Photoplethysmography Imaging (PPGI)
Fig. 1: Illustration of the vascular system of the human body.
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Project description
The PPGI is a contactless measurement system for the functional registration of blood perfusion in the upper skin layers. As an enhancement of the classical photoplethysmography (PPG), it is also based on measuring the optical damping of skin, which varies according to changing blood volumes. But for PPGI instead of a single PPG sensor, a high sensitive CCD camera is used. This enables detecting the skin perfusion with spatial resolution.
Measurement of slow, rhythmical blood volume shifts
With PPGI also low-frequency blood volume shifts (<0.25 Hz) can be analysed. During such examinations on several subjects’ forehead, local bounded “clouds” of phase synchronous oscillations in blood volume were detected. These continuous regions of same phase appear at frequencies around 0.1 Hz. It could be monitored that these clouds move along the forehead, sometimes vanish or arise new. An example of a video sequence of such measurement can be downloaded here.