Temperature compensation of the fiber-optic based system for the shape reconstruction of a minimally invasive surgical needle

This paper presents the methodology for temperature compensation of a system for shape reconstruction of a minimally invasive surgical needle. The system is based on four optical fibers glued along the needle at 90^∘ from each other and connected to the optical backscattering reflectometry interrogator. The interrogator measures backscattered light from four fibers, which shifts as a response to temperature or strain variations. During minimally invasive surgery the fibers sense both the strain change (due to the needle bending) and the temperature change (due to the difference between the temperature of the environment and the human body). Shape reconstruction is based on the strain measurements, so the temperature readings need to be compensated. The methodology of compensation is based on the two pairs of opposite fibers, which measure the same temperature change and opposite strain. The spectral shifts of the opposite fibers are added to find only the temperature component and the result is subtracted from the whole spectral shift to find the strain change detected by each fiber. This method has been validated by repeated constant insertion into a temperature-varying phantom. The algorithm has succeeded in the extraction of the strain component, which found to be the same in all trials despite the changing temperature.