Pilot Study: Utilising MRI to Measure Cardiac Function in the Sheep Foetus

Abstract

We assessed the feasibility of foetal sheep cardiac magnetic resonance (CMR) measurements of ventricular volume for chamber sizes and cardiac output against gold standard cine phase-contrast (PC) measurements made in the ascending aorta (AAo) and main pulmonary artery (MPA). Methods: 5 ewes with singleton pregnancies underwent surgery at 112–120 d (term = 150 d) to catheterise the foetal femoral artery. At 139–140 d, ewes were anaesthetised to undergo foetal CMR using the femoral arterial pressure waveform for cardiac gating. Short-axis cine imaging of the foetal hearts was acquired and the right (RV) and left (LV) ventricles were segmented to measure ejection fraction (EF), stroke volume (SV), right and left ventricular output (CO) and CVO. LV-CO and RV-CO were also measured by cine PC acquisitions of AAo and MPA flow respectively. All cardiac measurements were indexed to foetal weight. The ventricular output by ventricular volumetry and PC were compared by linear regression and Bland-Altman analysis. Results: Our results are in keeping with previously reported microsphere measurements and we found good agreement between LV-CO and RV-CO by ventricular volumetry versus PC but with underestimation of output of approximately 10% by ventricular volumetry, which we attributed to incomplete coverage of the entire ventricular volume (Fig. 1). Conclusion This data suggest that following appropriate modification of the field of view, this technique represents a valid approach to assessing cardiac function, chamber sizes, and cardiac output in foetal sheep.