MRI Compatible Hydraulic Arm

Enabling robotic surgery with real-time 3D imaging

Why a Robotic Arm?

Minimally invasive surgery typically involves inserting surgical tools into small openings (rather than large incisions) cut into a patient's skin. This reduces recovery time as there is much less trauma to the patient. However, it highlights a need for much higher precision and the ability to maneuver in tighter spaces. Robotic-assisted surgery allows surgeons to operate in spaces that may otherwise be difficult or impossible to access easily.

Why MRI?

Continuous 3D imaging is vital for minimally invasive surgery, allowing a doctor to reach a desired location with precision and minimal patient trauma. There are two primary mechanisms for 3D imaging of a patient: Computed Tomography (CT) and Magnetic Resonance Imaging (MRI). 

CT scanners use a series of x-rays to generate a 3D image of the patient's body internals. MRI machines instead use strong magnetic fields and radio waves. While the risk of using x-rays for single scans is not large, continuous imaging would subject the patient to constant ionizing radiation for the duration of the operation. On the other hand, the risk of continuous exposure to magnetic fields is much lower as there is no ionizing radiation. 

What's the problem?

Despite MRI being a better solution for continuous imaging than CT in theory, it comes with a major restriction: magnets and metal don't (usually) mix. Therefore, an MRI-compatible robotic system must be made of exclusively non-magnetic materials to avoid distorting the image or, in the worst case, be sucked into the MRI bore and injure the patient and/or damage the machine.

Final Design

The team developed a system of 2 degree of freedom (DoF) links, which allows an end effector to be positioned anywhere within the MRI bore without impacting the patient. The structure also has a mobile base for the arms to allow easy portability and secure placement during operation. The bulk of the structure is made of large aluminum tubes, which are readily available and easy to machine. Each link is counterbalanced with a combination of static and adjustable weights, which makes the positioning of the links easy to do with a single operator or a relatively low power actuator. 

The majority of the system is made in-house from stock materials, with the exception of small fasteners, bearings, and counterweights. Additionally, almost all components are made of flat plates, allowing rapid waterjet prototyping. This allows the overall cost to be relatively low, particularly for a system of this scale.

Performance Results