Compensating the Influence of Tremors on Impedance Measurements Through Fourier Analysis*

Electrical mpedance measurements are a promising method for detecting structural changes in tissue and can be used in oncology to differentiate between healthy and tumorous tissue areas. The impedance measurements are so sensitive that they are not only affected by changes in the tissue itself, but also by a fluctuating contact force between sensor and tissue. In this work, the correlation between impedance measurements and movements during the measuring process, such as physiological tremors, are analyzed. To do this, impedance measurements are taken on pig bladders and the sensor-tissue contact force is simultaneously recorded. The tremor frequencies are directly visible in the Fourier transform of the impedance measurement. To counteract these effects, a Butterworth filter is used to filter out tremor frequencies and remove unwanted artefacts. Additionally, placing an spring on top of the impedance sensor helped to achieve a steadier contact force between sensor and tissue to also remove low frequency disturbances in the impedance measurements.Clinical relevance— This approach can help to obtain more reliable impedance measurements on tissue both for ex vivo and in vivo applications.