(E-195) Using ultrasound to measure intracranial pressure an in vitro study

Introduction:: Intracranial pressure (ICP) monitoring is crucial for the diagnosis and management of various neurological conditions, including traumatic brain injury, hydrocephalus, and intracranial tumours. Current invasive methods, such as intraventricular or intraparenchymal catheters, pose significant risks to patients. Non-invasive techniques, while safer, lack the accuracy and precision needed for reliable ICP assessment. Microbubbles have been employed as ultrasound contrast agents (UCAs) for non-invasive blood pressure measurement. These microbubbles exhibit greater compressibility compared to surrounding fluid (e.g., blood) and thus can change size in response to pressure variations. The alteration in size can be observed in scattered signals, offering the potential for pressure measurement. The method known as Sub-Harmonic Assisted Pressure Estimation (SHAPE) utilizes the subharmonic amplitude of scattered signals for pressure measurement. While SHAPE has been used to estimate blood pressure, it has not been applied to ICP estimation due to the skull's hindrance to ultrasound signals by reducing signal intensity. This study investigates the potential of using ultrasound with microbubbles as UCAs for non-invasive ICP measurement.


Materials and Methods:: To simulate the vasculature of the brain while creating a controlled environment for pressure monitoring, a polydimethylsiloxane (PDMS) chip was designed and fabricated. The chip featured a network of interconnected channels that mimicked the dimensions and structure of cerebral vasculature. The PDMS chip was connected to a microfluidic system, consisting of a pair of syringe pumps to continuously control the flow of fluid and microbubbles, and several pressure sensors to monitor pressure at different sites. The chip was then mounted onto an ultrasound-compatible stage with an adjustable height, allowing for accurate positioning and alignment with the ultrasound transducer. A clinical ultrasound system with a linear array transducer was used for SHAPE analysis. The system was calibrated to determine the optimal gain and power settings for microbubble detection and imaging. The microbubble suspension was introduced into the PDMS chip, and b-mode imaging is performed to visualize the microbubbles. Subsequently, the SHAPE technique was applied to assess pressure based on the subharmonic amplitude of scattered signals from the microbubbles. A customized software was designed to visualize microbubbles and extract subharmonic amplitudes. The experimentally determined ICP values were compared with the actual pressure values recorded by the pressure sensors, allowing evaluation of the effectiveness of the methods.




Results, Conclusions, and Discussions:: The subharmonic signals generated by microbubbles have been observed using b-mode imaging with a filter in the subharmonic region, a technique known as subharmonic imaging. This method only visualizes microbubbles, as tissues do not produce subharmonics. A pressure difference has been noted, with higher pressure at the inlet and lower pressure at the outlet, aligning with measurements taken by pressure sensors. Our findings demonstrate it is possible to measure ICP using ultrasound with microbubbles as UCAs. However, further studies are needed to validate the technique's accuracy in clinical settings and to investigate the potential limitations of the technique, such as the impact of skull thickness on ultrasound signal intensity. In addition, the feasibility of implementing this technique in real-time clinical settings needs to be explored.






Acknowledgements (Optional): : This work is sponsored by China Scholarship Council and Royal Society of Chemistry.

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