IRM fœtale : une révolution en route

The use of image fusion in prenatal medicine

Fusion imaging (FI), the simultaneous display of the same anatomical region using two imaging modalities, has been used in other areas of medicine for both diagnosis and guiding interventions. Examples include positron emission tomography-computed tomography (PET-CT) imaging in oncology and ultrasound-magnetic resonance imaging (US-MRI) fusion in biopsies of the prostate gland. The underlying principle is to take advantage of the complementary information in each modality to improve accuracy, be it diagnostic accuracy or targeting accuracy in biopsies. For example, PET-CT overlays the metabolic activity of lesions on the superb spatial and anatomical detail of CT. While the historical mainstay of fetal imaging has been ultrasound, advances in ultrafast MR imaging together with advances in fetal MRI over the past two decades, have resulted in the opportunity to explore fusion imaging in fetal medicine. We present an overview of the principles of US-MRI fusion imaging in prenatal medicine, report our local experience, and review the literature in this emerging area. We share our perspective on how FI can improve diagnostic confidence, be used as an educational tool, and potentially enhance guidance in certain fetal procedures.

MRI and ultrasound fusion imaging for prenatal diagnosis

OBJECTIVE

A combination of magnetic resonance imaging (MRI) images with real time high-resolution ultrasound known as fusion imaging may improve prenatal examination. This study was undertaken to evaluate the feasibility of using fusion of MRI and ultrasound (US) in prenatal imaging.

STUDY DESIGN

This study was conducted in a tertiary referral center. All patients referred for prenatal MRI were offered to undergo fusion of MRI and US examination. All cases underwent 1.5 Tesla MRI protocol including at least 3 T2-weighted planes. The Digital Imaging and Communications in Medicine volume dataset was then loaded into the US system for manual registration of the live US image and fusion imaging examination.

RESULTS

Over the study period, 24 patients underwent fusion imaging at a median gestational age of 31 (range, 24-35) weeks. Data registration, matching and then volume navigation was feasible in all cases. Fusion imaging allowed superimposing MRI and US images therefore providing with real time imaging capabilities and high tissue contrast. It also allowed adding a real time Doppler signal on MRI images. Significant fetal movement required repeat-registration in 15 (60%) cases. The average duration of the overall additional scan with fusion imaging was 10 ± 5 minutes.

CONCLUSION

The combination of fetal real time MRI and US image fusion and navigation is feasible. Multimodality fusion imaging may enable easier and more extensive prenatal diagnosis.