Fariba Karimi, Esra Neufeld, Arya Fallahi, Andrea Boraschi, Jaco J. M. Zwanenburg, Andreas Spiegelberg, Vartan Kurtcuoglu, and Niels Kuster, NeuroImage: Clinical 2022, doi: https://doi.org/10.1016/j.nicl.2022.103170
Monitoring intracranial pressure and craniospinal compliance (CC) is frequently required in the treatment of patients suffering from craniospinal diseases. However, current approaches are invasive and cannot provide continuous monitoring of CC. Dynamic exchange of blood and cerebrospinal fluid between cranial and spinal compartments due to cardiac action transiently modulates the geometry and dielectric properties of the brain. The resulting impedance changes can be measured and might be usable as a non-invasive CC surrogate. A numerically robust and computationally efficient approach based on the reciprocity theorem was developed to compute dynamic impedance changes resulting from small geometry and material property changes. The approach was successfully verified against semi-analytical benchmarks, before being combined with experimental brain pulsation data to study the information content of the impedance variation. The results indicate that the measurable signal is dominated by the pulsatile displacement of the cortical brain surface, with minor contributions from the ventricular surfaces and from changes in brain perfusion. Different electrode setups result in complementary findings. The information content from the three investigated electrode pairs was employed to successfully infer subject-specific brain pulsation and motion features, which suggests that non-invasive CC surrogates based on impedance monitoring could be established.
The scientific and technical impact of the study can be summarized as:
- A reliable and efficient computational method was developed for solving subtle dynamic electromagnetic problems where variations in the geometry and/or dielectric properties are relatively small
- The method was used to investigate the measurable head impedance variation resulting from brain pulsation by combining detailed simulations with experimental brain motion data
- The relationships discovered permit determination of subject-specific brain pulsation features from head impedance variations
- The findings demonstrate the potential to establish a non-invasive CC biomarker for diagnostic and monitoring purposes
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