Comparison of Three Prototypes of PPG Sensors for Continual Real-Time Measurement in Weak Magnetic Field

Abstract

This paper is focused on investigation of three developed prototypes of sensors based on the photoplethysmography (PPG) principle for continual measurement of the PPG signal in the magnetic field environment with the inherent radiofrequency and electromagnetic disturbance. The tested prototypes differ in the used optical part of the PPG sensor and their working mode, control unit, power supply, and applied Bluetooth (BT) communication methods. The main aim of the current work was motivated by finding suitable and universal parameter settings for PPG signal real-time recording in different working mode conditions. Comparative measurements in laboratory conditions by certified commercial pulse oximeter and blood pressure monitor (BPM) devices show good stability and proper accuracy of finally determined heart rate values. The supplementary investigation certifies the necessity of the placement of the pressure cuff of the BPM device on the opposite arm than the tested PPG sensor. Measurement experiments inside the scanning area of the running weak field magnetic resonance scanner verify proper function and practical usability of sensed PPG signals for further processing and analysis in all three prototype cases. Additional testing shows that the BT transmission in the scanning area has no visible influence on the quality of the finally obtained scanner images.

Internet of Medical Things and Healthcare 4.0: Trends, Requirements, Challenges, and Research Directions

“…A PPG sensor measures changes in blood flow by placing a light source and a photodetector on the skin's surface. The PPG signal has recently attracted the attention of several academics interested in extracting further data from it [48]. The PPG signal's second derivative wave carries crucial diagnostic information.…”

Photoplethysmogram Recording Length: Defining Minimal Length Requirement from Dynamical Characteristics

“…Additionally, in many practical cases, lower-sampling-rate PPG data are used [ 45 , 46 , 47 ]. To broaden the applicability of this study, collected PPG recordings were two- and four-times subsampled to generate sparse PPG time series.…”

“…Examples of the resulting time series obtained using the original (𝜃 = 0) and noisy (𝜃 = 0.25) x time series are shown in Figure 3, where the addition of dynamical noise affected the amplitude of the time series and created additional fluctuations compared to the original time series. Additionally, in many practical cases, lower-sampling-rate PPG data are used [45][46][47].…”

Wearable Two-Channel PPG Optical Sensor with Integrated Thermometers for Contact Measurement of Skin Temperature

“…Age and gender as well as skin color and the temperature of the skin surface can have an influence on the PPG signal, too. Our previous solution of wearable PPG sensors [7] does not allow direct temperature measurement by any contact thermo-element during the PPG signal sensing. For precise determination of PPG wave parameters, the current temperature should be measured at the same time as the PPG signal is sensed.…”

“…In addition, we try to formulate a recommendation about a proper arrangement and timing of PPG signal sensing to obtain the desired PPG parameters with a sufficient accuracy. Described firststep experiments were realized in normal laboratory conditions, with planned further application for measurements inside a running low-field MRI device [7,8].…”