Physiological impact of vibration and noise in an open-air magnetic resonance imager: Analysis of a PPG signal of an examined person

The paper is focused on analysis of negative influence of the generated vibration and acoustic noise on a physiological and psychological state of an examined person lying in the scanning area of the magnetic resonance imaging (MRI) tomograph working with a low magnetic field. This negative influence on the human body and psychic can be monitored by measuring the blood pressure (BP), the heart rate (HR) and the speech signal recorded during MR scanning, as the stress is manifested by changes in the bloodstream and in the voice. The first part of the presented work is aimed at finding a methodology for measurement of different signals of a tested person lying in the scanning area of the MRI device. In the main investigation, the BP and HR parameters were measured in parallel for a person scanned during execution of the whole MR scan sequence. For this purpose, we apply the photo-plethysmography (PPG) using an optical sensor for non-invasive acquisition of vital information about the cardiovascular system from the skin surface. This optical sensor complies with the requirements for working in the magnetic field environment with present radio-frequency and electromagnetic disturbance. Variations in the photo-detector signal are related to changes in the blood volume inside the tissue. Signal filtering and further processing are necessary to obtain a clean PPG waveform that is then used to determine the instantaneous heart rate. In the frame of our experiments, different types of portable BP and HR measuring devices were tested and compared.