the blood perfusion mapping in the human skin by ... · the blood perfusion mapping in the human...
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THE BLOOD PERFUSION MAPPING IN THE HUMAN SKIN
BY PHOTOPLETHYSMOGRAPHY IMAGING
U. Rubins, R. Erts and V. Nikiforovs
University of Latvia, Institute of Atomic physics and spectroscopy, Riga, Latvia
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IFMBE Proceedings 25/VII: 754–756
REFERENCES
Hardware. The measurement technique of PPGI is shown in Fig. 1. Sony HDR-SR1 AVC
hi-definition (HD) Handycam® camcorder was used for video recording. As a source of
light 60W incandescent bulb lamp was used. Video clips were taken from human fingers
in light transmission mode and face in light reflection mode.
Software. Video stream from camcorder was copied to computer hard drive. Custom
developed software (Matlab®) was used for video processing (Fig. 2). Video content was
splitted to individual frames and loaded into image cube matrix. Then region of interest
(RoI) and RGB color was selected and light intensity variations were calculated in
selected RoI in each pixel of video frame. The next part of processing was visualization of
spatial distribution of PPG signal intensity – PPGI mapping. The potential application of
the PPGI is visualisation of blood flow perfusion in 2-D space.
The interface of PPGI software is shown in Fig. 3. Special algorithm exclude areas of
motions from all video frames (Fig. 3a). Evaluated PPGI map is shown in Fig. 3b.
METHODS
A CMOS camera-based imaging photoplethysmographic (PPGI) system is
described to detect the blood pulsations in tissue. Attention of PPGI is drawn to
the potential applications in visualized blood perfusion. Intensity variations of
three wavelengths (620 nm, 520 nm and 432 nm) were detected and analyzed in
each pixel of image. To obtain a two-dimensional mapping of the dermal perfusion
measurement, custom image-processing software has been developed. The high-
resolution PPGI images were derived from human fingers (transmission mode) and
face (reflection mode), evaluated at three wavelengths. The newly developed
system can be usable in skin blood perfusion monitoring for clinical applications.
ABSTRACT
PPGI mapping. Fig. 4a shows the image of the left arm fingers in penetrating light. Because
red light penetrates through the tissue in several cm depth, red light (620 nm) is selected
from RGB space. Fig. 4b shows the PPGI map evaluated from the video frames.
Fig. 5a-c shows the image of human face in transmitted light in three colors of RGB space:
red (620 nm), green (520 nm) and blue (432nm). The PPGI maps (Fig. 5d-f) shows blood
perfusion variations and depends on the wavelength of light. This is because optical
radiation of different wavelength penetrates and reaches vascular bed at different depths in
skin layers. Red light reaches more deeper blood vessels in contrast of blue light that
penetrates less than 1mm in deep.
In both transmission mode and reflection mode PPGI maps are not affected by non-pulsatile
component of skin surface reflection or tissue absorption and shows only pulsatile
component of blood.
PPG signals. Fig. 6 shows the PPG signal evaluated from the averaged pixel intensity
values of finger’s video. Both the arterial pulsation and the slowly changing respiration
rhythm can be seen clearly in the time domain. In frequency domain, the exact frequency
value of the heartbeat (about 1.1 Hz) with its higher-order harmonic and the low frequency
of respiration rhythm can be determined too.
RESULTS
a b c d e f
Photoplethysmography imaging (PPGI) is a non-invasive technique for detection of blood
flow pulsations in skin using backscattered optical radiation [1-6]. The optical radiation
after the penetration into skin is partially absorbed in tissue and it is modulated by blood
pulsations due to cardiac activity. Backscattered radiation can be detected by video
camera as weak light pulsations, invisible by human eye. In this research, a non-contact
PPGI system with original image processing software was developed. The software is
capable of monitoring blood perfusion in human skin in high-resolution images. The aim
of study is testing of the new technique for detection of PPGI at multiple wavelengths.
INTRODUCTION
Financial support from European Social Fund, project
#2009/0211/1DP/1.1.1.2.0/09/APIA/VIAA/077 is highly appreciated.
ACKNOWLEDGEMENTS
Figure 1. The measurement technique of PPGI
Video stream
Image cube
matrix
Select region
of interest and
RGB color
Removing of
motion artifacts
Evaluation of
PPG pulse
amplitudes
Normalizing PPGI mapping
Figure 2. The block scheme of PPGI algorithm
Figure 3. The interface of PPGI software
a b
CONCLUSIONS
We were performed measurements of light variations in human skin and we first realized
skin blood perfusion mapping in high resolution using consumer type camcorder. This
technique showed sufficient sensitivity to the visible light spectra, it is non-invasive and easy
to use.
Advantages. For mapping of blood perfusion consumer level camcorder can be used. As light source
incandescent bulb light can be used.
Disadvantages. For quality PPGI high power light source is needed. Electrical bulb light generates some
noise. The volunteer should be in still position, even slightest movements generates noise artifacts.
Figure 4. Video frame of fingers in penetrating red light (a) and evaluated PPGI map (b)
Figure 5. Video frame of human face in reflected light in red (a), green (b) and blue (c) colors and corresponding PPGI maps (d,e,f)
Figure 6. PPG signal evaluated from the averaged pixel values of finger’s video (a) and its power spectrum (b)
a b
a b