FBG-Based Estimation of External Forces Along Flexible Instrument Bodies

Abstract

A variety of medical treatment and diagnostic procedures rely on flexible instruments such as catheters and endoscopes to navigate through tortuous and soft anatomies like the vasculature. Knowledge of the interaction forces between these flexible instruments and patient anatomy is extremely valuable. This can aid interventionalists in having improved awareness and decision-making abilities, efficient navigation, and increased procedural safety. In many applications, force interactions are inherently distributed. While knowledge of their locations and magnitudes is highly important, retrieving this information from instruments with conventional dimensions is far from trivial. Robust and reliable methods have not yet been found for this purpose. In this work, we present two new approaches to estimate the location, magnitude, and number of external point and distributed forces applied to flexible and elastic instrument bodies. Both methods employ the knowledge of the instrument’s curvature profile. The former is based on piecewise polynomial-based curvature segmentation, whereas the latter on model-based parameter estimation. The proposed methods make use of Cosserat rod theory to model the instrument and provide force estimates at rates over 30 Hz. Experiments on a Nitinol rod embedded with a multi-core fiber, inscribed with fiber Bragg gratings, illustrate the feasibility of the proposed methods with mean force error reaching 7.3% of the maximum applied force, for the point load case. Furthermore, simulations of a rod subjected to two distributed loads with varying magnitudes and locations show a mean force estimation error of 1.6% of the maximum applied force.

Shape Representation and Modeling of Tendon-Driven Continuum Robots Using Euler Arc Splines

“…As a result, the linear assumption works well for continuum robots in several application scenarios, even for large deformations. It has been used to represent the shape of slender backbones affected by gravity [25], [26], contact forces with the environment [27], and forces due to tools mounted at the tip [28]. In our previous work [28], we provide a 2D static model to model tip forces on a single segment using Euler arc splines (EAS).…”

Progress in Probe-Based Sensing Techniques for In Vivo Diagnosis

“…Force sensing can provide intuitive, real-time, and interactive feedback to the operator. Therefore, it plays an important role in the high-quality diagnosis of biomedical environment [ 34 , 35 ].…”

3D Curvature-Based Tip Load Estimation for Continuum Robots

“…As their deformations are the direct reflection of external forces, their shapes can be used to estimate these interactions. This approach has been investigated using different deformation sensors as Bragg fibers [8], [9], [10] or cable tension sensors [11].…”

“…The principle is to create a system- like model that predicts deformations from desired external forces, and to make them converge by reducing errors between the predicted and the measured shapes. The model-based methods are usually based on the Cosserat theory [19], [10], or on simpler piece-wise constant curvature models [18] among others. However, these approaches are often slow because of model integration and challenging iterative optimization process.…”

“…In fact, the tri-dimensional deformations lead to increased complexity in the force estimation for various reasons including: the challenging accurate reconstruction of the 3D deformations, the necessary estimation of the torsion, the ill-conditioning issues, etc. One of the most advanced works dealing with the estimation of 3D external forces is probably the one reported in [10] yielding an accuracy of approximately 5.5% using several Bragg fibers embedded along the deformable rod.…”