A study of blood perfusion mapping was performed with a remote opto-physiological imaging (OPI) system coupling a
sensitive CMOS camera and a custom-built resonant cavity light emitting diode (RCLED) ringlight. The setup is suitable
for the remote assessment of blood perfusion in tissue over a wide range of anatomical locations. The purpose of this
study is to evaluate the reliability and stability of the OPI system when measuring a cardiovascular variable of clinical
interest, in this case, heart rate. To this end, the non-contact and contact photoplethysmographic (PPG) signals obtained
from the OPI system and conventional PPG sensor were recorded simultaneously from each of 12 subjects before and
after 5-min of cycling exercise. The time-frequency representation (TFR) method was used to visualize the time-dependent
behavior of the signal frequency. The physiological parameters derived from the images captured by the OPI
system exhibit comparable functional characteristics to those taken from conventional contact PPG pulse waveform
measurements in both the time and frequency domains. Finally and more importantly, a previously developed opto-physiological
model was employed to provide a 3-D representation of blood perfusion in human tissue which could
provide a new insight into clinical assessment and diagnosis of circulatory pathology in various tissue segments.
Non-contact reflection photoplethysmography (NRPPG) is being developed to trace pulse features for comparison with
contact photoplethysmography (CPPG). Simultaneous recordings of CPPG and NRPPG signals from 22 healthy subjects
were studied. The power spectrum of PPG signals were analysed and compared between NRPPG and CPPG. The
recurrence plot (RP) was used as a graphical tool to visualize the time dependent behaviour of the dynamics of the pulse
signals. The agreement between NRPPG and CPPG for physiological monitoring, i.e. HRV parameters, was determined
by means of the Bland-Altman plot and Pearson's correlation coefficient. The results indicated that NRPPG could be
used for the assessment of cardio-physiological signals.
A CMOS camera-based imaging photoplethysmography (PPG) system has been previously demonstrated for the
contactless measurement of skin blood perfusion over a wide tissue area. An improved system with a more sensitive
CCD camera and a multi-wavelength RCLED ring light source was developed to measure blood perfusion from the
human face. The signals acquired by the PPG imaging system were compared to signals captured concurrently from a
conventional PPG finger probe. Experimental results from eight subjects demonstrate that the camera-based PPG
imaging technique is able to measure pulse rate and blood perfusion.
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.
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