Magnetic Resonance Imaging Compatible Non-Invasive Fibre-Optic Sensors Based on the Bragg Gratings and Interferometers in the Application of Monitoring Heart and Respiration Rate of the Human Body: A Comparative Study

Abstract

The publication presents a comparative study of two fibre-optic sensors in the application of heart rate (HR) and respiratory rate (RR) monitoring of the human body. After consultation with clinical practitioners, two types of non-invasive measuring and analysis systems based on fibre Bragg grating (FBG) and fibre-optic interferometer (FOI) have been designed and assembled. These systems use probes (both patent pending) that have been encapsulated in the bio-compatible polydimethylsiloxane (PMDS). The main advantage of PDMS is that it is electrically non-conductive and, as well as optical fibres, has low permeability. The initial verification measurement of the system designed was performed on four subjects in a harsh magnetic resonance (MR) environment under the supervision of a senior radiology assistant. A follow-up comparative study was conducted, upon a consent of twenty volunteers, in a laboratory environment with a minimum motion load and discussed with a head doctor of the Radiodiagnostic Institute. The goal of the laboratory study was to perform measurements that would simulate as closely as possible the environment of harsh MR or the environment of long-term health care facilities, hospitals and clinics. Conventional HR and RR measurement systems based on ECG measurements and changes in the thoracic circumference were used as references. The data acquired was compared by the objective Bland–Altman (B–A) method and discussed with practitioners. The results obtained confirmed the functionality of the designed probes, both in the case of RR and HR measurements (for both types of B–A, more than 95% of the values lie within the ±1.96 SD range), while demonstrating higher accuracy of the interferometric probe (in case of the RR determination, 95.66% for the FOI probe and 95.53% for the FBG probe, in case of the HR determination, 96.22% for the FOI probe and 95.23% for the FBG probe).

Vital Sign Monitoring and Cardiac Triggering at 1.5 Tesla: A Practical Solution by an MR-Ballistocardiography Fiber-Optic Sensor

“…The next step was to smooth out the respiratory rate curve. A median filter with a window size = 3, which was statistically more robust was used for this purpose [44,66].…”

“…A same bandpass filter with a cut-off frequency from 5 to 20 Hz was used to determine the HR. These values were calculated based on approaches detailed in [44,66,67]. As such the filtered signal provided a more reliable representation of the cardiac activity.…”

“…The use of Fiber Bragg Grating (FBG) to monitor RR or HR is becoming more popular, as evidenced, for example, by publications [34,35,36,37,38,39,40,41,42,43,44,45,46]. These publications describe, for example, various types of FBG encapsulations in materials such as polydimethylsiloxane (PDMS), which are characterized by their inertness to human skin and EMI.…”

Fiber-Optic Breath Sensors: A Comparison Study

“…On the contrary, the effect of temperature is manifested by lower frequencies. For these reasons, a third-order lowpass filter is used to establish the breathing frequency (Butterworth type) with limit frequencies from 0 to 0.5 Hz [16]. This is followed by the process of normalization and centering of the signal to the zero, median, value and the detection of peaks.…”

Blood Pressure Sensors: Materials, Fabrication Methods, Performance Evaluations and Future Perspectives

“…The applied pressure subsequently modifies the light intensity or wavelength through a Fiber Bragg Grating (FBG) configuration [201]. FBG wearable sensors have gained interest as they have electromagnetic immunity and high sensitivity that make them ideal for the use in an MRI environment with no threat to the patient and no influence over the quality of imaging [202][203][204] while using electrically non-conductive, bio-compatible and low optical permeability materials such as PDMS [205] and PA [206]. However, FBG-based sensing is constrained with the necessity of using the sophisticated signal analysis to detect breathing and cardiac activity [203], the little resistance to mechanical stress [206] and the limited range of Bragg wavelengths [204].…”