Amasha H M, Anderson A P, Conway J, Barber D C
Department of Electronic and Electrical Engineering, University of Sheffield, UK.
Clin Phys Physiol Meas. 1988;9 Suppl A:49-53. doi: 10.1088/0143-0815/9/4a/009.
The objective of this study is a non-invasive assessment of the thermal dose in microwave hyperthermia. We intend to monitor the induced temperature rise via the change in the resistivity of body tissue, and hence control the microwave power during treatment. An initial feasibility study using electrical impedance tomography in vivo has indicated that a microwave induced temperature difference of a suitable magnitude can be mapped from a knowledge of the temperature coefficient of conductivity for tissue (typically 2% per degrees C). The accuracy of the currently employed reconstruction algorithm is assessed from data simulated by finite element prediction methods. A circular arrangement of electrodes surrounding a conductive sheet is used to evaluate the voltage distribution on the boundary of the sheet. A range of regions inside the circular field are chosen and the conductivity is changed uniformly by steps of 1% up to 10%. Images of these changes are produced. It is noticed that the algorithm underestimates the values of resistivity change for the small areas and overestimates the change for the larger areas. We are studying results for a variety of shapes of surface regions of the body that undergo resistivity change with microwave heating applied. Further work is necessary to account for three-dimensional current paths. Preliminary results are also presented of experimental investigations of the microwave-induced temperature rise in layers of carbon-loaded paper sheet.
本研究的目的是对微波热疗中的热剂量进行无创评估。我们打算通过人体组织电阻率的变化来监测诱导的温度升高，从而在治疗过程中控制微波功率。一项使用体内电阻抗断层成像的初步可行性研究表明，根据组织的电导率温度系数（通常每摄氏度2%）的知识，可以绘制出合适幅度的微波诱导温度差。从有限元预测方法模拟的数据中评估当前采用的重建算法的准确性。围绕导电片的圆形电极排列用于评估片边界上的电压分布。选择圆形场内部的一系列区域，并将电导率以1%的步长均匀变化，直至10%。生成这些变化的图像。注意到该算法低估了小区域电阻率变化的值，而高估了大区域的变化。我们正在研究身体表面区域各种形状在施加微波加热时经历电阻率变化的结果。考虑三维电流路径还需要进一步的工作。还给出了对含碳纸片层中微波诱导温度升高的实验研究的初步结果。
