Contactless Fiber-Optic Photoplethysmography-based Gating for Flow MRI.

Motivation: To reduce setup times of cine Flow MRI by using contactless fiber-optic photoplethysmography (PPG) on the forehead. Goal(s): To achieve robust contactless cardiac gating with minimal latency and acceptable jitter using contactless PPG. Approach: Undersampled, retrospectively-gated 2D and 4D flow MRI data were acquired with simultaneous contactless forehead-PPG and reference ECG recordings. Velocities were reconstructed with locally-low-rank reconstruction after cardiac binning based on either forehead-PPG or ECG. Results: Using forehead-PPG, we found a mean gating delay of 107.2±18.2ms with a jitter of 4.8±3.2ms for 2D scans, and 103.1±13.4ms with a jitter of 7.9±0.7ms for 4D scans, relative to ECG, yielding comparable velocity data. Impact: Contact forehead-PPG offers a simple approach to cardiac gating with reduced latency relative to peripheral pulse units, potentially easing clinical workload and enhancing patient comfort.