Optimization of Curvilinear Needle Trajectories for Transforamenal Hippocampotomy

Abstract

Background: The recent development of MRI-guided laser-induced thermal therapy (LITT) offers a minimally invasive alternative to craniotomies performed for tumor resection or for amygdalohippocampectomy to control seizure disorders. Current LITT therapies rely on linear stereotactic trajectories that mandate twist-drill entry into the skull and potentially long approaches traversing healthy brain. The use of robotically-driven, telescoping, curved needles has the potential to reduce procedure invasiveness by tailoring trajectories to the curved shape of the ablated structure and by enabling access through natural orifices.

Objective: To investigate the feasibility of using a concentric tube robot to access the hippocampus through the foramen ovale to deliver thermal therapy and thereby provide a percutaneous treatment for epilepsy without drilling the skull.

Methods: The skull and both hippocampi were segmented from dual CT/MR image volumes for 10 patients. For each of the 20 hippocampi, a concentric tube robot was designed and optimized to traverse a trajectory from the foramen ovale to and through the hippocampus from head to tail.

Results: Across all 20 cases, the mean distances (error) between hippocampus medial axis and backbone of the needle were 0.55 mm, 1.11 mm, and 1.66 mm for best, mean, and worst case, respectively.

Conclusion: These curvilinear trajectories would provide accurate transforamenal delivery of an ablation probe to typical hippocampus volumes. This strategy has the potential to both decrease the invasiveness of the procedure and increase the completeness of hippocampal ablation.

Keywords: Skull base; ablation; epilepsy surgery; interventional MRI; nonlinear trajectory; robotic needle.

FIGURE 1.

Photograph of the concentric tube needle concept for transforamenal ablation. Color version available online only.

FIGURE 2.

Illustration of the robotic transforamenal ablation system concept. Color version available online only.

FIGURE 3.

MRI-compatible robot actuation unit prototype in a benchtop mockup of the transforamenal ablation procedure. RF, radiofrequency; 3D, 3-dimensional. Color version available online only.

FIGURE 4.

A , initial transforamenal trajectory before numerical optimization. B and C, docking tube range of allowable motion. Color version available online only.

FIGURE 5.

Optimized concentric tube robot design for patient 4. Color version available online only.

FIGURE 6.

Optimized concentric tube robot designs for 20 hippocampi, axial view. Color version available online only.

FIGURE 7.

Optimized trajectory using the measured curvature and torsion of the prototype. Color version available online only.