Summary Background Two-dimensional (2D) ultrasound echocardiography is the primary technique used to diagnose congenital heart disease before birth. There is, however, a longstanding need for a reliable form of secondary imaging, particularly in cases when more detailed three-dimensional (3D) vascular imaging is required, or when ultrasound windows are of poor diagnostic quality. Fetal MRI, which is well established for other organ systems, is highly susceptible to fetal movement, particularly for 3D imaging. The objective of this study was to investigate the combination of prenatal MRI with novel, motion-corrected 3D image registration software, as an adjunct to fetal echocardiography in the diagnosis of congenital heart disease. Methods Pregnant women carrying a fetus with known or suspected congenital heart disease were recruited via a tertiary fetal cardiology unit. After initial validation experiments to assess the general reliability of the approach, MRI data were acquired in 85 consecutive fetuses, as overlapping stacks of 2D images. These images were then processed with a bespoke open-source reconstruction algorithm to produce a super-resolution 3D volume of the fetal thorax. These datasets were assessed with measurement comparison with paired 2D ultrasound, structured anatomical assessment of the 2D and 3D data, and contemporaneous, archived clinical fetal MRI reports, which were compared with postnatal findings after delivery. Findings Between Oct 8, 2015, and June 30, 2017, 101 patients were referred for MRI, of whom 85 were eligible and had fetal MRI. The mean gestational age at the time of MRI was 32 weeks (range 24–36). High-resolution (0·50–0·75 mm isotropic) 3D datasets of the fetal thorax were generated in all 85 cases. Vascular measurements showed good overall agreement with 2D echocardiography in 51 cases with paired data (intra-class correlation coefficient 0·78, 95% CI 0·68–0·84), with fetal vascular structures more effectively visualised with 3D MRI than with uncorrected 2D MRI (657 [97%] of 680 anatomical areas identified vs 358 [53%] of 680 areas; p<0·0001). When a structure of interest was visualised in both 2D and 3D data (n=358), observers gave a higher diagnostic quality score for 3D data in 321 (90%) of cases, with 37 (10%) scores tied with 2D data, and no lower scores than for 2D data (Wilcoxon signed rank test p<0·0001). Additional anatomical features were described in ten cases, of which all were confirmed postnatally. Interpretation Standard fetal MRI with open-source image processing software is a reliable method of generating high-resolution 3D imaging of the fetal vasculature. The 3D volumes produced show good spatial agreement with ultrasound, and significantly improved visualisation and diagnostic quality compared with source 2D MRI data. This freely available combination requires minimal infrastructure, and provides safe, powerful, an...

In MRI, motion correction for fetal body poses a particular challenge due to the presence of local non-rigid transformations of organs caused by bending and stretching. The existing slice-to-volume (SVR) reconstruction methods provide efficient solution for the fetal brain that undergoes only rigid transformation or 4D fetal heart with rigid states correlated to cardiac phases. However, for fetal body reconstruction, rigid registration cannot resolve the issue of misregistrations due to deformable motion. This results in propagation of registration error to the reconstructed volume and subsequent degradation of features. We propose a novel approach for non-rigid motion correction in 3D volumes based on an extension of the classical SVR method with hierarchical deformable registration scheme and structure-based outlier rejection. Deformable SVR (DSVR) method allows high resolution reconstruction of the fetal trunk and the robust scheme for structure-based rejection of misregistered slices minimises the impact of registration error. The method performance is evaluated by comparison to the SVR and patch-to-volume registration methods for reconstruction of fetal trunk on a series of fetal MRI datasets from 28-30 weeks gestational age (GA) range with varying degree of motion corruption. An additional phantom study with simulated nonrigid motion is used for the assessment of consistency of DSVR reconstructed volumes.