Brain satnav helps surgeons travel to a tumour

SATNAV is good at finding the easiest route to where you want to go. Now a version for the brain could allow a flexible probe to take the safest route to reach deep tissue. Together, the algorithm and probe could provide access to brain tumours that were previously deemed inoperable.

When surgeons want to take a biopsy from deep inside the brain, they face a problem - how to get there without damaging the brain tissue en route. Flexible needles are one solution. Ferdinando Rodriguez y Baena at Imperial College London and colleagues created such a probe in 2009, basing the design on the needle-like ovipositor that female wasps use to deposit eggs inside trees.

Just like the wasp's ovipositor, the probe has a number of interlocking flexible shafts, each of which can slide independently of the others. The probe naturally sticks to the soft brain tissue, providing traction, which means that when one of the shafts slides further into the tissue the probe will flex. By controlling the relative movement of each shaft it is possible to send the probe snaking along a path through the tissue.

Rodriguez y Baena's team has now begun to think about exactly which paths are best to take. "Some areas of the brain are more important than others and we needed a way to decide what route caused the least amount of damage to vital areas," says team member Seong Young Ko at Chonnam National University in Gwangju, South Korea. "You would want to stay well away from major blood vessels and sensory areas, for example."

The team has now developed an algorithm to direct the probe around these obstacles. It considers three factors: the distance from the scalp to the desired brain tissue, the proximity of the route to vital areas such as blood vessels or nerve bundles, and the accumulated risk along the way.

There is controversy over how to rate the importance of different parts of the brain, so the team tested the algorithm by giving arbitrary levels of importance to different areas. It revealed the path which should theoretically bring the least risk to a patient. Ko presented the algorithm at the BioRob 2012 conference in Rome, Italy, last month.

"The ability to take a curved path through the brain, selecting the most forgiving route to avoid critical regions, represents an intriguing breakthrough," says Katrina Firlik, a neurosurgeon in Greenwich, Connecticut, who was not involved in the research. "It could not only enhance safety but might even expand the surgical repertoire to include cases currently deemed inoperable."

That is the hope, says Ko. So far the probe has only been tested in animal tissue, but he says the goal is to use the algorithm to guide the safe implantation of electrodes deep in the brain and to improve the safety of taking biopsies from hard-to-reach tumours.

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