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Feasibility of long-distance heart rate monitoring using transmittance photoplethysmographic imaging (PPGI).

Amelard R, Scharfenberger C, Kazemzadeh F, Pfisterer KJ, Lin BS, Clausi DA, Wong A - Sci Rep (2015)

Bottom Line: For this purpose, a novel PPGI system was designed at the hardware and software level.Temporally coded illumination (TCI) is proposed for ambient correction, and a signal processing pipeline is proposed for PPGI signal extraction.Experimental results show that the processing steps yielded a substantially more pulsatile PPGI signal than the raw acquired signal, resulting in statistically significant increases in correlation to ground-truth PPG in both short- and long-distance monitoring.

View Article: PubMed Central - PubMed

Affiliation: University of Waterloo, Department of Systems Design Engineering, Waterloo, N2L3G1, Canada.

ABSTRACT
Photoplethysmography (PPG) devices are widely used for monitoring cardiovascular function. However, these devices require skin contact, which restricts their use to at-rest short-term monitoring. Photoplethysmographic imaging (PPGI) has been recently proposed as a non-contact monitoring alternative by measuring blood pulse signals across a spatial region of interest. Existing systems operate in reflectance mode, many of which are limited to short-distance monitoring and are prone to temporal changes in ambient illumination. This paper is the first study to investigate the feasibility of long-distance non-contact cardiovascular monitoring at the supermeter level using transmittance PPGI. For this purpose, a novel PPGI system was designed at the hardware and software level. Temporally coded illumination (TCI) is proposed for ambient correction, and a signal processing pipeline is proposed for PPGI signal extraction. Experimental results show that the processing steps yielded a substantially more pulsatile PPGI signal than the raw acquired signal, resulting in statistically significant increases in correlation to ground-truth PPG in both short- and long-distance monitoring. The results support the hypothesis that long-distance heart rate monitoring is feasible using transmittance PPGI, allowing for new possibilities of monitoring cardiovascular function in a non-contact manner.

No MeSH data available.


Example images for Experiment 1 (short-distance monitoring) and Experiment 2 (long-distance monitoring).The unprocessed frames (first column) contained uncontrolled ambient illumination (windows, overhead lights, etc.) as well as controlled active LED illumination near the fingers. Ambient correction using TCI (second column) removed the contribution of ambient illumination to the scene, yielding transmittance due solely to active LED illumination of which the spectral and power characteristics are known. See Video 1 and Video 2 for video results of ambient correction with varying illumination.
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f3: Example images for Experiment 1 (short-distance monitoring) and Experiment 2 (long-distance monitoring).The unprocessed frames (first column) contained uncontrolled ambient illumination (windows, overhead lights, etc.) as well as controlled active LED illumination near the fingers. Ambient correction using TCI (second column) removed the contribution of ambient illumination to the scene, yielding transmittance due solely to active LED illumination of which the spectral and power characteristics are known. See Video 1 and Video 2 for video results of ambient correction with varying illumination.

Mentions: Two experiments were performed to assess the feasibility of long-distance monitoring. In Experiment 1, the camera and LED were separated by 20 cm, serving as short-distance base case validation. The participants were asked to position their fingers between the LED and camera so that their fingers covered the beam of the LED. In Experiment 2, the camera and LED were separated by 1.5 m (“long-distance”), and the participants were asked to position their fingers at approximately 10 cm from the LED. Figure 3 shows example images of both experiments before and after ambient correction. For each experiment, a 10 s window was chosen that yielded a clean ground-truth PPG signal for validation. The normalised power spectral density (PSD) was computed for spectral analysis to demonstrate each signal’s dominant frequency components. In an ideal signal, the fundamental heart rate should be the dominant frequency. Furthermore, to assess temporal signal fidelity, the Pearson’s linear correlation coefficient ρ was computed between PPGI and PPG signals. This metric is offset- and scale-invariant, suitable for the problem of comparing unit-less PPG signals:


Feasibility of long-distance heart rate monitoring using transmittance photoplethysmographic imaging (PPGI).

