Development Of A Fiber Optic Force Sensor And Its Application To Identification Of Tissue Types And Boundaries

In a minimally invasive surgery (MIS), interactive force between slender surgery instrument and soft tissue is complicated and is difficult to measure. How to precisely measure the interactive force at the tip of a medical instrument is a challenging issue for MIS. Excessive manipulating force and tissue trauma caused due to the absence of tactile sensing information is currently a major drawback of MIS. It is significant to do some research in this area. The work done in this thesis is given blow.First, the forces applied to the tip of the needle are investigated in terms of the interaction model of needle insertion. It composes of stiffness force, caused by the soft tissue before its capsule is penetrated and cutting force, which is used to rupture the tissue after its capsule penetration. The force deforms the needle, and the strain along the shaft is simulated analyzed using finite element method, the result is used to design the fiber optic force sensor.Second, the principle to design a fiber optic force sensor is introduced based on the Fabry-Perot interferometer. The modulation and demodulation process is depicted, and the relationship formulation of the intensity of the reflected light with the length of Fabry-Perot cavity is derived. The optical link of the fiber optic force sensor is designed. The light source and the length of the Fabry-Perot cavity are determined using the strain information acquired. The fiber optic force sensor is fabricated and integrated into the inner cavity close to the tip of the needle.Third, the fiber optic force sensor is calibrated on a calibration platform fabricated. The relationship of insertion force with the output power of the reflected light is established. The performances of the force sensor such as sensing range, accuracy, and resolution, etc., are analyzed.Finally, Insertion experiments are conducted on ex vivo swine liver and belly using the needle integrated with the calibrated force sensor, and the data of interactive force is acquired, and its patterns are analyzed with wavelet transform theory, to identify the tissue types and boundaries.In this thesis, a fiber optic force sensor is fabricated, and used to acquire the interactive force data during a needle insertion into soft tissue, for the purpose of tissue types and boundaries identification. The insertion experimental results on ex vivo swine liver and belly show that the fiber optic force sensor is usable, and is able to apply to identify tissue types and boundaries.