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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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