Optimization of Curvilinear Needle Trajectories for Transforamenal Hippocampotomy

Abstract

BACKGROUND: The recently developed magnetic resonance imaging–guided laser-induced thermal therapy offers a minimally invasive alternative to craniotomies performed for tumor resection or for amygdalohippocampectomy to control seizure disorders. Current laser-induced thermal 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 computed tomography/magnetic resonance 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 (errors) between the hippocampus medial axis and backbone of the needle were 0.55, 1.11, and 1.66 mm for the 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 both to decrease the invasiveness of the procedure and to increase the completeness of hippocampal ablation.

Treating Epilepsy via Thermal Ablation: Initial Experiments With an MRI-Guided Concentric Tube Robot

“…As in [4][5][6][7] , it includes an outer straight stiff nitinol delivery tube (OD: 2.4mm, ID: 1.9mm) that reaches up to the foremen ovale, a middle flexible helical nitinol tube (OD: 1.4mm, ID: 0.9mm) that enters the brain, and a flexible, straight custom-made RF ablation probe (OD: 0.8mm) made from a nitinol wire shielded via heat-shrinkable PTFE tubing. A straight sheath of thin-wall nitinol surrounds the insulation at all times and prevents it from being damaged as the ablation probe slides in and out of the helical tube.…”

“…We have designed and fabricated an MR-compatible robotic system to provide high resolution actuation for helical needle deployment [5]. We have shown in simulation that the curved medial axis of hippocampus can be accessed via a helical needle that delivers the ablation probe into the brain [4]. These preliminary results suggest that MR-guided robotic transforamenal thermal therapy could potentially provide a less invasive approach for potentially curative epilepsy treatment.…”

“…Commercial products (e.g., Visualase, Medtronic Inc.; ClearPoint, MRI Interventions Inc.; NeuroBlate, Monteris Inc.) have recently been introduced for MR-guided laser-based thermal ablation. These products require the physician drill a hole into the skull for ablation probe placement, and may not always be able to ablate the entire seizure focus when the structure has a curved shape (such as the hippocampus) [4]. Incomplete ablation of the seizure focus would lead to seizure recurrence.…”

“…We have recently proposed concentric-tube steerable needles as a means to address these challenges [4][5][6][7]. They enable nonlinear trajectories and offer the potential to enter the brain through the patient's cheek via a natural opening in the skull base (i.e.…”

“…Ablation profiles along the needle trajectory were selected in keeping with the concept introduced in [4][5][6], in which the needle is delivered as nearly as possible along the medial axis of the hippocampus and delivers thermal energy radially in all directions along its path.…”