A needle-tip embedded fibre optical force sensor for tissue identification
The identification of biological tissue types during needle insertion is subject to a lack of precise monitoring techniques, especially in an intensive magnetic resonance environment. One approach to improve this situation is to attach optical sensors to the surgical needle. In this research, a temperature-compensated fibre optical tip force sensor based on the Fabry-Perot Interference (FPI) principle is developed and embedded into the tip of surgical needles. This was designed for tissue identification which it fulfilled via analysing the tip force of the needle during insertion. A novel structure for FPI signal temperature-compensation is proposed, based on the provision of another FPI sensor which is only sensitive to temperature change. After sensor fabrication, two FPI sensors are embedded into the needle’s tip according to the designed structure. The experiments with varying temperature and force demonstrate the designed sensing needle could detect temperature and force signals. The system signal processing is based on interference intensity modulation where the FPI light intensity has a cosine relationship with applied force. An algorithm is proposed to turn light intensity into its intensity phase signal which is linear with applied force variation. The sensing needle is then calibrated via a temperature chamber and commercial force sensors. The results show that the sensing needle successfully overcomes the influence of temperature and captures the applied force at its tip. In addition, as the reference FPI sensor could provide temperature information, the sensing needle is also calibrated in regard to temperature sensing. An optical circuit for the FPI sensors is built and its size is optimised to fit a control box, with connection terminals to the FPI sensor, a portable laser source, and a computer. The entire system is portable, economical and practical for Minimally Invasive Surgery (MIS). A Graphical user interface (GUI) is developed to display tip force and temperature information. Tissue identification is the main application of the sensing needle. To achieve this objective, a series of tissue experiments are conducted on phantom tissue and porcine tissues. A needle insertion platform is designed for the tissue insertion experiments. A database of tip forces versus tissue types is then obtained based on the tissue insertion experiments for use in tissue identification. In addition, the factors influencing tip force during needle insertion are also investigated. Based on the above results, tissue identification experiments are performed, the results of which indicate the possibility of tissue identification in specific body locations. In vivo experiments on mice are designed and conducted to further verify the concept of temperature compensated tip force sensing and tissue identification. The results of these experiments confirm the ability of the tip force sensing needle to identify tissue types, though some internal organs of mice are difficult to be penetrate and detect. An improved tip force sensing needle is fabricated for application to epidural space identification. The needle insertion experiments on porcine spinal samples show that the improved sensing needle could detect the epidural space effectively.
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