaging (MRI) data in demonstrating normal fetal brain development and to evaluate its potential clinical use throughout pregnancy.

This was a prospective study conducted at the Necker-Enfants Malades Hospital, Paris, France, from January to September 2021. We included normal singleton pregnancies between 16 + 0 and 36 + 0 weeks' gestation. Each patient underwent a 3D-US scan, with and without Micro-Vascularization Imaging Doppler, immediately followed by a T2-weighted MRI examination (1.5 Tesla) of the fetal brain. 3D-US and MRI images were merged using at least three registration landmarks, using modified 4D View Fusion software. The primary outcome was the success of US-MRI fusion imaging in obtaining three usable orthogonal planes. Secondary outcomes were the rate of entire neurosonogram visualization (on 3D-US acquisitions, MRI stacks and US-MRI fusion imaging) and the rate of visualization of each International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) neurosonogram anatomical landmark.

In total, 113 pregnant women were included in the analysis. We obtained usable datasets in the three orthogonal planes for 3D-US and MRI in 87.6% (99/113) and 97.3% (110/113) of cases respectively. Usable US-MRI fusion imaging in the three planes was achieved in 85.8% (85/99) of cases. The entire neurosonogram was obtained in 9.4% (8/85), 74.1% (63/85) and 87.1% (74/85) respectively of 3D-US acquisitions, MRI stacks and US-MRI fusion imaging volumes (P < 0.01).

We present a promising offline 3D-US-MRI fusion imaging tool that permits navigation within two merged volumes acquired on the same day. This technique seems easily achievable and may be of value for educational purposes and longitudinal follow up of fetal brain development in cases with increased risk of brain abnormalities. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.