Numerical Simulation of Inductive Phase Shift Due a Brain Hematoma

Abstract

We show a theoretically electromagnetic induction method to detect the changes of ∞uid volume into an organic tissue. This method is technique to detect a phase shift through measurements of induced electrical currents due a RF signal. This method was designed for volumetric brain edema monitoring. Circular and planar magnetron coils were evaluated and compared for their ability to detect edema in the brain through volumetric inductive phase shift spectroscopy. The circular coil was considered as a single turn wire and the magnetron surface coil conflguration was based on the principle of the cavity magnetron with successive slots. The brain cavity was modeled as an idealized sphere transversely centered with respect to the coils. The volumetric sensitivity to changes in the brain was examined by inserting in the brain cavity a spherical edema/haematoma. Spectra of inductive phase shift induced in a second circular or magnetron receiver coils were estimated between frequencies from 100kHz to 50MHz. Phase shift shows sensitivity to the presence of the edema/haematoma increased with frequency. The use of a planar magnetron as the receiver coil produced a substantial increase in sensitivity, in particular at higher frequency of 50MHz. Trauma to the head may results in the accumulation of liquids or blood in certain region of the brain. Edema is a medical condition in which the relative amount of liquid in tissue or organs increases. Haematoma is a pathological condition in which accumulation of blood occurs in a speciflc region. The characteristic of brain edema/haematoma is that it develops in a delayed and gradually progressive fashion after a head trauma or event has occurred, over a period of hours or days, and is a cause of substantial mortality (1). Detection of edema/haematoma in the brain is essential for assessment of the medical condition and treatment. Because the complex electrical properties of edema/haematoma are substantially difierent from a hose of normal tissue, various measurements of electrical properties of the brain where proposed to non-invasive detect the changes in there (2{6). In order to optimize the detection technology we have explored, in a recent study, the possible use of a magnetron coil (7) on the inductive volumetric phase shift of the brain in the presence of a edema/haematoma. We have compared the sensitivity of a magnetron coil with that of a circular coil. The results have shown that the magnetron coil has a somewhat greater sensitivity to the detection of a edema/haematoma than the circular coil. This study reveals that the location of the edema/haematoma has a substantial efiect on the sensitivity of the magnetron and circu- lar coils. Furthermore, we flnd that at certain difierent frequencies the various locations of the edema/haematoma produce no volumetric phase shift.