Mechanical Engineers Create First Fully Pneumatic Robot for Neurosurgical Interventions
Researchers affiliated with the Center for Compact and Efficient Fluid Power (CCEFP), an NSF-funded Engineering Research Center (ERC) headquartered at the University of Minnesota, have created the first fully pneumatic robot designed for neurosurgical interventions. This robot could be used to position a needle at the hippocampus to deliver thermal energy (e.g., via a laser, acoustic ablator, or other ablation technology) instead of surgical removal of the hippocampus. (The hippocampus is an anatomical structure about 1 cm across and 4 cm long located deep in the temporal lobe.)
Thermal ablation in the brain is an experimental procedure, meaning that much testing will be required to verify that heat can accomplish the same goal as surgery. Nevertheless, there is large potential benefit to patients of replacing open-brain surgery with needle insertion because trauma and risk of complications are greatly reduced. Since the surgery is guided by Magnetic Resonance Imaging (MRI) to allow the surgeon to precisely position the needle or other implement needed for the operation, it is essential to avoid magnetic fields in the operating area. Pneumatics does not generate a magnetic field.
One half to one percent of the population in North America and 50 million patients worldwide are affected by epilepsy, with a 7%–17% chance of sudden unexplained death if left untreated. In the majority of temporal-lobe epilepsy cases, seizures are caused by the hippocampus, and 60%–70% of patients who undergo surgical removal of the hippocampus become seizure-free for at least two years. Test results demonstrate that pneumatic actuation is a promising solution for neurosurgical interventions that either require or can benefit from sub-millimeter precision.
In addition, magnetic fields in the operating area interfere with the MRI image used for device placement. Electro-mechanical actuated robots cannot be used in MRI-guided surgery because they generate magnetic fields. Precision pneumatics do not cause magnetic fields. Also, the device is carefully designed to minimize materials that may cause stray magnetic fields.
Actuated by five non-magnetic pneumatic piston-cylinders, the steerable needle robot rests on the MRI scanner bed just above the patient’s head. (See accompanying figure.) Long lines of tubing tether the cylinders to remotely located pressure sensors and valves, which position the pistons to sub-millimeter precision. A five degree-of-freedom needle has been designed to target the hippocampus. The needle comprises a stiff outer tube and two tubes of a super-elastic memory metal called nitinol. Telescoping and rotating the tubes with respect to each other, the pneumatic robot steers the needle along a desired path in the patient’s brain. Before the procedure, the front end of one nitinol tube is set to a curved shape, and during the procedure the tube returns to this shape as it telescopes beyond the outer stiff, straight tube. At its tip the needle carries an MRI-compatible thermal ablator. The MRI scanner provides real-time feedback of the needle location as well as real-time thermal dose monitoring using MR thermometry.