David B. Comber

Design, Additive Manufacture, and Control of a Pneumatic MR-Compatible Needle Driver

This paper reports the design, modeling, and control of an MR-compatible actuation unit comprising pneumatic stepper mechanisms. One helix-shaped bellows and one toroid-shaped bellows were designed to actuate in pure rotation and pure translation, respectively. The actuation unit is a 2-degree-of-freedom (DOF) needle driver that translates and rotates the base of one tube of a steerable needle like a concentric tube robot. For safety, mechanical stops limit needle motion to maximum unplanned step sizes of 0.5 mm and 0.5°. Additively manufactured by selective laser sintering, the flexible fluidic actuating (FFA) mechanism achieves 2-DOF motion as a monolithic, compact, and hermetically sealed device. A second novel contribution is substep control for precise translations and rotations less than full-step increments; steady-state errors of 0.013 mm and 0.018° were achieved. The linear FFA produced peak forces of 33 and -26.5 N for needle insertion and retraction, respectively. The rotary FFA produced bidirectional peak torques of 68 N·mm. With the FFAs in full motion in a 3-T scanner, no loss in signal-to-noise ratio of MR images observed.

Design and Control of an Magnetic Resonance Compatible Precision Pneumatic Active Cannula Robot

The versatile uses and excellent soft tissue distinction afforded by magnetic resonance imaging (MRI) has led to the development of many MR-compatible devices for MRI-guided interventions. This paper presents a fully pneumatic MR-compatible robotic platform designed for neurosurgical interventions. Actuated by nonmagnetic pneumatic piston-cylinders, the robotic platform manipulates a five degree-of-freedom active cannula designed for deep brain interventions. Long lines of tubing connect the cylinders to remotely located pressure sensors and valves, and MRI-compatible optical sensors mounted on the robot provide the robot joint positions. A robust, nonlinear, model-based controller precisely translates and rotates the robot joints, with mean steady-state errors of 0.032 mm and 0.447 deg, respectively. MRI-compatibility testing in a 3-Tesla closedbore scanner has shown that the robot has no impact on the signal-to-noise ratio, and that geometric distortion remains within recommended calibration limits for the scanner. These results demonstrate that pneumatic actuation is a promising solution for neurosurgical interventions that either require or can benefit from submillimeter precision. Additionally, this paper provides a detailed solution to the control problems imposed by severe nonlinearities in the pneumatic system, which has not previously been discussed in the context of MR-compatible devices. [DOI: 10.1115/1.4024832]

Precision Pneumatic Robot for MRI-Guided Neurosurgery

Thermal ablation is an interventional technique that promises to enable percutaneous treatment of many cancers and other disorders throughout the human body. Acoustic ablation offers the possibility of steering thermal energy electronically [1], and is known to be MRI compatible, and thus amenable to real-time thermal dose monitoring through MR thermometry. We propose a pneumatically actuated robotic approach for delivering the ablator tip to a desired target, since a robot has the potential to be more accurate than humans, and can work within the confined space of a standard MRI machine. Our robot is designed to deliver a steerable needle made from precurved elastic concentric tubes.

Design and Precision Control of an MR-Compatible Flexible Fluidic Actuator

Magnetic resonance imaging (MRI) offers many benefits to image-guided interventions, including excellent soft tissue distinction, little to no repositioning of the patient, and zero radiation exposure. The closed, narrow bore of a high field MRI scanner limits clinician access to the patient, such that an MR-compatible robot is essentially required for many potential interventions. A robotic system of this kind could additionally provide the clinician increased accuracy and more degrees of freedom within the minimally invasive context. Fluid power is an excellent type of actuation to use inside the MRI scanner, as such actuators can be designed free of magnetic and electrical components. However, there are no fluid power actuators readily available that are suitable for use in the operating room. This paper reports a compact, intrinsically safe, sterilizable fluid power actuator. Using additive manufacturing processes, the actuator was printed in a single build. Thus, it is composed of several integrated parts in a compact design. Employing an inchworm-like behavior, the linear actuator can advance or retract a needle or mechanism rod in discrete steps; thus the device is intrinsically safe. The actuator is fluid agnostic, but a pneumatic prototype is presented here with initial testing results. For the pneumatic case, sub-step positioning control has been tested using a nonlinear, modelbased controller, and the mean steady-state error was 0.025 mm. Thus this type of actuator appears to be promising solution for use in MRI-guided interventions.

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.

Precision Position Tracking of MR-Compatible Pneumatic Piston-Cylinder Using Sliding Mode Control

This paper presents the nonlinear dynamics and sliding mode control design for a 1-DOF needle insertion robot. The robot actuator is an MR-compatible pneumatic piston-cylinder. A brief review of the dynamics for this type of actuator is provided. The reaction force of tissue on the needle remains an unknown for which our controller compensates. A sliding mode control law is formulated that relies solely on position and pressure measurements (no force sensor). Experimental implementation of the actuator and controller is described. The mean and maximum steady-state position errors for step reference positions were 0.018 mm and 0.028 mm, respectively.© 2011 ASME

Follow-the-Leader Deployment of Steerable Needles Using a Magnetic Resonance-Compatible Robot With Stepper Actuators

Epilepsy is a debilitating, potentially fatal, seizure-causing neurological disorder that will affect approximately 1% of people worldwide in their lifetimes [1]. Medication-based treatment is ineffective for an estimated 40% of epilepsy patients [1]. As an alternative to medication, surgical removal of the hippocampus (commonly, the origin of epileptic seizures) successfully cures epileptic seizures in about 70% of cases [2]; however, 50–90% of eligible patients forgo surgery due to risks associated with highly invasive brain surgery [2,3]. Magnetic resonance image-guided (MRI-guided) laser ablation of the hippocampus is a promising avenue for minimally invasive surgical treatment of epilepsy. Recent clinical trials using various needle-based, MRI-guided laser ablation systems to treat epilepsy have reported positive results; however, seizure outcomes were worse than those of epilepsy surgery [4]. These ablation systems exhibit one major limitation: linear needle trajectories are unable to traverse the entire curved structure of the hippocampus. Steerable needles—comprising concentric tubes of pre-curved superelastic nitinol—address this limitation by enabling curvilinear needle trajectories in soft tissue. The potential benefits of curvilinear trajectories are twofold: (1) they enable therapy delivery to a larger region of the hippocampus and (2) they enable accurate needle placement while avoiding sensitive, untreated tissue that might otherwise obstruct a typical linear trajectory [5]. To achieve curvilinear trajectories without shearing tissue, however, steerable needles must be deployed in a “follow-the-leader” (FTL) fashion, whereby the needle backbone follows the path created by the needle tip [5]. Precise coordination of needle insertion and rotation required for FTL deployment necessitates robotic actuation. Research on MRI-compatible robotic needle-actuation systems has focused primarily on straight needle placement (see, e.g., Ref. [6]; for a more general review of MRI-compatible robotics, see Ref. [7]). To enable use of steerable needles for MRI-guided epilepsy surgery, we previously developed a compact, pneumatically actuated, additively manufactured, fail-safe, MR-compatible robotic needle-driving system [8]. This paper presents a jointlevel trajectory coordinator for FTL deployment of a steerable needle using our MRI-compatible robot. FTL deployment is validated experimentally.