Abstract
Fast magnetic resonance imaging (MRI) led to the emergence of ‘cine MRI’ techniques, which enable the visualization of the beating heart and the assessment of cardiac morphology and dynamics. However, established cine MRI methods are not suitable for fetal heart imaging in utero, where anatomical structures are considerably smaller and recording an electrocardiogram signal for synchronizing MRI data acquisition is difficult. Here we present a framework to overcome these challenges. We use methods for image acquisition and reconstruction that robustly produce images with sufficient spatial and temporal resolution to detect the heart contractions of the fetus, enabling a retrospective gating of the images and thus the generation of images of the beating heart. To underline the potential of our approach, we acquired in utero images in six pregnant patients and compared these with their echocardiograms. We found good agreement in terms of diameter and area measurements, and low inter- and intra- observer variability. These results establish MRI as a reliable modality for fetal cardiac imaging, with a substantial potential for prenatal evaluation of congenital heart defects.
Highlights
Fast magnetic resonance imaging (MRI) led to the emergence of ‘cine MRI’ techniques, which enable the visualization of the beating heart and the assessment of cardiac morphology and dynamics
Cardiac imaging of the fetus is important in screening for significant congenital heart defects (CHDs), which occur at an incidence of about 6–19/1000 live births worldwide[5]
The quality of the diameter measurements with MRI were similar for both observers, a consistent offset was identified (Table 3), with the Bland–Altman analysis showing a bias of −0.44 mm (CI: [−2.39;1.51], p = 0.050), linear regression (LR): y = 1.00x − 0.45 (r2 = 0.748) (Supplementary Fig. S3)
Summary
Received: 19 July 2017 Accepted: 1 November 2017 Published online: 14 November 2017. Jerome Chaptinel[1], Jerome Yerly[1,2], Yvan Mivelaz[3], Milan Prsa[3], Leonor Alamo[1], Yvan Vial[4], Gregoire Berchier[1], Chantal Rohner[1], François Gudinchet1 & Matthias Stuber[1,2]. Cardiac MRI studies of the fetus mostly relied on static imaging techniques[16] or untriggered fast acquisition methods (typically based on real-time balanced steady-state free-precession sequences17) developed for organs other than the fetal heart[12,13,14] We first reconstruct real-time images of limited image quality but high temporal resolution These images are analyzed to extract a self-gating signal that characterizes the periodic contraction of the fetal heart, which in turn is used to retrospectively sort all readouts into their corresponding cardiac phase. Due to the high fetal heart rate (typically between 110 and 160 bpm), real-time images with high temporal resolution are required for accurately and precisely estimating the cardiac phases In our protocol, these images are reconstructed off-line (see Methods) and analyzed semi-automatically to extract a self-gating signal (for details, see the Methods section). This strategy had little adverse impact on image quality due to the resilience of the l1-constrained reconstruction and the properties of the radial golden-angle trajectory
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