Multi-Modal Fetal Cardiac Imaging: Simultaneous Fetal Magnetocardiography and Fetal Echocardiography
Abstract
Purpose
To demonstrate a multi-modal magnetomechanical imaging platform for fetal cardiac evaluation that integrates simultaneous fetal magnetocardiography (fMCG) and fetal echocardiography (fEcho). This is achieved by developing a methodology that, for the first time, allows fMCG to be recorded free of interference from ultrasound scanners.
Methods
The simultaneous fMCG-fEcho system was enabled by the use of optically pumped magnetometers (OPMs). OPMs are compact, practical and less complex, allowing them to be used within a 2.5m cylindrical magnetic shield. The shield contained small lateral access ports for the sonographer to reach in and scan the patient while the OPMs remained shielded from the scanner electronics. Artifacts from transducer movement were mitigated by stabilizing it with a holder. Recordings were acquired from 20 pregnant women (14 healthy; 6 high-risk – arrhythmias and congenital heart diseases) across various gestational ages (GA). fMCG signals and ultrasound images were aligned via a shared timing signal. FMCG QRS complexes were used to window both the fMCG and Doppler segments, which were averaged and superimposed to extract electromechanical intervals. Linear regression established GA–specific normative ranges (95% prediction intervals) for healthy fetuses. Data from high-risk fetuses were overlaid on the normative curves.
Results
We identified significant linear dependency on GA for the pre-ejection time (PEP) and atrial activation time (AAT), parameters previously never measured in fetuses. A case study of Ebstein’s anomaly showed a prolongation of PR, QRS, and AV intervals, exceeding the 95% prediction interval. Additionally, PEP was near the upper limit, suggesting early evidence of delayed ventricular electromechanical coupling.
Conclusion
The OPM-based fMCG-fEcho system enables direct comparison of electrical and mechanical rhythm and assessment of electromechanical function, which extends the diagnostic capability of each technique alone. This system is especially useful for the evaluation of complex fetal cardiac disease that exhibits electrical and mechanical dysfunction.