Photoplethysmography imaging and common optical hybrid imaging modalities

Abstract

Due to their obvious advantages, active and passive optoelectronic sensor concepts for monitoring cardiorespiratory vital signs and detection of rhythmical phenomena in dermal blood perfusion are being investigated by various biomedical groups, particularly their camera-based variants. Such methods are noninvasive and contactless, and allow spatially resolved skin perfusion studies. This chapter presents one of these medical imaging modalities (developed by and clinically tested at RWTH Aachen University), i.e., active photoplethysmography imaging (PPGI) for the mapping of dermal blood perfusion dynamics. PPGI is an enhancement of the classical photoplethysmography and pulse oximetry (SpO2) and describes the remote "opto-electronical measurement of arterial and/or venous blood volume changes". Approved algorithms from these established methods, e.g., algorithms that extract the heart rate, heart rate variability, respiratory rate, and/or pulse wave form-related stress/pain signals, can easily be adapted to PPGI. This remote monitoring technique allows measurement of body signals without contact (unobtrusive) and with spatial resolution; moreover, it can be adapted to specific measurement scenarios, such as the monitoring of neonates and acquiring vital information from within the area of a wound. Selected medical applications have been validated by our group using the PPGI technology in a stand-alone or hybrid camera configuration. Although these preliminary results are promising, additional research and development is necessary (especially for the detection and elimination of movement artifacts) before this novel technology can be transferred into a standardized clinical application.