Tissue fluid monitoring by magnetic induction spectroscopy

Problem: The monitoring of the local fluid distribution in human tissues still represents a difficult task. Established methods are either complicated and cost-intensive (e. g. tracer dilution, imaging methods) or exhibit poor reproducibility (bioimpedance methods). Tracer dilution and bioimpedance are hardly applicable for certain body compartments, such as the brain. However, the non-invasive monitoring of brain edema still represents an unsolved problem of intensive care medicine, where the method of choice is still the implantation of intracranial pressure- sensors. Suggested solution: Multichannel magnetic induction spectroscopy (MIS) is a new method for measuring the electrical conductivity of biological tissue via the perturbation of an alternating magnetic field at multiple frequencies. The feasibility of MIS has recently been demonstrated for homogeneous biological objects. As the conductivity is closely related to water fractions in the intra- and extracellular space, MIS is highly promising for hydration monitoring. The technique is contact-less and thus appears especially attractive for the monitoring of pathologies in the central nervous system, which are correlated with local fluid shifts. Such pathologies, e. g. brain edema, hemorrhages or epileptic events, are otherwise difficult to access continuously. Additional applications are local hydration-monitoring during hemodialysis and fluid-management. Objective: Goal of the project is the theoretical and practical demonstration of the applicability of MIS for contact- less monitoring of local tissue fluid shifts. This demonstration shall be based on both numerical studies and preclinical. experiments. A particular emphasis shall be lied on brain edema. Methods: In the first year the feasibility of MIS shall be investigated with electromagnetic simulation models for a human head and for a head phantom. The model shall provide information about the spatial resolution and the uncertainty of the parameters to be determined. Moreover it shall be used for the optimization of the coil- configuration for application and reception of the magnetic field. in the second year an experimental MIS-system shall be constructed, based on a recently developed prototype. The practical feasibility will be tested by measurements on phantoms. Expected benefit: If it feasibility is proven, the new method has not only the potential of complementing established methods for tissue hydration but represents a promising alternative to invasive pressure sensing in the brain for the monitoring of brain edema formation. This would mean a significant improvement of the monitoring and would probably lead to a marketable medical product.