Camera-Seismocardiography Based Cardiac Triggering for Magnetic Resonance Imaging: A Prospective Study.

Cardiac Magnetic Resonance (CMR) imaging relies on electrocardiogram (ECG) triggering to eliminate motion artifacts caused by cardiac contractions, but ECG triggering faces challenges such as waveform distortion caused by magneto-hydro-dynamic effects and switched magnetic gradient fields. Although camera-based photoplethysmography (Camera-PPG) triggering is unaffected by the magnetic field, there is a significant physiological delay caused by the pulse arrival time between cardiac contraction and blood volume changes at the facial skin, hence it cannot reserve more time for scanning preparation and data readout, which is unable to achieve higher quality MR images. Camera-based Seismocardiography (Camera-SCG) based on defocused speckle imaging demonstrated superior sensitivity in capturing tiny cardiac contraction motions. We present a novel concept of Camera-SCG triggering, offering a contactless alternative to ECG triggering. Camera-SCG directly measures cardiac motion from the chest and provides potential biomarkers (e.g., aortic valve opening (AO) peak) for cardiac triggering in CMR, instead of using surrogates like skin perfusion in Camera-PPG triggering. With an ultra-flexible chest coil, our preliminary study shows an average physiological delay between ECG R-peak and Camera-SCG AO-peak is of 31.0 ms, and it shows high availability of the measurement of 93.7% and decent performance (precision: 0.752, recall: 0.936, F1-score: 0.834), indicating its potential for MR system integration. Our prototype demonstrates a promising solution of contactless triggering for CMR, which is expected to reduce the scanning time and improve the workflow efficiency, as well as the patient comfort during preparation and MR scanning.