Ramos Airton, Bertemes-Filho Pedro
Department of Electrical Engineering, State University of Santa Catarina, Joinville, Brazil.
Electromagn Biol Med. 2011 Dec;30(4):235-45. doi: 10.3109/15368378.2011.589555.
The measurement of electrical impedance of skin using surface electrodes permits the assessment of changes in local properties of the skin and can be used in the detection of tumors. The sensitivity of this technique depends mainly on the geometry of the probe and the size of the tumor. In this article, the impedance method was used to estimate the sensitivity of a tetrapolar probe in detecting small regions of increased conductivity in a stratified model of human skin. The impedance method was used to model the potential distribution using fasorial analysis to solve the node equations of the equivalent circuit. Interpolation was applied to reduce discretization error. The skin was modeled as a three-layer structure with different conductivity and permittivity obtained from the literature. A tumor was modeled as a small volume with admittivity four times higher than the normal tissue. Sensitivity calculation was made as a function of electrode diameter and separation, tumor size, and excitation frequency. The simulations indicated that by inserting a one square millimeter tumor in the epidermis, the load impedance to the current source varies about 1% while the transfer impedance varied 8%. The sensitivity also increases nonlinearly with increasing tumor area and thickness. Additionally, it was found that the sensitivity of the transfer impedance has a maximum value when the electrodes are separated by 1.8 mm. The results show that transfer impedance measurements of the skin may detect small skin tumors with a reasonable sensitivity by using an appropriate tetrapolar probe.
使用表面电极测量皮肤的电阻抗，可以评估皮肤局部特性的变化，并可用于肿瘤检测。该技术的灵敏度主要取决于探头的几何形状和肿瘤的大小。在本文中，采用阻抗法来估计四极探头在分层人体皮肤模型中检测电导率增加的小区域时的灵敏度。使用筋膜分析对等效电路的节点方程进行求解，采用阻抗法对电位分布进行建模。应用插值法来减少离散化误差。将皮肤建模为具有从文献中获取的不同电导率和介电常数的三层结构。将肿瘤建模为一个小体积，其导纳比正常组织高四倍。根据电极直径和间距、肿瘤大小以及激励频率进行灵敏度计算。模拟结果表明，在表皮中插入一平方毫米的肿瘤时，电流源的负载阻抗变化约1%，而转移阻抗变化8%。灵敏度也随着肿瘤面积和厚度的增加而非线性增加。此外，还发现当电极间距为1.8毫米时，转移阻抗的灵敏度有最大值。结果表明通过使用合适的四极探头，测量皮肤的转移阻抗可以以合理的灵敏度检测小的皮肤肿瘤。
