The exciting alternative option of using Doppler ultrasound for MR cardiac gating allows to synchronize MR image acquisition with the fetal cardiac rhythm in a way that was previously not possible. Without this synchronization, motion artifacts typically render cardiac MR images useless for diagnosis.
Typically, cardiac MR utilizes either electrocardiography (ECG) or vectorcardiography (VCG) techniques to synchronize MR acquisition with the heart rhythm to “freeze” heart motion. Both methods require the attachment of electrodes to the patient’s skin, which makes the approach unsuitable for fetal cardiac imaging.
The recently introduced Doppler ultrasound device for gating, smart-sync, was developed by northh medical GmbH in Germany, in collaboration with Philips and clinical collaborators. This device can detect the heartbeat during MRI acquisition, and sends a gating signal to the scanner. This allows for the synchronization of MR data acquisition with the fetal heartbeat, resulting in fetal cardiac MR images of diagnostic quality. It allows for the use of standard cardiac sequences, so that acquired images instantly appear on the screen, allowing for immediate evaluation of slice positioning and quality – an important feature that allows for adjustments should the fetus change position.
High image quality can be obtained for morphological images as well as 2D and 4D blood flow measurements, in a normal clinical setting. Together with the acquisition speed of the Philips Compressed SENSE method, fast and well-directed imaging of the fetal heart and flow can be performed, opening up a new avenue for congenital heart disease diagnosis before birth.
The ultrasound-based trigger signal is reliable and easy to use due to its wireless connection. The signal also remains undistorted by the MR field, unlike ECG and VCG methods, and eliminates the need to attach electrodes to the skin. The positioning of the smart-sync probe is quite simple, only requiring the proper placement above the fetal heart.