A Wearable Device for Dynamic Monitoring of Cerebral Blood Flow Based on Electromagnetic Coupling Sensing

Assessment of cerebral blood flow (CBF) is essential for the prevention and management of strokes. In this study, the electromagnetic coupling sensor with a dual-layer planar spiral structure was designed to enhance electrical coupling and reduce detection frequency. Based on this sensor, a wearable device for dynamic monitoring of CBF was established, which reflected changes in brain conductivity and permittivity by measured resonant frequency (RF). The brine concentration and volume detection sensitivity of this sensor were evaluated in the basic performance test experiments. Its detection depth and range were tested on a model of simulated vascular pulsation. We further studied the feasibility of the wearable device to obtain different CBF responses corresponding to various internal pressure excitations. In addition, we recruited 24 healthy volunteers to simultaneously monitor cerebral oxygen (CO) and RF, and we examined the pattern of RF change throughout the caffeine-induced CBF disturbance. Based on the main frequency change characteristics of the RF signal after taking caffeine, the effectiveness of the wearable monitoring device to distinguish between normal and abnormal CBF states was analyzed. The results show that the measured RF has a significant linear relationship with brine concentration and volume, with sensitivities of 0.0751 kHz/(g/ml) and $2.2359e^{-5}$ kHz/ml, respectively. The frequencies of periodic changes in RF correspond to that of simulated vascular pulsation, and the sensor has a detection depth of 9 cm and a detection range of 4 cm. In CBF detection under various simulated intravascular pressures, the average RF exhibits the same trend of variation as the simulated intravascular pressure. These results indicate that the wearable gadget can detect CBF that has been triggered by various simulated vascular pulsation frequencies and internal pressures. During the process of increased cerebrovascular stiffness and decreased CO produced by caffeine consumption in healthy volunteers, the characteristics of RF pulsation exhibit a nonlinear downward trend. The abnormal state of CBF selected based on the turning point of the main frequency change under the short-time Fourier transform is significantly different from the normal state ( ${p} < 0.05$ ). The results illustrate that the electromagnetic coupling sensing (ECS)-based wearable device can assess immediate responses to abnormal intracranial blood supply and distinguish different intracranial overall CBF levels effectively.