A Statistical Metrology Approach to Compare the Quality of Optical Pulse Wave Signals
Dr. Janos Palhalmi (PhD) and Jan-Hein Broeders
Computing in Cardiology 2019
Biometric metrology is becoming increasingly important as the wearable application specific biosensors are capable of generating accurate raw signals representing certain vital states. A comparative statistical approach has been worked out to answer questions arising from a biosensor testing measurement technology perspective. In this specific work two high quality optical solutions (Analog Devices’ ADPD107 and ADPD188GGZ) were compared to analyse the deep data level similarities or differences between the photo-plethysmography (PPG) raw biomedical signals generated by the two individual systems.
Two minutes long parallel recordings were carried out with the evaluation boards of both optical systems (EVAL-HCRWATCH and EVAL-ADPD188GGZ) on 11 healthy human subjects. Recordings were repeated on both wrists to avoid side specific influence. Both systems have been controlled by Analog Devices’ user-interface called “Application WaveTool”. For the test, configuration settings were optimized to achieve the highest signal quality and lowest power consumption (5.1 mW at 100 Hz sampling frequency). The physiologically and biometrically irrelevant frequency bands (<0.25 Hz,>40 Hz) were filtered before the data analysis.
A wavelet coherence-based method was worked out to compare the relevant frequency bands and two different correlation-based methods were developed to compare the wave-to-wave stability and similarity of the two compared signals. Magnitude squared coherence values were above 0.9 in all the explored frequency bands (0.25-40 Hz). Correlation coefficients were never under 0.9 while p values were always under 0.001 in case of the PPG wave-to-wave comparisons. Based on the results we can conclude, that the quality of the PPG signal recorded by the new ADPD188GGZ integrated optical module, reaches the same performance level as the ADPD107 discrete module, with key benefits such as small PCB area, ease of use (especially for companies with limited Optical expertise) and shorter Time to Market.
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