First-Step PPG Signal Analysis for Evaluation of Stress Induced during Scanning in the Open-Air MRI Device

Abstract

The paper describes first-step experiments with parallel measurement of cardiovascular parameters using a photoplethysmographic optical sensor and standard portable blood pressure monitors in different situations of body relaxation and stimulation. Changes in the human cardiovascular system are mainly manifested by differences in the Oliva–Roztocil index, the instantaneous heart rate, and variations in blood pressure. In the auxiliary experiments, different physiological and psychological stimuli were applied to test whether relaxation and activation phases produce different measured parameters suitable for further statistical analysis and processing. The principal investigation is aimed at analysis of vibration and acoustic noise impact on a physiological and psychological state of a person lying inside the low-field open-air magnetic resonance imager (MRI). The obtained results will be used to analyze, quantify, and suppress a possible stress factor that has an impact on the speech signal recorded during scanning in the MRI device in the research aimed at 3D modeling of the human vocal tract.

Stress Level Detection and Evaluation from Phonation and PPG Signals Recorded in an Open-Air MRI Device

“…The determined LpMIN, LpMAX, LOFS together with calculated PPGRANGE and HPRIPP values are visualized in Figure 4. The used methodology of heart rate values determined via PPG wave has been described in more detail in [30]. In principle, the procedure works in three basic steps: (1) systolic peaks are localized in the PPG signal, (2) heart pulse periods THP in samples are determined, (3) HR values are calculated using the sampling frequency fs by a basic formula…”

“…This type of our most used MR sequence produces a noise with a sound pressure level (SPL) of about 72 dB (C); the background SPL inside the metal shielding cage is produced mainly by the temperature stabilizer and reaches about 55 dB (C) [29]. In this case, the physiological effect of the noise and vibration on the human organism and auditory system is small but still measurable and detectable [30]. During the phonation signal pick-up in the MF 1 and MF 4 measurement phases, the control room background level was up to 45 dB (C).…”

“…All these parameters together with an actual volume depending on a tested person's weight have influence on the intensity of the produced vibration and noise, on the time duration of the MR scan process, and finally on the stimulated physiological and psychological stress in the examined persons. In previous research [29,30] the measured PPG signals together with the derived HR have already been used to monitor the physiological impact of vibration and acoustic noise on a person examined inside the MRI scanning device.…”

Comparative Measurement of the PPG Signal on Different Human Body Positions by Sensors Working in Reflection and Transmission Modes

“…The methodology of HR determination from the PPG wave was described in more detail in [7]. In principle, the procedure works in three steps: the systolic peaks are localized in the PPG signal, then the heart pulse periods THP are determined, and finally the HR in [min −1 ] is calculated as HR = 60/THP.…”

“…In our previous research [6,7], the PPG signal was picked up from the little or index finger of the left or right hand using the sensor based on transmission principle only. The current work is focused on testing two types of PPG sensors working in transmission and reflection modes placed on different parts of a human body.…”