Multifrequency Microwave Radiation of Heterogeneous Medium for Brain Temperature Monitoring

The brain temperature monitoring is crucial for understanding the physiological and pathological processes of the brain. Its abnormal changes are often closely related to major brain diseases such as stroke. Although the microwave radiometry (MWR) method has been applied in medical diagnostics, the current research primarily focuses on exploratory experimental analyses. The microwave radiation mechanisms in complex multilayered brain structures remain insufficiently studied. This article focuses on the modeling and characterization of multifrequency microwave radiation in human brain tissue. A radiation transfer model for multilayer tissues based on a realistic anatomical model was developed. The distribution of brightness temperature (TB) across the multilayer tissues of the head was systematically investigated. This study elucidated the effects of frequency, incidence angle, tissue thickness, and arterial blood temperature on TB. In addition, a temperature measurement depth calculation model based on sensitivity thresholds is proposed to offer theoretical support for optimizing frequency selection in the MWR system and for accurately identifying thermally abnormal lesions. The simulation results show that the analysis under the completely passive perspective can provide accurate theoretical guidance for the MWR method. The thermodynamic temperature and TB co-simulation framework presented in this study provides a theoretical foundation for optimizing MWR system design and improving the accuracy of temperature inversion.