Towards the Development of a Tendon-Actuated Galvanometer for Endoscopic Surgical Laser Scanning

TL;DR

This work tackles the challenge of enabling precise, minimally invasive laser steering for neurosurgical endoscopy by introducing a tendon-actuated galvanometer (TAG) that can be embedded in a continuum joint. The authors derive a tendon-stroke to mirror-angle relationship, δ(t_s) = 45° + arcsin\left(\left(1 - \frac{2K_s L}{E\pi r^2}\right) \frac{t_s}{l} \right), and develop forward-kinematic mappings to relate galvanometer motion to the laser endpoint. Benchtop experiments validate both the geometric model (RMSE ≈ 3.51°) and the forward-kinematics model (RMSE ≈ 0.68 mm for laser endpoint displacement), demonstrating the TAG’s potential for rapid, multimodal laser steering in constrained anatomical spaces. While the prototype confirms feasibility, limitations such as size, unidirectional rotation, and optical aberrations motivate future work to shrink form factor, enable bidirectional steering, and integrate spectroscopy and OCT for endoscopic tumor identification. Overall, the TAG represents a promising step toward multimodal, endoscopic laser delivery in neurosurgery with potential expansion to broader continuum-robotic surgical applications, pending further optimization to fit within clinically relevant endoscope channels ($ ext{OD} obreak ightarrow obreak 2$ mm) and to withstand higher power delivery.

Abstract

There is a need for precision pathological sensing, imaging, and tissue manipulation in neurosurgical procedures, such as brain tumor resection. Precise tumor margin identification and resection can prevent further growth and protect critical structures. Surgical lasers with small laser diameters and steering capabilities can allow for new minimally invasive procedures by traversing through complex anatomy, then providing energy to sense, visualize, and affect tissue. In this paper, we present the design of a small-scale tendon-actuated galvanometer (TAG) that can serve as an end-effector tool for a steerable surgical laser. The galvanometer sensor design, fabrication, and kinematic modeling are presented and derived. It can accurately rotate up to 30.14 degrees (or a laser reflection angle of 60.28 degrees). A kinematic mapping of input tendon stroke to output galvanometer angle change and a forward-kinematics model relating the end of the continuum joint to the laser end-point are derived and validated.

Figures (7)

• Figure 1: a) Rendition of proposed TAG approaching a pituitary lesion to aid in resection. Note the tool's ability to both fiber and free-beam steer to reach otherwise limited locations on the lesion Biorender. b) Visual representations of the fiber and free-beam steering modalities. c) Rendition of proposed steerable surgical laser tool with fiber and free-beam steering capabilities.
• Figure 2: a) Assembled TAG in comparison to a U.S. dime (approximately 18 mm diameter). b) Front view of the TAG. c) Back view of the TAG.
• Figure 3: a) Schematic of TAG with variables relevant to the geometric and forward-kinematics modeling. b) Geometric modeling of TAG to obtain relationship between $\phi$ and $\Delta y$. c) Rendering of the experimental setup illustrating the actuation system, TAG, and laser assembly.
• Figure 4: a) Defined coordinate system used for deriving homogeneous transformation matrix to obtain end laser point, $p_{l}$, with respect to the end of the continuum joint, $p_{r}$. b) Diagram illustrating that the laser angle with respect to the global horizontal will equal twice the TAG rotation angle.
• Figure 5: a) Image of TAG taken when tendon stroke is 0.5 mm. b) Cropped image of TAG with detected edge and calculated angle.