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Objective: To determine the validity of the key mathematical assumptions used in electrical impedance tomography for human head tissues. Approach:Conductivity and permittivity data collected from available literature for each tissue within the human head have been evaluated and critiqued. The most relevant dielectric tissue data for each tissue was then used to assess the validity of the mathematical assumptions of electrical impedance tomography in terms of their suitability for human head imaging in order to estimate related errors. Main Results:For induced currents with frequencies greater than 200 Hz the internal current source density is negligible. The assumption that magnetic effects are negligible is valid to an error of 1.7% for human head tissues for frequencies below 1 MHz. The capacitive effects are negligible for CSF, dura mater, blood, bone (cortical), and deep tissue skin for frequencies less than 3.2 MHz, 320 kHz, 25 kHz, 3.2 kHz, and 130 Hz respectively. However, the capacitive effects are not negligible for brain tissues, as the minimum error for brain tissues across the frequency range of 10 Hz to 100 GHz is 6.2% at 800 Hz, and the maximum error is 410% at 20 GHz. Significance:It is often assumed that the mathematical reduction of the base equations is valid for human head tissues over a broad frequency range; this study shows that these assumptions are not true for all tissues at all frequencies. False assumptions will result in greater errors and local distortions within tomographic images of the human head using electrical impedance tomography. This study provides the relationships between injected current frequency and the validity of the mathematical assumptions for each individual tissue, providing greater awareness of the magnitude of possible distortions.

This paper proposes an innovative technique for monitoring the healing of severe bone fractures using a pair of radio frequency monopoles implanted in the fractured bone. It is envisaged that the screws and external fixation used to stabilise and align the bone will also act as monopole antennas. The proposed antenna configurations were measured inside three novel heterogeneous bone phantoms representing the radius, tibia and phalange bones, and the results were compared to computer simulations with a voxel model of a 26-year-old female from CST Microwave Studio's Virtual Family. The power transmitted from one monopole to the other (S 21) was measured and evaluated as an indicator for fracture healing as blood emulating liquid was injected inside the phantom emulating the conditions of a bone fracture. Finally, for the validation of the phantom measurements, an ex-vivo measurement was conducted using a lamb femur bone. In all cases, the power transmitted from one monopole to the other through the fracture decreased significantly as the volume of the blood representing the fracture increased. The proposed system could provide doctors with a quantitative monitoring tool regarding the healing progress of a fractured bone through the reduction of the wound's hematoma during the first four weeks after the trauma that are critical for bone restoration.