Experimental sensitivity study of inductive phase shift spectroscopy as non-invasive method for hypoperfusion vs bleeding volumetric detection in brain.

Hypoperfusion and bleeding in brain are medical conditions that involve a decrease and an increase of the relative amount of blood in tissue respectively. Both pathologies result in brain edema. This study evaluates experimentally the sensitivity of an induction based non-invasive technique for detection of changes of fluid volume through phase shift measurements as a possible method to distinguish brain hypoperfusion and bleeding process by volumetric monitoring. An induction coil-spherical head model was build and tested. The model involves two different diameter coils coaxially centered on a two-compartment glass sphere head model centrally placed with respect to the coils. Fluid volumes of physiological saline in 1 ml decrement and increments were used to simulate different hypoperfusion and bleeding levels respectively. Inductive phase shift measurements were measured in a whole bandwidth (1 kHz-1 GHz) by an experimental inductive spectrometer. The results show significant phase shift increase as a function of frequency and fluid volume in both pathologies simulated. At certain frequencies the hypoperfusion and bleeding phase shifts increase run in opposite ways. The experiments suggest that the tested technique has the potential to distinguish the processes of hypoperfusion and bleeding in brain by non-invasive, continuous and volumetric monitoring.