Remote simultaneous dual wavelength imaging photoplethysmography: a further step towards 3-D mapping of skin blood microcirculation

Abstract

This paper presents a camera-based imaging photoplethysmographic (PPG) system in the remote detection of PPG signals, which can contribute to construct a 3-D blood pulsation mapping for the assessment of skin blood microcirculation at various vascular depths. Spot measurement and contact sensor have been currently addressed as the primary limitations in the utilization of conventional PPG system. The introduction of the fast digital camera inspires the development of the imaging PPG system to allow ideally non-contact monitoring from a larger field of view and different tissue depths by applying multi-wavelength illumination sources. In the present research, the imaging PPG system has the capability of capturing the PPG waveform at dual wavelengths simultaneously: 660 and 880nm. A selected region of tissue is remotely illuminated by a ring illumination source (RIS) with dual-wavelength resonant cavity light emitting diodes (RCLEDs), and the backscattered photons are captured by a 10-bit CMOS camera at a speed of 21 frames/second for each wavelength. The waveforms from the imaging system exhibit comparable functionality characters with those from the conventional contact PPG sensor in both time domain and frequency domain. The mean amplitude of PPG pulsatile component is extracted from the PPG waveforms for the mapping of blood pulsation in a 3-D format. These results strongly demonstrate the capability of the imaging PPG system in displaying the waveform and the potential in 3-D mapping of blood microcirculation by a non-contact means.

Noncontact blood perfusion mapping in clinical applications

“…Our previous work demonstrated that this technology offers significant advantage over other blood perfusion scanning techniques, since there are evidences showing a viability of a low-cost iPPG system utilising a conventional web-camera [4] . Simultaneous monitoring of perfusion at different tissue depth using dualwavelength light source was also reported [5] , which could lead to the potential of non-contact 3D mapping of microcirculation. To date, however, iPPG has not found major appreciation in certified medical applications, despite numerous literature reviews of its clinical value and validity.…”

“…In order to create such evenly distributed light flux at distances greater than 50 cm from a target area, the illuminator is usually constructed using an array of individual LEDs, which has been reported in our previous work [5] [9] , as well as in [10] . One obvious yet underestimated disadvantage of this approach is inevitable spectral variation between individual LEDs even within the same production batch, with a typical value of around 20-40 nm.…”

Motion-compensated noncontact imaging photoplethysmography to monitor cardiorespiratory status during exercise

“…6 Furthermore, we have previously presented an integrated imaging PPG setup for the detection of tissue optophysiological properties. 11 Recent progress in iPPG research activities has stimulated our interest in the remote assessment of the cardiovascular system for evaluation of the influence of exercise.…”

A remote approach to measure blood perfusion from the human face

“…The feasibility of the camera-based PPG system has been previously demonstrated by means of blood perfusion visualization [6,7] . A previous research report [8] presents a remote reflection-mode CMOS camera-based system with a ring light of similar wavelengths (660 and 840 nm) capturing "heart cycle-related" pulsatile variations.…”