MRI-compatible Haptics: Strain sensing for real-time estimation of three dimensional needle deflection in MRI environments

Conventional closed-bore MRI scanners preclude direct “hands-on” device manipulation. There is a critical need for methods to quickly, accurately and easily manipulate instruments within closed MRI systems. Specifically, catheter, probe, and needle interventions can benefit from optical systems which measure tool positions and forces in real-time. During such procedures, it is useful to track any deviation from the planned trajectory to minimize positioning error and procedural complications. Recently, miniaturized fiber-optic-based force and deflection sensors based on fiber Bragg grating (FBG) technology have been developed and integrated into robotics for force feedback [1]. Our previous work illustrated the feasibility of using Fiber Bragg grating (FBG) sensors to estimate needle deflections in 2D [2]. FBG sensors reflect light with a peak wavelength that shifts in proportion to the strain to which they are subjected. The wavelengths are also dependent on temperature changes, thus the sensors have applications in cryosurgery and tissue ablation procedures. FBG sensors are inherently MRI-compatible, do not interact with the MRI process, and do not cause imaging artifacts. A shape-sensing stylet from an MRI-compatible biopsy needle was fabricated and instrumented with FBG sensors to measure the 3D shape of needle with sub-millimeter accuracy. Calibration, bench-top testing, and an animal experiment were performed with the sensorized needle.