Monitoring the Pulsing brain using Transcranial tissue Doppler ultrasound

It is well established that the brain pulsates with each cardiac cycle, yet relatively little is known about how these brain tissue pulsations (BTPs) are influenced by different physiological factors. Previous research suggests that measurement of BTPs could be used as a potential marker for brain pathology and impaired cerebral haemodynamics, however, existing methods used for BTP measurement are often costly, require an expert user, and are not suitable for continuous neuromonitoring. The aim of this thesis is to use transcranial tissue Doppler ultrasound to investigate factors that affect healthy brain tissue pulsations, and to aid the development of a prototype device developed at University of Leicester, in collaboration with Nihon Kohden (Japan), for clinical measurement of BTPs. An ultrasound phantom is used to investigate the impact of blood pressure on BTPs, along with a systemic state-space model of intracranial pressure dynamics. Numerous healthy volunteer studies are carried out to characterise

healthy BTPs, and determine which factors influence BTP amplitude. The system used was capable of obtaining quality data from numerous positions on the head, including the forehead. BTP signals were successfully detected in all volunteers studied, and the system was well tolerated. BTP amplitude was found to vary greatly between individuals, and with probe position, and increases with depth into the brain. A strong association between BTP amplitude and pulse pressure was observed in all studies.

This thesis introduces a new technique for measuring BTPs which has the potential to be used clinically to give real-time information on brain motion at the patient's bedside. BTP amplitude is strongly influenced by pulse pressure, which is a variable that can be greatly affected in critically unwell patients. Reference data from healthy subjects has also been generated, which can be compared to pathological cases in future work.