Steerable needles have the potential for accurate
needle tip placement even when the optimal path to a target tissue
is curvilinear, thanks to their ability to steer, which is an essen-
tial function to avoid piercing through vital anatomical features.
Autonomous path-following controllers for steerable needles have
already been studied, however they remain challenging, especially
because of the complexities associated to needle localization. In
this context, the advent of fiber Bragg Grating (FBG)-inscribed
multi-core fibers (MCFs) holds promise to overcome these diffi-
culties. Objective: In this study, a closed-loop, 3-D path-following
controller for steerable needles is presented. Methods: The control
loop is closed via the feedback from FBG-inscribed MCFs embed-
ded within the needle. The nonlinear guidance law, which is a well-
known approach for path-following control of aerial vehicles, is
used as the basis for the guidance method. To handle needle-tissue
interactions, we propose using Active Disturbance Rejection Con-
trol (ADRC) because of its robustness within hard-to-model en-
vironments. We investigate both linear and nonlinear ADRC, and
validate the approach with a Programmable Bevel-tip Steerable
Needle (PBN) in both phantom tissue and ex vivo brain, with some
of the experiments involving moving targets. Results: The mean,
standard deviation, and maximum absolute position errors are
observed to be 1.79 mm, 1.04 mm, and 5.84 mm, respectively, for
3-D, 120 mm deep, path-following experiments. Conclusion: MCFs
with FBGs are a promising technology for autonomous steerable
needle navigation, as demonstrated here on PBNs. Significance:
FBGs in MCFs can be used to provide effective feedback in path-
following controllers for steerable needles