Investigation of tissue bioimpedance using a macro-needle with a potential application in determination of needle-to-nerve proximity

Our research is concentrated on development of a ‘smart’ needle which will improve the safety of ultrasound-guided peripheral nerve block (USgPNB) by providing the clinician with bioimpedance data to identify the type of tissue the needle tip is in contact with. This paper outlines a feasibility study performed to determine the electrical bioimpedance of a number of different tissue types and the extent to which they can be differentiated from each other based on this variable factor. All cells have different electrical properties which results in characteristic bioimpedance profiles. A macro-needle was constructed to facilitate determination of this trait in lamb, pork and beef tissue samples. Frequencies of between 10 kHz - 100 kHz were identified as the optimum range for measurement of samples at both 12 °C and 37 °C. Our study showed that bioimpedance was inversely proportional to temperature. Further investigations in muscle, fat and connective tissue were performed at 30 kHz, 50 kHz and 70 kHz demonstrating significant order of magnitude of separation between all three sample types. These results allowed the determination of bioimpedance ranges for each tissue. The possibility of using bioimpedance to differentiate between tissue types was demonstrated successfully during this study and thus supports the concept of the ‘smart’ needle for this application.