Intracranial Sensors for Continuous Monitoring of Neurophysiology

Monitoring physiological parameters in the brain is important to identify early signs of secondary brain injuries. A variety of different intracranial sensors enable continuous monitoring of important brain parameters in clinical applications. However, many of the clinically approved and established technologies show drawbacks in zero-drift properties, accuracy and magnet resonance imaging (MRI) compatibility. This review gives a comparative overview of the established technologies and provides an outlook on fiber-optic sensors (FOS) with potential use in future intracranial monitoring applications. Neurophysiological parameters recorded by bioelectrical signals include intracranial pressure (ICP), brain temperature, brain tissue oxygenation, cerebral blood flow, and cerebral metabolism. The comparison of ICP sensors revealed that piezoresistive strain gauge sensors provide the highest accuracy and the smallest zero-drift in clinical catheters. Fiber-optic pressure sensors show a potential to be used in future intracranial applications. Thermistors and thermocouples prove to be reliable for temperature measurement in intracranial catheters, but have limited MRI compatibility. FOS show potential to be used in future intracranial catheters for temperature and oxygen measurement, as they provide higher accuracy and a better response time. Microdialysis catheters, in combination with new automated electrochemical and optical analyzers, provide the possibility of routine metabolism monitoring in clinics.