Three-dimensional catheter tip force sensing using multi-core fiber Bragg gratings

FIGURE 1. Catheter ablation scene: ① catheter tip force sensor, ② actuatable catheter, ③ medical delivery sheath, ④ zoomed-in view of the left atrium, ⑤ pulmonary veins, and ⑥ mitral valve.

FIGURE 2. Force sensor overview ⓐ exploded view ⓑ assembled view ⓒ sectional view illustrating the relevant spring dimensions such as total length L, wire thickness t, wire breath b, and mean coil diameter D. The central FBG location along the spring’s length is given as L FBG . The sensor’s components include: ① MCF, ② FBGs, ③ ablation electrodes, ④ insulation ring, and ⑤ side holes to inject adhesives for MCF fixation.

FIGURE 3. Illustration of the MCF pre-straining steps: ① the spring is fixed at the base and is initially free and unloaded, ② a longitudinal calibration force F c is applied at the spring’s end, ③ the MCF is inserted into the spring and fixed at both ends with appropriate adhesives (the longitudinal calibration force F c is still being applied at the spring’s end), ④ once the adhesive is fully cured, i.e., the end-points fixations are rigid, the longitudinal calibration force F c is removed and the spring extends to an equilibrium position.

FIGURE 4. Cross-sectional view of the MCF and spring combination. The MCF’s center is at a radial offset d r from the spring’s center and at an angular offset θ r with respect to a reference axis. θ b is the angle of the bending plane vector with respect to the reference axis and θ 1 is the angle between the center of the first outer core and the reference axis. r is the radial distance from an outer core to the central core, and d i for i∈1,2,3 is the perpendicular distance between the outer cores and the neutral axis crossing the central core. θ rb is the angle between the bending plane vector θ b − π and θ r .

FIGURE 5. Illustration of the calibration and experimental setups for (A) MCF pre-straining through spring initial compression (B) identification of d r and θ r (C) identification of the angle between the x − axis of EM two and the first outer core of the MCF (D) identification of the angle between the x −axis of EM one and the y −axis of the ATI force sensor (E) three-dimensional catheter tip force sensor calibration, and (F) dynamic force characterization. The calibration and experimental setups contain the following elements: ① catheter tip force sensor, ② ATI Nano17 force sensor, ③ bendable and actuatable catheter, ④ linear guide, ⑤ MCF, ⑥ EM field generator, ⑦ EM two sensor, ⑧ hanging weights, ⑨ 3D printed rigid base, and ⑩ linear servomotor.

FIGURE 6. Catheter tip force sensor calibration results: (A) central core strain and curvature profiles during the identification of d r and θ r , and (B) θ b and θ x2 profiles for different force sensor rotational configurations about its longitudinal axis.

FIGURE 7. Catheter tip force sensor calibration results: (A) relationships between the 3D measured and calibrated forces versus input measurements κ x , κ y and Δϵ long , (B) comparison of the ground truth and estimated 3D forces for different force configurations across time, (C) relationships between temperature change and wavelength shift for the three FBG sets, and comparison of temperature compensated and temperature uncompensated force estimations, (D) dynamic frequency-based force estimation bode plot and mean force error versus frequency.