Open-Loop Tip Accuracy of an MRI-Compatible Active Cannula Robot

INTRODUCTION Magnetic resonance imaging (MRI) is increasingly used intraoperatively, because it provides excellent soft tissue distinction and on-the-fly adjustment to imaging slice orientation without exposing clinician or patient to radiation. For neurosurgical procedures, intraoperative MRI holds significant advantages over traditional stereotactic methods (e.g. compensation for brain shift), and has thereby led to much research toward minimally invasive treatments of brain tumors, epilepsy, and other neurological disorders. Because the tight confines of MRI scanners limit clinician access to the patient, an MRI-compatible robot is potentially useful for many procedures and additionally offers the clinician increased accuracy and degrees of freedom within the minimally invasive context. Affecting 0.5 to 1.0% of the global population, epilepsy is a neurological disorder for which surgery has been reported superior to prolonged pharmacotherapy, yet only a small fraction of potential surgical candidates receive treatment [1]. Minimally invasive alternatives to conventional resection of seizure foci could side-step the potential morbidity and lengthy recovery associated with open brain surgery thereby making surgical treatment and cure available to a greater number of patients with less risk. Interstitial laser ablation of seizure foci has been clinically demonstrated using MRI to guide ablator placement and MR thermometry for thermal dosimetry [2]. This procedure currently requires multiple patient transfers between MRI scanner and operating room meaning that introducing an MRIcompatible robot could streamline surgical workflow. An alternative real-time MRI approach is high intensity focused ultrasound (HIFU), yet intracranial targets can be difficult to effectively treat due to high reflection and absorption of the ultrasound energy by the skull [3]. This paper reports a pneumatically-actuated active cannula robot designed for MRI-guided ablation of epileptogenic foci. An active cannula is a continuum robot consisting of concentric, superelastic nitinol tubes with pre-curved sections. Complex trajectories are realized by translation and rotation of the cannula tubes with respect to one another.