The antenatal diagnosis of important vascular abnormalities allows for both better informed parental counselling and the planned provision of potentially life-saving care after birth. The fetal vasculature can however be difficult to visualise with ultrasound,¹ and the prenatal diagnosis of conditions such as coarctation of the aorta may be based solely on subtle anatomical markers which may be difficult to detect before birth.² MRI is one of the few alternative imaging techniques which is safe to use in pregnancy,³ but it has been limited technically by unpredictable gross fetal and maternal movements.⁴ We sought to apply a novel motion-corrected slice-to-volume registration algorithm to antenatally acquired MRI data from fetuses with and without congenital heart disease, in an attempt to improve in utero visualisation of the thoracic vasculature.Multi-slice MRI sequences were planned to obtain full coverage of the fetal thorax in multiple orthogonal orientations, using overlapping 2D single-shot fast spin echo sequences (ssFSE) (Philips, 1.5T, TR = 15000ms, TE = 80-100ms, flip angle = 90 degrees, field of view = 350 x 350mm, voxel size = 1.4 x 1.4 mm, slice thickness = 2.5mm). The resulting motion-corrupted stacks of ssFSE slices (figure 1A) were processed using a novel parallel super-resolution algorithm for slice-to-volume registration.^5,6 This uses an iterative loop to optimise 2D/3D registration based on image intensities, incorporating edge-preserving anisotropic diffusion filtering and automatic exclusion of outlier data. To confirm anatomical accuracy, the resulting 3D volume was compared to fetal echocardiographic data by a clinician with experience in fetal cardiology. A surface rendering of the fetal vessels was then produced from the inverted dataset using Osirix™, an open-source DICOM reader. Final cropping and shading was performed using MeshLab (Visual Computing Lab - ISTI – CNR, meshlab.sourceforge.net).MRI data was acquired in two normal fetuses (at 38 and 39 weeks) and four fetuses with congenital heart disease (coarctation of the aorta at 36 weeks, hypoplastic left heart syndrome at 31 weeks, tetralogy of Fallot at 23 weeks and rightward cardiac axis with bilateral SVCs at 35 weeks). Motion-corrected super-resolution 3D volumes were produced for each patient with an isotropic voxel size between 0.40 and 0.55mm, which could be navigated in three dimensions using standard multi-planar reconstruction software (Osirix™, figure 1B). In each case, the reconstructed images accurately represented the general vascular anatomy in terms of connections and spatial relationships within the thorax when compared to fetal echocardiography, as demonstrated in figure 2. Surface renderings of the vascular data are shown in figures 3 and 4.Many forms of congenital heart disease are associated with important vascular abnormalities, which can be life-threatening in the immediate postnatal period if undetected. By combining prenatal MRI with advanced motion correction algorithms, we have demonstrated a novel and robust method of obtaining detailed imaging of the fetal vasculature whilst compensating for fetal and maternal motion - previously a major limiting factor to more widespread adoption of prenatal MRI.⁴ In conjunction with conventional modalities, these advanced techniques offer the potential both to improve the antenatal detection of important congenital vascular lesions, and to enhance our understanding of this complex group of abnormalities.We have demonstrated a novel technique for imaging the fetal vasculature, which offers a level of detail that is yet to be described in the literature. Further work is ongoing to validate these techniques and establish their prognostic value when combined with established antenatal imaging modalities.