Fiber optic based force sensor design for prostate biopsy procedure under MRI

Abstract

Fabry-Pérot Interferometry (FPI) fiber optic sensors with low error ratio and high sensitivity can provide reliable feedback to optimize needle insertion for MRIguided prostate biopsy. FPI based force sensing has also potential for diagnosis of prostate cancer (PCa) directly by providing data regarding mechanical characteristics of the tissue.In this thesis, design and fabrication of a fiber optic sensor based on FPI for force measurement at the tip of an prostate biopsy needle (18-gauge) is presented. The sensor is built upon an air cavity between two cleaved optical fibers with a diameter of 125 μm which are embedded and fixed into a borosilicate glass capillary with an inner diameter of 200 μm. Fixation of optical fibers within the glass capillary are achieved by applying medical grade UV adhesives through two micro-holes formed with CO2 laser processing on the glass capillary. The initial distance between the fiber endings is adjusted by using manipulators controlled by piezoelectric actuators and strain gauge readers with a resolution of 10 nm. A laser diode which has a wavelength of 635 nm is used as a light source for the operation of the sensor. The intensity from the laser diode is kept constant during operation with current feedback mechanisms and temperature controllers. Model predictive control approaches are adapted and implemented for the temperature control of the light source. A circuitry for the operational control of the system and signal processing is implemented. The sensor is calibrated and optimized with a commercial pressure sensor and a force testing machine. Dynamic range of the sensor is set to the linear operation region to avoid signal ambiguity while being able to provide a force measurement range of 0-13 N with a resolution of 0.1 N based on needle insertion experiments conducted.|Keywords : Optical Fiber Sensors, Fabry-Pérot Interferometry (FPI), Force Sensor, Needle Insertion, MR Compatibility, MRI Guided Prostate Biopsy.