Journal of Medical Robotics Research

Background: Cataracts are the leading cause of blindness and are treated surgically. Capsulotomy describes the opening of the lens capsule during this surgery and is most commonly performed by manual tearing, thermal cutting, or laser ablation. This work focuses on the development of a flexible instrument for high precision capsulotomy, whose motion is controlled by a hybrid mechanical-magnetic actuation system. Methods: A flexible instrument with a magnetic tip was directed along a circular path with a hybrid mechanical-magnetic actuation system. The system’s motion control and thermal cutting behavior were tested on ex vivo porcine lenses. Results: Position control of the magnetic tip on a circular path with radius of 2.9mm resulted in a relative positioning error of 3% at a motion period of 60s. The instrument’s accuracy improves with decreasing speed. A fully automated capsulotomy is achieved on an ex vivo porcine lens capsule by continuously coagulating the tissue under controlled conditions. Conclusions: Robot assisted capsulotomy can be performed with excellent precision in ex vivo conditions.

Magnetically controlled catheters and endoscopes can improve minimally invasive procedures as a result of their increased maneuverability when combined with modern magnetic steering systems. However, such systems have two distinct shortcomings: they require continuous information about the location of the instrument inside the human body and they rely on models that accurately capture the device behavior, which are difficult to obtain in realistic settings. To address both of these issues, we propose a control algorithm that continuously estimates a magnetic endoscope’s response to changes in the actuating magnetic field. Experiments in a structured visual environment show that the control method is able to follow image-based trajectories under different initial conditions with an average control error that measures 1.8 % of the trajectory length. The usefulness for medical procedures is demonstrated with a bronchoscopic inspection task. In a proof-of-concept study, a custom 2mm diameter miniature camera endoscope is navigated through an anatomically correct lung phantom in a clinician-controlled manner. This represents the first demonstration of the controlled manipulation of a magnetic device without localization, which is critical for a wide range of medical procedures.

We report the results of preclinical experiments for direct MRI-guided needle interventions in the brain. An MR Safe robot was incorporated into an intraoperative MRI system. Deep regions of the brain simulated in a cranial mockup were targeted with a needle under robotic assistance. The 3D accuracy of in-scanner targeting at an average depth of 95mm was 1.55mm, with no manual corrections.

Magnetic guidance of cochlear-implant electrode arrays during insertion has been demonstrated in vitro to reduce insertion forces, which is believed to be correlated to a reduction in trauma. In those prior studies, the magnetic dipole-field source (MDS) was configured to travel on a path that would be coincident with the cochlea’s modiolar axis, which was an unnecessary constraint that was useful to demonstrate feasibility. In this paper, we determine the optimal configuration (size and location) of a spherical-permanent-magnet MDS needed to accomplish guided insertions with a 100mT field strength required at the cochlea, and we provide a methodology to perform such an optimization more generally. Based on computed-tomography scans of 30 human subjects, the MDS should be lateral-to and slightly anterior-to the cochlea with an approximate radius (mean and standard deviation across subjects) of 64mm and 4.5mm, respectively. We compare these results to the modiolar configuration and find that the volume of the MDS can be reduced by a factor of five with a 43% reduction in its radius by moving it to the optimal location. We conservatively estimate that the magnetic forces generated by the optimal configuration are two orders of magnitude below the threshold needed to puncture the basilar membrane. Although subject-specific optimal configurations are computed in this paper, a one-size-fits-all version with a radius of approximately 75mm is more robust to registration error and likely more practical. Finally, we explain how to translate the results obtained to an electromagnetic MDS.