Laser HeartBeat: Feasibility of a Contactless Optical Gating Method for Cardiac MRI

Robust cardiac gating is critical for cardiac magnetic resonance (CMR) imaging; however, electrocardiography (ECG) and other contact sensors are often limited by electromagnetic interference and practical setup constraints. Hence, this paper presents Laser HeartBeat (Laser HB), a contactless gating method using defocused laser speckle imaging to track chest-wall micro vibrations. Specifically, Laser HB comprises (i) an MRI compatible optical acquisition module that projects and records defocused speckle patterns without contacting the subject, (ii) an integrated real-time processing and triggering pipeline, which incorporates our proposed Laser HB trigger algorithm to extract a robust cardiac-motion surrogate signal from speckle imaging and generate gating trigger signals in real time. To evaluate its feasibility in realistic occlusion scenarios with electromagnetic interference, we conducted two out-of-bore studies and one in-bore feasibility study. Comparative experiments show that Laser HB achieves 97.6% availability, with beat-wise precision/recall/F1 = 0.946/0.946/0.943. The extracted triggers exhibit an average 22.6 ms delay relative to the ECG R-peak. Moreover, integration of the Laser HB system decreased the phantom MRI signal-to-noise ratio (SNR) by 2.8 compared with the baseline condition. These results indicate that Laser HB is an MRI-compatible, low-latency, fully contactless gating method that can reduce setup burden, improve workflow efficiency, and enhance patient comfort.