Graph Connection Laplacian Allows for Enhanced Outcomes of Consumer Camera Based Photoplethysmography Imaging

Object This work introduces a novel method to minimize the effect of global phase deviation that is inherent in photoplethysmographic images (PPGI) captured by video.Method We analyzed the facial vascular network obtained from a consumer camera as a two-dimensional manifold. Subtle phase variations across skin sites are due to complex dynamics of the vascular tree. Utilizing PPGI, the phase is modeled as a vector field of the facial manifold. The phase variations over different skin sites are caused by different blood volume modulations. We propose using the Graph Connection Laplacian (GCL) technique to quantify the global phase deviation, with the hope that correcting for this deviation could improve the quality of the PPGI signal. It is also postulated that study of this phase deviation might reveal valuable anatomical and physiological information.Result The proposed algorithm appears to yield a higher-quality global PPGI signal. By correcting the global phase deviation estimated by GCL waveform features such as the dicrotic notch are emphasized. The perfusion map, with the global phase deviation (estimated by GCL as intensity), appears to reflect skin perfusion dynamics.Conclusion This algorithm enhances the quality of the global PPGI signal, facilitating the analysis of morphological parameters and showing promise for advancing PPGI applications in scientific research and clinical practice.### Competing Interest StatementThe authors have declared no competing interest.### Clinical TrialNCT03592290### Funding StatementThe work of Stefan Borik was supported by the National Scholarship Programme of the Slovak Republic (Application No. 47518).### Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:The study protocol was approved by the Institutional Review Board of Yale University (No. 2000031899). Informed consent was obtained from all subjects prior to the study. All methods were performed in accordance with the study protocol and with the Declaration of Helsinki.I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.YesI understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).YesI have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.YesAll data produced in the present study are available upon reasonable request to the authors