A Dual Defocused Camera System For Reconstructing the Cardiac Z-axis Vibrations

Regular cardiac monitoring can detect early signs of cardiovascular diseases and it's important for chronic disease management. Video-based seismocardiography (SCG) based on the defocused speckle imaging emerged recently, but signals extracted from speckle motions on the camera 2D imaging plane often contain coupled SCG and gyrocardiography (GCG) components. This study aims to investigate the feasibility of using two cameras with different defocus levels to measure speckle motion signals and reconstruct a pure cardiac Z-axis vibration signal (i.e. true SCG). Using chest-mounted accelerometer as the reference, we assessed the reconstructed SCG signals and raw speckle motion signals from two cameras with different focal lengths, from the aspects of the waveform similarity w.r.t. the reference and the accuracy of biomarker detection (including aortic valve opening/closure (AO/AC), mitral valve opening/closure (MO/MC), and isovolumic movement (IM)). The results obtained from an experiment involving 10 subjects with ice pack stimulation protocol showed that the reconstructed SCG signals have higher Pearson correlation with the reference signal (r=0.822) and better accuracies of biomarker detection (with a 6 ms allowable error range, accuracies are 99.43%, 71.83%, 69.49%, 69.30% and 81.50%). These preliminary results validate the effectiveness of using two defocused cameras with different focal lengths to reconstruct a true SCG signal, providing important implications for SCG-based cardiac monitoring and health management.