Continuous Monitoring of Changes in Dielectric Properties of Rat Brain After Global Ischemia

This study characterized time-dependent changes in the dielectric properties of rat brain tissue during the first three hours following global ischemia. Adult male Sprague-Dawley rats (n=10) were euthanized by decapitation to induce global ischemia, and each brain was immediately immersed in artificial cerebrospinal fluid maintained at 37 °C. Using an open-ended coaxial probe connected to a vector network analyzer, we measured complex permittivity and conductivity of gray and white matter at discrete 5-minute intervals across the 0.5-10 GHz frequency range. A detailed uncertainty analysis-based on NIST guidelines-quantified both systematic and random errors, confirming that observed property changes exceed instrumental variability. In gray matter, relative permittivity decreased by approximately 5-8 % over three hours, while conductivity showed a frequency-dependent reduction ranging from 18 % at 0.5 GHz to 12 % at 10 GHz, with the largest shifts occurring within the first 30 minutes post-ischemia. White matter exhibited smaller permittivity changes (< 10 %) and less pronounced conductivity alterations. These findings demonstrate that ischemic injury produces measurable, dynamic dielectric contrasts between gray and white matter. The results lay a foundational framework for microwave-based imaging and real-time monitoring of ischemic events and may inform future development of portable dielectric-sensing devices for stroke diagnosis and treatment assessment.