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.

目的：确定用于人体头部组织电阻抗断层扫描的关键数学假设的有效性。方法：对从现有文献中收集的人头部每个组织的电导率和介电常数数据进行了评估和批评。然后使用每个组织最相关的电介质组织数据来评估电阻抗断层扫描的数学假设在其对人体头部成像的适用性方面的有效性，以估计相关误差。主要结果：对于频率大于 200 Hz 的感应电流，内部电流源密度可以忽略不计。对于频率低于 1 MHz 的人体头部组织，磁效应可以忽略不计的假设是有效的，误差为 1.7%。对于频率分别小于 3.2 MHz、320 kHz、25 kHz、3.2 kHz 和 130 Hz 的 CSF、硬脑膜、血液、骨骼（皮质）和深层组织皮肤，电容效应可以忽略不计。然而，脑组织的电容效应不可忽略，因为脑组织在 10 Hz 至 100 GHz 频率范围内的最小误差为 800 Hz 时的 6.2%，最大误差为 20 GHz 时的 410%。意义：通常假设基本方程的数学简化对于宽频率范围内的人体头部组织是有效的；这项研究表明，这些假设并不适用于所有频率的所有组织。错误的假设将在使用电阻抗断层扫描的人体头部断层扫描图像中导致更大的错误和局部失真。这项研究提供了注入电流频率与每个组织的数学假设的有效性之间的关系，从而更好地了解可能的失真程度。