Amelard R, Scharfenberger C, Kazemzadeh F, Pfisterer KJ, Lin BS, Clausi DA, Wong A - Sci Rep (2015)

Example images for Experiment 1 (short-distance monitoring) and Experiment 2 (long-distance monitoring).The unprocessed frames (first column) contained uncontrolled ambient illumination (windows, overhead lights, etc.) as well as controlled active LED illumination near the fingers. Ambient correction using TCI (second column) removed the contribution of ambient illumination to the scene, yielding transmittance due solely to active LED illumination of which the spectral and power characteristics are known. See Video 1 and Video 2 for video results of ambient correction with varying illumination.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4594125&req=5

f3: Example images for Experiment 1 (short-distance monitoring) and Experiment 2 (long-distance monitoring).The unprocessed frames (first column) contained uncontrolled ambient illumination (windows, overhead lights, etc.) as well as controlled active LED illumination near the fingers. Ambient correction using TCI (second column) removed the contribution of ambient illumination to the scene, yielding transmittance due solely to active LED illumination of which the spectral and power characteristics are known. See Video 1 and Video 2 for video results of ambient correction with varying illumination.
Mentions: Two experiments were performed to assess the feasibility of long-distance monitoring. In Experiment 1, the camera and LED were separated by 20 cm, serving as short-distance base case validation. The participants were asked to position their fingers between the LED and camera so that their fingers covered the beam of the LED. In Experiment 2, the camera and LED were separated by 1.5 m (“long-distance”), and the participants were asked to position their fingers at approximately 10 cm from the LED. Figure 3 shows example images of both experiments before and after ambient correction. For each experiment, a 10 s window was chosen that yielded a clean ground-truth PPG signal for validation. The normalised power spectral density (PSD) was computed for spectral analysis to demonstrate each signal’s dominant frequency components. In an ideal signal, the fundamental heart rate should be the dominant frequency. Furthermore, to assess temporal signal fidelity, the Pearson’s linear correlation coefficient ρ was computed between PPGI and PPG signals. This metric is offset- and scale-invariant, suitable for the problem of comparing unit-less PPG signals:

Bottom Line: For this purpose, a novel PPGI system was designed at the hardware and software level.Temporally coded illumination (TCI) is proposed for ambient correction, and a signal processing pipeline is proposed for PPGI signal extraction.Experimental results show that the processing steps yielded a substantially more pulsatile PPGI signal than the raw acquired signal, resulting in statistically significant increases in correlation to ground-truth PPG in both short- and long-distance monitoring.

View Article: PubMed Central - PubMed

Affiliation: University of Waterloo, Department of Systems Design Engineering, Waterloo, N2L3G1, Canada.

ABSTRACT
Photoplethysmography (PPG) devices are widely used for monitoring cardiovascular function. However, these devices require skin contact, which restricts their use to at-rest short-term monitoring. Photoplethysmographic imaging (PPGI) has been recently proposed as a non-contact monitoring alternative by measuring blood pulse signals across a spatial region of interest. Existing systems operate in reflectance mode, many of which are limited to short-distance monitoring and are prone to temporal changes in ambient illumination. This paper is the first study to investigate the feasibility of long-distance non-contact cardiovascular monitoring at the supermeter level using transmittance PPGI. For this purpose, a novel PPGI system was designed at the hardware and software level. Temporally coded illumination (TCI) is proposed for ambient correction, and a signal processing pipeline is proposed for PPGI signal extraction. Experimental results show that the processing steps yielded a substantially more pulsatile PPGI signal than the raw acquired signal, resulting in statistically significant increases in correlation to ground-truth PPG in both short- and long-distance monitoring. The results support the hypothesis that long-distance heart rate monitoring is feasible using transmittance PPGI, allowing for new possibilities of monitoring cardiovascular function in a non-contact manner.

No MeSH data available.