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2Non-contact monitoring of cortical perfusion by imaging photoplethysmography
A.A. Kamshilin1'2*' A.V. Shcherbinin2, V.V. Zaytsev2, A.Yu. Sokolov3'4
1-Institute of Automation and Control Processes FEB RAS, Vladivostok, Russia 2- North-Western District Scientific and Clinical Center FMBA, St. Petersburg, Russia
3- Pavlov First Saint Petersburg State Medical University, St. Petersburg, Russia 4- Pavlov Institute of Physiology RAS, St. Petersburg, Russia
Intraoperative quantitative assessment of changes in tissue perfusion is extremely important as an objective quality control of surgical interventions, especially in brain surgery. The monitoring system should be easy to use, contactless and provide quantitative visualization of blood flow in real time. Various techniques have been proposed to solve this problem, but all of them have their drawbacks, leading to the fact that today neurosurgeons do not have a proper tool to assess cortical blood flow during surgery. In this presentation, we discuss a multimodal method of imaging photoplethysmography (IPPG) synchronized with an electrocardiogram (ECG), which we consider the most promising for assessing changes in cerebral blood flow parameters in the operating room. The results of both experiments on laboratory animals to assess changes in intracranial hemodynamics in response to various interventions and pilot studies on monitoring cortical perfusion during open-brain neurosurgery (44 different surgeries) will be presented.
Instrumental implementation of the IPPG system is very simple, since this requires only a video camera with proper illumination of the tissue under study. However, despite the fact that photoplethysmography has historically been the very first optical method for assessing blood flow in vivo, this technique has not yet found wide application in clinical practice. Most researchers believe that the main technical problem of IPPG is motion artifacts, which significantly exceed the light modulation at heart rate that bears useful information about perfusion. In our multimodal system, the efficiency of motion artifact compensation was significantly increased by using a special image stabilization algorithm, which includes correlation analysis of video frames with ECG. As a result, spatial distributions of cortical blood flow and their changes over time with a high signal-to-noise ratio were obtained in all neurosurgical operations and animal experiments without exception. It was our group that was the first to demonstrate the feasibility of cerebral perfusion assessment during open brain surgery using the multimodal IPPG system [1].
Nonetheless, despite the positive and reproducible results of these pilot studies, their interpretation is not always sufficiently justified due to ongoing discussions about the physico-physiological model of the origin of the IPPG signal. We are proponents of an alternative model of IPPG signal formation [2], which states that the key point is the elastic deformation of the microvascular bed by adjacent pulsatile arteries. According to this theory, the capillary bed serves as a distributed sensor-transducer for pulsations generated by deeper supplying arteries. Consequently, the amplitude of pulsatile component of the IPPG waveform is inversely proportional to the tone of blood vessels, and only arteries supplying the cortex are visualized in the perfusion maps evaluated in IPPG system [3]. In the presentation, we will show a number of experimental observations confirming the conclusions of the alternating theory of IPPG signal formation, which also underlines prospects of the multimodal IPPG system for important applications in clinical setting.
The study was carried out within the state assignment of IACP FEB RAS (Theme FWFW-2022-0003) in terms of the manufacture of the experimental equipment, software development, and data processing and analysis. Research planning, patient preparation, and surgical interventions were carried out with the financial support of the FMBA of Russia (project No. 122031500174-6).
[1] O.V. Mamontov, A.V. Shcherbinin, R.V. Romashko, A.A. Kamshilin, Intraoperative imaging of cortical blood flow by camera-based photoplethysmography at green light, Applied Sciences., vol. 10, p. 6192, (2020).
[2] A.A. Kamshilin, E. Nippolainen, I.S. Sidorov, P.V. Vasilev, N.P. Erofeev, N.P. Podolian, R.V. Romashko, A new look at the essence of the imaging photoplethysmography, Scientific Reports, vol. 5, p. 10494, (2015).
[3] O.A. Lyubashina, O.V. Mamontov, M.A. Volynsky, V.V. Zaytsev, A.A. Kamshilin, Contactless assessment of cerebral autoregulation by
photoplethysmographic imaging at green illumination, Frontiers in Neuroscience, vol. 13, p. 1235, (2019).
