Object: This work aims to introduce a novel method to mitigate the global phase deviation inherent in photoplethysmography imaging (PPGI) due to hemodynamics. Method: We model the facial vascular network captured by a consumer camera as a two-dimensional manifold, where the complex dynamics of the vascular tree lead to intricate phase variations across skin sites. Utilizing PPGI, we sample the vector field on the facial manifold encoding these intricate phase variations over different skin sites resulting from blood volume modulations. We propose leveraging the graph connection Laplacian (GCL) technique to quantify the global phase deviation, with the hypothesis that correcting this deviation can improve the quality of the PPGI signal and that the phase deviation encodes valuable anatomical and physiological information. Result: The proposed algorithm yields a higher-quality global PPGI signal by correcting the global phase deviation estimated by GCL, emphasizing waveform features such as the dicrotic notch. The perfusion map, with the global phase deviation estimated by GCL as intensity, reflects skin perfusion dynamics influenced by varying travel distances and anatomical structures. 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.

The authors have declared no competing interest.

NCT03592290

The work of Stefan Borik was supported by the National Scholarship Programme of the Slovak Republic (Application No. 47518).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The 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I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the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.

Yes

I 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).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data produced in the present study are available upon reasonable request to the authors