The New Frontiers of Fetal Imaging: MRI Insights into Cardiovascular and Thoracic Structures

Abstract

Fetal magnetic resonance imaging (fMRI) represents a second-line imaging modality that provides multiparametric and multiplanar views that are crucial for confirming diagnoses, detecting associated pathologies, and resolving inconclusive ultrasound findings. The introduction of high-field magnets and new imaging sequences has expanded MRI's role in pregnancy management. Recent innovations in ECG-gating techniques have revolutionized the prenatal evaluation of congenital heart disease by synchronizing imaging with the fetal heartbeat, thus addressing traditional challenges in cardiac imaging. Fetal cardiac MRI (fCMR) is particularly valuable for assessing congenital heart diseases, especially when ultrasound is limited by poor imaging conditions. fCMR allows for detailed anatomical and functional evaluation of the heart and great vessels and is also useful for diagnosing additional anomalies and analyzing blood flow patterns, which can aid in understanding abnormal fetal brain growth and placental perfusion. This review emphasizes fMRI's potential in evaluating cardiac and thoracic structures, including various gating techniques like metric optimized gating, self-gating, and Doppler ultrasound gating. The review also covers the use of static and cine images for structural and functional assessments and discusses advanced techniques like 4D-flow MRI and T1 or T2 mapping for comprehensive flow quantification and tissue characterization.

Keywords: 4D flow images; congenital chest pathologies; congenital heart disease; fetal cardiac gating; fetal cardiac magnetic resonance; fetal magnetic resonance.

Figure 1

Fetal chest MRI protocol: T2-weighted single-shot fast spin echo in sagittal, coronal, and axial (a–c) planes; T1-weighted three-dimensional (3D) GRE on axial plane (d); DWI EPI (e) on axial plane; balanced steady-state-free precession on coronal plane (f). DWI: diffusion-weighted imaging; EPI: echo planar imaging; GRE: gradient echo; MRI: magnetic resonance imaging.

Figure 2

Examination performed on a 1.5 T magnet. T2 sagittal (a) and axial plane (b), Trufi coronal plane (c). The fetus of 32 gestational weeks with type II cystic adenomatosis. At the level of the right upper lobe, non-homogeneous signal intensity is observed due to the presence of some medium and small cystic formations (diameter 10 mm) located mainly in the peripheral area.

Figure 3

T2-weighted half-Fourier acquisition single-shot turbo-spin echo (HASTE) images of the same fetus with a congenital diaphragmatic hernia (white arrows) in different gestational ages on coronal planes ((a)—23 weeks of gestation) and sagittal planes ((b)—31 weeks of gestation).

Figure 4

(a) Doppler ultrasound device positioned and fastened on the maternal abdomen in lateral decubitus and (b) fetal heartbeat track obtained with the DUS method.

Figure 5

Cardiac planes. The figure shows how to get specific fetal cardiac planes (yellow lines demonstrate how to orient acquisition planes): (a) T2 HASTE of the maternal sagittal plane; (b) T2 HASTE scan perpendicular to the fetal thorax to obtain fetal axial planes; (c) cine scan perpendicular to the interventricular septum to obtain short axis fetal cine; (d) a real 4-chambers view can be then found.

Figure 6

Cine images of the fetal heart: (a) short axis, (b) 4-chambers view, (c) 2-chambers view, and (d) 3-chambers view.

Figure 7

(a) T1 mapping of the fetal heart in 4-chambers view: a T1 myocardial value of 1726 ms was found, by tracing an ROI on the myocardial interventricular septum (yellow circle) and (b) 4D-flow imaging of the thoracic aorta of the fetus.

Figure 8

Thirty-week gestational age fetus with suspected left ventricular (LV) non-compaction syndrome at fetal echocardiography. fCMR confirmed the hypertrabeculation of the LV myocardium (white arrows) together with an increased cardio-thoracic ratio: (a) 4-chamber view, (b) short-axis view, mid-ventricular planes, and (c) 2-chamber view.