The Institute of Medical Device Technology researches various methods of electrical impedance measurement on needles. The research in the field of impedance measurements is supported by experts in microfabrication as well as clinical partners.
Sensitivity
Among other things, the spatial sensitivity of different electrode designs is investigated, as this is decisive for the achievable spatial resolution of the measurements. The better the resolution, the more finely the different tissue types can be identified. The investigations are carried out with the aid of FEM simulations. Figure X shows an example of a simulation of the voltage distribution on a bipolar needle electrode, carried out with COMSOL Multiphysics.
Multi-local impedance measurements
The fabrication and design of bipolar needle electrodes and the reduction of needle sizes used are also the subject of research at the IMT. The figure shows a bipolar needle electrode made from two commercially available needles, with a hand-held device next to it, signaling contact with venous blood. In addition to obtaining information about the tissue present at the tip, the IMT is also exploring multilocus impedance measurements along the needle shaft. These require patterning the needle with a pattern of electrodes.
The figure shows an exemplary design with seven circular electrodes near the tip of the needle. The focus of the research is on the manufacturing realization as well as the metrological evaluation and visualization of the measurement data.
Phantom manufacturing
Phantoms with realistic electrical properties are produced for experimental investigation. One of the main focuses of the research is also to improve the fidelity of the electrical and also mechanical properties. Measurements are performed using an ISX-3 (Sciospec) impedance analyzer or, in the case of a hand-held device, using individual impedance analysis chips (e.g. AD5933 from Analog Devices).
