Fundamentals of Camera-PPG Based Magnetic Resonance Imaging

In Magnetic Resonance Imaging (MRI), cardiac triggering that synchronizes data acquisition with cardiac contractions is an essential technique for acquiring high-quality images. Triggering is typically based on the Electrocardiogram (ECG) signal (e.g. R-peak). Since ECG acquisition involves extra workflow steps like electrode placement and ECG signals are usually disturbed by magnetic fields in high Magnetic Resonance (MR) systems, we explored camera-based photoplethysmography (PPG) as an alternative. We used the in-bore camera of a clinical MR system to investigate the feasibility and challenges of camera-based cardiac triggering. Data from ECG, finger oximeter and camera were synchronously collected. Compared to finger-PPG, camera-based PPG provides a higher availability of the signal and the PPG marker delay relative to the ECG R-peak is considerably less with a camera monitoring the forehead. The insights obtained in this study provide a basis for an envisioned system-design phase.