In keyhole neurosurgery, a small "burr hole" is drilled in the patient's skull, and their brain is then accessed through that hole. The procedure is much less invasive than many other types of brain surgery, and can be used for things such as exploratory endoscopy, biopsies, blood and fluid sampling, cryogenic and electrolytic ablation (tissue removal), and deep brain stimulation. It is used to treat conditions including tumors, hydrocephalus (fluid on the brain), Parkinson's disease, Tourette syndrome, and epilepsy. For a neurosurgeon, however, it can sometimes be extremely exacting work - a slip of even a fraction of a millimeter can cause permanent brain damage. That's why the European Union's ROBOCAST (ROBOt and sensors integration for Computer Assisted Surgery and Therapy) Project is developing a robotic system to help out.

The system consists of a human-computer interface with a haptic feedback control mechanism, an autonomous trajectory planner, a micro controller, a set of field sensors, and a robot - two robots, in fact.

The first, larger robot holds its smaller counterpart, and positions it around the patient's head as needed. It is able to move with six degrees of freedom (up/down, left/right, backward/forward), so it can place the smaller robot anywhere in three-dimensional space.

Once positioned at the burr hole, the little robot is then used remotely by the surgeon to insert the surgical instrument into the patient's brain - with some help from optical trackers, that is, which monitor both the end of the probe and the patient. Using a combination of sensors, the robot is able to modulate the position and force of the instrument, once it is inserted.

The autonomous trajectory planner figures out how the instrument will travel, both outside and inside of the patient's head. Should unforeseen circumstances arise during surgery, the system can adjust the trajectory to allow for the changes. The surgeon, of course, can take complete manual control at any point.

So far, the ROBOCAST system has been demonstrated on a dummy, and is currently being refined for use on live patients. A follow-up project known as ACTIVE will be looking into the use of robots for neurosurgical procedures in which the patient remains awake during the operation.

A somewhat similar system is currently in development in The Netherlands, which assists surgeons in performing eye surgery.