4D Cardiac MRI Flow in Neonates - Cardiac Output in full-term healthy neonates

Accurate assessment of cardiac flow and volumes is essential in children with heart disease. Cardiovascular magnetic resonance (CMR) enables comprehensive quantitative evaluation but is technically demanding and often requires sedation or contrast administration in neonates. Free-breathing four-dimensional (4D) flow CMR simplifies image acquisition and enables imaging without general anesthesia or controlled ventilation. However, most prior neonatal 4D flow studies have relied on sedation and/or contrast, limiting evaluation in healthy populations. Establishing normative data and assessing feasibility and reproducibility in unsedated neonates are therefore important for clinical translation. Accordingly, this study aimed to evaluate the feasibility, accuracy, and interobserver reproducibility of free-breathing, non-contrast 4D flow CMR in healthy unsedated neonates and to characterize postnatal development of cardiac flow.

One hundred healthy term neonates (mean age: 18.6 ± 7.6 days; 53% male) with normal echocardiograms underwent free-breathing feed-and-wrap axial 4D flow cardiovascular magnetic resonance imaging (ViosWorks) with ECG gating, followed by a transverse cine Steady-State Free Precession (FIESTA) stack. Cardiac output (CO), cardiac index (CI), pulmonary blood flow (Qp), systemic blood flow (Qs), and Qp/Qs were quantified. Interobserver reproducibility was assessed by three independent observers.

Free-breathing 4D flow acquisition without sedation was feasible in 70% of neonates, with a mean scan time of 9.3 ± 1.9minutes. Mean CO was 196 ± 39ml·min⁻¹·kg⁻¹. CI increased by 80% during the first 31 days of life (1.95 vs. 3.50L·min⁻¹·m^-², p<0.001), driven primarily by a 72% increase in stroke volume. Pulmonary blood flow was on average 17% higher than systemic flow (Qp/Qs = 1.17 ± 0.17). Inter-observer reproducibility was excellent, with intraclass correlation coefficients of 0.93 for the ascending aorta and 0.91 for the main pulmonary artery. 47 neonates remained calm after the 4D flow scan, allowing a transverse cine stack sequence to be acquired as well. Cardiac output derived from 4D flow showed good agreement with volumetric measurements with no significant difference (p=0.1).

Free-breathing, non-contrast 4D flow CMR was feasible in the majority of neonates, with rapid acquisition, excellent interobserver reliability, and good agreement with volumetric measurements. Neonatal CO increased markedly after birth, driven primarily by rising stroke volume, and mean Qp/Qs was modestly elevated.