Characterization of temperature dependent dielectric properties of biological tissue phantoms using an open-ended coaxial probe

Abstract

The dielectric characteristics of biological tissues, particularly at microwave frequencies, are essential for various medical applications, including imaging, therapy, and cancer treatment. This research focuses on understanding how electromagnetic waves interact with tissues and the temperature-dependent changes in tissue dielectric properties. Because these treatment procedures occur at temperatures beyond room temperature, the resulting change in tissue dielectric properties must be considered. Electrical tissue qualities have an immediate effect on the absorption of electromagnetic energy, which results in a heating generation; these features are thus critical to early-stage and clinical uses utilizing electromagnetic waves for heating, as well as thermal treatments in total because dielectric characteristic changes following heating will influence tissue distribution of temperatures and the ensuing thermal harm. For this reason, there is a need for biological phantoms that mimic the dielectric properties of tissues at these high frequencies and different heat rates. Tissue-mimicking phantoms, such as gelatin-based phantoms, play a crucial role in simulating tissue properties for research and clinical purposes. Many different forms of phantom materials can be used to mimic different tissues. One of the most preferred ones is phantoms produced using gelatin because they are affordable, easy to produce, made from easily available materials and stable. Dielectric properties are not directly measurable characteristics. Therefore, the data collected from measurement devices are converted into dielectric properties. Although there are multiple methods in the literature for this, the open-ended coaxial probe technique was preferred to measure the dielectric properties of these prepared oil-in-gelatin phantoms and to measure temperature-dependent changes. It is a widely used measurement technique that provides wide frequency range measurements for both in vivo and ex vivo environments. The mathematical method used to interpret measurement results and compare them with real tissues is Cole-Cole equation. All prepared tissue phantoms were measured first at room temperature and then at all temperatures from body temperature to 55 degrees using an open-ended coaxial probe. The obtained dielectric properties were compared with previous studies and the dielectric properties of real tissues available on the IFAC website and focused on the analysis of the change of dielectric properties with temperature. The findings obtained as a result of the experiments showed that oil in gelatin phantoms are successful material for tissue mimicking. As a result of the comparisons, it was proven that the dielectric properties of the phantoms were compatible with real tissues xxi and that they still showed tissue dielectric properties as a result of heating and cooling processes.