Split-Architecture Non-contact Optical Seismocardiography Triggering System for Cardiac MRI

GAO Qiannan; ZHANG Jiayu; ZHU Yinggen; WANG Wenjing; JI Jiansong; JI Xiaoyue

doi:10.11999/JEIT251098

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GAO Qiannan, ZHANG Jiayu, ZHU Yinggen, WANG Wenjing, JI Jiansong, JI Xiaoyue. Split-Architecture Non-contact Optical Seismocardiography Triggering System for Cardiac MRI[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT251098

Citation:

GAO Qiannan, ZHANG Jiayu, ZHU Yinggen, WANG Wenjing, JI Jiansong, JI Xiaoyue. Split-Architecture Non-contact Optical Seismocardiography Triggering System for Cardiac MRI[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT251098

Citation:

GAO Qiannan, ZHANG Jiayu, ZHU Yinggen, WANG Wenjing, JI Jiansong, JI Xiaoyue. Split-Architecture Non-contact Optical Seismocardiography Triggering System for Cardiac MRI[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT251098

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Split-Architecture Non-contact Optical Seismocardiography Triggering System for Cardiac MRI

doi: 10.11999/JEIT251098 cstr: 32379.14.JEIT251098

1.
School of Electronic Information, Hangzhou Dianzi University, Hangzhou 310018, China
2.
Department of Precision Instrument, Tsinghua University, Beijing 100084, China
3.
Nursing Department, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 100084, China
4.
South University of Science and Technology of China, biomedical engineering, Shenzhen 518055, China
5.
Lishui Hospital of Zhejiang University , Lishui 323020, China

Accepted Date: 2026-01-12
Rev Recd Date: 2026-01-12

Available Online: 2026-01-27

Abstract

Abstract

Objective Cardiac-cycle synchronization is required in cardiovascular magnetic resonance (CMR) to reduce motion artifacts and maintain quantitative accuracy. At high field strengths, electrocardiogram (ECG) triggering is often affected by magnetohydrodynamic effects and scanner-related electromagnetic interference (EMI). Electrode placement and lead routing also add setup burden. Contact-based mechanical sensors still require skin contact, and optical photoplethysmography can introduce long physiological delay. A fully contactless, EMI-robust mechanical surrogate is therefore needed. This work develops a split-architecture, noncontact optical seismocardiography (SCG) triggering system for CMR and evaluates its availability, beat-wise detection performance, and timing characteristics under practical body-coil coverage. Methods A split-architecture system consists of a near-magnet optical acquisition unit and a far-magnet computation-and-triggering unit, connected via fibre-optic links to minimize conductive pathways near the scanner (Fig. 2). The acquisition unit uses a defocused industrial camera and laser illumination to record speckle-pattern dynamics over the anterior chest without physical contact (Fig. 3). Dense optical flow is computed in a chest region of interest, and the displacement field is projected onto a principal motion direction to form a one-dimensional SCG sequence (Fig. 4). The sequence is processed with drift suppression, smoothing, and short-window normalization. Trigger timing is refined using a valley-constrained gradient search within a physiologically bounded window to reduce spurious detections and improve temporal consistency (Fig. 4). A benchmark dataset is collected from 20 healthy volunteers under three coil configurations: no body coil, an ultra-flexible body coil, and a conventional rigid body coil (Fig. 5, Fig. 6, Table 3). ECG serves as the reference, with CamPPG and radar recorded for comparison. Beat-wise precision, recall, and F1 score are computed against ECG R peaks, and availability is reported as the fraction of usable segments under unified quality criteria (Table 4). Backward and forward physiological delays and delay variability are summarized across subjects and coil conditions (Table 5, Table 6). Key windowing and refractory parameters are examined for sensitivity (Table 2). Runtime is measured to assess real-time feasibility, including the cost of dense optical flow and the overhead of one-dimensional processing and triggering (Table 7). Results and Discussions Under no-coil and ultra-flexible-coil conditions, the proposed optical SCG trigger achieves high availability (about 97.6%) and strong beat-wise performance. F1 reaches about 0.91 under the ultra-flexible coil. (Table 4, Table 5) The backward physiological delay remains on the order of several tens of milliseconds, and delay jitter is typically within a few tens of milliseconds. (Table 5, Table 6) Under the rigid body coil, performance drops sharply. Mechanical decoupling between the coil surface and chest wall weakens and distorts the vibration signature, which blurs AO-related features and increases false triggers. (Fig. 1) This degradation appears as lower precision and F1 and as a shift toward longer and more variable delays than in the other coil conditions. (Table 4, Table 6) Relative to CamPPG, which tracks peripheral blood-volume dynamics and typically lags further behind the ECG R peak, the optical SCG surrogate provides a more proximal mechanical marker and reduces trigger phase lag. (Fig. 9, Table 5) EMI robustness is supported by representative segments: ECG waveforms show visible distortion under interference, while the optical SCG surrogate remains interpretable because acquisition and transmission near the scanner are fully optical and electrically isolated. (Fig. 8) Parameter analysis supports a moderate processing window and a 0.5 s minimum inter-beat interval as a stable choice across subjects. (Table 2) Runtime analysis shows that dense optical flow dominates the cost, while one-dimensional processing and triggering add little overhead. Throughput exceeds the acquisition frame rate, supporting real-time triggering. (Table 7) Conclusions A split-architecture, noncontact optical SCG triggering system is developed and validated under three representative body-coil configurations. Fibre-optic separation between near-magnet acquisition and far-magnet processing improves EMI robustness while preserving real-time trigger output. High availability, strong beat-wise performance, and short physiological delay are demonstrated under no-coil and ultra-flexible-coil conditions. (Table 4, Table 5) Rigid-coil coverage exposes a clear limitation caused by reduced mechanical coupling, motivating further optimization for mechanically decoupled or heavily occluded scenarios. (Fig. 1, Table 6)
- Cardiac Magnetic Resonance,
- Optical Seismocardiography,
- Contactless Gating,
- Split-Architecture System,
- High-Field Environment

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References(35)

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