Study population:
A total of 29 fetuses, with a gestational age greater than 30 weeks and without fetal known cardiac abnormalities, were enrolled in this study between November 2023 to December 2024.
The patients underwent MRI for other fetal pathologies, including central nervous system abnormalities, infections and placental disorders.
The absence of cardiac abnormalities was supported by normal heart anatomy on fetal echocardiograms in these patients.
fCMR protocols:
fCMR exams were performed using a 3.0T scanner (Magnetom Vida, Siemens), with participants positioned in a supine or left/right lateral decubitus position according to their comfort.
Fetal cardiac-gating was achieved using an MR-compatible Doppler Ultrasound (DUS) gating device (Smart-Sync, Northh Medical GmbH, Hamburg, Germany).
The DUS device was placed on the maternal abdomen and fastened with an elastic belt.
fCMR protocol consisted of a stack of high-resolution localizers using True Fast Imaging with Steady-State Free Precession (TRUFI) sequences covering the entire fetus. Typical TRUFI sequence parameters employed the following: field of view (FoV) = 380 mm, FoV Phase = 80,5%, Slice Thickness = 3,5 mm, TR/TE= 597/1,88 msec, breath hold = 1, Slices 24, Distance factor = 0%, Phase Oversampling = 50%.
Subsequently, retrospective gated cine balanced steady-state free precession (bSSFP) sequences were acquired in multiple planes and slices during maternal breath-hold. These acquisitions included four-chamber views (2-3 contiguous slices), and short-axis views, covering the entire left and right ventricles from base to apex (5–7 contiguous slices).
Cine bSSFP images employed the following sequence parameters: FoV = 300 mm, FoV Phase = 80%, slice thickness 5 mm, TR/TE = 31,4/2,25 msec, breath hold = 5, Slices = 8, Distance factor = 0%, Phase Oversampling = 50%.
Volumetric analysis:
The Volumetric analysis was conducted both on four-chamber and short-axis view to assess End-diastolic volume (EDV), End-systolic volume (ESV), Stroke volume (SV), Ejection fraction (EF), Cardiac output (CO), and Shortening fraction (SF) using dedicated software (Cvi42, v6.0.2; Circle Cardiovascular Imaging).
Left ventricular (LV) (assessed both in short axis and four-chamber views), right ventricular (RV) volumes (assessed in short axis view only) and function were calculated from short axis stacks by tracing endocardial borders at end-diastole and end-systole.
In order to obtain the end-diastolic and end systolic diameter a line has been drawn from the mitral and tricuspid annulus to apex at end-diastole and end-systole from the long axis images.
The SF was calculated as follows: SF = (End-Diastolic Diameter x End-Systolic Diameter)/(End Diastolic Diameter).
Additionally, the cardio-thoracic index (CTI) was calculated by measuring the maximum horizontal diameter of the heart and dividing it by the maximum internal horizontal diameter of the thoracic cage. Specifically, the heart’s width was determined by identifying its most lateral borders at the level of the atrio-ventricular valves, while the thoracic diameter was measured between the inner margins of the rib cage at the same level.
Statistical analysis:
Statistical analysis was performed using a dedicated software.
Data are presented as counts and percentages for categorical data and mean with standard deviation for continuous parameters. The normal distribution of all variables was tested using Kolmogorov–Smirnov and Shapiro–Wilk tests.
Statistical comparisons were made using paired t-tests.
A p-value < 0.05 was considered statistically significant.