Biological Tissue Microwave Measurement Method And Its Application

Accurate measurement for the biological tissue plays an important role in detecting the tumor. The large difference between the internal structure of tumor tissue and normal tissue leads to their huge difference of permittivity which can be used to detect the tumor accurately through microwave image technique.There are many methods to measure the permittivity, such as reflection coefficient method, transmission coefficient method, perturbation method and some others.The reflection coefficient sampled by the measurement probe loaded with biological tissue at one end can be converted to the permittivity of tissue under test with the reflection coefficient method, anyhow, which is only accurate for the biological tissue of high permittivity but is unstable for that of low permittivity. The measurement probe can be divided into three types.The first one is a traditional open-ended coaxial line, the second is the coaxial monopole, and the third is the planar microstrip probe. The first one is accurate and stable in measurement can find wide applications; however, the fabrication becomes increasingly difficult when the size decreases, and the cost becomes increasingly high because of its non-planner structure. The second can be also accurate in measurement, but it is hard to insert the monopole into the sample due to its large ground at the end, thus it fails to be applied in measurement. The last one can also be classified into three. The first is the open ended stripline; the second is the open sided stripline while the third is stripline with an annular aperture at one ground plane. All three kinds can be fabricated and integrated easily with low cost, but improvement due to its unstable measurement is still required. After getting the reflection coefficient by one of these probes, five math models can be applied to transfer the reflection coefficient to permittivity, including capacitance model, virtual line model, admittance model, antenna model and rational function model.The first three models are suitable for coaxial probe and planner probe, antenna model is suitable for monopole and the last model is suitable for coaxial probe and the planner microstrip probe. Five models are analyzed and compared in this thesis.The trend of permittivity during the process of tumor treatment is investigated by the microwave heating is investigated. The porcine liver is tested instead in this paper because of its similarity with tumor tissue. After heating the porcine liver by the PMCT connected to the MPC (microwave percutaneous coagulator), the reflection coefficients after different heating time are sampled by the coaxial probe and then converted to the permittivity, and the temperature trend of permittivity of porcine liver can thus be found.