Identification of tissue types and boundaries with a fiber optic force sensor

The absence of tactile force information at the tip of a medical instrument makes precise minimally invasive surgery difficult and is prone to resulting in serious outcomes. In this paper, a fiber optic force sensor is fabricated based on Fabry-Pérot interferometry and integrated with a puncture needle. The force sensor is attached to the needle tip, where interactive force arises as it inserts into soft tissue. Needle insertion experiments have been conducted on ex vivo swine liver and belly with the calibrated force sensor. Using wavelet transform method, the acquired force data are analyzed and used to identify layered tissue types and boundaries. We found that the force amplitudes are not always identical, but the patterns of forces are almost the same, which enables us to identify layered tissues and to realize a safe needle insertion procedure under robot control.